Balancing stops with no apparent reason on BQ78PL114

Maxime Champagne

Other Parts Discussed in Thread: BQ78PL114

Hi,

I'm using the BQ78PL114 to manage a 4 cells battery pack. Actually, my BMS is not able to stabilize the cells.

When my pack is on the charger, the mosfet open when cell1@3.35V - cell2@3.35V - cell3@3.90V - cell4@3.35V. It is correct because COV is set at 3.9V. At this point, the balancing is stopped, does someone know why?? The balancing restart when cell4 fall under 3.84V (I found this value doing test - I've not parameter at 3.84V or 0.06V...). When the cell4 reach 3.8V, the charge mosfet is enabled because COV recovery is set at 3.8V. And it restarts again and again...

Why is the balancing disabled? Regarding the spec, I didn't expect the balancing to be disabled in this case.

Thanks

Max

over 13 years ago

0 ThomasCosby over 13 years ago

TI__Guru 73830 points

Maxime,

One of the other safety thresholds may be causing the problem. Can you send me your ppcsv and a pack parameter dump to review? COV is not supposed to turn cell balancing off, but SOV will disable it.

Thanks,

Tom

0 Maxime Champagne over 13 years ago in reply to ThomasCosby

Intellectual 480 points

Here is the answer:

COV is not turning off cell balancing. The device will automatically disable cell balancing if the cell imbalance is greater than 500mV. This is an internal parameter that cannot be changed.

Thank Tom !

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Balancing stops with no apparent reason on BQ78PL114