# Need Help with Mini BMS



## dimitri (May 16, 2008)

Jamie,

You need to start looking at your BMS modules installed on your cells, during this 30 second period while charger is running. I suspect one of the cell modules has a loose connection, causing the voltage to rise quickly and tripping the cell loop. Also, the failure of 2 modules in the middle of the pack is not normal at all, it should not happen. Please check all your terminal connections, make sure all have proper washers and lock washers. Sometimes your bolt may be tight because it bottoms out inside the terminal, but connection itself might still be lose. You have to try to wiggle ring terminals to see if they can move, indicating loose connection. I can't think of any other reason for blown modules and BMS tripping. I had a customer who forgot a lock washer and had similar issues. There was also a report of terminal bolts bottoming out due to the hole being too shallow, requiring additional washers to be used. Tight cell connections are very critical. Another possibility is poor connection between the terminal and the copper link. Terminal tops can be dirty and/or oxidized causing poor connection. Its recommended to clean terminal tops and put Noalox paste on them before putting copper link on top. Obviously BMS ring terminals go on top of copper links, not under them. The sequence should be Terminal/Noalox paste/copper link/BMS module/washer/lock washer/bolt. 

Also, you should not have to disconnect 12V from BMS, just cycle ignition key to reset the BMS.

The key in troubleshooting BMS and battery issues is to look for cell modules which shut off the green light few seconds before BMS trips or have green off completely.

Another test is to take a short drive with heavy acceleration , stop and quickly touch terminal bolts ( one at time ) with your finger, to see if some of them get too warm, or much warmer than most others, indicating poor connection, which heats up due to higher resistance.


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## EVfun (Mar 14, 2010)

Might check to make sure the BMS control board has a good ground connection. I know that if my ground comes loose the buzzer weakly squeaks, indicating a fault. That was an oops on my part as I was trying to pull a cell loop wire as part of setting the time delay.


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## cruisin (Jun 3, 2009)

EVfun said:


> Might check to make sure the BMS control board has a good ground connection. I know that if my ground comes loose the buzzer weakly squeaks, indicating a fault. That was an oops on my part as I was trying to pull a cell loop wire as part of setting the time delay.


Try having the ignition on while charging, when it shuts off the green light on a cell has shut off and will remain off until the ignition is turned off. This way you can find the cell that is shutting down the BMS.


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