I'm into a preliminary design of a eletrical vehicle that uses BLDC permanent magnet motors for motion (3 phases 36V 300W hub motors in wheel). For safety compliance this vehicle needs to provide a breaking mechanism that stops the vechicle when there's a power failure. My first choiche will be using reverse-action brakes/clutches that will triggers in case of power-loss unfortunately I have no room around motor and wheels.
I'm thinking about another solution that uses relays.
My idea is to place an SPDT relay (with coil bound to the primary power source) between motor driver phase output (relay NO) and BLDC motor phase (relay COMMON) all relays NC will then be connected togheter (trough a resistor?).
- In normal operations relays will be forced into NO position allowing drivers to handle motors.
- In case of power loss all relays will return to their NC position and thus all phases will be shorted togheter. If the vehicle is then forced to move (because a slope or something pushing at it) BEMF will react in opposition to the motion.
I don't think this idea is something new I will only know if someone sucessfully used this or if there are hidden dangers/pitfall into my approach.