Why are my batteries failing in my solar setup?

Question

I have a simple setup: 1 55w Panel in 12v mode, feeding a Trace C35 charge controller with a 15amp meter in series, charging 4 17aH 12v batteries connected in parallel. Then a 300w inverter with a 15amp meter feeding off the batteries. I have used the inverter only minimally 1 or 2 times a week for a few hours to power two table lamps with 15w CF lightbulbs. After a month or so the batteries seem to lose there charge and last fewer hours until they fail to charge up again. I have put a trickle battery charge on them to try and bring them back with little success. Is my setup wrong? I have an 88aH AGM battery I used for a while, then it seemed to do the same thing, so now I am on my second full set of 4 new batteries.

Answer 1

You have at least two problems:

1. your solar array is too small, especially for short winter days,  it may only be pumping in a total of 150watt hours per day.

2.  your inverter is probably draining too much power when idling, maybe just 10  watts per hour, but in a day that is more than your array puts in.

for quick solutions, get a second solar array and parallel the original, also turn your inverter off when not in use.

Other things to do are to get a good Soneil charger to start your batteries off with a good full charge, and make sure you have no other loads on your battery and inverter.

A trickle charger on a 64ah battery bank  would be useless, you need to be hitting each battery with about 3 amps apiece to bring them back up.

Answer 2

i'm not good in electric things but maybe you are not following some of the guidelines needed to be followed. if you are sure you are following it, maybe it is your things which has the problem. try to ask an expert about it so that you can be guided more.

Good Luck!

Answer 3

I'd like to know the answer to that too!!!

Answer 4

It don't matter if a battery is setting on concrete or not.

Your system is undersized big time for the amout of batteries and just truning on your inverter will use about 20 watts with no load. 12 volts times 1.5 amps is 18 watts so it is pulling more then your solar panel is putting in the batteries.

Read on and you will see where I got the 1.5 amps and 18 watt out put from your solar module even if it is a 55 watt module.

55 watt module at 17.2 volts you have about 3.2 Amps.

Using the C35 controller you loose 5 volts and the amps that goes with it because the C35 will not down convert. It connects the solar module direct to the batteries. This pulls the 17.2 volts down to the battery voltage. So you loose about a third of your power.

So you are down to about 2 amps at 12 volts.

Now going from memory you lose about 12% in the C35 so you are down 1.76 amps.

It takes about 15% more to charge a battery then what you took out of it. So you are now down to 1.5 amps

In the real world you are only getting about enough power to charge about 15 AH in batteries.

On to the batteries. If you discharge your batteries below 50% discharge and leave them that way very long you will kill your batteries very fast. If they are not deep cycle batteries they have too thin of lead plates and are doomed.

12.6 volts is full charge

10.0 volts is dead (you hit this level you buy new batteries)

So 11.3 volts is 50% discharge

You said you had a battery of 88AH. 50% is 44AH so at 1.5 amps it would take 29.3 hours of sunlight to charge it back up. Which you could never do any way. You need about 8 amps or 120 watt solar panel with an MPPT controller to even get close. Would still take over 6 hours of good bright sun.

Answer 5

for this kind of use you need deep cycle batteries as in golf cart batteries or Marine type.

I have a set of four deep cycle six volt batters that I charge with a gas generator and I get enough ac power to operate two televisions and a game and sat receiver for eight hours and then in the morning I can make a pot of coffee before recharging them

Answer 6

This may be a bassic question, but are you using deep-cycle batteries too?  Or golf-cart batteries?  If you're using car-batteries, you're cycling them down too far.

Answer 7

Rockies answer is very good

There is one additional thing about the batteries though, if they are set directly on concrete they will be drained an wear out quickly.

Answer 8

You failed to mention what readings you are seeing, nor over how many hours you are seeing them.

That info is critical to diagnosis.

If your PV panel is putting out  55W for 8 average hours, with no periods of partial shade, you should expect to add  55*8/12  or about  36 ah of charge, which, if the controller is not limiting voltage correctly could be doing a lot of overcharging those batteries.

If your  connection is panel to controller to load to meter, you should be seeing net charging amps, We would  hope to see amperage drop close to zero when the batteries are charged. If that is not happening, the controller is not working. If your amperage is not 4 when no load and only-slightly charged battery, are you in some shade?