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BMS, 7s, Li-Ion (3.7v), >35A, common port, >60v MOSFETs

Posted: Oct 19 2019 5:59pm
by mrbill
Five years ago I bought six 7s batteries from EM3EV made to order using Samsung INR-18650-29E cells, ca. 2014. These batteries have been running well for the last 5.5 years, and their capacities are around 90-95% what they were when new. All six of these batteries have operated normally and have been trouble-free.

Recently one of these batteries suffered a BMS failure. The battery would discharge but could not be charged. EM3EV informed me based on my description of the symptoms that the BMS had failed. Unfortunately, they no longer stock the 7s BMS I was using and are unable to recommend a suitable replacement.

Although I initially used these batteries in a 25-volt system, I now use a 50-volt system, running these 7s batteries in series pairs to make a composite 14s battery. Fortunately, the BMS used 100v MOSFETs (IRFB4110) which are capable of switching the series voltage.

I have found several replacement BMS candidates, but upon inquiring with the sellers have been told that the BMS will not handle placing two such batteries in series. One vendor informed me that Vds on its switching MOSFETs was 40 volts.

Can anyone identify the BMS that was in my pack and where I might find a replacement, or recommend a substitute?

The BMS measures (LxWxH in mm): 108 x 60 x 11

Photos of the defective BMS are below.