New JBD BMS Voltage variance

[adamween]

Any insight on voltage calibration on JBD units? BMS is a new 7-20S AP20S.
The unit originally wouldn't power on, but did eventually after it was "jostled" around (possible short internally?).
Now that it is "working", the cell voltage displayed on the app is inaccurate on every cell.. The app shows the voltage as higher than actual.

(checked the voltage with a Fluke 787 that is work calibrated - so I am confident in the readings)

OVERAGE VDC	CELL	OVERAGE VDC
0.022	1 | 7	0.014
0.012	2 | 8	0.012
0.010	3 | 9	0.013
0.012	4 | 10	0.014
0.011	5 | 11	0.014
0.010	6 | 12	0.014

I've been working with Docan (where I bought it) for days with no luck at all - "I'll give you a reply later, consulting an engineer".

One thing is for certain... They don't want to exchange it for a good one.

It has been trouble from the start, and they aren't getting me any answers.

 

[Ampster]

Any insight on voltage calibration on JBD units? BMS is a new 7-20S AP20S.

I do not think there is any calibration. I have three JBD BMSs and have never seen less than a third of one percent accuracy. If I did the math correctly that would be the difference between 3.64 and 3.65 volts as to when my high voltage disconnect cuts in. I never expected scientific accuracy from a $100 BMS. I also have an $800 automotive BMS and honestly never checked to see if it was any more accurate.

 

[meetyg]

Actually you can calibrate the JBD BMSs with a special UART/RS485 to USB adapter (available on Aliexpress and I think Overkill Solar). You connect this to a PC and run the JBDTOOLS software. From there you can calibrate alot of stuff, including cell voltages.

 

[Ampster]

Actually you can calibrate the JBD BMSs with a special UART/RS485 to USB adapter (available on Aliexpress and I think Overkill Solar).

I bought that adaptor from Overkill and forgot about it. Good to know. I also have a vague memory that my expensive BMS can calculate inter cell resistance and adjust voltage but not sure if the JBD can do that. In the automotive environment the packs sometimes get split up and the bus bar resistance can vary because of the distance.

 

[NorthTown2022]

Same BMS, pretty much same issue with inconsistent voltage readings. With the battery resting overnight the BMS is reporting cell voltages 6mv to 11mv higher than my DVOM (fluke and same reading as another good meter from NAPA). Readings were taken at the cell terminals and confirmed exact same measurement at the connector to BMS. While charging I metered 15mv+/- discrepancies.