JBD BMS apparent v drop

[SWSL]

Hi. I am assembling my first battery pack build (4S) and while connecting up the new JBD SP04S304 200 amp BMS and following instructions, I ran into an apparent problem that may not be an issue but out of an abundance of caution, I'm checking in first to make sure.

• I connected the sensor leads to each 3.2 battery as indicated and tested the voltages of each lead relative to the negative to be ascending correctly but have NOT plugged in the harness yet. I understand that this is the final step.
• I then connected the total pack Negative to the BMS B- point.
• The instructions indicate to now test the B- to battery pack total positive and compare to C- output before proceeding to verify same voltage (within .4v). This is where I have an issue. With the sensor harness disconnected still, the B- side of the BMS reads same as battery but the C - side reads 1 volt lower.

Now in the enclosed instruction step it does show the sensor lead harness to be already connected, so it's perhapd just because I still have not connected the harness. I want to be sure all is correct first. I don't want to damage anything on an expensive device. The drop between B- and C- does not seem right. But again, the BMS is not connected in any other way, just acting as a black box for the total negative at the moment.

Is this a concern or should I go ahead and connect the little 4S harness and then test the B- to C- difference again? I'm guessing that the BMS requires some power from the harness to open up the two sides fully...

Thanks for any insight.

 

[42OhmsPA]

If everything metered correctly in ascending order plug it in and start using it.

You may have to give it a charge to wake it up and/or switch the charge / discharge FETs in the app.
I'd also review all the pre programed settings and make adjustments as needed.

 

[SWSL]

If everything metered correctly in ascending order plug it in and start using it.

You may have to give it a charge to wake it up and/or switch the charge / discharge FETs in the app.
I'd also review all the pre programed settings and make adjustments as needed.

OK, thanks. That did it. It needed the harness to get full throughput and now the V is the same on both B- and C-
Silly question, but again, abundance of caution. A lot of warning about not frying the BMS.

Another ? Do you or anybody know about the switch function? They included a harness but no clues. I'm guessing that it must be closed to turn off charging or throughput.

 

[42OhmsPA]

OK, thanks. That did it. It needed the harness to get full throughput and now the V is the same on both B- and C-
Silly question, but again, abundance of caution. A lot of warning about not frying the BMS.

You're welcome. It's good you're extra cautious, lots of energy on tap...

Another ? Do you or anybody know about the switch function? They included a harness but no clues. I'm guessing that it must be closed to turn off charging or throughput.

Can't help with that one, I've never used the switches. I'm sure someone else will chime in.

 

[SWSL]

OK, I found out that the switch has a software toggle in the app. If not activated, it does nothing, but activated the leads must close to enable discharge.