Ron, You have made a connection that I would not have made, and while I may be wrong here, it has got me thinking. I have never equated low water level with SG, nor have I ever read in battery maintenance guides that I should maintain a particular water level before measuring SG. I'm not convinced that electrolyte level has any connection with measured SG, although it would seem logical on the surface. I have always thought that if the correct concentration of acid was installed at the factory and not lost thereafter (such as due to a spill or chronic overfilling), the SC is only a function of SOC. I'm interested in others' opinions here.
Allan Positive Energy On Mon, Oct 24, 2011 at 1:49 AM, Ron Young <solarea...@solareagle.com>wrote: > Hi Larry, > > I immediately assumed sulphated battery when I heard the customers > description a couple of weeks ago but the hydrometer readings didn't jive. > Any sulphated battery I've encountered, and I defer to your greater > experience, has always revealed itself with a simple S.G. test and these > batteries were reading above 1.265. I then thought the possibility of a > defective hydrometer and had them test with another but we just got > confirmation of the same thing. > > The weird drop in voltage also isn't explained by your description. Why > would this just happen without loads or charging present (except maybe the > DC Sunfrost load) at the same predictable time at 4 a.m. The fact that when > the generator was turned on and sent a surge of current into the system and > the problem went away made the detective in me think there had to be another > explanation. The bank was at rest for several hours through the night and > the voltage dropout was cured by a brief application of charge current. > > When I arrived on site my discovery that the client was under watering the > batteries and this chronic condition resulted in a very rich electrolyte, > reading well above 1.265 - into the 1.280 range made me think that was the > problem and it seems to have gone away now that the electrolyte level was > raised and the batteries given a good charge. But it still nags at me that > something else is lurking in the shadows. Your description of the sulphate > converting to a crystalline form has me worried because if this is the case > this expensive battery bank is in danger. I would have to camp out at the > site and monitor the charging over a day or so. I'm going to forward some of > your comments and those of others that have generously offered suggestions > and we'll see if I can convince the client who now believes everything is > A-Ok. > > Best Regards, > *Ron Young* > earthRight Products - Solareagle.com > Alternative Energy Solutions ~ Renewable Energy Products > > On 2011-10-22, at 12:06 PM, Larry Crutcher, Starlight Solar Power Systems > wrote: > > 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 > > > > > On Oct 21, 2011, at 11:39 AM, Ron Young wrote: > > Hi Maverick & everyone, > > I visited the site a couple of days ago and load tested the batteries, > checked individual voltages in the string of six Surrette 4KS25's (4.3v > each), checked all connections etc. The client told me that when they would > go to bed battery volts read 25.7. Through the night this would seem to stay > steady. About 4 a.m. as far as they could tell the voltage would drop to > about 24.5. This happened without a load present and with no charging > present (calm, no wind, no sun). They would start up the generator for five > minutes in the morning and see the voltage come up to just above 29v then > turn off the generator (a small Honda 2500) and the voltage would settly at > 25.7 and remain there most of the day even when using their light loads, > some lights, phone system, laptop and the Sunfrost. > > When checking the batteries I noticed they needed watering and mentioned > this to the customer. The electrolyte was just over the plastic screen above > the plates by about 1/4 inch. He said he had just watered them and always > kept them filled. I replied that they were low and when he looked he said > no, that's where I keep them! When I checked the specific gravity reading it > was very rich reading around 1.275 - 1.280. I topped them up properly to > about 1/4 inch below the bottom of the cell channel which took about 5 cups > per each battery. Of course as soon as I topped them up the s.g. dropped to > around 1.175. I told him to put the generator on for about ten hours and > call me in the morning. > > I heard from the client today and in the last two days the voltage has only > dropped from 25.6 to 25.4 overnight and s.g. reading is at 1.260 or better > so problem seems to be solved. > > So it appears the battery was under watered for several years. I'm still > not sure why this would result in a sudden voltage drop, especially in the > middle of the night with no loads present and no charging. Any additional > thoughts appreciated. > > Best Regards, > *Ron Young* > earthRight Products - Solareagle.com > > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > > > _______________________________________________ > List sponsored by Home Power magazine > > List Address: RE-wrenches@lists.re-wrenches.org > > Options & settings: > http://lists.re-wrenches.org/options.cgi/re-wrenches-re-wrenches.org > > List-Archive: > http://lists.re-wrenches.org/pipermail/re-wrenches-re-wrenches.org > > List rules & etiquette: > www.re-wrenches.org/etiquette.htm > > Check out participant bios: > www.members.re-wrenches.org > > >
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