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Importance of testing batteries / cells in series

pops106

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Joined
Aug 24, 2020
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141
Hoping this might help someone else.

I have made several posts over the last year trying to understand why I have had a few problems keeping batteries in sync with each other in my case 12v batteries in 36v or 48v series string. Many many times people have said you need to test the batteries to confirm there health and I have tried a few things with a 12v inverter and a lamp but I finally bought a battery capacity tester and started testing.

I cant recommend enough you buy one if you are in this situation I grabbed one of these for £33

My plan for each battery is;
  1. Charge the battery with a 7 stage charger
  2. Test using the capacity tester 10amp pull for 55ah and 2.5amp for 12ah cut off at 12v arguably around 50% DoD
    1. Record AH
    2. Record run time
  3. Charge the battery again
    1. Record charge time
    2. Record WH going in
  4. Roughly figure the health of the battery peukert number and use that as a good/bad indicator using this website
  5. Run a repair on the battery
  6. Retest again
10 x 55ah batteries to test
4 x 12ah batteries to test

Will keep updating numbers as it goes but

Results for 55ah;

Battery 55AHAHTimeCharge StartCharge EndCharge TimeCharge WH StartCharge WH FinishWH InPeukert
B1
23.38​
02:20:16​
14:33:07​
20:45:07​
06:12:00​
4​
543​
539​
1.07​
B2
9.39​
00:56:20​
20:48:52​
23:47:52​
02:59:00​
543​
778​
235​
1.45​

Results for repaired 55ah;

Battery RepairedAHTimeCharge StartCharge EndCharge TimeCharge WH StartCharge WH FinishWH InPeukertAH Gain% Increase
B1
23.33​
02:20:03​
15:45:22​
21:49:47​
06:04:25​
120​
666​
546​
1.07​
-0.05​
-0.21​

Results for 12ah; (I know these are dead age wise but fully charged, but they quick to test)

Battery 12AHAHTimeCharge StartCharge EndCharge TimeCharge WH StartCharge WH FinishWH InPeukert
S1
1.02​
00:24:15​
20:09:57​
20:44:42​
00:34:45​
0​
22​
22​
2.9​
S2
2.5​
01:00:05​
20:50:57​
21:51:27​
01:00:30​
22​
90​
68​
1.9​
S3
0​
00:00:03​
22:51:27​
23:01:05​
00:09:38​
90​
91​
1​
10​
S4
1.45​
00:34:44​
23:10:27​
23:59:59​
00:49:32​
92​
125​
33​
2.6​

Results for repaired 12ah;

Battery RepairedAHTimeCharge StartCharge EndCharge TimeCharge WH StartCharge WH FinishWH InPeukertAH Gain% Increase
S1
1.43​
00:34:26​
15:39:22​
16:30:07​
00:50:45​
91​
125​
34​
2.6​
0.41​
40​
S2
3.47​
01:23:20​
17:13:12​
18:24:47​
01:11:35​
128​
204​
76​
1.6​
0.97​
39​
S3
0.61​
00:14:39​
18:25:07​
18:51:22​
00:26:15​
204​
218​
14​
3.4​
0.6​
6000​

I am hoping this will explain my battery voltage issues I see below;

volts.PNG

Around 5:45am inverter powers on and we see drain until about 8am ish when my shade goes away and it steadily charges until around 54v (13.5v) then all hell breaks loose and I see some of the batteries start to leap up to 14.8v whilst others 13.8v for example but then my balancers kick in and smooth things out but they cant keep up with the ups and downs as there is draw from the house.

So in many many days time after many many hours I can hopefully pair up my good batteries assuming I have some and see a much smother looking line.
 
Last edited:
So good news is chargers work as expected and the charge wh going back in matches what the capacity test shows so I think methodology works.

batt.PNG

First block is B1, second block is B2 desulfurs, soft starts, bulk, absorbs, tests, toped up, floats

B1 23.38ah tested to 12v and took 539wh measured on the AC side so probably ~370>380wh DC back in
B2 9.39ah tested to 12v and took 235wh measured on the AC side so probably ~165>170wg DC back in

So confirms B2 is ready for the bin unless the magic "repair" function triples capacity.

The smaller batteries are a real mess but I have no use for them to be honest.

12ahbatt.PNG

1st block S1, 2nd S1, the couple of spikes is S3 and S4 did a bit of charge a test and a bit more charge

S1 1.02ah tested to 12v and took 22wh measured on the AC side so probably ~15>16wh DC back in
S2 2.5ah tested to 12v and took 68wh measured on the AC side so probably ~47>50wh DC back in
S3 0ah tested to 12v and took 1wh measured on the AC side so probably ~0.7>0.8wh DC back in
S4 1.45ah tested to 12v and took 33wh measured on the AC side so probably ~23>25wh DC back in
 
Turns out the repair takes about 16 hours to run, must be a timed thing as it was the same for small and large battery. I believe it pulses the battery and then finishes with a charge.

1628858123294.png

But it starts at about 12w and ends up at 5w so god knows how it helps but I have gained about 40% on the first small battery that I know are bad.
 
Ok I think I might of found something odd and planning to revise my testing but wondering if someone can sense check it before I spend another 3 days at it to change the testing all again.

The 10 x 55ah batteries I have got are all Lucas LSLC55-12 55/20hr, they come with cords on top as carry handles, 2 of them are white and 8 of them are black. The good looking battery I have tested up to now is the white corded one, the 3 bad tested are black corded.

But something doesn't make sense.

I charged one of the black cord batteries last night, it was down around 11.6v which took in roughly 523wh into a 660wh battery.

I then capacity tested 10amp down to 12v which only gave me roughly 108.36wh, then charged again and the battery took 142.1wh back in which to me makes me think 10amp to 12v isn't anywhere near 50% DoD for this black corded battery and all 3 of them at the moment have the same results within 1ah of each other.

Now the white corded battery after a charge tested down to 10amp 12v gave me roughly 280wh, then charging it took roughly 382wh back in so I would say that is roughly around 50% DoD for the white corded battery.

Could it be Lucas changed the battery pretty significantly but with the same model number, marked with a different cord ? seems mental to me.

So my plan;
  1. Charge battery
  2. Cap test at C20 2.75amp to 10.5v to get true ah of the battery
  3. Charge battery
  4. Cap test at C20 2.75amp until it reaches 330wh and record voltage and assume this as 50% DoD
White vs a couple of black corded ones to see if this is what has been causing my problems.

Does that make sense ?

Cheers
 
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