Did my BMS go Bad?

[larrylwill]

Yesterday I went to my MH to check out everything prior to a trip. Everything has been working for a while. I have a 4s Lipo4 battery and 150a smart bms, charged through a 280A alternator and Renology 60A DC2DC.
The MH had been sitting for a couple months plugged in with a charger on the battery, set to come on if the battery got low.

Yesterday I cranked up the air condition on battery and it started and a couple seconds later everything died. I found that my AC switch had a loose wire from the Inverter, which I fixed and the inverter is ok and the battery is OK and the Air works ok on AC but not DC through the inverter.
I then nocited the C- on my BMS is read around 1v to B+. I unwired it and checked all connections but I can't get it to turn on. There is no protection activated. Although the program says charge on discharge off. The only other thing unusual is the total pack voltage has about 180mv between cells. The first 2 are high 3.5 something compaired to the other 2 at 3.4 something. Im doing a new top balance now.

I am about to declair the BMS defective. I checked all the fets and all check good. The MH will power up on the battery without the BMS. The cell wiring to the BMS is good and the bluetooth works but does not show any current out of the battery but does show cell voltage and it agrees with my VOM. Yesterday for a while it showed current in from the charger, I did notice tonight it flashed the MH lights on for a second a couple of times, while connected to the BMS. Like it is shut down for some reason and releised.

Where do I go from here? I could build up a small 68750 12V pack and try the BMS on it..

 

[sunshine_eggo]

Sitting for a couple months means your battery went out of balance. Extremely common.

Some BMS have a setting for a total deltaV cut off in addition to cell limits. If yours has something set like that, loads may trigger it.

 

[larrylwill]

Sitting for a couple months means your battery went out of balance. Extremely common.

Some BMS have a setting for a total deltaV cut off in addition to cell limits. If yours has something set like that, loads may trigger it.

I was looking for something like that but could not find anything. Although the day before the lights came on and the charger worked proper, it was only after I tried the Air condition and disembled everything to find the problem, this problem started. Yes I suspected something hooked back wrong but I cant identify anything. Also I did not disemble the cell battery monitering wires, only the B+ on the Renology, B- and C- on the BMS.

 

[larrylwill]

In case anyone is interested, I found the problem. With my BMS you must attach the B- to the battery before you connect the C-. I built up a 81650 pack to play around and I found the solution.