Batteries not balanced during absorption

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akram asked Apr 20, '19

Batteries not balanced during absorption

Hello everyone

I recently got four new Trojan agm 205 ah batteries for my easysolar 24/3000/70, during absorption the two batteries on the negative side have a higher votage of upto 15v than the two batteries on the positive side reach upto 13.8 only, I tried swicthing the batteries but got the same results. Absorption voltage recommended by Trojan agm is 14.4 so two batteries will overcharge and the other two undercharge and I don't what to ruin my new battery bank, what could be wrong please assist

See diagram and pics below

battery charging

img-20190420-134548.jpg (3.0 MiB)

img-20190420-072434.jpg (3.8 MiB)

img-20190420-072441.jpg (3.6 MiB)

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Modifications Space

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Answer 1 · 2019-04-20T18:14:50Z

Charlie Johnson answered · Apr 20, 2019 at 06:14 PM

You show 4 x 12V batteries in a series/parallel situation to yield 410aHR at 24VDC. For discussion, designate the top two series batteries as A1 and A2 and the bottom two series batteries as B1 and B2.

If you move the main B+ lead from the positive post on B1 to the positive post on A1, all of the batteries will be exercised (charged and discharged) equally and should mitigate most of the imbalance.

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akram commented · Apr 20, 2019 at 07:48 PM

Thank you very much Charlie, it fixed the problem voltage difference very minimal now, about 0.1v-0.2v, really appreciate your help

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akram akram commented · Apr 20, 2019 at 08:45 PM

It was fine at bulk but now at absorption stage same thing is happening I'm measuring 13.8v and 14.6. still have a problem

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klim8skeptic ♦ commented · Apr 20, 2019 at 08:41 PM

Battery wiring in photo and wiring diagram looks correct.

Seek further advice.

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Answer 2 · 2019-04-21T07:47:46Z

PeterM answered · Apr 21, 2019 at 07:47 AM

Perhaps get a Victron Battery balancer or two

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Answer 3 · 2019-04-21T09:05:34Z

JohnC answered · Apr 21, 2019 at 09:05 AM

Hi Akram. Just some comments I hope can help.

1. I agree with klim8skeptic that your wiring as posted is ok (G'day Shane, Zack here! Ha.).

2. If this has happened since just 'yesterday', then it may settle down over time.

3. Switch the batts around to pair the 'low V' ones to the same string. The strings then may accept different A, but the V's should be ok (at least better) in terms of overcharging.

4. Peter suggested a balancer, and that'd be nice. Consider also just a smaller wire between the centrepoints of both strings. Add a fuse there to help prevent surprises.

5. Notify the batt supplier of your observations in writing/email for warranty protection.

6. Always measure your batt V's directly from the batt terminals, never over the wires. Even the best looking connections/crimps can bob with 0.1 or 0.2V differences. Your wires don't appear especially large, so take care there.

Good luck too. Let us know how you go.

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akram commented · Apr 21, 2019 at 09:53 AM

Hello John

The batteries are only three days old, and configured the multiplus 24/3000 charger setting recommended by Trojan Battery company ( absorption: 28.80 / float: 27.00 / maximum absorption phase time : 2 hours).

During bulk and float the difference is on the lower figure 0.2v-0.6v, but what worries me is during absorption the difference is 0.6v-1.3v. I'm still monitoring the voltages frequently hoping they will balance

Cable size I'm using is 35mm I believe that's 2 AWG

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JohnC ♦ akram commented · Apr 21, 2019 at 10:22 AM

Yeh, 35mm2 cable between batts should be fine. Try firstly switching the batts around (my point #3) to help 'balance' the midpoint V's.

The higher abs diff may be a current (A) thing. Take care too with your terminal joints and feel with your fingers for any high temps on terminals/batts, anywhere.

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akram commented · Apr 23, 2019 at 11:44 AM

Hello

Made further observation , I have two charge controllers 150/70 and 100/50 plus a BMV-700 battery monitor. The 150/70 is sensing 0.5v higher than the 100/50 and the BMV. In color control I set battery monitor to Automatic and it auto selected the BMV since I took this action I see improvement but will further monitor the voltages

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klim8skeptic ♦ akram commented · Apr 23, 2019 at 01:06 PM

Hi Akram,

You better expand your post a little.

I see 2 separate systems,

System 1 with the 100/50, BMV700, Phoenix 1200, and a 12v battery.

System 2 with the Easysolar 24/3000/70, and a 24v battery.

The Color control monitors both systems?

The BMV is for system 1/2?

"The 150/70 is sensing 0.5v higher than the 100/50 and the BMV"

What does this mean?

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akram klim8skeptic ♦ commented · Apr 24, 2019 at 06:03 PM

Both charge controllers and BMV are connected to 24/3000, the 12v system has a separate charge controller

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Answer 4 · 2019-04-21T10:36:19Z

boekel answered · Apr 21, 2019 at 10:36 AM

Always charge new batteries to 100% before connecting in series, best is to parallel them all for this initial charge.

A battery balancer can help, but also expects batteries to be balanced before connecting, as it is not a magical device.

Once all at the same charge, balance should stay good until the batteries are worn out / overdischarged / etc.

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