SSR and two speed AC motor

[Dumuzi]

I am using an SSR to start/stop a two speed 230VAC motor from a computer. The motor has 3 wires (neutral, low speed and high speed). When the high speed wire is connected to the SSR it works as it should. When the low speed wire is connected the motor will not stop. The motor draws around 50mA which is in the load current range of the SSR. What is the cause for this and is there an easy fix? I guess it has to do with zero crossing, or....

 

[OperaHouse]

50mA is pretty small. Try a .22 or .47uF across the motor supply lines.

 

[ScottyUK]

A small SSR is probably triac-based rather than antiparallel thryristors as would be found on a bigger type. Under some load conditions the triac won't recover a blocking state after the current zero crossing before being forward biased again. This is inherent in triacs, which conduct twice per mains cycle unlike a thyristor which conducts once per mains cycle.

Easy fix... find a thyristor-based SSR designed for inductive duty.



----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[Dumuzi]

I use a Crydom DPA6111 and the data sheet claims it has SCR output. Will try a capacitor across the motor supply lines as suggested.

 

[jraef]

I wouldn't put a cap across an SCR...

 

[Dumuzi]

A 0.33uF in parallel with the load (motor) solved the problem. Thank you.