How does the electric brake work ?

[nuz69]

Hello,

I always thought that the electric brake work like that : the ESC turns the motor into alternator mode and it restitutes electric energy to the battery. Am I wrong ?
Is it just a simple resistive shortcut of the motor phases ?

Thanx

Tom.

[BrianG]

Have you ever taken a motor, short the phases together (not hooked to an ESC or anything), and try turning the shaft by hand? Well, that's basically how it works. Except and ESC will quickly turn on and off the "short circuit" giving you variable braking. When the short-circuit is removed during one of these pulses, the stored energy in the motor charges the battery.

[nuz69]

Yes, I already have done it ;) But it's not clear, the short current is no dissipated into heat in the ESC but goes to the battery ?
There is another interesting experiment, short the ESC battery input together (without battery) and try to move the car. Above certain speed, the motor brakes.

[Pdelcast]

Originally Posted by nuz69

Yes, I already have done it ;) But it's not clear, the short current is no dissipated into heat in the ESC but goes to the battery ?

That's correct. The ESC could not dissipate all the energy on its own (it would overheat very very quickly,) so it dumps the extra energy onto the bus.

The ESC operates like a boost converter when braking.

http://en.wikipedia.org/wiki/Boost_converter

Take the schematic and substitute the low side mosfets for the switch, the high-side mosfets for the diode, the motor for the inductor, and the battery for the load (on the right side) and that will give you the approximate idea of what's going on.

Thanx!

Patrick