Electronics > Power/Renewable Energy/EV's

Reconditioning old/dead lead acid batteries.

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Fflint:
I've built a simple discharge tester so I can measure battery capacity with various discharge currents. I can also set various voltage cutoff points.

With this I measured the 100AH battery that would keep a 12V 40W car light bulb lit for only half an hour when it came to me. I've used magnesium sulphate (10%concentration only) with it and it was on trickle charge for about a week, plus my pulse desulphation was run on it for about 10h.

The battery lasts only 5 minutes when 55A are drawn from iit, but measured with a 55W light bulb until 12.0V cutoff I got 20AH out of it. This would suggest 40ah total capacity currently. The electrolyte measured 1.28 when charged and 1.24 after the 20ah test.

Thats much better than "keeping a 40W bulb lit for half an hour", but the battery seems to exhibit very high Peukert factor. Peukert factor is a way to express smaller capacity of a battery when discharged with higher current.

Unfortunately I can't tell if the reason is sulphation (plates seem to look OK), positive grid deterioration, loss of active material by shedding or something else. (electrolyte seems clear)

I read in an old 1922 lead acid care battery book about another desulphation method. The method involves charging the battery as far as it goes based on electrolyte density then dumping the electrolyte and replacing it with distilled water. Then charging again.

I'll probably try that next.

floobydust:
Have you considered measuring the battery's ESR? That does flush out mechanical (corrosion) issues as well as sulphation.
There are many automotive car battery ESR meters out there now, instead of doing a hard load test which doesn't differentiate between state of charge and capacity.

Fflint:

--- Quote from: floobydust on December 19, 2021, 08:52:27 pm ---Have you considered measuring the battery's ESR? That does flush out mechanical (corrosion) issues as well as sulphation.
There are many automotive car battery ESR meters out there now, instead of doing a hard load test which doesn't differentiate between state of charge and capacity.

--- End quote ---

I haven't yet. Good idea.

I'll do some research to find out if ESR of a battery can be measured using the usual measuring equipment rather than purpose built meter. I only have few batteries to check so I would prefer not to buy one (for around $60).

HarryDoPECC:
I'm always in two minds reading "restore lead acid" threads because while it's certainly possible to reverse some of the deterioration, it's also the case that many cells will be more like those torn down by TerraHertz (who is here from time to time):

http://everist.org/NobLog/20180430_lead_acid_ruin.htm

Seems to me that the biggest problem is not designing a reconditioner but obtaining the xray vision needed to decide which cells are even worth a try.

Fflint:

--- Quote from: HarryDoPECC on December 26, 2021, 12:29:05 am ---I'm always in two minds reading "restore lead acid" threads because while it's certainly possible to reverse some of the deterioration, it's also the case that many cells will be more like those torn down by TerraHertz (who is here from time to time):

http://everist.org/NobLog/20180430_lead_acid_ruin.htm

Seems to me that the biggest problem is not designing a reconditioner but obtaining the xray vision needed to decide which cells are even worth a try.


--- End quote ---

True, two of my batteries were unrecoverable. Fun fact, I had to glue them back together or the seller wouldn't accept them for exchange / recycling. We have a law here that if you're buying a new lead acid battery you have to return the old one (or pay a fee). So I got two new 6V 195ah batteries.

However, I think I was successful restoring an old 12v car battery (details in previous posts). I have been using it as a starter battery in my tractor for last few weeks and it started the tractor reliably every time (no extra charging required). There were even few starts when the temperature was around - 8C (it is a diesel tractor that usually requires a 1000cca battery).

I'm quite happy with the result with this one.

As for, how to choose the batteries to restore? My advice would be, if you only have few batteries, try it on all of them or do the following :
- open the cap and look inside the cell. Does it look OK, or is it all twisted/deformed?
- can you see heavy grid corrosion with sections missing?
If the answer to the above is yes I would probably not attempt to recover it.

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