Quick Stop-Split Phase Motor

[dmorse03]

I have designed a lift utilizing a 1/2 HP Cap Start 1725 RPM motor.
Problem is when limit switch cuts power to motor, motor turns a few more revs
causing the mechanism to jam. I know with DC perm mag field motors,
the motor can be stopped instantly by removing power to arm and simultaneously
shorting arm terminals. Can this be done with split phase AC motors somehow?
Don
Dmorse02@twcny.rr.com

 

[SteveKW]

Applying DC will stop the rotor. An electromagnet attached to a brake may be best since you wont want the shaft to tun any more and that would lock it from freewheeling. They sell motor and brake combinations just for the task you describe.

 

[Marke]

The normal way to achieve this is by using a brake motor. This is a specially designed motor incorporating an electromagneticly operated brake. When power is applied to the motor, the brake is removed, and when power is removed from the motor, the brake is applied. This is a failsafe system which works under power failure situations.
An alternative is to apply DC to the stator when the power is removed form the motor. The DC current provides a stationary field in the stator and the rotor attempts to spin at the speed of the stator field. It therefore acts as a brake. The DC should be smooth for best results and therefore needs to be full wave rectified or better. While DC is applied, power is dissipated in the motor, so it's application should be for long enough to stop the motor only.

The level of DC current determines the brakeing torque. The voltage required is a function of the stator resistance. The DC injected brake option is not a failsafe system unless it is battery powered. Mark Empson

http://www.lmphotonics.com

 

[dmorse03]

thanks to you both for the input. I'll get the DC approach a try.
Don