Lithium Cell Balancing - How Long ?

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miya asked Jun 30, '21

Lithium Cell Balancing - How Long ?

Hi All

Helping a friend on his yacht commission his Lithium - and cell balancing is happening.

Set up -

3x 200AH Smart Lithium
VE.Bus BMS
Multiplus 3K

The balancing is happening exactly as the manual says it will.....

"Be aware that in case of unbalance, the charger will be turned off and on by the BMS multiple times. This will manifest as follows: The charger will be on for a short period of time, then the charger will be off for a few minutes and then on again for a short time and so on. This might be repeated many times. This is nothing to be worried about. This is part of the charge process in case of unbalance and is expected behaviour. If the cells are balanced, the charger will not be turned off until the battery is fully charged."

My question is - does anyone know how long this will take ?

Only 1 battery is out of balance - and it is just 1 cell in that battery that has a high V.

Despite the BMS switching the Multiplus on and off, for nearly 2 hours, the one cell doesn't seem to be making any progress to balance with the other 3 cells in the battery.

The bank of 3 batteries keeps hitting 13.90v - and the Multiplus is switched off by BMS - and despite doing this for 2 hours - it is getting no closer to absorption 14.20v.

Can this take many many hours ?

Thanks

Tim

Lithium Battery BMS

2 |3000

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Answer 1 · 2021-06-30T09:29:55Z

Stefanie (Victron Energy Staff) answered · Jun 30, 2021 at 09:29 AM

Hi @Miya ,

this process can take many hours, in some cases even longer. Patience is required. And make sure you only use a very low current.

If it takes too long, I would recommend isolating the one battery and charge/balance it isolated from the other two.

5

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miya commented · Jun 30, 2021 at 09:35 AM

Hi Stefanie

Many thanks. We have 600AH of batteries - we are charging at 90A. I will reduce it. How low would you reduce it to ? Thanks, Tim

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Stefanie (Victron Energy Staff) ♦♦ miya commented · Jun 30, 2021 at 09:38 AM

I have 4x100Ah. It took me quite some time, can't remember really how long. Maybe a day.

In order to limit voltage rising too fast, I had to reduce charge current to 1A per battery (balancing all 4 in parallel), 90A is definitely too much.

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miya Stefanie (Victron Energy Staff) ♦♦ commented · Jun 30, 2021 at 09:47 AM

Brilliant advice Stephanie - we have reduced to 10A - it is helping - I can see the cells already get closer V. You are a star !

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Stefanie (Victron Energy Staff) ♦♦ miya commented · Jun 30, 2021 at 10:08 AM

Thanks for the star ;-)

If that still doesn't help, you can also reduce absorption voltage to 13.80V and then gradually increase the voltage over time until you're at 14.20V. Still everything with a very low charge current.

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miya Stefanie (Victron Energy Staff) ♦♦ commented · Jun 30, 2021 at 10:09 AM

Great - many thanks Stephanie ! I will let you know how we progress.

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