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exsailor
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# Posted: 12 Oct 2012 10:40
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I know very little about battery maintenance. I have heard a weak or dead battery could be made useful by desulfating or reconditioning. For example my Brother-in-law has several batteries that were used with a trolling motor. The previous owner didn't know or care about battery maintenance. The batteries were used hard to discharge and recharged repeatedly. Yes, I know continuous deep discharges are death on a battery. These batteries will not take a charge or take a charge and discharge quickly. Can these be reconditioned to a useful life? How would you do it? Thank you for your time and effort in answering this question.
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Dillio187
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# Posted: 12 Oct 2012 11:17 - Edited by: Dillio187
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98% of the time, they're junk. The sulfate is usually so caked onto the lead plates it won't come off.
What you can try doing is called equalization. It involves charging the battery at a higher than normal voltage (usually around 15.3V for a 12V bank) which causes the electrolyte to bubble more aggressively, which can dissolve or knock off light or fresh sulfate. It rarely works on batteries that haven't been taken care of, but is more of a maintenance item on good batteries.
if they were mine, I'd save my time and go get new batteries.
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MtnDon
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# Posted: 12 Oct 2012 13:19 - Edited by: MtnDon
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The creation of lead sulfate occurs when the battery converts the chemical energy it contains into electrical energy. When the battery is fully recharged the lead sulfate crystals fully convert and disappear. These first crystals are soft in nature and small. The problem arises when batteries are not fully recharged in a timely manner. The crystals then grow on each other and become hard. A battery left sitting partially or fully discharged for maybe a week will have hard crystals. Hard crystals mean death. A battery sitting for a month will definitely become junk in quick order.
So all of our batteries become sulfated with use. Batteries hooked to enough PV modules to permit a daily full charge will readily convert those crystals and the plates will look as new. FYI, it is the negative plates where the sulfation happens. One of the reasons I don't like systems that rely on generators for recharging is that those batteries are very likely never going to be really fully charged. Those batteries will likely fail earlier than batteries with a well designed PV system. By well designed I mean sufficient capacity to enable the batteries to reach float charge every normal day.
Therefore, if the batteries are well maintained there should be no problems with sulfate; no reason to have to desulfate. So I don't believe in the process.
BTW, desulfation is similar to equalization in that a higher voltage than normal is used. In a 12 VDC system desulfating and equalizing are carried out at 15 to 16 volts. The current in desulfating is very low; maybe 300 to 400 milliamps, depending on battery size. It is done for 24 hours at a time, or more. Some literature indicates it may be more effective at warmer temperatures (125 F). The equipment I've read about also use a series of rapid pulses rather than a normal DC current. They claim it helps. I maintain it is less work in the end if the system is properly designed and used.
Equalization is performed for different reasons. After a while (months) the cells in a battery may become unevenly charged. The specific gravity will be different. Sp gr is the only real way to check; voltmeters are useless for determining whether or not a battery needs to be equalized.
The Trojan battery company only recommends equalizing when low or wide ranging specific gravity (+/- .015) are detected after fully charging a battery. The reason is that un-necessary equalizing can cause erosion of the lead plates and that will shorten life rather than extend it. Equalizing is done at the same, more or less, voltage as desulfating however the current is measured in amperes, maybe 2 or 3 amps for a battery. It is carried out only long enough to equalize the specific readings of the cells. That could be a couple hours or maybe more, but not overnight. Because the amperage is higher there will be more loss of water and the fluid levels should be watched. BTW, never add water before fully recharging a battery unless the plate tops are dry. Battery acid volume increases when a battery is brought from a partial charge to a full charge.
Equalizing causes lots of H2 and O to be created and off gassed.. The bubbling helps remix the electrolyte and even out the ability to charge a charge. This is probably the most dangerous time, the time when a battery explosion could happen. Lots of ventilation should be provided. I always leave the battery compartment doors wide open.
In closing those old batteries that have been sitting around for who knows how long, in an uncharged state are good only for use as cores when buying a new battery. A total waste of time and energy to try and breath new life into them.
If you have a 3 or 4 stage charger, which you really should have to get the best out of your batteries, a truly good indication that the battery has been fully recharged is that it reaches and maintains float charge for a period of time. On a normal operating day our PV system reaches float and stays there for at least an hour or two. I credit that to why the tops of the battery plates in the photos I took back in 2009 don't look any different from what I see today.
I have never done a desulfation; don't have the equipment. The last time I equalized our batteries was in June. Going by the specific gravity readings it doesn't look like it will be really necessary this fall... there are a couple cell readings that are approaching an .011 difference. Most likely I'll run an equalization for a couple hours in November to exercise the generator and to feel better about leaving the system over the winter.
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TomChum
Member
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# Posted: 14 Oct 2012 23:56
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Thanks Don, that was a great read!
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toyota_mdt_tech
Member
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# Posted: 15 Oct 2012 08:58
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I have a Intelli-Charger with a smart wizard in my enclosed toy hauler cargo trailer and its designed to keep plugged in all the time. Every 4 days or so, it hits the battery with 15 volts of charge for about 15 minutes. This is supposed to help that problem. I have one of those Odyssey batteries. Super heavy. If you dont have shore power, like Mt Don said, a PV system to keep them up to snuff all the time. Dead batteries also contain water which freezes.
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