ZEV Tips and Troubleshooting



ZEV7100, 84 volt nominal system

The customer reported that the bike shuts off.

The bike was test ridden.  It does not shut off, but it does slump in power or stutter, not a full shut down.  In fact the bike was found to run extremely good, as long as hard throttle was not used for acceleration.

The bike was put on charge.  The BMS began clicking indicating an over or under charge.  Given that the bike had been run and voltage measured only 80 volts, it had to be an over charge signal.  This meant that there was either a bad connection on a terminal or one of the BMS flat cables was not connected right.  The bike would not charge to over 84 volts further reinforcing this conclusion.

Visual inspection showed nothing out of place.
Each plastic terminal cap was lifted and the connection tightness checked.  When the next terminal was to be inspected – note the slight bulge at the bottom of the cap on the red cable end

Pulling off the cap showed heat on the terminal had melted the cap and burned it inside.  The bolt had gotten so hot it was burning the plastic.

The bolt was found to be loose.  Tightening the bolt made the connection and the bike ran perfectly.  The bike now charged to 95 volts and the BMS stopped making noises.

(On another bike the exact same situation was found.  In that case the bolt had been over tightened stripping the threads.  A slightly longer bolt was used to re establish the connection.  The holes in the battery are tapped about 7 mm deeper than the reach of the bolt when the BMS chips and cables are installed)

What was happening was that the connection was just enough loose that it would only arc under hard acceleration, high amp draw.  Under light throttle the connection was good enough to make the bike run.   The BMS saw the bad connection and was only allowing the charger to charge up to the bad connection.  So only part of the battery pack was receiving a charge that was meant to charge the entire pack.  So the BMS was trying to shed voltage and acting as if it was getting an over charge – which it was, on the first cells.