BQ40Z80: Full Charge Capacity variation

Reed Christiansen

Part Number: BQ40Z80

Hello,

On my setup with the BQ40z80 and a 6s lipo in a relatively high discharge application (3C), I am seeing a variation in Full charge capacity at the end of discharge and the end of charge - by about 5%

After charging, the FCC is at its highest - ~250 wh,

On discharge when the pack hits cell term voltage, FCC goes to about 235 wh, during relax, it creeps around.

The more accurate FCC is the lower FCC calculated at cell term. Is there any way to "lock" this in?

Thank you

The graph below shows FCC over about 25 charge relax, discharge relax cycles.

over 1 year ago

0 Jose Couso over 1 year ago

TI__Mastermind 27321 points

Hello Reed,

Do you have the smoothing feature ON? This will help prevent FCC drops.

Regards,
Jose Couso

0 Reed Christiansen over 1 year ago

Prodigy 100 points

SMOOTH is enabled,

RELAX_SMOOTH_OK is enabled

RELAX_JUMP_OK is disabled

0 Jose Couso over 1 year ago in reply to Reed Christiansen

TI__Mastermind 27321 points

Hi Reed,

Please share your log and gg file.

Regards,
Jose Couso

0 Reed Christiansen over 1 year ago in reply to Jose Couso

Prodigy 100 points

shared to your profile

0 Jose Couso over 1 year ago in reply to Reed Christiansen

TI__Mastermind 27321 points

Hello Reed,

The reason why FCC (usable capacity) is dropping is because the temperature increases abnormally in the application. Why does temperature increases by more than 30C? It's getting extremely hot.

Possible solutions are to tell the gauge to ignore temperature increase. This is done by controlling thermal parameters.

Have you submitted data to the GPCRB tool? This tool will provide the thermal model parameters needed to account for the temperature rise.

Regards,
Jose Couso

0 Reed Christiansen over 1 year ago in reply to Jose Couso

Prodigy 100 points

HI Jose,

The thermal rise is due to the high discharge drone application - about 26 minutes for complete discharge. Not much we can do about it.

I did submit data to all three options available for the BQ40Z80 on the GPC website.

chemid
room temp optimization
room temp and low temp

The resulting parameters are included in the gg I sent you.

I also submitted for the low temp, room temp, high temp (low and high discharge) - however, it looks like the BQ40Z80 does not support the parameter set provided - so not usable for me??

What parameters would I experiment with to have the FG ignore the temp rise?

Reed