Mixed Panels and Controller Confusion: Advice Needed for Wilderness School

Re: Mixed Panels and Controller Confusion: Advice Needed for Wilderness School

Anima Center wrote: »

I mentioned our load early on, at least as measured by the controller which shows us using a very steady 9 to 10 amps of power at 12v, from 7am til 11pm, 16 hrs per day. We use no AC except the satellite internet box, run through a small 150watt inverter that is turned off at night. The only other significant draw is our two dual processor mac laptops. Does this mean 160 amp hrs of use a day, or is my math wrong?

You saw in one of my first posts in this thread how to evaluate your power usage. More or less, for the month of June, you will AVERAGE 140 +/- Amp*Hours per day production and you are using ~160 Amp*Hours per day...

For the most part, that is really too close... You either need more solar panels (2x as much would not be a waste of money) and/or a backup genset to make up for the lack of panels and sun (in bad weather).

As per battery bank size... 160 AH at 12 volts and 3 days of no sun and 50% maximum discharge:

• 160 AH * 3 days * 1/0.50 max discharge = 960 Amp*Hour @ 12 volts

In any case, if you discharge your bank that deeply--you really need a good backup genset and battery charger to get that bank back up above 80% state of charge (for good battery life). The following are min/max recommendations--not hard limits for recommend charging current:

• 960 AH * 5% charge rate = 48 Amp charger minimum
• 960 AH * 13% charge rate = 125 Amp charger maximum

A Honda eu2000i running a good quality 40-50 amp charger is probably about its limit (somebody here can probably tell you their experience)...

Iota 45 amp 12 VDC charger
Xantrex TC2 40 or 60 amp models

In theory, the Xantex TC2 60 am[p should be able to operate just fine on a Honda eu2000i (1,600 watt) generator--but I would want somebody to confirm that as I cannot.

Would like to be able to run the above for 3 days of clouds, rare as that is.

From a load point of view--the Flooded Cell battery bank is a better match for your requirements (storage capacity wise)--And with more panels (another 15 amps) and/or backup genset--would be a good fit (assuming the batteries are still good).

The AGM's are a bit small--but can also give you at least a couple days...

In the end, you may end up having to test the battery banks under your operational load and see how each works.

Plan is to remove the Trojans for now at least, wondering if I should get a larger controller and another panel, and if I should run the panels from lowest output to highest and then to controller?

In either case, I would get more panels (double what you have would not hurt) and wire them up. See how your existing bank(s) work.

-Bill

Re: Mixed Panels and Controller Confusion: Advice Needed for Wilderness School

What are your plans to connect the second 30 amp charge controller? In parallel with the existing panels, or getting a whole bunch of new panels?

Regarding a 55 amp IOTA charger on a Honda eu2000i--The maximum AC current input is listed at 12 amps (108 vac*12amps=1,296VA --Should be OK for the 1,600 Watt / VA rated Honda--but hopefully somebody with more experience with this setup can confirm). You might call the store and/or IOTA Engineering directly and ask (make them earn their money ).

It would be nice to get a Kill-a-Watt meter to monitor your charge controller's power usage--so you can monitor the battery bank as it gets full and the charge controller starts cutting back. Once you get to 1/4 power or so--you can turn off the genset and let the solar finish off the charge). Also, if you are going to use an extension cord between the genset and the charge controller--get a nice 12 or even 10 AWG heavy duty cord (if you can)... And keep it short. Don't get a 100' standard cord--too much voltage drop for the heavy power you want to efficiently move.

I would also get an inexpensive DMM (Digital Multi-Meter) that has, at least, 3.5 digits of accuracy (1.XXX).

And before you take things apart, measure the voltage at various points in your system when charging (and/or under heavy load). That will help you find if you need heavier gauge wire or not (for a 12 volt system--you almost surly need heavier gauge wire--but copper cable is not cheap).

For example. Measure the voltage to the input of your charge controller (should be ~16 volts minimum in full sun to ensure your are moving all of the available current to the battery bank). If you measure less than 15 volts (under full sun with batteries needing charging)--then you absolutely need heavier gauge wiring (and/or have bad connections somewhere).

The charge controller needs Vbatt+1 or 2 volts higher input voltage to properly charge the battery bank. If the input voltage is too low, then the output voltage will be low too (note: for pwm solar input voltage, if the battery voltage is really low--say 12-13 volts, the solar input voltage will be dragged down too).

Then measure the output voltage of the charge controller. Hopefully, later in the day you are seeing 14.4 volts or so (with low batteries, you may be seeing less while they charge).

At the battery bank, ideally, the voltage measured at the charge controller should only be ~0.100 volts higher than your 12 volt battery bank (with 30 amps of charging current). If the voltage difference is ~0.300 volts or more (cable voltage drop)--then the cable is defiantly costing you charging power into your batteries.

The charge controller needs to measure the exact battery voltage while charging--if there is too much voltage drop--then the controller will think the batteries are more charged than they really are and cut back on charging current.

If you can figure out the gauge of wire (diameter) and the run length (distance between source and destination)--and how much current is used/needed for each run, we can help you figure out the correct wire gauge.

And, at the battery bank, each battery should be seeing nearly exactly the voltage at the "common bus connection point" while under load/charging. If not--either the cables are too small and/or you have dirty/loose/corroded electrical connections.

Another warning--people rarely put fuses/circuit breakers in their battery bank wiring where needed (basically every parallel battery connection should be fused, plus any wiring leaving the bank and going to a load or charge controller)... And for systems with large numbers of parallel battery connections--properly fusing is expensive. So, for now, make sure your battery bank is in a realtively non-flammable area (and not sharing living space with your family, etc.). Battery fires are nasty business.

-Bill

PS: You are at a critical point in the design for your off-grid solar system... Your current system needs some work--Do you spend money on getting the system sort of working? Or should you not spend the money on the existing system and instead spend it on a "new system" that meets your needs and will work better in the long term.

My guess is you are going to patch what you have... It is the cheaper option short term.

Once you get it working better--When it comes time to replace your battery bank, come back and ask more questions. You will have more Solar RE experience, know your loads/requirements better, and we will be able to help you avoid some of the more common pit falls (like large numbers of paralleled batteries).

Re: Mixed Panels and Controller Confusion: Advice Needed for Wilderness School

Jess,

Ask NAWS about the Iota and eu2000i--they should be able give you the exact answer. By the way, Iota has an IQ-4 option--you don't need that at all--It is for long term float charging of a battery bank with utility power. Does not make any sense to run with a genset (that I can see).

Regarding the size of the genset--Honda (and others) do make larger and fairly quiet gensets too... Also, see if their is an RV wrecking yard around your area--sometimes nice 3-6kW RV gensets are available for not too much money (and have electric start too--may be a plus if you are not always around to start one).

Also, look at what makes sense for fuel... Gasoline is the default choice for many--but it is difficult to transport and store (need fuel stabilizer if stored for more than a couple months). If you have propane for other needs around your place (great for storage, clean burning), or diesel (you may be getting tractor fuel without road taxes, less flammable--does need a bio-cide to keep growths out of stored fuel)--a good diesel engine operated correctly will last almost forever. etc...

In the end, a genset sized to your needs can save you lots of fuel costs. Don't get an 8kW monster because somebody donated it... Those will take somewhere around 1/2 gallon per hour if they are running a 4kW load or a 400 watt load.

And, sometimes, you get several gensets. A small / quiet one sized to your (smallish) battery charging loads, and a second cheap/larger one to run your shop tools when needed.

Generators, ideally, should be operate at ~50% of their rated load minimum---They become substantially less fuel efficient as the loads go below that. Diesels, should be operated at 50-60% minimum of rated load or they carbon/"coke" up (with light loads).

-Bill

Re: Mixed Panels and Controller Confusion: Advice Needed for Wilderness School

I think it was Jess' intent to use two different Morning Star controllers--one programed for AGM, the other for flooded cell.

Probably also needs to figure which battery(ies) are good. Bank wise, based on his needs, the larger flooded cell bank is a better fit (if the batteries are still good).

In any case, balancing charging energy with bank capacity--and getting everything fully charged is important.

Eventually, a Battery Monitor of some sort (Victron Energy, etc.) will be nice once you have your "final bank"... It will help you immensely in managing your battery bank. It is almost the difference between having a car with or without a gas gauge for the fuel tank. (yes--battery monitors are not perfect either--because what they measure, batteries, are not perfect either).

The DC Amp*Hour/Watt*Hour meter (DC Energy Monitor) that AntronX recommended is a less sophisticated version of a battery monitor--and well worth having just to monitor your DC loads too.

-Bill

Re: Mixed Panels and Controller Confusion: Advice Needed for Wilderness School

An automotive charger may, or may not, do a good job of bulk charging the batteries. The automotive charger probably won't do a proper equalization.

The Iota's charge at 14.2 volts when the "jumper" is in. And float at 13.6 when the jumper is removed (PDF manual)... For off-grid applications, there would be no reason to ever "float" the bank at 13.6 unless you run the generator 24x7 (which is not going to happen at your place).

I still don't thing the IQ-4 module will be of much use for off-grid charging.

My preference for a charger would be the Xantrex TC2-40 or TC2-60... The original TC family was a nice charger and, I hope, the TC2 family is good too. The TC2 has power factor correction (as well as optional battery temperature sensing). NAWS lists the TC2-20 (too small for this application) and Xantrex has been way late on bringing out this product line and NAWS did not want list something that was back-ordered for 6+ weeks (from what I understood in earlier posts)... Check with NAWS to see if the 40/60 units are available from them.

But, I have no experience (or have read anything about them)--so I would at least ask NAWS about their opinion regarding the Xantrex TC2.

About remotes--Many devices have remote "heads" (like MorningStar for there charge controller, Xantrex for their TC2 chargers). Others, like the battery monitors have you install a "shunt" (large precision resistor) at the battery bank, and you run 2 pairs of small wires to carry the voltage information 25+ feet back to the instrument).

Of course, some of these options are not "cheap". And, since your battery bank is the "heart" of your system--Having the Battery Monitor mounted in a convenient location is probably the #1 priority.

Note that the suggested use for the Generator battery charging is to start the genset "early" in the morning and get the batteries 80-90% charged (at this point, the AC charger has cut way back on the charging current and the genset is probably beginning to be a waste of fuel)--then turn the genset off and let the solar panels take the batteries up the rest of the way.

However, if your battery bank is nearly dead (say 20% charged) and you want to get it above 80% state of charge. And you have a 1,000 AH battery bank:

• (80%-20%)*1,000 AH / 55 amps = 10.9 hours of charging

So, the first time, it may take 10+ hours to recharge your battery bank to 80% state of charge... And another 3-6 hours to get the last 20% charging (assuming the batteries are still good--not sure at this point).

Once you have your bank stabilized--then sharing charging with solar panels, you can probably get the generator run time down to a few hours per week (or none during the sunny months of the year).

You have a very large battery bank and it takes quite a bit of energy and time to get those guys fully charged.

-Bill