Matching a BMS and Motor Controller: Current Limits and Regen
An integration guide to battery-side current, peak duration, regenerative charge limits, CAN messages and fault behavior for low-speed EVs.
Confirm where the current was measured
Motor phase current describes drive behavior. Battery-side current determines the load on the pack, connectors and wiring. Curtis documents how current on the two sides can differ during launch and low-speed operation in its controller family. Record current and voltage at the battery DC side with a documented sample rate, sign convention and operating condition.
Describe current peaks with time and repetition
Check sustained operation against the temperature of cells, terminals, connectors and enclosure. For a peak, record its magnitude, duration and repetition interval along with temperature and state of charge. A single maximum current number misses the difference between a long grade and a sequence of frequent starts.
Treat regenerative braking as a separate case
During regen, the controller may send current back into the pack. The allowed charge current may drop near full charge or when the pack is outside its normal temperature window. Agree how limits are communicated and how the vehicle preserves safe braking when regen is restricted. Validate edge cases under a vehicle-team-approved test procedure.
Specify CAN data and communication loss
Agree bus speed, message timing, units and byte order. Define the signals required by the application, such as state of charge, charge and discharge current limits, temperature and faults. Set expected vehicle behavior for timeout, invalid data and restart. Record BMS and controller firmware versions in the acceptance report.