Jk bms power consuption

[glamsland]

Hello.
I have two jk B2A8S bms mounted on two 250a 24v li ion batteries. All working fine. No alarms.

I find that one of the batteries selfdischarges faster over time(several weeks) than the other one. The battery Main switch is turned off at this time.

Can one of the bms be foulty?
I would like to test the bms with a multimeter, can you instruct me where on the bms i should messure the current flow internally in the bms?

What is ok current consumption for this bms?

Have a Nice day

 

[OffGridForGood]

How are you determining that one battery is self discharging faster than the other? If you are going by the BMS SOC - this is highly unreliable.
Do you have the blue-tooth option on the JK?
I recall reading (on this forum) a year or two ago, the typical BMS power consumption was about 5mA however x 2 or x 3 with BT enabled.
I am told this is the reason the BMS shuts down the BT if it is not active for a period of time is to reduce this current draw.
- I am not sure I could accurately measure 5mA current with anything in my tool kit. It would seem a typical LFP pack, even over several weeks, is not going to show this low consumption.

 

[profesor79]

if I will be in similar position then I probbably will do this:

• swap bms on battery pack
• add a switch to turn bms off in not needed ( with some JK startup is painfull if you don't have a dedicated switch or lcd screen)
• switch off lcd screen (if applicable)

5mA is a small current to be measured with clamp meter, so to measure in that case a good quality multimeter shall be used.

 

[profesor79]

To measure BMS consumption we need to connect amp metter to power source on the BMS, so this is line B+ or B-

 

[Steve_S]

JK's are actually very Polite when it comes to self-consumption but there is a Gtcha that catches people... IF you are using Active Balancing and not set to a proper voltage it can potential consume power IF there is a weak cell or two that it keeps trying to keep up by draining down the other cells to transfer that energy. Active Balancing is best to operate above 3.400 Volts or even better at 3.42 Volts with the correct charge profile.

JK has an ON/OFF switch (4 wire) as well as a screen/switch combo. This actually physically turns off the BMS, preventing any power use.

 

[profesor79]

. IF you are using Active Balancing and not set to a proper voltage it can potential consume power I

this is great point!

 

[glamsland]

Thanks for answers, I'l do some testing and report back my findings..

I will also check the balance setting.

The batteries are of the same type cells, all cells are tested with a capacity tester. After a storrage period on my cabin, with main switch off, its allways battery 2 that is slighty lower lovtage thn battery 1. Might be the balancing in this battery that was still going when i turned off the main when i left. Not sure. Its a monitor on each of the bms, this might have a small current, it automatic turns off when no current goes thru the bms.

i also have a switch on each that with a longpress turn off the bms.
The bms is normally not turned off.

I'l do the current messurment with my multimeter(fluke) on both bms and see what i find.

 

[Steve_S]

Note that JKBMS won't register Amperage below 0.6A regardless if In or Out bound.
This is the case with most BMS' on the market presently.