280Ah cell top balancing

atti

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While I am on it, I want to order something good which can be reused if this pack stabilizes. Remote monitoring will be a big plus.
Any experience with this product from AliExpress?

I am in the UK and only reasonably priced product I can find is this, it is 8S so I need to buy two, it is also coming from China, looking at the delivery dates. Also it is open circuit which is quite dangerous imo where so many open cables will be dangling around.
 

Just John

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While I am on it, I want to order something good which can be reused if this pack stabilizes. Remote monitoring will be a big plus.
Any experience with this product from AliExpress?




I am in the UK and only reasonably priced product I can find is this, it is 8S so I need to buy two, it is also coming from China, looking at the delivery dates. Also it is open circuit which is quite dangerous imo where so many open cables will be dangling around.

An active balancer left on during charge/discharge can actually unbalance your cells. Top balance once and be done with it, if the cells are decent quality the limited balance current supplied by the BMS is adequate to keep them in balance. FYI, you need a 16 cell active balancer, they are really not rated to run in series.

On the other hand, if you have poor quality cells, you will have lots of problems.
 

time2roll

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An active balancer left on during charge/discharge can actually unbalance your cells.
I am not really buying that.

In the middle the voltage is close enough the balancer turns off. Only if your cells are bouncing off the bottom for an extended period will they switch from top balance to bottom balance. And if they are bouncing on the bottom it will only help to have them balanced there. Then when there is more sun or the issue is fixed and the cells are often back at the top they will all go back to being top balanced. With any luck the cells are good and will not have severe balance issues.
 

time2roll

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The NEEY seems to be a good product to me. I have a couple of the 5A Heltec capacitor units and they are good but much slower than the 5 amp rating implies. Once the cells get close the amps drop quickly. Does work.
 

noenegdod

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An active balancer left on during charge/discharge can actually unbalance your cells. Top balance once and be done with it, if the cells are decent quality the limited balance current supplied by the BMS is adequate to keep them in balance. FYI, you need a 16 cell active balancer, they are really not rated to run in series.

On the other hand, if you have poor quality cells, you will have lots of problems.
I have this balancer and it works really well. I am of the mind that you just turn it on once in a while when you are going to take them right up to 100%SOC and then turn it off for day to day use.

An active balancer left on during charge/discharge can actually unbalance your cells.
I am not really buying that.

Channel error can and will cause this. If tolerance is +/- 5mv when at 100% SOC, who cares, but as you draw the battery down cells actual voltage will balance and voltages should all essentially be equal on a cell to cell basis but if they are equal and one channel on the balancer reads+5mv and another reads -5mv, then the balancer will start to suck the huge amount of current out of one and into the other, unbalancing the pack. Then as you charge back up and approach 100% SOC, the one cell that had all the energy dumped into it trying to balance at a low SOC will hit 100% far sooner and the one that had its energy taken will be lagging far behind. Its a thing.

Turn it on, top balance, turn it off. Check balance once in a while and correct if necessary.
 

Hedges

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Good that I asked. :(

I told you what, but not who (or where, or when, or why)

 

atti

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Those powersupplies are crud. Waste of Time & Money and as for ICCOGOGO run like the dickens.
Thanks for sharing your experience. Can you please recommend me something for the purpose of quickly do top balancing. from my experience iMAX B6 is not good enough to bring these cells to over 3.4v.
 

atti

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Configure the cells into a 16s battery complete with bms.
Charge the battery to 54.4 volts(3.4 volts per cell) with a charge current of ~28 amps.
If the bms trips report back with the cell voltages after they settle for 2 hours.
If they don't trip increment the charge voltage to by 100 milli-volts and repeat until you get to 56.8 volts.
Depending on how far out of whack the cells are and at what voltage the bms trips we will decide the next move.
I am in process of doing it and I will share graphs once done.
 

Just John

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Thanks for sharing your experience. Can you please recommend me something for the purpose of quickly do top balancing. from my experience iMAX B6 is not good enough to bring these cells to over 3.4v.


Use the "Top Balancing LiFePo4 Cells using a low cost benchtop power supply." document, it has section 3, "Pre-charging the cells to get them ‘mostly’ charged." that will speed things up considerably. Recommendations would be influenced by what voltage is your final pack to be.
 

atti

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This is when I ingested today's cell level data from the BMS and plotted. I have Seplos BMS and they give this data over RS485 bus.
As you can see in the begining my cells were wildly out of balance but BMS was hitting 100% according to set Ah, which I keep tweaking to force charge it as high as possible as Joey suggested.

Towards the end I could smooth them out a bit but I think I need to keep doing it to balance these cells.

BMS Data.PNG
 
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atti

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Cells went out of balance wildly upon high current load in past two days. Started charging them and now the graph is looking like this:

Screenshot 2022-01-22 010244.png
 
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