Charging correctly.

klrskiesklrskies Solar Expert Posts: 30
I started off badly, but am learning on an in-expensive pv system before diving into a larger system. I discharged my 31 series, no maitaince, marine-type battery to sub 12v levels a few times, then read here that one shouldn't discharge so low,so I then stopped discharging at 12.2v under a lite load, recovering to 12.35 after resting. I was also charging my battery at too low of a voltage level, not disolving the sulfate crystals and stirring up my electrolyte suffeciently. I believe by then my ,abused, sulfated battery appeared to be showing the characteristics of false charging ...charging up to normal voltage levels much too quickly, due to the sulfation / poor electrolyte mixxing causing the batteries voltage to indicate that the battery was fully charged...but with greatly dimished capacity.

Thanks to the knowledgable, helpful people here and the information they provided, I started a new process of not discharging my battery so deeply, stopping the discharge at 12.2v, and being sure that the battery voltage is up to at least 14.9v during the bulk charge and absorbtion phase, and I've equalized my battery once at 16v for 2 hours to try and de-sulfate it / stir the electrolyte. I listen to the battery with a stethascope and hear it bubbling and it doesnt gain much warmth while charging/equalizing.

In order to test the batteries pereformance I charged it and placed it under a small, consistent load of .75a overnite (two 5watt compact florescent dc bulbs), then let it rest about 1/2 an hour until the voltage stabilized, and checked it's voltage to determine its SOC. When I started testing my battery, the voltage indicated it was down to 50% SOC after drawing about 9ah . After changing my practices as indicated above, I'm now at 80~90% SOC after drawing out 9ah. That would indicate my battery has about 90ah capacity, and if I discharge no more than 25ah from it, I feel I would be OK. I appear to be lucky enough to have stopped my battery abuse early enough to have not totally ruined it, although I don't expect a long life from this type of battery...I'll do as well as I can while learning.

Is there any harm in de-sulfateing at 16v thru an equalizing cycle, I'd like to do a few more to see if battery capacity improves? Is there something else I should be aware of in my practices?

many thanks, and best regards,


  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Charging correctly.

    Ken; on behalf of us all, glad we could help. :D

    Equalization charging won't fix what's broke. Once the sulphur starts adhering to the plates it's all over but the crying. It's like coating them with insulation, and the less exposed plate area the lower the battery capacity goes.

    What's more, EQ is rough on batteries. High charge Voltages create more heat (inside on the plates) that can end up damaging them as well. Some batteries have higher recommended charge Voltages than others (like Trojan's 14.8 vs. "typical" FLA's at 14.4 - Interstate has recommendations of 15+ on some of theirs). But usually EQ is held at 15 - 15.5 Volts. Another half a Volta won't really help, and may do more harm. The trick with the EQ cycle, I've found, is to limit the time to 1 hour; then recheck the SG and see if it's improved, then repeat until no more improvement is had. This allows the battery to cool in between attempts so the internal temp isn't pushed up so high.

    Others may have different recommendations.
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