Author Topic: One Low Cell  (Read 63 times)

Matrix

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One Low Cell
« on: May 11, 2018, 02:57:00 PM »
My Trojan Batteries have been humming along very well for the past 8 months. I have regularly checked the SG and added water when needed. Have never had a cell get low in water. And the gravities have always remained fairly consistent within 15 points. I have run regular EQs about every other week or so.

Last week while checking all of the cells in the 24 volt system I found one cell that was lagging behind in SG pretty well when all other cells were reading fully charged. It was not a problem when the soc was at 70%, all cells read close to the same. But at 100% charged this one cell had a pretty large gap. I decided to let it ride for a week. Today checking the cells when the classic reads that I am at 100% charged, and the gravity is at 1.282 in other  cells. The gravity in this one cell is reading 1.252

I assume my first line of defense is a Hardy EQ. But my absorb charging voltage for the classic has been set at 31.3 to be able to reach 100% in the first place. I am doing a 2 hour EQ now at 32.4v to see what happens.
Grid-Assist Off-Grid
REC TwinPeak 2 285W 3S-3P 2565w-STC 1926w-NMOT Array / Classic 150 / Conext SW 4024 Inverter
Trojan L16H-AC 435Ah bank 4S  with 10' of 4/0 cable
24 volt system /  Need 3200Whs Daily
My System Install

Vic

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Re: One Low Cell
« Reply #1 on: May 12, 2018, 01:47:55 PM »
Matrix,

Yes,   you are doing what Trojan suggests,   for this  degree of SG variation.

It is not clear just what your EQ voltage should be,   given your very high Vabs setting for full-charge.

Assume that you are still running fairly heavy Opportunity loads during Absorb,   but,  do you also run  that heavy-ish load during EQ?

Good Luck,   it is a very good thing,   that you are paying such close attention to your batteries,   and,   ACTUALLY  measuring SGs of each cell,   often.

FWIW,   Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

Matrix

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Re: One Low Cell
« Reply #2 on: May 12, 2018, 08:50:02 PM »
No I do not run loads during EQ Vic.    I did about an hour of EQ yesterday when I had sun and about 2 hours today.   Seemed to bring the lazy cell up within 13 points of the other cells.   Guess that is good enough.  I did not have enough sun to know if that was as hi as all cells would go ... but all cells managed to get to between 1.277 (that lowest cell) and 1.295 (the highest cells). 

Would you push the bank any harder ... or just cycle and do a deeper discharge or 2 over the next several weeks.

Other than that,  I think I might be over EQ-ing the bank.  I have not been waiting to do an EQ when there is a 30 point spread (as Trojan Suggests).    I know I am running my Vabs ... but that is the only way I can get the SG of all cells to rise to at least 1.277 and NOT sit droning on and on at 2 amps for hours and hours in absorb. 

Is it possible to over EQ a bank?  I am guessing too often and you are "shredding" too much material off the plates?

I did find a discussion that I think you may have been a part of.  It was one of the most through discussions on batteries I have read ... in simple terms. 

http://www.outbackpower.com/forum/viewtopic.php?f=1&t=7401
Grid-Assist Off-Grid
REC TwinPeak 2 285W 3S-3P 2565w-STC 1926w-NMOT Array / Classic 150 / Conext SW 4024 Inverter
Trojan L16H-AC 435Ah bank 4S  with 10' of 4/0 cable
24 volt system /  Need 3200Whs Daily
My System Install

Vic

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Re: One Low Cell
« Reply #3 on: May 13, 2018, 02:37:05 PM »
Hi Matrix,

You are doing the correct thing,  with increasing the Vabs,  to get the measured SGs where they belong,  without doubt.

Yes  FLAs can be overcharged,    and over-EQed,  but appears that the EQ that you just ran,  did quite a bit of good with that lagging cell.   I would do more EQing,  until that cell stops rising in SG,   and then  run the EQ a couple of additional hours.

The cycling the bank  deeper,   often solves the issue of some cells having SGs  15, or so points above the manufacturer's  target SG for full-charge.   Although  deep-cycle batteries are designed to be,   and  "like"  to be cycled,  at least,   on occasion.

IIRC,  your Hydorvolt reads about 5,  or so points high,   so your SG readings on the high cells are not  really  abnormally high.

Will add,   that it is best to add Distilled Water,  during Absorb,   during the last half,   if at all possible,   and maybe do a short EQ  after that Absorb finishes  (your Vabs may well be high enough to not really require the mini-EQ).   This is particularly important,  as batteries age,   and,   especially with relatively tall batteries  ...   IMO.

Later,   Good Luck,   Vic
« Last Edit: May 13, 2018, 02:41:06 PM by Vic »
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!