Top Balance - JKBMS - drift voltage between pair and odd cells

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discharge the battery again until the voltage comes down below 27.6.

Lower the charge voltage to 28volts(3.5 per) and try again.

If it fails again the same way, discharge to 27.4, lower the charge voltage to 27.6(3.45 per) and try again.
 

Andre Magro

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discharge the battery again until the voltage comes down below 27.6.

Lower the charge voltage to 28volts(3.5 per) and try again.

If it fails again the same way, discharge to 27.4, lower the charge voltage to 27.6(3.45 per) and try again.
The charge voltage was set to 26.8V as you suggest, during the charging it start to increase.
 
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The charge voltage was set to 26.8V as you suggest, during the charging it start to increase.
That makes no sense.
You can't get a battery to 28.1 volts with a charge voltage of 26.8.
You need to discharge the pack to 27.4 and then start charging at 28.4
The fact that you were charging with 26.8 volts either means you misunderstood me or I mis-typed.
 

Andre Magro

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That makes no sense.
You can't get a battery to 28.1 volts with a charge voltage of 26.8.
You need to discharge the pack to 27.4 and then start charging at 28.4
The fact that you were charging with 26.8 volts either means you misunderstood me or I mis-typed.

Sorry, you are right.
I set the voltage in power supply to 28.4V, when it started to charge the voltage showed in power supply was 27...V, and I tuned the Amps so I could lower it to 26.8V. Only after that the voltage started to gradually increase above 28V.
 

RCinFLA

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Discharging is not going to help you as all cells are dumping same current on all cells. You will end up back where you started with highest state of charge cell getting close to overvoltage. Balancing should continue if you stop charging. The one above 3.6v should bleed down. Once it gets down a bit so you are not so close to cell overvoltage you can pick up charging again.

Looks like your BMS model is 0.6 amp not 2 amp balancer model.

Charging absorb limit is set by total stack voltage so if you have a high cell (but not overvoltage) and a lower cell, it may meet the absorb voltage and start current taper off.

Cheap switching power supplies may drop off on their constant current as they get within about 0.1 to 0.2v of their constant voltage limit setting. With 5 amps of charging it may take a while to finish off.
 

740GLE

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Any reason you can’t unassemble the pack and do a top balance with all cells in parallel?

Then reconnect in 8s pack and then try and cycle the battery and note any anomalies?
 

RCinFLA

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From the screen, charging current has dropped to 1.97 amps due to power supply getting close to its constant voltage limit.

With 2 amps of charge current and the lowest cell at 3.38 v, you still need about 15% capacity of charging on that cell. At only 2 amps of charging on 280 AH cell, that will take about 15 to 22 hours to inject 0.15 x 280 AH = 42 AH of charge.
 
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Discharging is not going to help you as all cells are dumping same current on all cells.
I suggested that because I don't want to wait for the pack to settle.
I want the highest cell to not trip the bms while the psu holds the battery at a voltage in the high knee with little current flow so that the cells can balance.
 

RCinFLA

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I suggested that because I don't want to wait for the pack to settle.
I want the highest cell to not trip the bms while the psu holds the battery at a voltage in the high knee with little current flow so that the cells can balance.
Probably better off to just stop charging and lets the balancer bleed the highest voltage cell down before starting charge again.

I don't believe JK active balancer BMS does the stupid thing some other BMS's do, requiring it see charging current to activate balancing.
 

Andre Magro

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Any reason you can’t unassemble the pack and do a top balance with all cells in parallel?

Then reconnect in 8s pack and then try and cycle the battery and note any anomalies?

I was just following the "simple" process suggested by the community.
Cell in series, charge with BMS til 3.5V per cell, in my case the charger was set to 8*3.5V.
Switch cells to parallel, charge to 3.65V.

Are you suggesting, with this voltage difference between cells, to put them in parallel ?
 
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Probably better off to just stop charging and lets the balancer bleed the highest voltage cell down before starting charge again.
The balance won't be as accurate as the cells settle.
But if you think that is ok, then I don't object.
 

Niz76

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This may be a bit on the objectionable side- most of the stuff I do with batteries usually is haha- but I've found most balancing functions to be verryy slow and have occasionally "helped" the balancing along by hooking a 12v automotive bulb to the highest cell to drain it down some. Just something to consider...
 

pierre

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My 16 cell battery has never been happier since I installed a Heltec 5A cell balancer. I leave it permanently connected and average 1 - 8mV cell delta. BMS is a JBD 200A version with balance function turned off.
 

RCinFLA

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This may be a bit on the objectionable side- most of the stuff I do with batteries usually is haha- but I've found most balancing functions to be verryy slow and have occasionally "helped" the balancing along by hooking a 12v automotive bulb to the highest cell to drain it down some. Just something to consider...
You can do that. It is pretty safe for inexperience person to do.

With the active balancer, he not only gets the approx 0.5 amp average bleed from highest cell but also pushes about 0.5A average current into weakest cell.
 

RCinFLA

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My mistake, I looked at the 0.6 amps at top. This reverses what I said on charging current. to fill in the 21% deficient charged cell.

So, you are converging the highest and lowest cells at about 1.6 amp rate (with balance current duty cycle dilution) plus pushing 0.6 amps charge into weakest cell. At least for current status, weakest cell which is 21% down is getting 2 amps net gain. This will drop as cells get closer to balance so you still have a long way to go.
 

Andre Magro

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My mistake, I looked at the 0.6 amps at top. This reverses what I said on charging current. to fill in the 21% deficient charged cell.

So, you are converging the highest and lowest cells at about 1.6 amp rate (with balance current duty cycle dilution) plus pushing 0.6 amps charge into weakest cell. At least for current status, weakest cell which is 21% down is getting 2 amps net gain. This will drop as cells get closer to balance so you still have a long way to go.
I really don't mind the time that could take, since in the end I could get balanced cells .

But what I would like to understand is the pair and odd cells "thing". Why there are two groups with very similar voltages?
 
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