Battery bank wont hold charge with minimal load? help

[Twistit]

We have a 1.5kw array with 4x200ah deep cycle lead acid batteries in parrallel, a 1.5kva inverter and 1kva charger that runs 12hrs overnight on generator (for various reasons).
During the day we only have an amplifier and internet modem running off the sun and batteries, this draws .22amps.
The problem is the batteries will be charged to full (12.5v) from overnight, and as soon as i flick the breaker to power this small load, the volts drop down to 8v within 20mins, and then i have to open circuit as the outputs way too low obviously.
Given its overcast, thats still unacceptable isnt it??

So im assuming these batteries are sulfided, although i dont have a hydrometer or load tester to prove it...

What would the cause be?

Thanks

[Twistit]

also, once they are depleted, the pannels will charge them back to full within half an hour when open circuited and no loads on them.

[mapmaker]

So im assuming these batteries are sulfided, although i dont have a hydrometer or load tester to prove it...

What would the cause be?

Get an hydrometer... a good one costs less than $20. Your batteries do sound sulfated.

What could cause that? Sulfation is caused by undercharging. I need a lot more detail about your system to know why/how you have undercharged them. It could be as simple as having the wrong charge parameters set in your controller.

Also, four batteries in parallel is a recipe for misery. When you charge them, the current does not get divided equally among them... one may be doing all the work. It's possible that after you turn off the charger, some batteries are discharging into the other batteries.

--mapmaker

[Sunking]

This is extremely easy to answer. YOUR BATTERIES ARE TOAST, DEAD, SHOT, KAPOOT, DONE, FINNISHED.

Your description is text book sulfated battery DEATH. When that happens, it is over. Symptoms are voltage will collapse when a load is applied. When put on a charger, the charger is immediately fooled into thinking the batteries are charged up and turns off. Sound familiar?

Sulfated batteries have very high resistance, so when you draw current, voltage collapses. When you apply current to charge the voltage spikes.

[Tedx]

I have the same problem: 800 watts feeding a 24v battery bank totaling about 16 deep cell 6v, 200 ah batteries. On a sunny day, the bank is fully charged by noon with the charge controller citing 29v for the bank. I check the individual series and each are about the same. I check the individual batteries with my volt meter, and they are at 7v or a little higher. My hydrometer rates the electrolyte at over 13 except for the new one I bought to replace one with a dead cell. It is a little lower.
By 6pm, the voltage for my bank is down to 26.4 with almost no load. The charge controller shows it half depleted.
Most of the batteries were bought pre owned, but the hydrometer says they are perfect. What gives?.

[SunEagle]

I have the same problem: 800 watts feeding a 24v battery bank totaling about 16 deep cell 6v, 200 ah batteries. On a sunny day, the bank is fully charged by noon with the charge controller citing 29v for the bank. I check the individual series and each are about the same. I check the individual batteries with my volt meter, and they are at 7v or a little higher. My hydrometer rates the electrolyte at over 13 except for the new one I bought to replace one with a dead cell. It is a little lower.
By 6pm, the voltage for my bank is down to 26.4 with almost no load. The charge controller shows it half depleted.
Most of the batteries were bought pre owned, but the hydrometer says they are perfect. What gives?.

16 x 6v batteries configured as a 24v system still requires 4 string of 4 wired in parallel. Parallel wiring will result in uneven charging and discharging which can cause one or more batteries to do most of the work and fail sooner then expected. And with only 30 charging amps (800w / 24v = 33.3 amps) that 800Ah system will never get back to 100% SOC since it needs about 80 charging amps.

On top of the parallel wiring strike, used batteries have a major drawback.

[Tedx]

Maybe my battery bank is alright after all. I did some research and learned that on a 24v system, 25.46 to 25.6v is considered a full charge (depending on who you ask). I ran my generator with a battery charger on the bank for about an hour at dusk because voltage had dropped from 27 to below 26 after the sun began to set. I have been burning three regular light bulbs, a ceiling fan, a mini fridge and wifi from a satellite dish and gaming lap-top computer for a few hours. It's after 12 and my battery bank is holding at 25.4v, The icon on my MT-50 remote meter shows the battery bank half empty, when it was topped off when I turned off the generator. That what has me confused. According to my research, 80% charge will be 25v. Running lower than that may harm the batteries.

[Tedx]

Sun Eagle, Thanks for the tip. I did not know parallel wiring caused uneven charging. I do have 4 parallel strings of batteries in series. But I have the negative and positive leads going to opposite ends of the bank. Will that help even things out? Also, one of my strings is made of two 12v deep cell batteries instead of four 6v. Does that matter?
My charge controller is rated at 40 amps. I am currently adding an additional 1200 w of panels and a second 40 amp charge controller of the same make. I am also thinking of adding 200w of panels to my current 800w array, so the charge controllers will be handling identical (virtually) amps to a common battery bank. What's the skinny on that plan?

[Bala]

My 24V bank drops to 25.2 basically as soon at the sun drops. it is running a fridge and freezer lights, TV laptop etc. By morning it will be around 24.8.

It has been pretty much the same for the last 12 years.

[SunEagle]

Sun Eagle, Thanks for the tip. I did not know parallel wiring caused uneven charging. I do have 4 parallel strings of batteries in series. But I have the negative and positive leads going to opposite ends of the bank. Will that help even things out? Also, one of my strings is made of two 12v deep cell batteries instead of four 6v. Does that matter?
My charge controller is rated at 40 amps. I am currently adding an additional 1200 w of panels and a second 40 amp charge controller of the same make. I am also thinking of adding 200w of panels to my current 800w array, so the charge controllers will be handling identical (virtually) amps to a common battery bank. What's the skinny on that plan?

Uneven charging/discharging is the result of non equal resistance paths. The more paths (parallel strings) you have the better chances of being unequal.

If you add the variable of different type batteries (6V & 12V) you increase the risk again of different resistance paths.

There is a website called SmartGauge that provides different wiring options for parallel batteries. Read that and while I feel Method 3 is best you may find the beter solution for your system.

[Guest]

Current battery charging technology relies on microprocessors (computer chips) to recharge, using 3 stage (or 2 or 4 stage) regulated charging. These are the "smart chargers", and quality units generally are not found in discount stores. The three stages or steps in lead/acid battery charging are bulk, absorption, and float. Qualification, or equalization are sometimes considered another stage. A 2 stage unit will have bulk and float stages. It is important to use battery manufacturer's recommendations on charging procedures and voltages, or a quality microprocessor controlled charger to maintain battery capacity and service life.

[Guest]

Sorry for hijacking this thread, as i can't create a new thread. I wanna ask if anyone knows the impedance specification range(factory specification) for a 6v deep cycle golf cart batteries ?

[Mike90250]

Sorry for hijacking this thread, as i can't create a new thread. I wanna ask if anyone knows the impedance specification range(factory specification) for a 6v deep cycle golf cart batteries ?

An admin will be able to allow full posting .

As to your question, it doesn't matter. If you are really interested, you can contact the prospective battery mfg, and get the data from them. AGM will have lower internal resistance than flooded, and DataCenter GEL batteries, possibly even lower.
The spec I believe you are looking for is Internal Resistance. Impedance is more of an AC resistance, it can vary widely with frequency, and would not be expected to be tested for in solar applications.