diy solar

diy solar

420mV Voltage Drop across JK BMS - SOLVED


New Member
Mar 25, 2022
Putting final configuration parameters in a new system and noticed a difference in voltage measurements between a Victron SmartShunt and a JK B2A24S15P.

Battery measures 53.33v between cells 1-16. (Using two different multimeters.)

BMS measures 53.33v.

SmartShunt measures 52.89v and manual measurement confirms that.

Measurement across the B- & P- of BMS shows 420mv. (Using two different multimeters.)

The math between 53.33v & 52.89v is 440mv (not 420mv) but I can accept a 20mv measurement error, connection and cable losses.

Is that sort of voltage drop in a JK BMS to be expected?

What do other forum members experience wrt BMS voltage drop?

Note that the SmartShunt is connected to the P- side of the BMS.
Is that voltage drop with or without a load? Is the BMS getting warm?
If there is no load on the battery and the BMS is turned off that could be a valid reading.
Is that voltage drop with or without a load? Is the BMS getting warm?
There is no load - not yet connected to Inverter/Charger.

BMS is cool (about 24C).

BMS is turned on. When turned off, I wouldn't expect to get any readings across the BMS.
There will be slight leakage through the mosfets even if they are turned off. Digital multimeters are extremely sensitive so I'm not surprised you're getting a reading.
This has been resolved.

The BMS had Charge set to Off - once Charge was set to On, the voltage drop disappeared.

Not sure about the internal workings of JK BMS, but I suspect the voltage drop was associated with either diodes or Mosfets being engaged when Charge is Off.