Thanks. I know that brushless motors require AC input, and in my mind it classifies them as AC motors. Of course, this means that you can't bypass the controller and connect the batteries directly to the motor as a fallback plan in case of a partially failed system, unlike DC motors.
So for a brushless (AC) system, the normal current overload protection (fuses or breakers) should suffice for safety purposes and a "panic button" disconnect is not really needed.
Fair winds,
Eric
Marina del Rey
--- In electricboats@
>
> Hey Eric,
>
> As I understand standard Transistors failing with thermal overload and
> lock closed. Mosfets fail open.
>
> AC motors require alternating current cycles to rotate. If the system
> were to lock open in the H bridge, the motor rotor would lock as if it
> were a brake. You are right in assuming the motor would not go full bore.
> You might note that brushless motors are in fact a form of AC motor.
>
> All said there is a hazard. A full open circuit may cause a fire
> without proper circuit protection. Fuses vs. breakers? Breakers leave
> the users hands out of harms way if installed correctly. Fuses installed
> in accordance to the NEC will have a main disconnect before the fuse in
> higher voltages, and a good practice for all circuits. Most Machinery
> has fuses at the machine. A disconnect in sight of the machine. And
> breaker protecting the circuit. Fuses can be purchased in slow blow, or
> standard. Motors because of the start load typically use slow blow so
> their rating can be a little lower to protect better.
>
> I hope this helps in your designs, don't cut corners to save a buck, but
> there is no need to over engineer.
>
> Kevin
>
>
>
> Eric wrote:
> >
> >
> > Is this potential problem of runaway controller limited to DC
> > controllers? Should this be a consideration for a system using the
> > open frame Mars motor? It seems like a DC to AC convertor won't fail
> > in a full on condition.
> >
> > I can understand the issue with a DC system which is typical in EV cars.
> >
> > Eric
> > Marina del Rey
> >
>
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