# Equalize Battery Bank



## CMcD (Nov 11, 2018)

Hello All

We have been homesteading in an off grid location (hydro is not an option) for the last 17 years. I have slowly been expanding and making improvements to our power supply.

I have a problem caused by a new inverter purchase. For long-term battery life, you should never, ever, exceed 50% discharge, meaning below 12.1 volts. The ideal is actually 70% or 80% discharge. The new inverter was shipped (stupid idiots) with a low voltage cut-off setting of 10.5 volts. The battery bank never got that low in steady use, but I am sure it exceeded the setting under heavy draw (water pump), as it did shut down. The inverter manual is ridiculously complicated and very hard to follow (after 17 years and many purchases, the absolute worst I have owned). I took me forever to find this vital setting and change it. By that point in time, the damage had been done.

I am trying to see if I can salvage my batteries (18 Rolls s-1450). The batteries initially would not take a full charge, and trying to equalize only reached 15.2 volts. I separated the parallels to charge 6 in series at a time, and ran an equalization charge to bring some life back to them. I am at the point where all 18 are connected together again, and they will take an equalization charge as a group.

The equalization charge will remove the sulfation that has built up on the plates due to the low voltage. The advice I need is, how long? I know testing the specific gravity of electrolyte solution tells you when to stop. There are many variables to the time required, including the size of the battery bank. One article I read suggested 10 or 15 hours might be required. Is this true? Does it need to be maintained for the full 15 hour? Or, should I do 5 hours and the test the electrolyte? Then do 4 more and test, etc.

I have never been in this situation before. Any suggestions or advice would be greatly appreciated.


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## ShannonR (Nov 28, 2012)

How many volts is your system? The beginning of your post made me wonder if you are using a 12v inverter on a 24v (or more) battery bank. Or maybe your inverter is just on the 12v setting? 

My charge controller handles the equalizing for me, can you program it to zap the battieries uniformly for a few hours? I can set how many hours I want to equalize for, usually 2-4 hours and I can also program the charge controller to charge to a specific voltage. For my 12v system, that would be 14.4v. For the purpose of trying to restore the batteries, longer may be good but keep an eye on the liquid levels because they're gonna boil good.


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## Bearfootfarm (Jul 13, 2006)

I'd suggest doing some reading at this site:
https://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage


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## CMcD (Nov 11, 2018)

Hi Shannon

Thank you for your reply. Yes, I have a 12 volt battery bank. The manufacture say to bulk charge at 14.7 volts, which is slightly higher than yours. To equalize, I need to hold the charge at 15.6 volts. As regular maintenance (preventative charge), this should be done every two to six months, depending on how much abuse your batteries take. Until this recent inverter purchase, my batteries were in excellent condition. I ran the generator maybe 10 times since May, as we have a good cushion for cloudy days.

The low voltage has caused sulfation of the plates. I now need to a corrective equalization to try to bring the batteries back to usefulness. My immediate problem is, how long I should charge them for? When I separated the parallels, I did a 4 hour equalization. So, I have recovered them to the point that I can now equalize the whole battery bank, but they still have no storage capacity. I obviously need a longer charge, but how long is the question.


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## ShannonR (Nov 28, 2012)

CMcD said:


> Hi Shannon
> 
> Thank you for your reply. Yes, I have a 12 volt battery bank. The manufacture say to bulk charge at 14.7 volts, which is slightly higher than yours. To equalize, I need to hold the charge at 15.6 volts. As regular maintenance (preventative charge), this should be done every two to six months, depending on how much abuse your batteries take. Until this recent inverter purchase, my batteries were in excellent condition. I ran the generator maybe 10 times since May, as we have a good cushion for cloudy days.
> 
> The low voltage has caused sulfation of the plates. I now need to a corrective equalization to try to bring the batteries back to usefulness. My immediate problem is, how long I should charge them for? When I separated the parallels, I did a 4 hour equalization. So, I have recovered them to the point that I can now equalize the whole battery bank, but they still have no storage capacity. I obviously need a longer charge, but how long is the question.


Try 6 hours the next time you equalize the bank as a whole. It may take several equalizing cycles to get the batteries back up to par. I have beaten up a pair of T-105's pretty well, but after several equalizing cycles they began to gradually hold a higher charge. You may see improvement in increments, as you have discovered already. I think that's pretty normal.


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## CMcD (Nov 11, 2018)

Bearfootfarm said:


> I'd suggest doing some reading at this site:
> https://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage


Thank you. I have joined that group, but waiting for admin to process before I can post or ask for clarification in a reply.


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## wy_white_wolf (Oct 14, 2004)

CMcD said:


> ...
> The equalization charge will remove the sulfation that has built up on the plates due to the low voltage. The advice I need is, how long? I know testing the specific gravity of electrolyte solution tells you when to stop. There are many variables to the time required, including the size of the battery bank. One article I read suggested 10 or 15 hours might be required. Is this true? Does it need to be maintained for the full 15 hour? Or, should I do 5 hours and the test the electrolyte? Then do 4 more and test, etc.
> 
> I have never been in this situation before. Any suggestions or advice would be greatly appreciated.


You should check the SG hourly until they all reach the desired level. If one is lagging far behind the others you should apply an equalize charge to it individually to catch it up without having to damage the others. Depending on how bad they are sulfated you may never get some to equalize.

The 10.5 volt cutout on the inverter is to protect the inverter, not your batteries.

WWW


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## wy_white_wolf (Oct 14, 2004)

Also what is your normal charge rate and equalization charge rate in comparison to the battery AH rating?

WWW


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## wy_white_wolf (Oct 14, 2004)

The problem isn't/wasn't your inverter. The problem is a poorly designed system. At 12v that makes a 4356Ah battery bank. There is no way you could apply a 400+ amp charge rate to properly charge them. They sulfated over time because of that. You just never noticed the problem until recently. A partially sulfated battery will show voltage as fully charged until enough of the plates are covered that they cannot maintain voltage under load.

WWW


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## Darren (May 10, 2002)

Anyone desulphate your batteries?


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