AGM batteries voltage drop .

CsolarVI · August 2018

I am looking into the temperature probe discrepancy or if there is one I took this image. On 10 June at 1:45pm. if I recall correctly it was a very hot day that’s what spurred me to take the image of the batteries As you can see by the range chart on the right-hand corner the highest temperature in the image is 88.1° looking back in history for the entire month of June the highest temperature recorded was 32° C which is 89F. In my experience sensors don’t fix themselves. Looking back in the history The highest voltage ever recorded was 33°C So I can only assume that these temperature readings are correct. More questions than answers

mcgivor · August 2018

Thanks for sharing the image, it really demonstrates the importance of placing the RTS in the center of a bank.

Estragon · August 2018

> @CsolarVI said:
> In my experience sensors don’t fix themselves. Looking back in the history The highest voltage ever recorded was 33°C So I can only assume that these temperature readings are correct. More questions than answers

A transient sensor problem isn't common, but can happen. A bit of corrosion on a conductor of an rj type connector would do it. Wiggle, vibrate or remove and reinsert it, and enough crud scrapes off to restore function. I used to see it more than you'd think in a previous life supporting telecom stuff.

Was your statement "highest voltage ever recorded was 33°C" a typo? At highest temps, you should be seeing lowest peak voltage in logs.

Interesting pic. With warm ambient, I'm a bit surprised at how much warmer the core appears to be than the outside.

mcgivor · August 2018

The sheer mass of lead takes both a long time to heat up and cool down, so ambient temperatures have a slow effect, a week of 47°C max 36°C min really makes a difference.

jonr · August 2018

Bringing battery temps down by 8C would approximately double their life.

Put more space between them to improve cooling. Maybe even a chilled water bath and/or a small fan bringing in outside air at night.

CsolarVI · August 2018

So I have a question open to everyone. say I did boil off all the electrolytes in the batterys what’s stopping me from adding electrolytes back to the battery’s?

Estragon · August 2018

They're typically sealed with a one-way vent to prevent excessive internal pressure. I don't think they would vent electrolyte per se, but gasses associated with charging. With flooded, water would be added to replace.

Even assuming you could add water (by drilling an access hole or otherwise), I'm not sure how well (if at all) it would mix with the electrolyte bound in a glass mat. Partly dried out mats may have also formed voids with some irreversible plate damage, similar to where levels drop in a flooded battery to expose plates.

That said, if the remaining capacity is insufficient and you're considering replacement, I don't think the scrap value would be impaired much by trying. I've never heard of it having been tried. Maybe others with more AGM experience could chime in.

If you do try something like this, please share methods and results!

BB. · August 2018

Generally, you mostly "boil off" the water (hydrogen+oxygen) from gassing (charging at higher voltages a near full/fully charged AGM/sealed lead acid battery).

So, technically, you would only need to add distilled water to the cells. And there was a company or two that sold replacement catalysts to fix batteries with failed catalysts.

A little discussion here (and a couple of links to details):

http://forum.solar-electric.com/discussion/342418/vrla-battery-recovery

-Bill

Marc Kurth · August 2018

Rapid boil-off from over voltage would leave obvious residue around the vent on top of the battery (tiny hole on top, center line, near the (+) terminal) Very gradual boil-off can sometimes leave no visible evidence, but that would take at least a couple of months.

Are the mounted upright, or horizontally?

Do you see any obvious signs of swelling?

Marc Kurth

Mabank, TX

CsolarVI · August 2018

I’ve inspected all the batteries there is a vent hole with no signs of a discharge . None of the batteries Profile are distorted. And the batteries were sitting upright

CsolarVI · August 2018

Thank you all very much for the information that you have share. And I’ve come to the conclusion that these batteries have lost their electrolytes.
Any recommendations on replacement batteries
Does anyone have experience with
Trojan SIND 06 1225.

jonr · August 2018

You might also look into lithium batteries (such as LG RESU).

mcgivor · August 2018

Flooded lead-acid is the way to go with LA chemistry, IMHO , sure there is maintenance involved, checking SG, electrolyte levels and so forth but it keeps one actively involved in what they are doing, with the added benefit of being way more forgiving than AGM. The use of AGM should be considered where maintenance is difficult, as in a remote locations, sadly they are often promoted as an easy solution of being, quote, unquote, maintenance free. Having said that, I'm in the process of moving away from LA to Lithium, which I'm sure will bring more challenges, but from all indications it's not as complicated or dangerous as most percieve.

mike95490 · August 2018

If you have AGM and they have prematurely failed, LFP batteries are a BAD idea, because currently, you do not understand what killed the AMG, and the same will happen, but in a possibly more spectacular manner with LFP batteries.

Estragon · August 2018

+1 on the advice to consider flooded replacements. With larger banks, a single string of 2v cells is generally preferable to multiple strings of 6v. Among other advantages, for a given capacity, 2v will be 1/3 the number of cells to check SG and water vs a bank made up of 6v batteries (except the silly 2v batteries made by putting 3x2v cells in parallel!).

Trojan are generally well regarded AFAIK. I think they recommend somewhat higher charging voltages than some other flooded though, so you may want to check inverter etc for maximum voltages. In your climate, it likely won't be an issue, but worth checking.

westbranch · August 2018

search for poster DAPDAN for some interesting information on AGMs

http://forum.solar-electric.com/search?adv=1&search=agm+&title=&author=Dapdan&cat=all&tags=&discussion_d=1&discussion_poll=1&comment_c=1&within=1+day&date=

Marc Kurth · August 2018

mike95490 said:

If you have AGM and they have prematurely failed, LFP batteries are a BAD idea, because currently, you do not understand what killed the AMG, and the same will happen, but in a possibly more spectacular manner with LFP batteries.

This is very good advice.

1) The existing batteries have a history of running many years in off grid deep cycle applications.

2) They have a 7 Year warranty on PV applications .

3) It would appear that your batteries died in less than a year of use. Not one or two batteries - 24 of them!!

Before throwing thousands of dollars more at the problem, It only seems logical to identify exactly what the problem is.

Marc

CsolarVI · October 2018

Speaking with individuals at fullriver And other battery experts i.e. manufacturers. It seems that my batteries failed due to three string parallel. I was told that it makes it very difficult charging. Three strings of AGM and it’s not a good idea or so I am told. The system was designed for me by solar Company out of California . they’re refusing any sort of warranty on my batteries although they Sized and Design my equipment down to the individual battery cables. They also Gave me the charging primaries to run the system by and it failed within four months?
So there you have it $13,000 down the drain !

jonr · October 2018

I'd like to see data (not a really misguided instantaneous simulation) that shows that three parallel strings could shorten the life of all batteries in a bank by say 7x. Or at all :-).

My understanding is that Trojan explicitly says it is OK.

Estragon · October 2018

FWIW, I'm also skeptical about blaming a 3 string in parallel setup for a < 4mo life. Lots of other things occur to me as more likely culprits.

I certainly wouldn't just replace the bank with fewer strings and assume that's the end of the problem.

BB. · October 2018

I am not a fan of lots of parallel strings of batteries... But that is mostly because a single failure (bad connection, bad cell, etc.) can cause one string to fail "silently" (less than obvious failures) (open/high resistance connection, open cell). But that would only affect the single string (and give you bank 1/n less capacity).

The other is a shorted cell, that would cause one string to take too much charging current (over charge other batteries in string) and potentially discharge the other battery strings (and reduce bank capacity).

Given that you have a DC Clamp Current DMM and have measured the string currents and found them to be within ~1 amp (this is for both charging and discharging???)--I would not be pointing at the number of parallel strings as being the issue here.

Did you ever take your DMM and measure the voltage across each 6 volt battery in the bank--Looking for differences--I.e., most batteries at one voltage +/- 0.x volts, and one or two batteries +/- 0.5 or 1+ volt different? Measured at different states (charging, discharging, resting).

It sounds like all batteries failed the same way, it sounds like something else. The something else(s) would include over charging, too high of charging voltage (loss of electrolyte), too high of charging current, over discharging/setting at low state of charge for days at a time (sulfation).

Battery bank temperature by itself, say you have 3.5 mV/cell/C compensation--Just to be clear, it is supposed to be "negative" (-3.5 mV/c/C) compensation (it is possible that some controllers may not report the "-" sign, or can be set for + or - compensation--that is beyond my knowledge). As batteries get hot, the charging voltage is supposed to be reduced.

Temperature does dramatically affect battery life... And running 10C (18F) over ~25C (35C=95F) can/does reduce expected life by 1/2... But running 3 months at 95F is the equivalent of 6 months at 77F... Even if that is what happened, that does not explain the batteries failing in less than 1 year for 7 year battery life (vs expected aging life of ~3.5 year @ 95F).

Marc Kurth is the Fullriver battery expert here on the forum (lots of real life experience). And nothing you have said sounds like it would kill 24 batteries all at once.

About the only thing that (would seem) to affect all batteries similarly, and not be (directly either factory or your "fault"), would be if the batteries were improperly shipped/stored... Typically AGM batteries are stored at room temperature (25C or 77F) or less (colder is better).

If stored for over ~6 month without charging at room temperature, or stored "hot" for shorter periods of time (~35C and 3 months) without being recharged the batteries could sulfate rather quickly (although, AGM batteries may not sulfate as quickly/same as flooded cell batteries--Marc Kurth would be a better person to address this question--I am not a battery engineer).

Short of "cooking the battery bank" (high charging voltage/high charging current while batteries are near 100% capacity) or taking the bank dead for days/weeks at a time--I am hard pressed to see how the entire bank could go south in just a few days/weeks...

I am really sorry the problems are you seeing. I hope you can find out what did happen.

-Bill

CsolarVI · October 2018

So after some debate and discussions. With the company that designed my system Hey have agreed to a store credit. Which I’m very happy with . I replaced my battery is with Rolls 2v batteries. Have operating on them for the past couple months and My new battery bank works great. SG’s are where they should be 👍👍 .

They believe the reason the batteries failed was twofold not enough absorb time coupled with the three strings of AGM’s ?
Maybe we’ll never know for sure however it’s way easier to determine if my batteries are getting fully charged with flooded.

JLFH · December 2018

CsolarVI said:

We have tried charging the batteries running multiple absorb cycles at 58.8 V as recommended by battery manufacturer we have tried charging the batteries running multiple absorb cycles at 58.8 V as recommended by battery manufacturer.

Isn't 58.8v to high for AGM, mine enter to absorb at 56.6v

AGM batteries voltage drop .

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