JBD 150A BMS misreads ah%

[tilroh]

what's wrong with this picture?


Suddenly both my JBD BMSs started giving faulty ah% readings.
I checked the config on both.
Any ideas on what to check?
Thanks, Mack

 

[niktak11]

When did you last charge it fully? Also your balance turn on voltage is too low.

 

[tilroh]

They were charged and discharged to this yesterday.
Balance is set low b/c cell #2 jumps to 3.65v and triggers the BMS.

 

[Luxpower_Gilbert]

Whenever any of the cell over-voltage protection the bms thinks the battery is full..

 

[tilroh]

Whenever any of the cell over-voltage protection the bms thinks the battery is full..

and one cell certainly is. What would make the amp count so far off?

 

[Luxpower_Gilbert]

What ah capacity of your bank?

 

[tilroh]

What ah capacity of your bank?

8, 302A cells in 2, 12v batteries, each with a JBD BMS. This configuration is the only way they'd fit in the boat.
302A at 24v.

 

[Luxpower_Gilbert]

on the app it say 13%.
300*13%=39ah
app say 37.76 so 39 is close enough.
what seem to be the problem?

 

[tilroh]

on the app it say 13%.
300*13%=39ah
app say 37.76 so 39 is close enough.
what seem to be the problem?

yes but at 13.34V?
Yesterday I took the batteries down till one cell got to 2.65. Then I put about 280A (24v) back in. Later I pulled 70A for an hour. This is the state of the pic.

 

[DJSmiley]

What are the cell fulland otherl settings?

The JBD BMSses do require an occasional full cycle to remain accurate in my experience.

If you change settings in the meantime, you might need to do a new cycle.

I would set cell full to 3.5V, and do a full charge with 14.2V. Discharge at 0.2-0.5C, with BMS cell disconnect set to 2.5V, till the BMS cuts out, and recharge till full.

 

[tilroh]

I should have said that both BMSs showed 100% after charging but dropped to 13% and 34% shortly after apply a test load.

 

[Bob B]

It looks like the BMS is tracking via a voltage guestimate rather than tracking amps in vs amps out .... this will happen each time you write any parameter change .... and then you must do a full cycle to get it back to tracking amps.
What are your settings for the "Cell Full Voltage" and the settings for all the "Cell xx% Cap. Voltage"

If you have 2 doing the same thing, it is probably one of your parameter settings .... maybe you could take screen shots of all of them.

 

[tilroh]

Thanks, I have 2, doing the same thing but to different degrees. Both read 100% after charging but soon after applying a 70A load, they dropped to 39 and 13%. I've had the batteries a year and the BMSs have not had an issue till now.

 

[Bob B]

I think the 3 key settings here are the cell full voltage, cell over voltage, and the cell 100% cap voltage.

When BMS is tracking via voltage, it will thing the battery is 100% capacity when the voltage is at 3.38 volts.
It won't reset the BMS to start tracking via amps in and amps out til you have reached the cell full voltage ... which is set at 3.65 volts. Since the cell over voltage is also set at 3.65 volts ... if you a cell ever reaches the full threshold, the over voltage will also triggered.

I would have the cell full voltage and the cell 100% Cap voltage set the same .... 3.38 seems a little low for the for the 100% cap voltage, but will probably work correctly if you set the cell full voltage the same ... and leave the over voltage set to 3.65.

Once you reach the cell full voltage, it should ignore those xx% Cap Voltage settings and start tracking amps.

 

[tilroh]

Thanks BB, I'll change the Cell Full voltage.
I checked the BMSs and the starb. BMS (the one in the first pic showing 13%) is now showing 91%. I haven't even touched the old iphones I use to monitor or charged or dis charged. (!)

 

[tilroh]

I think the 3 key settings here are the cell full voltage, cell over voltage, and the cell 100% cap voltage.

When BMS is tracking via voltage, it will thing the battery is 100% capacity when the voltage is at 3.38 volts.
It won't reset the BMS to start tracking via amps in and amps out til you have reached the cell full voltage ... which is set at 3.65 volts. Since the cell over voltage is also set at 3.65 volts ... if you a cell ever reaches the full threshold, the over voltage will also triggered.

I would have the cell full voltage and the cell 100% Cap voltage set the same .... 3.38 seems a little low for the for the 100% cap voltage, but will probably work correctly if you set the cell full voltage the same ... and leave the over voltage set to 3.65.

Once you reach the cell full voltage, it should ignore those xx% Cap Voltage settings and start tracking amps.

Thanks again BB, I set full cell V to 3.650 and now both BMSs are reading 90%. Cheers!

 

[Bob B]

Thanks again BB, I set full cell V to 3.650 and now both BMSs are reading 90%. Cheers!

I thought it already was at 3.65 .... Weren't you going to make it the same as the 100% cap voltage?

 

[tilroh]

I thought it already was at 3.65 .... Weren't you going to make it the same as the 100% cap voltage?

I guess I did. Here's what it looks like now.

 

[Bob B]

Yeah .... it just recalculated the % based on your voltage settings when you wrote the parameter change ... now, get it up to the "cell full voltage" so it will start tracking amps.

 

[niktak11]

They were charged and discharged to this yesterday.
Balance is set low b/c cell #2 jumps to 3.65v and triggers the BMS.

Balancing at too low of a voltage can easily make the pack MORE imbalanced