DIYbanter - View Single Post - Solid State relay kills induction motor fans

M Philbrook

In article ,
says...

On Tuesday, July 28, 2015 at 3:15:20 AM UTC-4, N_Cook wrote:
On 28/07/2015 03:06, Deane Williams wrote:
I set up a thermostat in my garage that comes on at 80 degrees F. and sends a 6 VDC battery voltage to control a 120 VAC solid state relay which powers up the vent fan. The fans always quit within 2 months to a year with no obvious defects. These are inexpensive 20 inch box fans with induction motors. I have tried several brands and styles of fans. The latest was a Home Depot unit that only lasted 2 months.
Does anyone know of a reason why I can't run an induction motor from a SS relay? What is killing the fans? I have taken two apart and there is no smoke smell, no visible damage and if there is a capacitor it tests OK.
Thanks for any ideas. I am going to switch over to a mechanical relay.

Dean

Do you do TIG/MIG welding in this garage?

No. I don't own a TIG/MIG welder.

You need a non inductive load on the same circuit, along with a
capacitor across it..

Your motor windings are getting killed by the drop out of the TRIAC
at each phase angle. You need to suppress it somehow so that both the
HV pulse that shouldn't be there and lack of lower Z at the base of the
sine wave, for the motor and cap of the motor to properly operate..

These are cheap motors and they run warm to start with, minimum copper
and coating on the wire is used.

Try getting your hands on a motor run capacitor, somewhere around
3..5uf at the proper rated voltage and put that across the load side
of your SSR.

ALso, putting a non-inductive load on the output helps, too...

If you can get a low wattage incandescient bulb that would be fine or
maybe a 5 watt R at around 400 ohms or so across the SSR load, along
with the run cap.

Also, I suspect when you connect these components, you'll also hear a
slight difference of motor noise, which indicates this issue..

SSR switches don't always have a proper snubber in them, so you may
also want to use a 100R and .1 Cap in series around the SSR, back to the
soure so that the load will cycle back to the line on spikes.

Have a good day
Jamie