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Overkill/JK BMS cell voltage inaccuracy at warmer temps? (+-0.007mv)

hipringles

Solar Enthusiast
Joined
Jan 31, 2021
Messages
214
I've noticed in these absurdly warm PNW days my voltage on the JK smart bms app is not correct on the cell level. It will show cells off by up to 13mv, yet when I manually probe them they are all within 1-2mv (using a medium-high end multimeter). All will read say, 3.331, but the BMS will say 3.325 to 3.338

When it cools down a bit overnight it seems to get a little less sloppy to +-6mv.

Also worth noting, i've probed on the cells themselfs, and at the connector to the BMS. I will disconnect the cable strand, probe the entire line to get 3.331 aross 10 cells, then plug it in to see the BMS app being off. Has anyone else seen this before?
 
My first guess would be clean your connections:

 
Voltage per cell, current per cell & even temperature all need to be calibrated during BMS setup if you want a high level of accuracy. Medium-high end multimeter means little when it comes to accuracy. Meters need to be calibrated periodically. If you're interested in accuracy then maybe buy a higher end meter meter and send it in for calibration periodically. Pay particular attention to the DC accuracy specifications in the voltage ranges you're concerned about when shopping for a multimeter. Example: ±(0.1% + 3 counts) would be good. If meter DC voltage accuracy is listed as ±(1.2% + 3 digits) for example then when measuring 3.65V it could display 3.604V to 3.696V and be within spec so not a good choice for DIY LFP battery setup in my opinion. Much greater accuracy would be preferred. You can also buy a Voltage Reference or Voltage Standard to use to check how inaccurate your meters are. These units https://voltagestandard.com/ seem to get good reviews.
 

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