Thank you Darryl. The important thing is internal temperature. Any current up to the manufacturers specification can be used but C/20 means I usually don't need to baby sit the battery temp during long term recovery attempts. Adjust accordingly.
One thing I didn't mention is that it's not harmful to deficit charge a battery for a few days or perhaps a couple weeks as long as the battery gets a 100% charge within that time frame. This may require more frequent equalization. Larry On Oct 23, 2011, at 6:22 AM, Darryl Thayer wrote: > Thanks Larry, this is one of the best explanations I have seen. I am saving > it for my customers and students. I would emphasize the C/20 (as you said) > or a little less for perhaps C/30 for this long term equalize or desulfation. > Too fast an equaliziation can loosen (blow the plate material off the plates) > . (I built a 60 hZ desulfator and have used it twice in 40 years, it seems > to work) > > Thanks again great piece of writing and explanation, everyone should read > Darryl > From: "Larry Crutcher, Starlight Solar Power Systems" > <[email protected]> > To: RE-wrenches <[email protected]> > Sent: Saturday, October 22, 2011 2:06 PM > Subject: Re: [RE-wrenches] intermittent battery problem; ...Battery Sulfation > > Hi Ron, > > As many on this list have suggested, it sounds like a sulfated battery > condition. In your last message you revealed something to me that absolutely > confirms this but perhaps you didn't recognize it. > > Battery voltage readings are deceiving because they do not indicate capacity. > 25.7 volts sounds like a fully charged 24 volt bank, but is it? Only if the > battery was at rest for 5-6 hours could you have some confidence that the > bank was full at this voltage. But this is not the case because the bank is > in daily use, always charging or discharging. However, there is one useful > indication that voltage can be used for: detecting a sulfated battery. > > You mentioned that the the battery drops to 24.5 in the early AM without any > heavy loads on. For the 4KS25 battery this equates to about 800AH at the 72 > hour rate. Then you said that the customer ran a 2500 watt generator for 5 > minutes and drove the voltage up to 29 volts. Here's the Ah-Ha moment: That > is EXACTLY the behavior of a heavily sulfated battery bank. A fast rise in > voltage indicates sulfation. It is impossible for that tiny generator, or > any charge source they own for that matter, to replace the hundreds of AH it > would take to drive a healthy battery up to the absorb voltage of 29 volts. > The bank is about 45,000 watt hours (72h rate). There would have to be over > 20,000 Wh removed to be at that voltage. How many Wh's are replaced in 5 > minutes by a 2500 watt genny? I'm sure you are getting the picture. > > Why did this happen to these expensive batteries? Glad you asked. Battery > plates are not uniformly efficient in the electrochemical process leaving > some portions with lead sulfate even after 8 hours of charging. Unless these > portions are cleared off regularly by achieving 100% SoC and occasional, > thorough equalization, the amorphous sulfate will convert to a crystalline > form and grow. 99% charge, if not corrected in time, will always cause > premature battery failure. > > Undersized RE charging systems, or perhaps oversized batteries, is the > culprit that contributes to this all too frequent phenomenon of chronic > undercharging. I say contribute because there are other factors. Fact: it can > take 10-12 hours to fully charge a lead acid battery. Fact: The time element > of battery charging is a highly misunderstood part. With only a few daily > sun-hours to work with, how do we get a battery charged with PV solar? > Properly sizing the PV array to the battery AND consumption is critical. One > method I think is essential for nearly all PV systems is use a generator and > charger, appropriately sized to the battery. By bulk charging early in the AM > you can reduce the finish time to perhaps 5-6 hours of constant voltage > charging, something easily done with a PV system. > > Ron, you might be able to recover some capacity in this bank if the sulfate > has not formed hard crystals by now. You can try a very long charge time, up > to 24 hours, at high voltage, about 31 volts. You will need a larger > generator. Monitor the temperature and reduce current if they get up to 125F > internal. In our shop I have recovered sulfated batteries with high voltage > charging, as much as 3Vpc (do not do this with any loads connected), at > reduced current, about C*.05, and a 1 kHz pulser that I built. My findings > over the years is the current will begin to rise very slowly, peak then drop > if the recovery is working. > > Sorry that this post is getting so long. There's just so much. OK, one last > thing. In my last post to you I recommended a battery AH monitor. This > problem could have been detected and perhaps prevented if they had one. > > Larry Crutcher > Starlight Solar Power Systems >
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