Pint VESC FM BMS bypass (the proper way)


Pint VESC FM BMS bypass (the proper way)

As we further develop our Pint/XR conversion to VESC it has been determined that the old way of bypassing the discharge path of the FM (Future Motion) BMS was less than ideal. The old way (bridging the positive post) was successful in bypassing the discharge path but unfortunately it also bypasses (disables) one of the most important safety features of the BMS. The old way disables the BMS ability to stop charging if 1 or more cell groups are overcharging (>4.3v). Normally the charger should stop charging once the desired voltage is reached (63 volts) but there may be instances wherein the BMS may need to intervene and stop charging (broken charger, faulty cell group preventing the pack to reach 63 volts leading).

The latest guides out there suggest pigtails that involve extra XT60 connectors inside the battery box. Unfortunately the Pint enclosure is so small that extra XT60 connectors will not fit.

I was finally able to achieve the proper way of bypassing and wanted to share images. I am sure there are other ways of doing this on the Pint but these are 2 ways.

Method one leaves the stock harness alone but involves folding the wires on itself. This was doable but in the end I did not like the idea of high amp wires folded in a tight space.

Method 2 involves cutting the stock harness to avoid the extra folded wires. In the end I went this way as I don’t foresee going back to the stock pint controller. I can always make an extension if that need arises.