Battery Restoration Questions

lrice648 · February 2015

Hi, I am trying to determine the best and safest way to restore some sulfacted batteries that I didn't take particularly great care of.

I have 4x 6V US battery L16 ~360 Ah batteries in a 2-string 12V system. I think I improperly sized the battery bank relative to my PV capacity (initially, 2x 220w schott panels), which lead to the batteries gradually losing capacity. I also did not equalize them enough because I do not live where the setup is (it is at my parents house) and enabling equalization required the flipping of a small switch (blue sky 3024iL cc), so I would usually do it when I was there rather than having them do it for fear of the wrong switches getting flipped. I don't think the batteries were being discharged heavily, we've been careful about that and the inverter makes a warning noise and cuts off if the voltage drops too low which has happened very rarely.

A few months ago I upgraded to ~1500 watts of PV, but it appears that this isn't enough to bring the batteries back on its own. The new CC is a midnite classic 150, and on a sunny day it tends to hit float mode by noon or early afternoon at the latest. If I check SG at float, it registers as low to middle of fair, at best. There is also slight variations with all the cells. I have equalized using the classic, which did bring the SG up some, but this winter has been brutally cloudy and I haven't been able to bring the SG up with the few equalization sessions I've been able to do. I also have an AC 3 stage charger as well (powermax PM3-55 and then a PM3-75), but these are not either able to bring the SG up, my theory being they are also "intelligent" chargers and they are determining that the batteries are at a higher state of charge than they really are, or they are correctly detecting that the batteries are not functioning correctly and shutting down.

My question is: how can I most-safely restore these batteries using AC generator power? I have access to car-battery-chargers, but my understanding was that bulk-chargers could damage batteries when attempting to charge them past 80% or so, hence the use of 3-4 stage chargers. If there is a way to use a standard "dumb" car-battery-charger, what would be the process (ie, changing of current or voltage if the charger supports it)? I have been looking for a 6 or 12V charger that has an equalization function that isn't automatic and have not been able to find one that isn't very expensive (and also would more or less be a replacement for my existing AC chargers). If I had more consistent sun I would perform longer equalization through the CC, but the suns ability to disappear whenever I'm in a position to do it us borderline suspicious.

In my google-searching, I also ran across a number of less-than-legit-sounding desulfator liquids and devices, through reading around the forums they do not seem to have a solid consensus. I was not considering the use of the devices (I agree with other posters that correct charging and maintenance should do the trick), but could the liquids help out in my case?

Thanks for the help, I've been ordering from NAWS for a while but I am new to the forums, which could have probably helped me avoid this problem in the first place ;-)

CALLD · February 2015

Recovery lost capacity due to sulfation generally depends on how long it's been since the batteries received a fully saturated charge to bring them up to 99.999% SOC (since 100% is practically impossible, but we always try to get as close as possible).
Also, be sure that it is sulfation which has caused the loss of capacity and not grid corrosion or loss of active material from the plates as the latter are caused by overcharging and the methods for removing sulfation will makes these worse.

If the batteries were left in a cold environment you could perhaps recover them if they were left for no longer than a few weeks without a full charge, in hot conditions this is reduced to a few days at most. Once the sulfate hardens you cannot do anything to recover the lost capacity.

The basic recovery process is as follows:
Apply a high current bulk charge of C/5 or a little higher until the battery voltage rises to 2.5vpc (7.5v for a 6v battery). It's good if the battery temperature rises until it's warm but not hot to the touch as this further helps to break down the sulfate. Then allow the voltage to rise to about 2.6 or even 2.7vpc and monitor the temperature carefully to make sure it doesn't go above 50°C. Check the SG every half-hour and at the point where SG readings don't rise further you have done the best that you can, stop the process, and or leave them on float charge at 2.35vpc and check back every day to see if there is any improvement (although unlikely)

lrice648 · February 2015

Thanks for the help, couple follow up questions.

1. For C, my batteries are 360AH, so for 1 12v string thats 72A? That seems like will necessitate separating the bank, our charger can do 40 or 100 amps, would 100 be too high? Ill buy one if I need to.

2. How can I tell between sulfacted plates and grid corrosion? Ill take some pictures tomorrow.

I think that they were consistently not getting above 80/90% for a long period, but they werent getting heavily discharged or overcharged (unless my cc or ac charger malfunctioned).

There is a good chance ill be getting a new bank sometime in the near future but I would like to get the most out of these as long as I can.

Thanks again.

BB. · February 2015

I would suggest you do batteries singly. If you have several in parallel, and one gets a shorted cell, the one battery can be taking most of the charging current and overheat.

For corroded positive grid/plates--They expand. You may see the positive post of the battery "extruding" out of the battery top, and/or sides of the battery swelling.

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-Bill

lrice648 · February 2015

I looked online for a good 6 volt charger but wasn't finding much, can you recommend one or a place to get them? I did consider that first as the ideal, but 12v chargers are so much more common. It sounds as though it would need to be farely high current as well.

Thanks

Mountain Don · February 2015

Something like this.... Switching DC Power Supply, 1-16V, 60A

http://www.alliedelec.com/b-k-precision-1900/70146271/

with dedicated voltage sensing leads for accuracy. Other models for higher volts, but lesser amps.

CALLD · February 2015

If you're thinking of buying a stock-standard 12v auto-battery charger just be aware that transformer-rectifier chargers don't really put out their claimed amperage except for when the battery voltage is very low at the beginning of the charge. Quite often you will see a "12amp" charger put out about 10amps when the battery voltage is at 12v and the amps will have declined to about 3 or 4 amps by the time the voltage has climbed to 14.5v. A switched mode power supply or professional battery charger like the ones built into inverter/chargers keep their current at the maximum rated current right up to the end of the bulk charge cycle - this is what you want:)

lrice648 · February 2015

Sweet, thanks For all the replies. Im probably gonna make the trip back out in 2 weeks and ill purchase a new charger before then, ill post a followup with some results for posterity afterwards.

toolworker · March 2015

I just tried equalizing a 420 Ah battery bank (4 105 Ah 12v batteries in parallel) using my Xantrex inverter-charger. (It's on a boat but I have PV at home so hopefully I qualify for help here.)

It charged for about 4 hours at 21 amps (Xantrex recommends equalizing at 5% of capacity) and never got above 15.2 volts. Almost all the cells are between 12.55 and 12.65 specific gravity, but the one weak one is still at 12.25.

Any ideas why the voltage won't rise?

mike95490 · March 2015

take the battery bank apart, and test & charge each battery individually, why BBQ 3 good batteries ?

Battery Restoration Questions

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