[RE-wrenches] intermittent battery problem; ...Battery Sulfation

Mon Oct 24 04:45:29 PDT 2011

Ron,

Sorry to beat a dead horse, but a Pentametric will reveal what happens at 4am (or any other time). At a minimum all you need is the sending unit, 2-3 shunts and the serial converter. You then use your laptop to download and analyze what happened in the past few days, etc. of course, the display unit can show the customer details as well. 

The Pentametric can also monitor SOC and has a relay that can start the generator or turn on a "Start the Genny Now" indicator.

As for sulfated batteries, I think SG will be higher with less water in the batteries for a given state of charge. That's just my gut talking not some advanced Molarity vs SG vs concentration calculation that I can vaguely remember doing.

The bottom line, you "still don't know if the customer will bounce another energy check since they are not keeping a check register to know the daily balance." 

Thank you,

Maverick

Maverick Brown
BSEET, NABCEP Certified Solar PV Installer ®
President & CEO
Maverick Solar Enterprises, Inc.
Office:     512-919-4493
Cell:        512-460-9825

Sent from an iPhone. 

On Oct 24, 2011, at 2:49 AM, Ron Young <solareagle at 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
>>> 
>>> 
>> 
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