Battery Bank setup for a Skoolie conversion (with PV to be added later)

Hello all,

I have come over from Skoolie.net with a question about battery bank setup to use in my bus conversion.  People there say this is the place to ask about anything PV/power for offgrid use....

Before I go any further, here is the project bus (which I have named Jasmine):



So.... my plan is to use 6 volt 230AH batteries, 2 in series by 6 in parallel, for a 12V/1380AH bank, connected into an AIMS 3000 watt pure sine inverter.  I also intend to use a homebrew 12v generator setup connected into the battery bank to keep it charged up until I can deploy a PV array on the roof of my bus which should have room for 8 panels at a minimum.  I might be able to squeeze 10 on it if I can get small enough panels.

By my calculations I will need a minimum of 825AH of capacity to power my intended loads for the durations I estimate.  With only a 25% depletion before topping off I figure I will have to run my generator at least 2-3x a day to keep the battery bank charged.

So, what I need to know....

My inverter calls for using 4/0 cable from the battery bank to the inverter.  Can I safely use a smaller gauge of wire from each pair of batteries (with appropriate size inline fuse/breaker) from each pair of batteries to inverter?  The table I used specified 4 gauge for the ampacity the line will carry, but going up to 2ga would certainly be doable.  Or, would it be better to connect each pair to a bus bar and run the 4/0 to the inverter in one run, using the inline fuse/breaker on the main line?  The cable run will be short (I intend to have the battery bank inside the bus near the rear, in a compartment vented to the outside).  Also, would the 4ga cable be enough to make the connections between the two batteries in each pair?

Second, I know I will need an MPPT charge controller to connect the panels to the battery bank.  What I don't know is how many watts of panels I will need... and if I can connect them in one large array, or if I will need to split them up into multiple arrays with multiple CC's... but then the battery bank will also need to be split up into two or more arrays, which would mean multiple cable runs to the inverter.  Some quick and dirty math I did a while back indicates that 8 300 watt panels would *probably* be enough but I'm not for sure on that.  I don't want to buy too much panel and have wasted power... likewise I don't want to undersize the array and be having to run the generator to play "catch-up".

The ideal scenario would be to have enough panels to run all my loads and keep the battery charged up to near full capacity at all times to where I only have to run my generator on cloudy days (or if I need to run air conditioning, I know it's a losing battle to try to run A/C off a battery bank).

Oh and also, I intend to mount the panels in such a way that I can angle them for optimum power production capability when parked, but have them snug against the bus roof when traveling.

Any advice would certainly be appreciated.
As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.

Comments

  • AlleyCat67AlleyCat67 Registered Users Posts: 14 ✭✭
    I just realized I posted this in the wrong section.... if an admin or moderator could move it to the RV section it would be appreciated.
    As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.
  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    I have moved your thread to the RV forum.

    My first question--Do you need a 3 kWatt AC inverter? That is pretty big and would need a minimum of 1,200 AH @ 12 volt battery bank to reliably operate at rated output current (assuming flooded cell lead acid batteries at ~400 AH @ 12 volts per 1 kWatt of AC inverter output).

    In general, for off grid/solar power, extreme conservation is your friend. Hauling around a large/heavy lead acid battery bank is not great, as well as a relatively large solar array and backup AC charging system to keep it happy.

    Next question, do you need 12 VDC or can you go with a 24 volt battery bank (or higher)? A 3,000 Watt 12 volt inverter will draw (at full power):
    • 3,000 watts * 1/0.85 AC inverter eff * 1/10.5 battery cutoff voltage = 336 Amps
    I usually suggest around an 800 AH maximum battery bank--And go to the next higher voltage (12 to 24, etc.) rather than having a high AH battery bank (and high operating/charging currents).

    Charging wise, you should have 5% to 13% rate of charge. 5% minimum (weekend/seasonal off grid usage), and 10%+ rate of charge for full time off grid. For your proposed 1,380 AH @ 12 volt battery bank--Your non-solar charging source should be around 10% (20% maximum)--So at least 138 Amps (if home brewed genset--You should look for truck or Balmer (marine) type alternators--Automotive do not really output rated current for more than a handful of minutes before getting hot and cutting back on current. Also deep cycle batteries generally charge at 14.75 volts or so (higher for equalization). A Balmer with an external-adjustable regulator (or equivalent) is recommended for full/quick battery charging.

    For solar array, the recommended array would be:
    • 1,380 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,299 Watt array minimum
    • 1,380 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,599 Watt array nominal
    • 1,380 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 3,378 Watt array "cost effective" maximum
    People have made folding awning style solar arrays too (fold flat to side of RV for traveling) to add to panels on roof.

    Note, most solar charge controllers have a maximum (operational charging current) maximum in the 60-80 amps or so. For larger solar arrays at 12 volts, a 10% rate of charge would have a current of:
    • 2,599 Watt array * 0.77 panel+controller derating * 1/14.5 volts charging = 138 amps nominal maximum charging current from array
    Or you would need at least two full size (typical) MPPT charge controllers to use a 10% rate of charge array.

    If you did nothing else but arranged the batteries into 4 series * 3 parallel (24 volt @ 690 AH), your peak current (and charging current) would be cut by 1/2--Much smaller wiring needed, and only one (~$600) MPPT charge controller.

    Also, I am not a big fan of lots of paralleled battery strings. A 24 volt battery bank with Golf Cart batteries would be 3 parallel strings--A better operating configuration (in my humble opinion).

    Power usage is a highly personal set of choices--What would work for me (my choices of loads) may not work for you. What loads do you plan on using where you would need a 3 kWatt AC inverter? If you could cut back by 1/2 (peak and average wattage)--Your system would be 1/2 as big (fewer batteries, fewer solar panels, smaller genset, less copper for DC wiring, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AlleyCat67AlleyCat67 Registered Users Posts: 14 ✭✭
    I chose 12v over 24v because I will have several DC loads coming off the battery bank.... LED lighting, water pump, tank heaters, and heater blowers that I know of.  Also because I already had the almost-new 12V inverter from my last project bus (which never came to fruition).  I know the 24v would be better for all the reasons you stated...  would it actually be more efficient to step down 24v to 12v to power my DC loads?

    My AC loads consist of a laptop, printer, microwave, toaster oven, TV w/satellite receiver, Blu-Ray player, Xbox One, Wii, standalone ice maker and SodaStream machine, and sometimes the water heater (normally will run off propane but will have 120VAC connected as a backup, or when connected to shore power).  This accounts for around 550AH of my capacity (already corrected for inverter efficiency).  This does not include any heat sources for wintertime use (I will be fulltiming in this bus), still undecided if I will be using electric or propane heat (condensation is a huge issue with propane).

    Granted, not everything will be running all at the same time, which is why I figure a twice-daily charge cycle will be sufficient.
    As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.
  • mike95490mike95490 Solar Expert Posts: 9,581 ✭✭✭✭✭
    I too, will suggest a 24V system.  You are expecting too much from parallel batteries.  install a 24V truck alternator, there should be space in the engine bay to add one in.   Get a good isolator, and build a small house 12V system for the 12V loads and leave the heavy lifting for the 24V gear.

     It will be cheaper to buy ice than to make it, microwave is useful, but toaster over wastes LOTS of heat that does not end up in the food
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 32,639 admin
    Have you looked at Diesel water/air heating? (assuming the bus is diesel). Direct vented outside--So no combustion gasses from propane into the RV (catalytic heaters typically).

    https://www.webasto.com/int/markets-products/recreational-vehicles/heating-solutions/

    No--24 vs 12 volts is not going to be an efficiency issue. It is the simple size of copper wiring you would need to support 336 Amps (3kWatt AC inverter @ 12 volts--Remember that you have 2x the current for inverter surge power). If you use NEC (which is more conservative):
    • 336 amps * 1.25 NEC derating = 420 Amp branch circuit minimum (wiring+breaker/fuse rating).
    You are (if single cable) looking at ~600 kcmil copper wire. (roughly $10 per foot).

    https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    And if you want to run 336 amps on 600 kcmil wire, with a maximum of ~0.5 volts drop for 10-15 feet maximum (one way run) or so...

    If you have experience with working with heavy cables (or multiple parallel X/0 cables) and breakers/fuses... That is great. Personally, I would suggest avoiding it.

    If you get a modern AC-Inverter (not cheap)--They include not only the inverter function, but have a nice internal (programmable) battery charger function too. Use shore power or an AC genset for battery charging when needed (nominally a better solution than a DC genset/charger).

    I am all for "balanced" system design. When you go outside of the "comfort zone" (high AH battery bank with low voltage; large inverter for RV, etc.). And for off grid living--It is almost always cheaper (cost effective) to embrace extreme conservation and using alternative fuels for heating/cooking/hot water (vs solar electric).

    With larger off grid systems, electric cooking (microwave, toaster oven, crock pot, etc.). But it is all math. Use a Kill-a-Watt type meter to measure / estimate your AC loads for various things.

    Different loads "stress" your power systems in different ways... Microwaves can take 1,500 Watts for 20 minutes per day -- That requires a big battery bank+inverter to supply peak power. A laptop computer+stuff at 60 watts for 12 hours per day needs a large battery bank because of the many hours of energy usage:
    • 1,500 Watts and 400 AH per 1,000 Watts of load = 600 AH minimum battery bank (@ 12 volt) (based on peak current/power)
    • 1,500 Watts * 1/0.85 inverter eff * 1/12 volts * 1/3 hour per day = 49 AH per day (based on energy used per day)
    • 60 Watt computer+stuff * 12 hours * 1/0.85 inverter eff * 1/12 volts = 70.5 AH per day (based on hours of use/energy used per day)
    So, the Microwave "forces" a very large battery bank based on peak power usage.. If you want 2 days of storage and 50% maximum discharge (recommended/typical optimum for full time off grid cabin):
    • 49 AH per day (Microwave) * 2 days * 1/0.50 max discharge = 196 AH (at 12 volt) battery bank (microwave)
    • 70.5 AH per day (computer+stuff) * 2 days * 1/0.50 max discharge = 282 AH (at 12 volt) battery bank (laptop computer)
    Each load has its own profile and performance requirements. When you do off grid--You are the power systems engineer looking for optimum/cost effective/maintainable solutions .

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • AlleyCat67AlleyCat67 Registered Users Posts: 14 ✭✭
    The bus is diesel, yes... and I have looked at radiant in-floor and forced-air (like the stock school bus heaters).  That actually is the direction I want to go for heat.  Problem there is, the boilers are a bit out of my reach price-wise for new ones and I simply cannot find used ones close by.  The condensation is caused by the unvented propane, a situation I seriously want to avoid.

    I don't really have much experience with big cables.... the largest I've ever messed with is 4AWG to connect a 2500 watt inverter in my truck back when I was over the road.  Dual 4AWG input and output thru a 500 amp breaker.  It was fun trying to get those cables made and installed.... this is probably gonna be a lot worse.

    Agreed on the price of the inverters... that 3kw 12V inverter was like 600 bucks when I bought it for my last bus (that project fell through) and I can't imagine they've gotten any cheaper.... kind of why I was wanting to use it rather than pop for a new one.... but if it's really that much better then perhaps I should take another look.  And that inverter did include a charging function so I'm familiar with that aspect of them.

    I hear you on the alternative fuel for some things.... my water heater will primarily be propane powered, with the 120V strictly as a backup for if I run out of propane unexpectedly, or when on shore power.

    I don't have a Kill-a-Watt (yet)... I've just been using the manufacturers power ratings to get my power baselines.  I'm sure they're not entirely accurate but I need some base to start from.

    Regarding the earlier comment about toaster ovens generating a lot of waste heat.... yes, they do.  But, you can't bake a cake in a microwave.  I tried it once..... let's just say that the experiment was less than successful.  The main thing the toaster oven would be used for would be things that don't cook right in the microwave.  And the other appliances I listed are things I already have that will be used, that's the only reason I listed them.  Just can't see paying storage on things that I could use while boondocking.  But I'm getting off track again....

    The power estimates I was using, I tried to estimate higher than my actual usage would be to include a safety factor so as not to deplete the batteries too far.  I'll have to go back in and look at my numbers again, and change the formulas to use 24V rather than 12, to see what I get, and what I might need to change.

    Thanks everyone for the input thus far.... don't want to make an expensive mistake with this stuff.
    As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    One of my cousins has one of these on his boat and gives it rave reviews everytime he talks about it.

    just sayin... YMMV   http://www.myboatsgear.com/hurricane-ii-combi-heater

     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • AlleyCat67AlleyCat67 Registered Users Posts: 14 ✭✭
    That's a nice one all right but way out of my reach.
    As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    there should be a more economical option for  boats somewhere....?
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    There are a lot of fishing boats which have diesel stoves with hot water tanks, they heat the boat, heat the water and you can cook, has an oven to boot, you can bake those cakes you were talking about and ditch the toaster oven, during the winter at least. There are many decommissioned fishing  boats as the industry is dying especially in British Columbia Canada perhaps you could pick up a used one, try Popeyes sailors exchange, North Vancouver BC. Tried to copy a link but failed Google will find it. Think of your bus as a boat with wheels.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • AlleyCat67AlleyCat67 Registered Users Posts: 14 ✭✭
    edited November 2016 #12
    Boat with wheels..... yea I guess it kind of is...... the term land yacht comes to mind as well.  Multi-purpose units like you were talking about would save money but the downside of that is that if it goes out that's several things that won't be available.... the hot water would be the main thing but there again I could just keep the existing LP/AC water heater as backup, as the system I have designed has bypass valves in for winterization or if it would need to be serviced/replaced.

    EDIT:  According to Google, Popeyes Sailors Exchange is permanently closed.  :-(
    As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.
  • mcgivormcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    Try marine consignment as a search, those stoves are slick and quiet too.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • AlleyCat67AlleyCat67 Registered Users Posts: 14 ✭✭
    That I will, the new stuff is a little out of reach, some gently used stuff should be a lot cheaper and last a while too.
    As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.
  • oil pan 4oil pan 4 Solar Expert Posts: 767 ✭✭✭✭
    If you have 6 batteries in parallel you could run a 6 gauge wire from each battery to the inverter and be all set.
    Put a 50 amp fuse on each wire as close as possible to the battery.

    To get a 13% charge rate on 1380ah is about 180 amps. If you went absolutely panel crazy and figured out how to put eight 300 watt panels on there that would give you 184 amps. If you had the optimal angle towards the sun at any given time.
    If you set the panels flat they are only going to produce around half of their rated amps at peak.
    I say put as many as you can fit. Since you have around 4x the amount of battery you will use in a single day you have the potential to run for more than one day.
    The more panels you put up the less generator run time you will rack up.

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • AlleyCat67AlleyCat67 Registered Users Posts: 14 ✭✭
    edited November 2016 #16
    I've got about 35 feet of length to play with so eight panels should certainly fit with no problem (four down each side, figuring they're about 2 feet by 4 feet, give or take).... and parking with one side or the other facing south would mean leaving the panels on that side down against the roof while jacking the ones on the other side up to maximize exposure, if I understand it correctly.  Granted in the winter I won't have a lot of usable sun but summertime will be better.  And yes, I was kind of hoping to have multi-day capacity in place just in case, after all it's not gonna be sunshine every day.

    Appreciate the info!
    As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.
  • Iceni JohnIceni John Solar Expert Posts: 103 ✭✭
    edited November 2016 #17

    Hi AlleyCat,

    It sounds like you plan on having something broadly similar to my bus's PV installation.   I have eight grid-tie panels in two separate sets of four, each panel individually tiltable from 21 degrees down against the roof, to level, or to 21, 33 or 45 degrees up.   Each set of four panels is wired in parallel and feeds its own 60A charge controller that in turn charges its own set of four golfcart batteries wired in series and parallel, then the two battery banks' outputs feed through 250A Schottky diodes to a common DC load center that powers the inverter and house DC loads.   I use 4/0 and 2/0 for all my battery cables, and 4/0 to the inverter.   You really can't have too fat cables when dealing with large DC currents  -  if I could find 250MCM-size cable and lugs I would have used that instead!   It's important to crimp the lugs well when making cables for high currents:  the common hammer-type crimpers won't do a good enough job, so a set of good circumferential crimpers like the FTZ 94284 are well worth it.   NAWS is still the cheapest source of tinned 4/0 lugs, less than $2 each, and decent 4/0 welding cable is no more than $4 a foot from eBay, so it's really not much more cost to do it right the first time, instead of using too thin cable and then having voltage loss.   I use Blue Sea switches and VTE pass-throughs and fuse holders, good quality and reasonably priced.

    Before you buy an AIMS inverter you may want to research them carefully first  -  some folk have had less than satisfactory experience with them.   There are other brands which may be better quality for not much more money.   NAWS sells good inverters  -  check them first.   Samlex/Cotek are decent-quality inexpensive inverters, especially their SA-series that can handle reactive loads better than other budget inverters.

    I would suggest aiming for the ideal 13% upper charge rate for however many batteries you'll have, if only because bus roofs often are not oriented ideally compared to home installations, then you should be able to keep the batteries correctly charged even in winter or if parked at less than the ideal position to catch the sun.   My 2kW of panels will (theoretically) charge 900aH of batteries at about 13%.   I still have enough space for two tiltable water-heating panels which should provide my hot water most of the year without needing to use my propane water heater, and any excess power from the PV in the afternoons after the batteries are fully charged can be fed into the water heater's electric element instead of going to waste.   I will use electricity quite sparingly, so 900aH should be plenty, enough to normally only discharge the batteries to about 75% SOC after each night.   With careful use of electricity I should be able to last three days before reaching 50% SOC if the sun's not cooperating, at which point I'll use the emergencies-only generator to bulk-charge the batteries back up to 85% or so.   I plan on using one or two small chest freezers, one converted as a fridge and the other maybe as a freezer, and they will be powered by their own separate small inverter to minimize standby power consumption.

    I looked at a few Thomas buses before I found my Crown.   I almost bought a 1989 Thomas WestCoastER, but was outbid by a church   -  that was a neat bus, with full air suspension and disk brakes.   What engine and transmission does your bus have?

    John 

    40' Crown bus with 2kW of tiltable panels on the roof:

    Eight Sharp 255W, two Morningstar TS-MPPT-60, Magnum MS2000, Champion C46540 generator converted to propane, eight golfcart batteries, and maybe a small Exeltech inverter for the fridger.

    Southern California

  • littleharbor2littleharbor2 Solar Expert Posts: 1,698 ✭✭✭✭
    Early in this discussion you mentioned "8- 300 watt panels". Keep in mind 300 watt panels are not "2 foot by 4 foot, give or take" You might be able to find a 60 cell 300 watt panel which is approx. 39" x 65". More likely a 300 watt panel will be a 72 cell version which is more like 39" x 77".

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

  • AlleyCat67AlleyCat67 Registered Users Posts: 14 ✭✭
    edited November 2016 #19
    Hey John.... yea we talked about your setup over on Skoolie.net a little while back and you showed me video of how your panels were set up.... I liked the idea so I want to do something similar.

    My Thomas has the MBE906 engine, which I know tends to use oil so will have to watch that.... still trying to figure out what transmission it has, I'm thinking Allison 2000 series but the ID plate doesn't say... the print has faded off and the stamped numbers are meaningless.

    I already had the AIMS 12v inverter, was gonna use it until I can afford something bigger and better.  Just because I'm boondocking doesn't mean I won't want a few creature comforts... I do like my satellite TV and XBox a little too much.  Hopefully by getting back to nature I won't use them as much, but I'm getting off track.  With the 12 battery bank I was planning to use changing from 12v to 24v won't require much rewiring.

    I was pricing all the PV components a little while back... pricey to say the least so will probably have to do it in stages... but if something is worth doing it's worth doing right the first time... so maybe I will sell that AIMS inverter and use the proceeds to finance a 24v one like was talked about earlier in this thread, if I can find one I like.

    Glad I heeded the advice over on Skoolie.net to come here for PV advice.... it's given me plenty to think about, things I hadn't considered before.... enough in fact that I'm gonna have to redesign my DC power plan to take all this good advice and put it into the new plan.

    Littleharbor.... thanks for that info... I now know that I can put a maximum of 10 panels on my roof instead of the 12 I was thinking I could get up there.  This too will have to be factored into the redesign.
    As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.
  • AlleyCat67AlleyCat67 Registered Users Posts: 14 ✭✭
    Well..... I found an online calculator to calculate battery bank and array sizing..... and the results are less than encouraging for sure.  I've about come to the conclusion that I may as well forget about a solar array because with the amount of peak sun time around here I will need 15 of the 300 watt panels to power just the AC loads thru 24v inverter (not including a/c or heat, or anything else I hadn't gotten around to adding in).  I was able to get it down to 8 panels by making some load concessions (on paper) but some of them I'm not willing to make, so my genny will be running quite a bit, and if I'm running the genny anyway that kind of defeats the whole purpose of deploying solar. So I guess that side of it is out, or at least reduced in scope by transferring some of the loads to shore/generator only.  I was SO hoping I could deploy a system that would power everything so I would only have to run a generator if it was cloudy/rainy/etc, or if I need to run a/c, do laundry, that sort of thing....

    There will still be a 12v system in place to power lighting, water pump and tank heaters, and other 12v accessories (phone chargers and such), with 2 140 watt panels and 6 batteries I can power that for up to 2 days solely off batteries and only go to 25% depth of charge, unless it's gray and dreary for longer than a day or so..

    Hummmm....... wonder if looking at 48v systems would make a difference, or if it would be too cost-prohibitive to do...... of course they don't make a 48v alternator that I know of so it would strictly be PV or generator to recharge them....
    As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Don't go to 48V if you can not feed a 24V bank.... you will be way worse off WRT using PV to recharge.... Unless you halve the AH  rating of the 48V bank... ie draw same number of Wh in each voltage, 24V & 48V

    When planning our place, all OG, i sat down and filled in my projected use to a spreadsheet divided in hourly increments at first and then I did the estimate in  15 minute usages.  I came out with ~3Kwh per day with a 3 day autonomy... and so far this year we have had several cloudy rainy spells and we got down to 75% SoC after 3 days of ~ 0.1KWh input...  and only 1680W of panels so far, more to come...
    try the spreadsheet way, with time across the top going from 07:00 to 22:00 and the night is one time space to itself... Vertically list each of the power gobbling items, even the small wall warts count up in a hurry.. then review each until you get to see just what your system WILL power for you and use the gen periodically to boost your batteries...
    I would send you the workbook but it is at home and I am at the LAKE!
    enjoy
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • AlleyCat67AlleyCat67 Registered Users Posts: 14 ✭✭
    That might be an option.... fortunately I am somewhat fluent with Excel so shouldn't be too difficult to work something up and see how it shakes out.... as I said before not everything will be running at one time but as an overall number seems way high.  Maybe broken down into blocks, and give 'em a good charge before retiring for the night....
    As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    edited November 2016 #23
    I urge you to read and reread Bills post#3, again and again until it makes sense. Otherwise youll make all the same mistakes most people make. With an RV most often people work backwards from the roofspace. See what battery that PV will support (0.1C) and what inverter that battery will support (0.25C). Its not rocket science (but not too far off it, feels like sometimes).
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    My work book is about 6 or 7 sheets and goes right through the calcs / comparisons needed.... I head in to town on Monday afternoon.  Will try to locate the file and advise
    Definitely do the assessment as you may have done something like double counting or ??

    have fun...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • AlleyCat67AlleyCat67 Registered Users Posts: 14 ✭✭
    I don't think so but you never can tell.... maybe the workbook I did the initial calculation in was wrong and the online tool gave me the real numbers.... I'll have to plug everything back in since I closed them and post it.
    As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    I just twigged that you have ~ 150% of what I have in Ahr for batteries, mind you I don't need Air Con... or MicroWv, but we do use n induction cook top in the summer  1800W max.. keep it < 1500w....  so there should be some excess in there.
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Marc KurthMarc Kurth Solar Expert Posts: 953 ✭✭✭✭
    If it were my rig, there would be 2 battery banks. Not as scary as it might seem at first.

    One chassis bank at 12v to include starting duty plus 12v devices - and maybe a 500 watt intverter for accessory type loads. The house bank at 24v with the larger inverter - but not over 2500-2800 watts at 24v in one inverter, without a good reason to do so. I prefer multiple inverters if more than 2500 to 2800 watts is really required. It is done all of the time.

    Many conversion projects install the 12v bank first in order to get functionality, then grow the system on the 24v side as budget permits. Since the house bank is connected to its own alternator and its own inverter/charger, there is little complexity to the wiring.

    I like providing a little "boost" power with a small highly efficient generator to supplement when needed. But large alternators can make your life easy when sized based on your loads, battery type and expected time underway. A little bit of engine operation with a pair of large alternators can put a whole lot of energy back into your battery banks in a big hurry when really needed. Not to mention helping to support rooftop air on the road......assuming you are set up for it. To be extreme,

    I have been involved in many conversions from Prevost's down to Sprinter's to teardrop trailers, but no school buses yet. Some have monster battery banks with 2000 ah at 24v, on down to one Group 27 - and everything in between.

    Battery selection is critical for the reasons already outlined clearly:
    How much load can you put on them without causing excessive voltage sag at lees than 100 SOC?
    How fast can you charge them without shortening their lifespan?

    One thing that I've learned is how little that I know.


    I always have more questions than answers. That's the nature of life.
  • AlleyCat67AlleyCat67 Registered Users Posts: 14 ✭✭
    A quote I heard once, not sure who it is atrributed to.....

    "I am unsure of everything except the fact that I'm certain to remain unsure."

    That's me in this scenario.  I do know some.... just enough to be dangerous.  Never having taken on a power project of this magnitude, it is a little overwhelming.  I've installed plenty of electrical stuff in the past, both 12v and 120v, but designing a power system from the ground up.... it's new territory to me.  So I'd rather make the mistakes now, in the design stage, then get something built and have to tear it back down to re-do it.  I'm actually more confident in my AC power design right now than I am in this.... at least with AC as long as you observe proper connections and don't connect a hot to a neutral or ground it's pretty straightforward...

    I've got another setup I'm looking to pursue for road air..... drive an a/c compressor and a small automotive alternator with about a 20hp engine mounted under the bus somewhere and use the alternator output to charge the 12v house batteries while underway, and use them to power the blowers.  The trick there will be getting the condenser and evaporator placed and the lines run.  The smaller components are much more flexible in their placement, as long as they're connected at the proper point in the system.  Plus I'll be able to run the air with the road engine shut down.  (This is still very much a work in progress.)
    As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.
  • scrubjaysnestscrubjaysnest Solar Expert Posts: 175 ✭✭✭
    We spend 6 to 8 months off grid, boondocking. Some thoughts a little beyond what has already been mentioned. Microwave/convection oven, run a generator. Air conditioning go to a campground with shore power or run the generator.  Propane heat is what we use, if you properly vent the bus condensation will not be a problem; this is a trail and error thing.
    Conversation, conserve, conversation; learn what you can really do without. We got by on 200 watts of solar until August when I added another 100 watt panel. Our worst case usage is ~50Ah in a 24 hour period. Most of that is the propane refrig with electronic controls.
    2 - laptops & tablets, 1 phone, and 3 fans.
    Rather then use the hot water heater boil water on the gas stove. It's all about learning to conserve.
  • AlleyCat67AlleyCat67 Registered Users Posts: 14 ✭✭
    Yes it will definitely be a learning curve to go offgrid...... I have a coleman stove and a propane BBQ grill so boiling water on one of those as needed would also be an option, I actually had not considered that.

    Thanks for the info.
    As a level 1 burglar, Bilbo got a pony when he accompanied the level 60 dwarves on the Smaug the Dragon raid.  Those powerlevelers probably invited him solely so he could trigger fellowship attacks for them.
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