Trying to find the weak link in my solar setup

[littlebunnyhead]

I recently purchased a converted shorty with a solar setup installed and am having trouble diagnosing what needs to be upgraded in order to solve the problem I’m having. .

I have 500W of panels on my roof, and my 2x200ah deep cycle gel batteries are charging up to 12.7v+ most days if my daytime electrical use is moderate to low. However, even trying to keep our electrical consumption low, our battery monitor has been showing that the battery charge is pulled down below 12.1v overnight even running just a couple of small 12v fans and led lights.

Generally speaking, in a situation like this, would you add more panels (and upgrade the charge controller etc etc) so that the batteries are receiving more charge during the day, or add another battery or two to the bank to increase capacity? Or are both absolutely necessary?

Here are the components of my current system:
3x100w panels, 1x 200w panel
50a renogy mppt dc-dc battery charger/charge controller
2x 200ah renogy deep cycle hybrid gel batteries
1x 3000w inverter


Edited to add: I have read the mobile solar power book, and still have this question. So recommending that I read the book won’t help me out of this pickle.
thank you!

[rossvtaylor]

Hi LBH,

There are a few considerations here...and with what you've provided I'm looking at the batteries...or maybe the inverter draw. It looks like your system is charging, so we need to figure out why your system won't carry you through the night.

First, what's the "phantom" draw from that 3000W inverter? Do you know how much it draws when idle? I'd measure that, and the energy used by the fans and lights, to see if that would account for the battery drain.

If they don't then you might have bad cells in those batteries. I keyed on the Gel part. Gel cell batteries are super sensitive to overcharging and can be damaged, losing capacity, with just one overcharge or a charge done too rapidly.

With AGM or FLA batteries, the electrolyte is a liquid and the gasses produced during a charge...especially an overcharge event...bubble through the liquid. But in a gel battery, the electrolyte gel can be pushed away from the plates by bubble pockets and that separation of the electrolyte gel from the plate can remain...and wherever the electrolyte no longer hugs the plates it no longer works as a battery. So, one single overcharge event can damage the batteries permanently and, for this reason, I am not a fan of gels.

[Bert06840]

I agree with Ross above. If it’s not your inverter, you probably have killed batteries.

Buy one of these off Amazon (DC clamp meters), $29

And trace where the current goes:

[Rucker]

Five hundred watts of solar and a fifty amp charge controller should recharge your batteries easily unless you live in the Arctic Circle.

Does the charge controller show the panels are charging? If you can't tell, you will probably need that amp meter Bert suggests to check if the positive cable from the charger is providing amps to the battery.

Then, as others indicated, check vampire load/leakage. Turn off solar charger, and then turn off all devices being fed by the batteries, and either put an amp meter on the positive cable coming from your battery, or pull the positive cable off your battery and put a voltmeter on it. If any current or voltage is present, that's part of your problem. You can chase that down by systematically removing fuses one by one to see which circuit is leaking.

If there is no leakage, the symptoms you describe are most likely because your batteries have failed. I'm not an expert in batteries (or much of anything else, really) so I can't tell you why yours might have failed however the most common problem other than usage, age or improper charge configuration is too deeply discharging the batteries.

Do you live in a cold climate? That may be another factor for some battery types.

[Danjo]

I think that right now in North America, assuming a flat panel penalty of 25%, you’re parked in full sun, your panels are clean, and assuming your wiring is up to the task, you’re probably making around 1800Wh/day.

How much are you consuming?

Do you have a more accurate way of measuring the voltage on the battery bank? Maybe just around sunset and in the morning?

I have a very similar setup, but I haven’t been monitoring the batteries. I only have the charge controller to indicate percentage and I don’t trust what it says.

But if I did, my 600W/400Ah AGM setup can run a 12v fridge and lights and be around 85% in the morning. If my 1000W inverter sits on standby, it’s like 75%

[Simplicity]

All of the previous reply posters know more about this than I do, yet from one less knowledgeable person to another (the OP), I suggest you do some research on each of the components of your system. The more you understand each of them and how they interact, the easier it will be for you to use and maintain your system.

It's my understanding that (and yes, I fully expect to be educated if what I'm saying is not accurate):

Using similar solar panel is a positive. That said, knowing what type of panels and using consistent wattage may provide more consistent charge.

Using identical batteries that are in the same "health". One bad battery (like one bad apple) can spoil the whole bunch. You didn't clarify, but I'm assuming your batteries are 12v parallel (not 6v in series).

Inverters suck up some energy even if they are not inverting, yet are on, even in standby. Knowing your inverters features is really helpful.

Wires. Having the right size wires to carry the loads efficiently is helpful. Too small a wire can heat up under load, and heat that's not being converted to potential is wasted.

I know in some of your (OP) earlier threads that you bought this bus already converted. I hope some of the issues you were having then are getting resolved.