Generator power consumption experiment - for estimating battery bank size
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Once again Bill this is all great info. I agree with you about the fun in this. This is also great for brain exercise!
What jumps at me from your calculations and note that going to 100% is "hard" is that I will need almost immediately a small solar array for light charging since I might leave cabin at 85-90% SoC during the warm months and that small array can bring it back up to 95%... then in winter as well.
I can have an insulated box with fan vent or just venting holes 9 month of the year. I also plan on keeping a temp gauge in the power box with batteries and equipment so I can keep an eye on the temp (mostly in warm months). I wonder if the Victron is smart enough to keep track of the temp and only start charging when batteries are warm enough... I know it comes with a temp sensor. If it is smart enough then in winter i can start generator upon arrival, have it heat up the batteries until they are hot enough for being used... I should not discharge them when they are tool cold, right?
I will go with the Victron 24V 2000W. This one: (sorry for giving a link to the manual haha)
https://www.solar-electric.com/victron-energy-multiplus-inverter-24-2000-50.html
When you have time to look at my funny wiring drawing let me know. I can cut all those wire in half since it is 24v and not 12v as it was first set to be - I think? Also not sure about breakers sizing now that it is 24v.
I just realized that I might have a duplicate there on my drawing... I can't tell but the Victron might only have one connection for my bank - and it will use that same connection to either discharge (and send ac to my breaker box) or charge through the same one... ? Before I had an inverter and standalone charger so I removed the charger but kept wiring... wow if that is true than it is even simpler to connect.
That battery monitor has some good reviews. We shall see...
Yeah 12V loads is something I need to get back to you on. I plan on having for now some 5v charging usb ports for phone and tablet charging. And also have my toilet fan (draws almost nothing) on that.. I might actually leave it on when I leave but I believe with the size bank I have and a 90% SoC when I leave and solar array - it will make almost no difference. Fan rating they give is : 12v/3.5w/210mA.
In the future I might run much larger things on my 12v.... ceiling fan and led tv. But it is not in the cards for at least a year or two so I am not going to think about it.
Another thing... I was thinking to make a stand alone box near generator (35ft away from cabin) for battery and inverter... for the slim chance of fire so it is away from cabin. Not sure if that is necessary. I could instead mount it on the outside wall of my cabin (support floor for batteries obviously) Benefit is that my 12v run can be shorter (or I can put the buck in cabin so 12v is short...) and that I can maybe heat batteries using cabin heat when I am there...
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When saying charging to 100% SoC is "hard"--I intended to say that is is "hard on the batteries themselves"--And trying to get to 100% SoC every day will (typically) shorten the life of the battery bank... Getting >90% SoC is usually "good enough" unless you are planning on letting the bank sit idle for the next 1 month (flooded cell) or 6 months (AGM) at 75F/25C.
Yes, you should not cycle (charge/discharge) a frozen or "slushy" Lead Acid battery.
As long as the AGM/Lead Acid battery is >~50% State of charge, it will take temperatures down to -4 or to -16F or so to actually freeze.
http://www.trojanbattery.com/pdf/TrojanBattery_UsersGuide.pdf
Cold batteries also have less "apparent" AH capacity...
Remember that your aim is to keep the batteries >75% SoC so they don't sulfate quickly. That may be -60F before the batteries freeze. Again, AGM don't cycle when frozen... But they will generally survive a hard freeze... Don't think you will see -60F in your area...
Again--I know nothing about "real life" cold climates... But you can find battery heaters (these are 120 VAC units for trucks):
https://www.etrailer.com/Vehicle-Heaters/Kats-Heaters/KH22300.html
I have no idea if these work work for your needs--But seems like a good combination for battery bank and smaller 120 VAC genset (this is 160 Watt heater blanket).
AGM batteries are not supposed to vent--But your battery box should have venting. If over charged (and towards end of life) AGM batteries will vent hydrogen--You don't want to trap that gas in the box. Also oxygen and possibly some sulfuric acid mist too if venting (don't store family antiques or expensive items near your battery bank).
For wiring/transfer switch/plugs... You may want to have some way of quickly connecting your genset directly to your cabins 120 VAC wiring. Just in case you need power when the inverter or battery bank fails. Or some manual bypass/transfer switches (i.e., you can pull the inverter-charger for service and keep the cabin powered).
For the composting fan--You might want to look for a native 24 VDC fan--And not bother with the DC to DC converter.
Always a bit of a risk leaving a fan/loads on when going away... Say you have 10 Watts of loads (fan, cell based alarm/camera system, somebody forgot to turn off the AC inverter, whatever).
You would ideally like to not discharge below 75% state of charge:- 400 AH * 0.25 discharge = 100 AH
- 10 Watts / 24 VDC battery bus = 0.42 amp load
- 100 AH / 0.42 amp load = 238 hours = ~10 days of no sun charging (drifted/snow covered panels, failed charge controller or wiring, etc.)
24x7 loads can be big issues for off grid systems and limited winter charging.
I am not the expert on fire and off grid power--Thinks I suggest is don't wall mount to plywood--Use sheetrock or cement backer board/etc. to give you a bit of a fire proof barrier (or use metal conduit/trays for cabling).
Same for floor--Some sort of fire resistant ceramic tile or similar. You have a fair amount of stored energy in the battery bank... And shorts can still melt and set on fire "flame resistant plastics and such" which will drip down walls and onto floors.
And using correct sized wire for loads, fuses and circuit breakers (breakers are nice because you can also use them as on/off switches).
Similar issues with gensets and stored fuel, fuel lines, any fuel pumps, etc... The building in New York City 9/11 (city emergency operations center)--Diesel fuel in basement, gensets a few floors above. Battery backed power too. Debris broke a fuel line and the battery backed fuel pump kept pumping fuel up into the fire a few floors above (as I recall).
If you have lightning in the area--Surge Protectors are nice to have. Reduce the chance of damage to your equipment. For many off grid lightning failures--It is the 120/240 VAC inverter output that gets toasted (less chance for the DC battery bank side).
https://www.solar-electric.com/search/?q=midnite+surge
You are the "power and safety engineer" here... Do things "right".
Stuff happens.
I will closer at the manual and your drawings tomorrow some time...
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Great points here Bill. Much appreciated.
I understand this 100% SoC being not a goal. I think winter will be a very different ball game - start up generator when I arrive to warm up batteries, I won't leave any dc loads when leaving (no need really since it will freeze the waste in the compost toilet, and so on. I think this is more for warm weather and what you called 9-10 months of the year - where I have good sun and warm weather and can allow the fan to run when I am not there.
Trying to understand that math for fan... It is rated at 2.5 watt and 210ma. So if I do use it (I am also totally open to not use it and instead use an inline 24v fan but for now let's see this math): 2.5w / 12V = 0.21 --> 100/0.208 = 20 days. Really not a long time if no solar charging.
You say 75% to add a mistake cushion to not reach under 50%? If so then maybe 60% is also ok? in that case I have 48 days.
Nonetheless, this point you make is extremely valid and just hammers the nail further - I will need a small solar array. I might be able to avoid it this year since by the time I have this power system set up it will be winter and I won't be going there for a few months so I can just bring it to 95-100% SoC then close for the season (obviously without any loads on it). Then next year set up the solar array since in the warm weather I will leave the fan running so need a solar array.
Also you point out to the need to have a 'by-pass' so I can hook up genest straight to my ac loads in case issue with power bank - which is what I have now. I think I can just use the current one I have... The question is if I need to have some kind of disconnects since I will have two "feeding" leads to the ac breaker box: one from inverter and one from genest bypass. So when inverter is running the wall plug for genset will be live. And vice versa - if geneset is hooked up to bypass it might send power back the other way to the inverter? Better to have some kind of disconnect. Might be simple to do?
Yes believe me I will be very careful setting up the box for it in terms of safety. I tend to over engineer really.
I feel like I am basically set with battery bank and inverter unless very different information coming out of my watt-o-meter this weekend.
Exciting. I am truly amazed how much that Victron simplifies the wiring and equipment. It will all fit in a 2f x 4ft x 4ft box which leaves even room to expand batteries if I need.. Btw Victron manual says 20--500ah bank for 2000w 24v inverter.
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For "storing" lead acid (and AGM) batteries, you want them to not go below ~75% state of charge--Or they begin to sulfate more quickly. Sulfation is when the "fluffy" gray lead sulfate turns to hard black crystals--When that happens, the crystals no longer are part of the charge/discharge chemistry. The battery loses capacity at that point.
A typical AGM battery will self discharge in ~6 months at 77F. And cold batteries will self discharge much slower. Roughly for every 10C/18F below 25C/77F, the "chemistry" slows down by a factor of 2 (conversely, hot batteries sefl discharge much faster):- 77F-32F= 45F lower temp
- 45F/18F= 2.5 cooling factor
- 2^2.5= 5.7 slower self discharge
- 5.7 x 6 months = 34 months to self discharge if bank is at 32F or longer
For running the genset when the inverter is down/off... Yes, you still need some sort of transfer switch.
There are "interlocks" (basically sliding sheet metal parts) for some breaker panels. Either breaker "A" is on (say to inverter), or breaker "B" is on (say for genset), but the interlock prevents A and B from being on at the same time.
Or there are manual transfer switches. And you can use a relay transfer switch (power to relay transfer switch--Energizes relay--And passes genset current to your AC wiring):
https://www.interlockkit.com/ ("kit" for breaker panel interlock--exact kit design depends on brand/model of breaker panel)
https://www.solar-electric.com/search/?q=transfer+switch (separate "simple" transfer switches)
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Thank you Bill.
During winter I will not leave any loads on. Batteries will be sleeping at 95-100% SoC for the entire time until I come back so about 4 month.
Even once I start using the cabin year around (in a year or two) - still it doesn't make sense to leave compost fan on when I am away during winter since the waste will freeze and won't smell.
So essentially the only time the fan will be left on when I am away - is during warm weather.
So assuming you will help me figure out the right amount of solar array (next year..) to compensate for fan and give me a better cushion plus assuming I will be at the cabin every week or so but even if I am not for a month - I will not let SoC drop below 75% during the warm weather.
Your remark that I should not go below 75% - you mean only for storing purposes during winter, right?
I'll be able to go to close to 50% SoC during my regular visits?
Yeah I will speak with my electrician about these sliding breakers. That sounds like exactly what I need.
I couldn't figure out but I believe the Victron only has one connection for batteries. In other words it will either discharge or charge them through the same connection. If that is true then I will update my diagram that currently shows two (2) sets of wires between inverter and batteries.
Looking forward to your remarks on wiring diagram with wire size, correct size breakers, and so on.
*Edit - read a bit more of the manual. I did find the wiring diagram and there is indeed just one negative and positive connection for the battery. Wow - saves so much work and cost on cables. If I understand correctly: It says that I need a circuit breaker on AC IN. This means power coming from generator? It says 50A or smaller according to AC input so I am guessing that since generator can only do 15amp - we will have a 15 amp breaker there? Not sure what is an inline Ac breaker.. i guess there is such a thing...
It also says a earth leakage AND a breaker is needed for AC OUT. This is basically inverter ac feeding breaker box in my cabin? if so then the grounding rod connected to my breaker box works for that purpose? it says also a breaker (which I am not sure if there is a main breaker but instead I have several breakers for my different feeds (AC, outlets, lights, fridge-microwave-toaster, and utility wall - rv pump, water filter uv light, and tankless gas water heater - so 5 breakers in total) I guess I need to add a main breaker if I don't have one... ?
Battery price went up by $10 since I posted but it haha. Also, the NEG and POS on those batteries are in the front so I can really have short cables between batteries, batteries and bus terminals, and bus terminals and inverter . I am sketching it in 3d so I can plan sizing of box and wires accordingly. I will post an image later on
*Edit #2 - I finally found the list of options one has when connecting the Victron to a computer using their MK3 adapter. Hopefully we can use it together Bill to see what settings are needed for my system: https://www.victronenergy.com/media/pg/VE.Bus_Configuration_Guide/en/description-of-settings.html -
The rough guide is don't let the Lead Acid batteries sit at or under 75% state of charge (i.e., self discharge from 100% to 75% is "normal" storage range--Hit 75% or less SoC, recharge batteries). Avoid days/weeks/etc. below 75% SoC--Batteries will sulfate (quicker) and die.
For cycling, yes, you can go below 75% as long as you recharge the next day (or at least begin to recharge the next day).
You can check the charts for your batteries. For example, you may have 3,000 cycles at 25% Discharge, 1,500 Cycles at 50% discharge, and 750 Cycle life at 80% discharge. We usually suggest not going below 50% SoC for Lead Acid/AGM--Give you longer battery life. But you can go down to 20% SoC as long as you recharge (suggested as "backup capacity" for bad weather, failed genset, etc.). Going much below 20%, and you risk "damaging weak cell/cells" (weak cell goes to zero volts and starts "reverse charging"--A killer for most rechargeable battery types).
Sort of like a 10 gallon fuel tank... taking 25% out and refueling vs taking 80% out and refueling--You, overall, still are using the same amount of fuel---Just visiting the service station more often--And you have less reserve left if you have an emergency (keep tank 1/2 full or more, vs folks that drive until empty--I have done both
).
Cycle life charge for Lifeline AGM batteries (high end vendor):
http://lifelinebatteries.com/wp-content/uploads/2015/12/6-0101-Rev-E-Lifeline-Technical-Manual.pdf
There is a lot of good information in this manual--Worth a quick read.
Yes, the Victron should be pretty easy--120 VAC in (genset). 120 VAC out (your loads). And 24 VDC bidirectional bus connection (discharge and charge).
General design rules (I am not disagreeing with the manuals, just explaining the general reasoning for such stuff).
50 Amps @ 120 VAC maximum into Victron. That is what it has been designed/tested too... More current than that, the unit could have a meltdown or fire if there are internal failures or shorts on the AC or DC outputs). A typical utility pole transformer for homes--Are rated for 10,000 Amps maximum current. And if you look in detail, you will see the 15 amp home breaker is rated for 10,000 AIC (Amp interrupt current--Or something like those words).
Your genset has a definite output limit. Since it is less than 50 Amps, you do not really need a breaker from the genset.
Breakers are there to protect the wiring... You can use the NEC (national electric code) for the pages and pages on designing and protecting your AC system (ambient temperatures, conduit fill, wet/dry locations, power factor, continuous current flow, etc.)...
As a starting point, here is a handy/simplified NEC ampacity vs AWG (and insulation rating) chart:
https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm
The max current for an eu2000i is around:- 1,600 Watts / 120 VAC = 13.3 Amp continuous
- 2,000 Watts / 120 VAC = 16.7 Amps peak (inverter-generators typically have lower surge current rating vs other gensets)
To be conservative, I treat charging batteries as a continuous load (since they can be charged for many hours at full current--Not like running a blender or washing machine at home for a few minutes at time/per cycle). Two checks:- Assume 20 amp max output (I think that is the eu2000i breaker rating) = 12 AWG wire minimum
- 13.3 amps * 1.25 NEC derating for continuous current = 16.6 Amps derated (12 AWG is still OK)
The genset is already equipped and you are using large enough wiring to be safe (12 AWG or heavier). Breakers are designed to "protect" downstream wiring. It is not there to protect 'upstream' wiring--But is allowed for short runs (like wiring from battery box to breaker ~18" or less away, then protect downstream wiring--Assuming upstream wiring is too short to get into trouble, and is installed correctly (no sharp sheet metal to cut insulation, etc.).
If you ever decide to put two eu2000i in parallel, or a larger genset, you will need to rethink the AC input to your breaker box.
The dip switch settings seem to be a good place to start--The USB/Bluetooth/etc. features--Just depends on "how deep" you want to go.
-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
SoC -
So making sure I get it - it is ok to let batteries reach 50% SoC as long as I don't keep them at that state for more then a day or so. My hope is to go from 95% SoC to 55-60% SoC in 48 hours then go back up to 95% SoC the next day with Genset charging. Is that ok?
I think I will have a better sense at where my batteries SoC should be after this upcoming weekend and following weekends. I will measure cabin usage for day 1 (short), night one, and full day 2. The combine Kwh should tell us where I should be about after 48 hours. Then I can decide on charging every night vs charging only on 2nd night.
Breakers -
Between genset (I think I'll run 10awg just so I don't have to redo anything in the future) and inverter "AC IN" - no need for breaker. Great done.
Then how about "AC OUT" is that also not needed since that is power going from inverter to breaker box and breaker box has breakers already?
Genset bypass -
I looked at the link you gave for interlocking kits which seems great. My breaker box is tiny. Model is: BRP10B100. Seems like Eaton makes a specific interlocking kit for it... BRMIKBR.
The installation instructions are basically useless. I am guessing that since this breaker box doesn't have a specific place for "main breakers" then main breakers simply seat where the other breakers are? I think I will need to order this and then ply on my panel to see how this will work.
Wirings questions:- Cable size needed between batteries? (parallel and series..) - distance is really small - terminals are in the front so between 6" and 18" max.
- Cable size between battery bank and inverter? distance is under 18".
- Breaker size between bank and inverter?
- I got these bus bars: https://www.amazon.com/gp/product/B07THLYYH3/. Are they correct rating? It says total voltage 48v and each connection is rated at 250amp at 12dc... So with my current wiring scheme I have two cables for neg and two for pos going from batteries to the bus bar then from there to inverter - one cable to pos and one to neg. Bus bars are not correct for this?
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SoC--Yes, cycling down to 50% SoC and recharging is fine... Just understand that your batteries may last 3,000 charging cycles 100% to 75% SoC cycles. And 100% to 50% SoC cycling, they may last 1,500 charging cycles.
Not that is the 'end of the world'-- 1,500 Cycle life (to 50% discharge) / 3 cycle days a visit = 500 visits. Take 500 visits / 24 three day weekends a year = 20.8 years to "cycle out" a good quality AGM battery bank... And in reality, those batteries typically last 5-7 years or so.
In the above example, even cycling deeper (to 50% SoC)--That will not be the death of your battery bank (assuming you recharge the next morning/evening). They will "age out" first.
Breakers -- For AC out of the inverter, you need to read the specifications closely. For example, because the unit as a 50 Amp @ 120 VAC transfer switch capability, and the inverter can "boost" or "assist" the genset output, the Victron's 120 VAC output in your case is actually:
https://www.solar-electric.com/lib/wind-sun/Manual-MultiPlus-Compact-2000-120V-EN.pdf (section 4.3):• AC-in The AC input must be protected by a fuse or magnetic circuit breaker rated at 50A or less, and cable cross-section must be sized accordingly. If the input AC supply is rated at a lower value, the fuse or magnetic circuit breaker should be down sized accordingly.Or, more or less, 17 Amps from Victron + 13 amps from eu2000i genset = 30 Amps max output from Victron... Either wire for 30+ amps from Victron, or use smaller wire+smaller breaker if you do not want the "assisted" high current output to your AC breaker box.
• AC-out With its PowerAssist feature the Multi can add up to 2kVA (that is 2000 / 120 = 17A) to the output during periods of peak power requirement. Together with a maximum input current of 50A this means that the output can supply up to 50 + 17 = 67A. An earth leakage circuit breaker and a fuse or circuit breaker rated to support the expected load must be included in series with the output, and cable cross-section must be sized accordingly.
Breaker Bypass -- Yes, in the case of a "sub panel", you would have (for example) two interlocked breakers next to each other (as required for interlock kit). One breaker to Victron, second breaker to genset. Interlock prevents both breakers from being turned on at the same time (and damaging the Victron or genset AC outputs by shorting them together).
Battery Cables -- Victron remcommends 2 AWG for the 24v/2000w unit... Just to double check:- 50 amps charging maximum
- 2,000 Watts * 1/0.85 inverter eff * 1/21.0 volts battery cutoff = 112 Amps max continuous
https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm
Any of the "better insulation types" (75C or higher) are good for 115 Amps or more--So that is consistent.
Using a 120 Amp fuse or breaker is fine (technically 90C insulation).
For voltage drop calcuations, 2 AWG @ 4 feet (one way trip) is fine. Comes to 0.18 volt drop @ 112 Amps:
https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=7&necconduit=steel&necpf=1&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=24&phase=dc&noofconductor=1&distance=4&distanceunit=feet&eres=112&x=70&y=20&ctype=nec
Your bus bars look to be rated for voltage/current you need in your battery system. Note that this are not UL/NRTL rated. Just keep an eye on them when first used to ensure that they do not "run hot" when loaded.
And if you run parallel string of batteries (to get AH rating of bank higher), then review this website on how to "match" cabling resistance to ensure batteries share load and charging currents:
http://www.smartgauge.co.uk/batt_con.html
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Thank you Bill. We just got back so I'll read your post again and more closely later today.
I have new power usage readings from this two night three day trip-
- 100pm-743pm 0.726kwh day 1 "short"- 743pm-700am 1.208kwh night 1- 700am - 740pm 1.861kwh fay 2 "long"- 740pm- 654am 1.065kwh night 2
-645am - 830am 0.274kwh day 3 "shortest"
This time the highest pull was 1450watt. Not sure what was that. I mixed thinnest using my mixing gun so maybe that did it.
Total used two night 3 day trip is just under 5kwh. I wonder if such low usage is due to the colder weather.
If had a battery bank - first short day I would have gone to 92% SoC (right?) so charging the first night would have been a bit silly... If I hadn't charged first night then by the 2nd night my SoC would have gone to 61% SoC before doing a 12 hour generator charge. I guess once I have the system set up I'll need to track it and make decisions about charging all nights vs only 2nd night. -
Got around to going over your notes more carefully Bill.
Generator bypass - Since then a 4th breaker has been added for ac. So I have two slots left I believe.. I found a few other types of interlocking kits that hook up to the breaker itself and might work for me.. let me know your thoughts:
https://www.amazon.com/Mechanical-Interlock-BQ-Circuit-Breakers/dp/B007ICICBC
https://www.amazon.com/Square-D-D-QO2DTI/dp/B007IAGBN0
I believe the breaker box model i mentioned before was wrong and this is the one I have:
https://www.homedepot.com/p/Eaton-BR-125-Amp-6-Space-12-Circuit-Indoor-Main-Lug-Loadcenter-with-Surface-Door-BR612L125SDP/100177026
I will double check.
Anyhow, it doesn't have a "main" breaker but I believe (someone actually commented about it on Amazon) that I can "run your entry wire through one of the breakers in this panel, it becomes your main".
If that is true then I can just add two breakers: for generator and inverter. then use one of those interlockers I linked? Someone mentioned them working on Eaton breakers.
Side question... My electrician came to my cabin (I begged him and paid him handsomely to make the trip) to help me with ductless install. He then discovered my father in law's electric mistake: the generator neutral float thing. So he fixed it by, I believe, connecting my neutral to my ground or to the box? Anyway... It is obviously still connected as such. Is that an issue for the inverter?
Wire between batteries and inverter:
My old wiring for 12V system shows 2/0 between batteries and inverter. How about now in 24V? I am estimating about 12" run.
Connection for batteries
Since the bus bar I have isn't UL listed.. Can you recommend something else I can use to connect all my batteries together nicely?
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We started with two reasons for "12 hour" generator runtime...
The first was because that was your panel--To run the genset overnight. While that is also good for the batteries, it will probably be wasteful of fuel if you do not have (roughly) 400 Watts or more of load overnight (at least 25% genset loading on eu2000i Honda).
The second was a roughly 11+ hour recharge from 50% full to 100% full--Typically needed for putting "the system to bed" for a long winter shutdown. AGM batteries at 77F will store (no load) for ~6 months between charges. At 32F, they will go over a year between charges (obviously, temperatures will vary from summer to winter and you are looking at 3-4 months of "storage"--And even possible winter usage at times).
Otherwise, I don't think you need 12 hours of genset runtime at the end of the weekend (as an example). Some math/modeling:- 100% to 75% = 25% capacity
- 100% to 75% => optimum state of charge storage range for Lead Acid Batteries
- 25% capacity / 6 months storage = ~4% per month self discharge
- Run genset from 50% (or whatever) to ~85% SoC, gives you ~10% of self discharge capacity (85% - 75%) or >2 months of storage time (4% per month self discharge @ 77F). And that would be much closer to 4-8 hours of genset runtime (vs 12 hour).
From section 4.3 of this manual:
https://www.solar-electric.com/lib/wind-sun/Manual-MultiPlus-Compact-2000-120V-EN.pdf4.3 Connection of the AC cablingSo--The Victron inverter can (and should) have the Neutral bonded to Ground for NEC type operation--So inverter will not be "harmed" (either floating or neutral bonded).
This is a Safety Class I product (supplied with a protective grounding terminal). Uninterruptible protective grounding must be provided at the AC input and/or output terminals and/or chassis grounding point located externally on the product.
The MultiPlus is provided with a ground relay (relay H, see appendix
that
automatically connects the Neutral output to the chassis if no external AC
supply is available. If an external AC supply is provided, the ground relay H will
open before the input safety relay closes. This ensures the correct operation of
an earth leakage circuit breaker that is connected to the output.
─ In a fixed installation, an uninterruptable grounding can be secured by means of the grounding wire of the AC input. Otherwise the casing must be grounded.
─ In a mobile installation (for example, with a shore current plug), interrupting the shore connection will simultaneously disconnect the grounding connection. In that case, the casing must be connected to the chassis (of the vehicle) or to the hull or grounding plate (of the boat).
In case of a boat, direct connection to the shore ground is not recommended because of potential galvanic corrosion. The solution to this is using an isolation transformer.
The Honda eu2000i genset has floating AC output. Obviously it works just fine floating (can argue safety issues of floating output). And it will work fine if driving a Neutral bonded main panel.
The "Ground Relay" in Appendix B... Typically used where you have an RV or Boat with internal power (genset, inverter, etc.) and need to provide your own "neutral+ground bond"--And for connecting to shore power which has the Neutral+Ground bond in the shore power electrical box (somewhere). Multiple Neutral+Ground bonds are typically a problem when you have a GFI breaker/outlet between the two N+G bonds (such as shore N+G going through GFI into RV/cabin/etc. then to a main panel with another N+G bond--The GFI will trip because of two N+G bonds (some current through Neutral wire--that is good--And some current flow through grounding/green wire--problem).
Regarding breaker interlocks... Obviously way overpriced for what they are. And are intended to prevent somebody accidentally turning on two "AC sources" at the same time to the panel. And are easily bent if somebody wants to be "stupid". I know it will not be you--But if family/friends/visitors are there and have "power problems" (run batteries dead, can't start genst, etc.)--Who knows what they will do.
I have no additional knowledge into what is the best/most cost effective solution here--So not much more that I can help you decide.
For $25 for an interlock... Almost worth using a $63 transfer switch/relay--Plug genset in, start up, a few seconds later, the relay switches over to genset 120 VAC input power...
https://www.solar-electric.com/pomaxpmautrs.html
One less thing for guests to worry about--In anycase, we are now talking about belt and suspenders--Victron has transfer switch, and this second transfer switch is really only there if you are taking the Victron out of service for repairs. The relay option is probably just a step too far.
Check around at electrical supply houses and such for interlocks... Amazon is not always the cheapest--And they have "interest" pricing. I have a friend who is a machinist, and sometimes I help him with researching tooling and such... After a few minutes of both he and I searching, the original price of some obscure part will go up by 20-50% just from us two hitting the link during searches and talking on the phone (the wonders of capitalism/market based economies).
For example, just searched on the Siemens part number in your first link... $25 from Amazon and $15-$16 from other sources (EBay and others). Did not lookup shipping charges. Amazon does make it easy.
https://duckduckgo.com/?q=ECQML12&ia=web
The Victron DC wiring is suggested at 2 AWG (minimum) for 24 VDC (technically, need "90C" rated insulation for >112 amps--Such as a 120 Amp fuse/breaker) using NEC chart.
Voltage drop is not a problem (and almost never a problem with "short wire runs"--When you get to 10 feet or more, can be an issue):
https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=7&necconduit=pvc&necpf=1&material=copper&wiresize=0.4066&resistance=1.2&resistanceunit=okm&voltage=24&phase=dc&noofconductor=1&distance=1&distanceunit=feet&eres=112&x=0&y=0&ctype=nec
Voltage drop: 0.042
Voltage drop percentage: 0.18%
Voltage at the end: 23.958
Regarding the Bus Bars--I am not saying those are bad. Just watch them under load--If they stay cool, then you are fine.
Just been burned by cheap knockoffs and poor designs. UL/NRTL does not guarantee that the product is "good"--But if the companies do the NRTL work, they are not looking to cheap out on the product.
Of course, China is known for fake UL Listing holograms and such too.
Victron does make busbars too:
https://www.solar-electric.com/search/?q=victron+bus+bar
To be honest, those are probably not UL/NRTL Listed either. An anything with thick copper--Is going to cost $$$.
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Thank you Bill! Great info as usual.
Then just to make sure I have this right: wire gauge between batteries (so for my series and parallel connection) = 2AWG.
Then between the battery bank and the inverter also 2AWG? that is much small than the 2/0 I had in my 12v system plan (granted with 600ah)
I am attaching the updated wiring plan with correct breakers rating and wire gauge you wrote here - let me know if I got it wrong since last time there was quite a large difference in cable size between inverter and batteries vs between batteries themselves
12 hours charge cycle... Looking at my loads from this weekends with my kwh meter I think I will be find for final night 12 hour. I will then leave in non winter time with 85-90% SoC so I am good.
If at night without charging too much power was used and I get up with 60% SoC - i will just keep an eye on it and worst case start my 12 hour night charge earlier than 7pm to not deep under 50% SoC.
power system location -
Option 1: Right up against the cabin.
Pros:
- short run from inverter to breaker box
- short run for dc loads
- easier to build? can literally make a closet on the wall...
Cons:
-farther from solar array site (maybe 80ft?)
-farther from genset at 35ft
- less safe? if fire - it is on cabin,
Option 2: Near generator so about 35ft from cabin and about 45ft from solar array area
Pros:
-maybe can use generator exhaust heat to warm up batteries in winter?
-safer? fire is farther from cabin
-closer to solar array clearing
Cons:
-dc loads are farther... about 35ft away
-long run for ac from inverter
Edit 1*
I have reviewed the list of options and setting for Victron. Very interesting. I definitely hope you can help me program it. Many options I am not sure what they should be set to. Happy Victron is giving this detailed list of options and explanations.:
https://www.victronenergy.com/media/pg/VE.Bus_Configuration_Guide/en/description-of-settings.html#UUID-46f1d4ea-7875-cba1-eb83-08c91030b805
Fingers crossed... I will order it in 2 weeks from now. Maybe sooner. One interesting thing - I viewed a video of setting it up and they say you can hook it up to batteries or an ac source... I will do ac at home before bringing it up to the cabin. I guess I will buy a cheap extension cord and cut it to connect it...
Edit 2*
Since you said I only need one breaker (between batteries and inverter) I found this one made by Eaton I think and that it is UL listed... They only have them in 150amp and 200amp. If it is indeed a good quality UL listed breaker then maybe better to spend a bit more (it is about 2.5 times the Chinese ones on amazon) and get a UL eaton one?
https://www.waytekwire.com/products/1654/Eaton-s-Bussmann-Surface-Mount-Circuit-Breakers/
-
Sorry for double posting but something that you wrote a few posts ago and kind of flew over my head and I just realized that is extremely relevant to me...
"Sort of like a 10 gallon fuel tank... taking 25% out and refueling vs taking 80% out and refueling--You, overall, still are using the same amount of fuel---Just visiting the service station more often--And you have less reserve left if you have an emergency (keep tank 1/2 full or more, vs folks that drive until empty--I have done both )."
and
"Not that is the 'end of the world'-- 1,500 Cycle life (to 50% discharge) / 3 cycle days a visit = 500 visits. Take 500 visits / 24 three day weekends a year = 20.8 years to "cycle out" a good quality AGM battery bank... And in reality, those batteries typically last 5-7 years or so."
These quotes beg the question - does it not make more sense to let the batts go below 50% (but not lower than 20%) and have a large solar array so to get them to fully charged while I am gone (10-7 days) since I will have more cycles than actual battery life span?
The renogy battery I am interested in: at 50% it shows cycles between 700-800 cycles. At 75% DOD - about 450-500 cycles (other better quality batteries have better graphs but they also cost twice as much so they aren't really worth it..).
Going back to your math, if I go 75% DOD, I get about 450 cycles. 450/3= 150. 150/24 = 6.25 years. Which is right on the lower estimate of the 7-10yr life of agm, right?
If my math here is correct: doing 20.5 (25% DOD) years or 12.5 years (50% DOD) is irrelevant if battery dies at 7-10 years anyway and who knows where I will be in 20 years! haha... doesn't seem like I should care about not going below 50%.
Then the other question: Is there an array size (24V so max is what 2500-3000watt array?) that will put back about 280 ah into my 400ah in 7-10 days? (assuming non to negligible draw while they charge and I am away)
I am going to guess you will say a very large array of 2000w+ and that it won't work in winter....
If that is true then math might work as well - cost of array, mppt, and cables vs cost of running generator for all those hours and years plus the maintenance on it. Solar might win... or might be pretty close.
Again, I have no clue and you might come back and say the array needs to be too big so no go.
But even if you do say that - I think charging once a night is the clear winner and maybe not even charge in summer if I am only coming for one night.
BTW -I do not understand how is a cycle determined... if I let a battery go from 95%-100% down to 50% over the course of 3 days without charging it back and then I fully charge it back without using it Is that one cycle or 3 cycles?
-
Then just to make sure I have this right: wire gauge between batteries (so for my series and parallel connection) = 2AWG.2 AWG will work for both connection to inverter, and for battery to battery connections. You could use something like 4 AWG for the battery to battery series interconnects for two or more parallel strings (save $$, copper, and even provide a little better current balancing between parallel battery strings--The bit of extra equal cable resistance helps "steer current" equally between parallel battery strings). But probably not worth getting a second 4 AWG cable and different crimp ends.
When you get to three or more parallel strings, you should have a fuse/breaker per string to prevent a short circuit in one string from being feed by the other two or more strings... (how many people install a fuse/breaker per string--Not a whole lot from what little I have seen).These quotes beg the question - does it not make more sense to let the batts go below 50% (but not lower than 20%) and have a large solar array so to get them to fully charged while I am gone (10-7 days) since I will have more cycles than actual battery life span?We are talking about "in theory" here... Getting a battery vendor to guarantee the cycle life (or replace a early cycle failure) may not be easy (i.e., they just go by years of warranty--2-3 years replacement, 3-5 prorated, etc. (or whatever is for your batteries you buy).
I suggest not going below 50% for "planned" operations. Yes, you have a longer cycle life--But for a 1/2 year weekend system--Not sure what it "buys you". Also, as the batteries age and have reduced capacity... 20% loss of capacity (for one brand) is "end of life"... But trying to keep over 50% in normal operations does give you some room for loss of capacity from aging (battery with 40% loss of capacity--Your system still meets your needs) and for the "oops" occasions (ran out of fuel, can't start genset, company used up more power than planned).
No hard and fast rules... These rules of thumbs seem to give good battery life and good cost for the battery system.The renogy battery I am interested in: at 50% it shows cycles between 700-800 cycles. At 75% DOD - about 450-500 cycles (other better quality batteries have better graphs but they also cost twice as much so they aren't really worth it..).I probably would "plan" on 5-7 year AGM life... But because you are in a cold climate, during winter they will age much slower (every 10C below 25C, 2x longer aging life). Not that I have any special insight here--Just from talking with folks here in general.
Going back to your math, if I go 75% DOD, I get about 450 cycles. 450/3= 150. 150/24 = 6.25 years. Which is right on the lower estimate of the 7-10yr life of agm, right?
If my math here is correct: doing 20.5 (25% DOD) years or 12.5 years (50% DOD) is irrelevant if battery dies at 7-10 years anyway and who knows where I will be in 20 years! haha... doesn't seem like I should care about not going below 50%.
Remember too, you have (possibly 4x) multiple batteries here in your bank. Generally, one cell/battery will start to fail before the rest. Sometimes you can find a reason (failing electrical connection), or just deep cycling/full recharging can bring it back for a bit longer... I suggest checking and logging the voltage across each battery (discharging, charging, resting when you open up for the weekend, etc.)... You have multiple batteries and any one that "stands out" as different--Usually worth trying to figure out if there is anything you need to address. (you can also check with a DC current clamp DMM for proper current sharing).
Batteries can also fail by not supplying the load/surge current you need (down the road, partially charged bank, cold weather, aging bank).
Then when you finally have that weak batteries--Then what, replace just that one and limp through for another year--Replace all, or what).Then the other question: Is there an array size (24V so max is what 2500-3000watt array?) that will put back about 280 ah into my 400ah in 7-10 days? (assuming non to negligible draw while they charge and I am away)Back to the math... 5%/10%/13%/+... 5% for weekend/sunny weather system & minimum rate of charge. 10% minimum suggested full tome off grid (and minimum rate of charge for deep cycle storage batteries as suggested by various manufactures). 13%-20%+ if you have special needs (lots of power during the day, not much at night/during bad weather/not much sun especially during winter if occupied, etc.).
I am going to guess you will say a very large array of 2000w+ and that it won't work in winter....- 400 AH * 29 volts charging * 1/0.77 * 0.05 rate of charge = 753 watt array minimum
- 400 AH * 29 volts charging * 1/0.77 * 0.10 rate of charge = 1,506 watt array nominal
- 400 AH * 29 volts charging * 1/0.77 * 0.13 rate of charge = 1,958 watt array "typical" cost effective maximum array
I don't remember if you said where the cabin is located... Solar panels need full sun... I you are in a forest, in a valley with no direct winter sun, panels covered by drifted snow, etc. then solar is not going to work at this time. Pick something like Albany NY:
http://www.solarelectricityhandbook.com/solar-irradiance.htmlAlbany
Measured in kWh/m2/day onto a solar panel set at a 47° angle from vertical:
Average Solar Insolation figures
(For best year-round performance)
How long to recharge 280 AH in winter (no shade):Jan Feb Mar Apr May Jun 3.09
3.89
4.40
4.46
4.67
4.92
Jul Aug Sep Oct Nov Dec 5.02
4.91
4.56
3.88
2.83
2.73
- 280 AH * 24 volts = 6,720 WH
- 2,000 Watt array * 0.77 panel+controller derating * 2.73 Hours of sun (December average) = 4,204 WH per average December day
- 6,720 WH / 4,204 WH per day (December) = 1.6 days "average" December recharge time
If you get any sort of decent December sun, even a 5% array will bring it up:- 753 Watt array * 0.77 panel+controller derating * 2.73 hours of sun average December day = 1,583 Watt*Hours per day (Dec)
- 6,720 WH to recharge / 1,583 WH per Dec Day = 4.25 December Days to recharge
But even if you do say that - I think charging once a night is the clear winner and maybe not even charge in summer if I am only coming for one night.The whole idea is to keep the battery bank "happy". Don't let the batteries "set" for days/week/longer at a time below 75% SoC. Don't pump too much current or voltage into them (especially AGM--Don't vent them). Keep them charged (biggest killer of batteries is undercharging).BTW -I do not understand how is a cycle determined... if I let a battery go from 95%-100% down to 50% over the course of 3 days without charging it back and then I fully charge it back without using it Is that one cycle or 3 cycles?Everybody feels that a cycle to 85% SoC is much easier on a battery than a cycle to 20% SoC... And anytime they asked a battery mfg... The answer was "both" were one cycle.
Some charge controller manufacturers have even software that will "force" a battery down to 75% (adjustable) SoC to prevent "shallow cycling" from prematurally cycling the battery to death by daily 10-15% discharge/charge cycles.
Regarding you wiring diagram... Some quick comments.- ROMEX to genset--Make sure direct burial/wet location type if left outside (direct bury/conduit/etc.).
- ROMEX to AC breaker panel--Use 30 amp breaker maximum if 10 AWG cable
- 2 AWG from Bus to Battery (+ and -)--You want all cables to be same (total) length--Your drawing has longer cable run to upper battery and shorter run to lower battery--That would "steer" current to the lower battery string (less resistance).
- 170 Amp DC Breaker with 2 AWG cable. 2 AWG cable is only good to 130 Amps (90C insulation). Per code, that is too large of breaker--But marine wiring standards (and exposed wiring outside of conduit) certainly support higher current of 210 Amps
- Random DC Wiring... If using 14 AWG, you can use 15 Amp breaker/fuses (most "cigarett" adapters assume 10 Amps current at least... Use 15 Amp branch circuit at least).
https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm (NEC AWG current standard)
https://www.westmarine.com/WestAdvisor/Marine-Wire-Size-And-Ampacity (example of Marine current standard)
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
power system location -These are decisions you will have to make... Some thoughts:
Option 1: Right up against the cabin.
Pros:
- short run from inverter to breaker box
- short run for dc loads
- easier to build? can literally make a closet on the wall...
Cons:
-farther from solar array site (maybe 80ft?)
-farther from genset at 35ft
- less safe? if fire - it is on cabin,
Option 2: Near generator so about 35ft from cabin and about 45ft from solar array area
Pros:
-maybe can use generator exhaust heat to warm up batteries in winter?
-safer? fire is farther from cabin
-closer to solar array clearing
Cons:
-dc loads are farther... about 35ft away
-long run for ac from inverter
Lead Acid batteries gas--Need to vent hydrogen to the outside for safety. AGM batteries are not supposed to gas, but if overcharged (or getting old/near failure) they will gas too... Gasing also can include electrolyte (acid+water) mist--You don't want that near electronics/valuables/some folks are very sensitive to sulfur (rotten egg) smell from battery gassing. Keep battery wiring safe from kids/falling tools/etc. Make the batteries easily accessible for voltage/current measurements (adding water if Flooded Cell)--And for checking voltage/current. Mount on north wall to keep out of sun (batteries like cool--age faster if hot).
I would not use genset "waste heat"... The little euxxxxi gensets generally mix exhaust and hot air--You do not want the moisture from the exhaust (roughly 1.5 gallons of water for every 1 gallon of fuel). And you do not want carbon monoxide in the home.
Mounting on outside cabin wall... Weatherproof enclosure, venting for gasses, possible heating from inside in winter (Muffin fan). Suggest the interior of box be fire resistant materials, and acid resistant/sacrificial that you can change later, etc.). Make sure wiring is protected from cuts/insulation failure).
If you ever installed Li Ion type batteries--Those really worry me if there is a fire. They can produce some incredibly dangerous chemicals (such as hydrofluoric acid) and make it a toxic waste site (cannot simply "clean")--Also there is nothing you can really do other than let them burn themselves out. For a large Li Ion bank--I would install it away from any structures and things I care about--Just in case. (Li Ion do not like below 40F or so--Need heat when cycling).
Sending DC power any distance is always problematic. 24 volts is "easier"--Installing a buck type DC to DC converter inside the cabin (24 to 12 VDC) works OK.
For any "reasonably" sized solar panel system you will be designing--Most likely you will use an MPPT type charge controller... There are models that have 100-150 VDC max input voltage (around 60-100 Vmp-array max voltage). And for larger arrays, even 600 Volt systems. Those will let you use smaller copper cables for those long distances.
In general, you want the battery bank and power systems close to your home/cabin so you can keep an eye on everything--You don't want to trudge through 150 feet of snow or trail just to do your monthly inspection and maintenance (AGM are low maintenance--Not like you have to water FLA batteries).
The details do matter--So finish up your back of the envelope design (batteries, inverter-charger, solar charger, solar array, DC loads, etc.) and start picking the hardware to support those units.
And you can get DIN rail DC rated breakers for pretty reasonable prices too:
https://www.solar-electric.com/residential/circuit-protection/circuit-breakers.html
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
"I suggest not going below 50% for "planned" operations. Yes, you have a longer cycle life--But for a 1/2 year weekend system--Not sure what it "buys you". Also, as the batteries age and have reduced capacity... 20% loss of capacity (for one brand) is "end of life"... But trying to keep over 50% in normal operations does give you some room for loss of capacity from aging (battery with 40% loss of capacity--Your system still meets your needs) and for the "oops" occasions (ran out of fuel, can't start genset, company used up more power than planned)."
My cabin is currently 6 month out of the year while 6 months of winter it will sleep in freezing temps at 95-100% SO but i do hope to use ti year around in 2-3 years.
Then during the "season" I do use the cabin, I hope, to arrive at the cabin, use it, leave and have the batteries charge while I am away via solar array.
Cabin will be dormant between Nov-Apr. So those months are not relevant for the next 2-3 years. And when I do start going there in those months I will need generator to charge. I am near Port Jervis NY FYI.
Now I know I wrote 280ah but that is probably never going to happen. Only way for it to happen is if I use much much more than I measured on my last trip (not likely at all) + I get zero sun during those 3 days and solar panels won't charge. So not very likely.
Using your math, average between Apr-Oct: 4.6. Let's assume 1200 watt array:
1,200 Watt array * 0.77 panel+controller derating * 4.6 Hours of sun (Apr-Oct average) = 4,250 WH per average Apr-Oct day
I think I can even go with a much smaller array and still not ever reach 50% plus have them fully charged when I come back. Looking at my measurements last time and instead of 1200watt use 600watt array:
- 100pm-743pm 0.726kwh day 1 "short"
Batteries would have been probably almost fully charged by night time since so little usage plus half day or so to charge. So this day is almost irrelevant- 743pm-700am 1.208kwh night 1
Woke up to batteries at about 88% SOC (almost full..)- 700am - 740pm 1.861kwh fay 2 "long"
So assuming 1.9kwh usage, 2.1kwh back from 600 watt array, and batteries started the day at 88% SOC...
9.6 kwh (batteries at full aprx) - 1.21 (night before) - 1.9 (day use) + 2.1 (daily solar output of 600watt array) = when I went to sleep at night: 89% SOC..... So again batteries are almost fully charged even if I am using 600w array. So yes - this day could have been overcast completely and zero output from solar panels. If that was the case then SoC would have been 67% by night.- 740pm- 654am 1.065kwh night 2
So continuing this worst case scenario of zero solar charge the day before plus now a full night means that I would have woken up to 44% SOC. under 50% but not by a ton... Now if today is technically my short day so nearly no usage (0.27kwh) = bringing my batteries to 41%. SOC. but now - no more usage and many days to charge.
Then the conclusion is that if I do not have a "good" sunny day during my long day or in the next following days while I am gone.. batteries will dip to 44-38%. but they should eventually get back to full easily within a couple of days of charging even on a small 600watt array.
If I get a decent sunny day then they will essentially be almost always at a full SOC or very close to that...
Then question is... is it that bad for the batteries if they dip under 50% a few times a year? knowing that agm only last 5-7 years in general?
I can easily and cheaply just keep a 900-1200 array instead (pricing of panels seems to be quite low) - this won't fully proof the under 50% dips during the year but it just means that it will likely happen even less often. So maybe in the entire year maybe 3-4 times dipping under 50%... or zero.
What seems to really proof it completely is going to 600ah bank. If I do that then those numbers look much much different and it becomes basically impossible for batteries to even reach 50% and will likely stay above 75% all the time...
But that is not cheap and requires another $700... And what I gain from it is extending the life of my batteries way past what they should live anyway (the whole dilemma of my previous post - questions the importance of keeping batteries at 50% SoC when anyway they will day way before I finish my cycles)
My gut tells me to keep at 400ah, get a 900watt~ array, and see how it goes. If I find that batteries dip too often during the year under 50% - bump up my bank to 600ah and sleep quietly at night.
"Some charge controller manufacturers have even software that will "force" a battery down to 75% (adjustable) SoC to prevent "shallow cycling" from prematurally cycling the battery to death by daily 10-15% discharge/charge cycles."
Wow. that seems to be what will likely happen to me, right? assuming 900w~ array and looking at my usage. I feel like this will be a very common thing for me to happen since I do not use batteries that much and array will easily charge them back... so if that is "bad" should I get a charge controller that will do that?- ROMEX to genset--Make sure direct burial/wet location type if left outside (direct bury/conduit/etc.).
I plan on burring those pvc conduits and snaking wire inside.- ROMEX to AC breaker panel--Use 30 amp breaker maximum if 10 AWG cable
Thank you for the note. I will add this. I knew I needed a breaker for invertor for the whole interlocking generator bypass thing but I didn't note that it needs to be 30amp since it can send up more power.- 2 AWG from Bus to Battery (+ and -)--You want all cables to be same (total) length--Your drawing has longer cable run to upper battery and shorter run to lower battery--That would "steer" current to the lower battery string (less resistance).
Yes I know it looks like different length cables so thank you for pointing that out. I do remember that I need to keep all my cables in the same length. So on my diagram: blue cables (series) and yellow cables (parallel) will all be same length, Not sure if my red and black cable going from bus banks to inverter also need to be same length but I will keep those at same length as well (easy and all short runs).
Sorry for my repeated questions it is just that I want o make sure:
blue cables (series) = you said I should use 4awg but should I go 2awg just for the slim chance of doing 600ah bank in the future?
yellow cables (parallel) = same note as above.
red and black cable going from bus banks to inverter = 2 awg, right?- 170 Amp DC Breaker with 2 AWG cable. 2 AWG cable is only good to 130 Amps (90C insulation). Per code, that is too large of breaker--But marine wiring standards (and exposed wiring outside of conduit) certainly support higher current of 210 Amps
Sorry for confusion. in my 12v diagram I had a 250amp breaker. In this 24v diagram - you noted that I need a 170amp breaker instead. So do I need to also get a bigger wire? or small/bigger breaker. I will do what you say and to code or even better than code.- Random DC Wiring... If using 14 AWG, you can use 15 Amp breaker/fuses (most "cigarett" adapters assume 10 Amps current at least... Use 15 Amp branch circuit at least).
After reading your notes about power closet location -
I will put it away from cabin but closer and not next to generator. So probably about 15ft from cabin. So toilet fan will be about ft away... Then future led lights, ceiling fan, and tv - between 15-25ft. what awg am I looking at for 24v over such distances?
Finally,
My diagram is almost complete. But I do need to start looking at solar:
1. going back to what you said: should I pick up an mppt that will "force" battery to 75% before charging?
2. panels: I see on craiglist: used 300w panels for $85 and new 265watt for $150. Online on this site I see 330w panles for $213 (plus shipping). Big no no to buy used ones?
3. possible mppt's.. Victron 150v/35amp ($325) vs Victron150v/45smp ($392) vs epever 150v/40amp ($176). Any thoughts on these? Do any or both of them have that option to force to 75% like you mentioned? -
Midnite "The Kid" and Classic have a "rebulk" setting--I.e., the battery voltage needs to fall below xx.x volts to begin recharging:
https://www.solar-electric.com/midnite-solar-kid-mppt-solar-charge-controller-black.html (30 amp version)
https://www.solar-electric.com/lib/wind-sun/kidManual.pdfRebulk: Rebulk is the Voltage set-point at which the Float stage will terminate and return to Bulk. In Float, The KID will return to Bulk if a load placed on the battery bank reduces the battery bank voltage below the Rebulk set point for two minutes. The KID as a load controlNeed a second shunt and "MidNite Solar MNWBjr Whiz Bang Jr Current Sense Module" to allow controller to measure end charging amps (if you wish to use that to end solar charging)--May fit with shunt from Victron????
I did not see the "rebulk" option in the other two controllers you mentioned. I don't have anything to add about the choices you mentioned. Both seem to have happy users--The Victron family seems to be newer and offering a lot of new features (Bluetooth and high function smaller to mid-sized controllers that did not exist that long ago).
And there is always the idea of getting everything with the same brand--Networking functions between units (logging, remote control, integrated control) are very useful. You might want to look into that (integration with the Victron inverter-charger).
I would not worry too much about "shallow cycling"--But it does point to not "over-sizing" your battery bank too. Midnite makes nice controllers--But if (for example) Victron features are useful for you and make for a better "integrated system"--I would not choose Midnite over all those other bullet points for another brand.
Again--Most batteries are killed by under charging/over discharging. You could, for example, turn off your solar array for one day to get below the "shallow cycling"--But what if you forget to turn on the array the next day (or before you left)--Then you run the risk of over discharging/killing your battery bank. I really like a well designed system that you do not have to fuss with. Somebody will forget to "do something" manually and make for more problems down the road. Let the system shallow cycle and avoid manual intervention. People are unreliable.
These days, solar panel companies seem to come and go (especially in this economic climate)--So it is a good chance that you will end up "funding" your own warranty (if ever needed).
Standard "glass cover" mono and poly crystalline panels have a long life--And if you do not see any surface defects (chips, punctures in rear, cracks in cells, browning/blackening of cells, etc.)--They do have a long life.
Larger panels (>~140 Watts) typically ship truck--So ordering one or two panels can be expensive for packing and shipping. Larger panels (>~170 Watts or so), are heavy and awkward--So usually need two people to move around/install. Sometimes you can find a few panels from a local solar installer and get them cheap (no shipping costs). Don't buy panels (or any hardware) until you have done the paper design. You have to (more or less) match the panels (Vmp/Imp, series/parallel, distance) to the charge controller. A 150 VDC max input MPPT controller is a good place to start. Do the paper array design (array voltage and your minimum temperatures) and check the distance you need to run the cable and AWG size.
You may be overthinking the cycling/depth of discharge issue... Yes, deeper cycling is shorter cycle life.. But going to 25% SoC (deeper than 50% SoC) may cost you an "extra cycle" (i.e., if 75% = 1 cycle, 50% = 2 cycle, 25% = 3 cycle) out of a 3,000 cycle life (at 75% SoC)--It is not a big issue when deep cycles happen "on occasion".
What I try to do is help set "reasonable" expectations both in what the system can provide energy wise, and what the costs will be (battery life, hardware life, etc.)--With normal care and operation. If your first AGM battery bank lasts 5 years, you are doing well... Not unusual for a "new user" to "murder" their first battery bank (or two) with poor operational practices, or even the occational "oops" (left inverter on when leaving and came back a few weeks later, or in spring, with a dead battery bank--And need to buy a new bank).
Batteries are "consumables"--And you use them--Cost of solar power.
In your case--I would probably suggest staying with the smaller battery bank (say 400 AH @ 24 volts) and not go oversized on the array... For several reasons--Yes, you may "murder" your first bank--No reason to risk more money. And second, theft. Avoid lots of expensive hardware/batteries/etc. if you have a risk of theft (rural areas--It is amazing what people sometimes steal). At this point, even a "small to nominal" array will meet your basic needs (sunny weather weekends), and you are already committed/happy to use a genset as needed.
Get a couple of seasons under your belt and see how it works out. Maybe it fits your needs--Maybe in 3 years you move in and want to expand the solar/battery power system for full time use... "Expanding" systems is always a bit of give and take... Adding batteries to an older bank--Now you have issues of 1/2 a bank failing in a few years, and other batteries still working OK--Replace all or several years down the road the other 1/2 of the bank starts to go bad... With solar panels and charge controllers--Adding panels may require a second controller--And you may not find "matched" panels 4 years down the road for your existing set (matching Vmp/Imp as needed). Maybe you want a single larger controller, or add a second solar controller to your existing system... Power needs are a highly personal set of choices--And trying to predict your needs in the future--I am not going to guess.
A 600-800 AH @ 24 volt system will usually run a very efficient home (lights, fridge, clothes washer, water pump of some sort, LED TV, Laptop computer, cell phone charger, etc.)--In deep winter, the genset may get more use unless you "oversize" the solar array (a choice down the road--Not today). If you start adding A/C or Heat pump system, and making a full size home and more energy usage--Then pretty much new system design/installation is probably needed (48 volts, xxx AH, xxxx Watt inverter, etc.)....
How far for 24 volts... Say you want to send 10 amps @ 24 volts (240 Watts) 20 feet. LED lighting, DC to DC converter, etc. And a maximum of 1.0 Voltage drop:
https://www.calculator.net/voltage-drop-calculator.html?necmaterial=copper&necwiresize=2&necconduit=pvc&necpf=1&material=copper&wiresize=3.277&resistance=1.2&resistanceunit=okm&voltage=24&phase=dc&noofconductor=1&distance=20&distanceunit=feet&eres=10&x=47&y=25&ctype=size
20 Feet @ 10 AWG @ 10 Amps:
Voltage drop: 0.40
Voltage drop percentage: 1.66%
Voltage at the end: 23.6
As always, I suggest that you try one or two LED lights (say 24 VDC) on your system first and make sure that (for example) they don't flicker when you cycle other 24 VDC power... Some have pretty stable outputs, other may flicker with even minor voltage changes/surges (I had compact fluorescent "twisty" lamps that flickered even with normal 120 VAC voltage variations).
150 or 170 Amp breaker on 2 AWG cable... That is going to be your choice. If you put the wiring inside conduit--Then it has less ability to cool from normal air circulation. I have seen 14 AWG wiring @ 19 amps actual load @ 15 amp breaker (240 VAC electric water heater) run for 70 years without issues from the original apartment builder (eventually, had to address--Brand/model of breakers no longer available and I was getting "false trips" every few weeks with old 15 amp breaker).
Because of your short wiring runs--Voltage drop is not going to be an issue.
150 Amp breaker:
https://www.solar-electric.com/mrcb-150-amp-dc-circuit-breaker.html
4 AWG vs 2 AWG for battery interconnect cabling... That depends on the AH capacity of the batteries and the current you plan on drawing. If you draw 60 amps per string of 200 AH batteries... Then 2x or 3x parallel strings, you are still drawing 60 amps per string maximum... And if you keep the 2 kWatt inverter-charger, that is 120 amps / 2 strings = 60 amps per string vs 120a/3strings= 40 amps per string--So even less current per string...
The comment about 2 vs 4 awg cabling--It was more just an aside about the secondary issues you wan run into with battery banks. Balancing current between strings--And the "extra" little bit of resistance of smaller AWG cables in series strings can help balance current flow if you turn out to have "balance" issues in your bank. At this point--A roll of 4 AWG cables, a bag of 4 AWG cable crimp ends, and a 4 AWG cable crimper--Keeps your parts and tools list "simple".
You cable runs are short and easy to access. I would not "oversize" at this point. If you decide on a new/larger inverter--You will probably be changing/redesigning a large part of the system (solar array, charge controllers, new inverter-charger, new/larger battery bank, etc.). Design for the system you have "today".
Two loads I don't remember you mentioning (you may have, but this thread is getting long). A refrigerator and a clothes washer...
Refrigerators are what drive from a "small" off grid system to a mid-size system (typically 1,000 to 1,500 Watt*hours per day for an energy star "simple" fridge--And if you turn on the fridge and load "warm" food for the first day, it may draw 2,000 to 3,000 WH that first 24 hours). And having a clothes washer--Another labor saving device (use on sunny days, and/or with genset if needed).
An example of variable and "growing" loads as you hit weekend or full time usage...
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Sorry for getting this thread long Bill. I really really appreciate your help. Maybe I will start a new one to paper layout my solar.
150amp breaker - if that is what you recommend as the safest - that is what I will put in. Done
Battery and inverter cables - I do not plan on making my own cables. I will order them. I don't have many and I rather have them made well with a commercial press. Seems like the total cost of cables for me will be quite low anyhow. No run is longer than 14".
Then since I am buying them premade I will do 4awg for interconnecting cables.
I am attaching my final diagram. If you see anything wrong or that I should change please tell me.
I'll post a new one for the solar planning..
-
You can keep this thread going--I just did not remember if we ever discussed Fridge/Water pump loads for present or future use.
Your diagram looks good... Except for the bottom DC section. No Wire AWG, 24 volts from battery terminals (do not "center tap" a 24 volt battery bank for 12 volts--That will unbalance the State of Charge from the low vs high 12 volt batteries.
Technically, since you are using 10 AWG wire from genset socket to breaker panel/interlock--You could use 30 amp breaker (and even a 30 amp receptacle) if you ever bring a bigger genset (or parallel two smaller gensets) to your cabin. But this is "small stuff" you can address down the road when needs happen with a quick trip to the hardware store (pulling wire is usually the pain you don't want to repeat).
Other eventual wiring... Outside 120 VAC sockets (lights, sound, etc.) for summer use. Your system is getting large enough that you may stay with 120 VAC power for small DC appliances (TV, USB chargers, cabin lighting). Many of the small 120 VAC appliances these days are very energy efficient when compared to their 12 volt counter parts. May not be worth making a local 12 VDC bus for those devices.
I did not mean to suggest that 10 Amp @ 24 volt was what you needed (typically on, at least, 14 AWG wiring and a 15+ amp fuse or a 10 AWG cable to keep voltage drop "down" and a 15-30 amp fuse/breaker--Again max breaker based on wire rating)... Just an example of how to work the math and voltage drop. You talked about only needing 2.5 Watts for a 24 volt fan (12 volt in drawing). I know you probably have not focused on this section of your drawing yet.
If you want some 24 to 5 VDC usb power supplies, there are lots of those available:
https://www.amazon.com/s?k=24+volt+usb&ref=nb_sb_noss_1
Think also about how you shut down all loads during winter... I.e, one breaker (or other form of "master off" switch) from battery bus to a second bus that powers all of your DC Loads? One breaker on/off to put system to bed.
And a second breaker from battery bus for (eventual) solar charger to charge bank after gone and float during winter? Vs a set of "random" breakers that you have to flip on/off for winter shutdown (Inverter-charger, DC lighting, fan, usb outlets, 24 to 12 VDC converter, etc.). Big believer in keeping things "simple" (i.e., one master on/off switch for winter shutdown, but leave other circuits energized as needed). If you add 24x7 loads later that run during winter/off use (such as security/cell alarm, camera system)--You want to be able to install another breaker for addition branch circuits if/when needed.
All wires that leave the battery bus need a breaker sized to the wiring. Big breaker to AC inverter. Small breaker/fuse to fan wiring.
-BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
Yes you are right I did not work on dc loads yet since the only one I really need is the toilet fan... Which I am actually thinking of bypassing the one in the toilet (12v) and just running a 24v on the vent line instead. So I will just need to run power for this. II will need to create a switch or breaker for winter shut of for those.
Good point about those efficient 120v and not needing to go crazy with dc loads.
I came across something very interesting:
They make an inverter/charger/mppt - all in one!!!
The Victron one is perfect but it costs nearly 2k.
I saw this other one that costs a 1/3 of that and has many threads on this other solar forum (mainly people using it with lifepo4). People are saying it is a very good device... but we will see. For that price it is worth a shut especially since it saves SO much wiring and it has one nice all in one
I just need to verify that it has some of the functions that are important to me but from the looks of it - it has a ton of settings.
https://www.mppsolar.com/v3/split-phase-lv/
This is the manual that shows all the settings. There is no search mode and I am not sure how it works when connected to generator - if it still pulls power from batteries or ti does generator only. also not sure if I can limit power coming from generator but I doubt it. again for this price it is wild. $650 vs $1800 same Victron. And now with solar panels my dependency on generator is lower.
http://www.mppsolar.com/manual/SPLIT PHASE LV/LV2424 hybrid manual-20190717.pdf
Basic question about solar panels:
If I buy 4x 420w panels where each has about 49 VOC - can I then wire two pairs together in parallel and then in the two pairs together in series - so I stay under 100 VOC?
This all-in-one will go to 150v but they say the min you reach over 115v it stops charging not sure why.
I keep reading the manual. It has a list of options in order that you go in one by one and set. Many seems pretty straight forward. I will post a list tomorrow about those that I am not sure about.
I will start buying all parts in the next two weeks.
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