SS Relay causing failure of induction motors?

Deane Williams

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May 31, 2015, 10:35:14 AM5/31/15

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I have installed a thermostat in my garage to control a fan placed on a shelf in front of the peak vent. The thermostat box has a 6V AA battery pack which switches control voltage to SS relay near the fan. The relay says "Silicon Power Cube" on it and is rated for 240V and 3A. I am using it on 120VAC. The control voltage is specified at 3 to 32 VDC. This system works perfectly. I have been using common 20 inch box fans. The problem is they only last a year or so and then they just stop working. Sometimes they fail over the winter when they never run. I have tried to troubleshoot the fans but can't find out why they have failed. The capacitors on the motor measure the correct value. I suspect there is something in the SS relay that is causing them to fail but I have no idea how. Are SS relays compatible with induction motors? I am on my fourth fan in about 5 years now and these fans usually last forever.
Thanks for any ideas.
Soartech

M Philbrook

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May 31, 2015, 11:15:02 AM5/31/15

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In article <364ff67b-95e1-4156...@googlegroups.com>,
pyroar...@gmail.com says...

If you are refiring to the generic cheap window fans you get in the
store, I find for the most part, they only last a year anyway..

You must check to see how stiff the rotor is, many times the bushings
will dry out from the heat. Also after some run time the bushings will
loosen up and when this happens, dust in the area will migrate its way
into the bushings, what you normally end up with is a fan that worked
last year but now is having a hard time starting, due to drag.

These box fans operate hot anyway, due to their design.

You may want to think about getting a real vent fan for agricalture, a
motor type design to last in plases like chicken coops etc...

P.S.
Shop around at your local hardware store with a vent fan with this
type of motor on it.

Jamie

Deane Williams

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May 31, 2015, 1:03:04 PM5/31/15

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Jamie,
Thanks but I believe the problem is electrical. The fans still turn easily with little or no drag after they have stopped working. Two years ago I bought a higher quality fan from Home Depot and I thought I had solved the problem as it lasted through 2 summers, but this year it only ran a couple of days and then failed in the same mysterious way as the cheap box fans.
Even stranger, I went out and bought my 4th fan at Home Depot which looks very similar to the one I had and when connected to the SS relay it won't run. It just sits there and hums. So I put it on a timer which is not as good as a thermostat.

Samuel M. Goldwasser

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May 31, 2015, 3:54:54 PM5/31/15

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THat's perhaps a clue that your SS relay is defective and only switching
one polarity of the line. So you get DC, the fan hums and doesn't turn,
then the motor burns out if left connected.

One kludge but effective solution would be to have the SS relay control
an AC/DC relay that switches the fan.

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M Philbrook

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May 31, 2015, 8:24:45 PM5/31/15

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In article <7a9cad5f-f783-4bb4...@googlegroups.com>,
pyroar...@gmail.com says...

>
> Jamie,
> Thanks but I believe the problem is electrical. The fans still turn easily with little or no drag after they have stopped working. Two years ago I bought a higher quality fan from Home Depot and I thought I had solved the problem as it lasted through 2 summers, but this year it only ran a couple of days and then failed in the same mysterious way as the cheap box fans.
> Even stranger, I went out and bought my 4th fan at Home Depot which looks very similar to the one I had and when connected to the SS relay it won't run. It just sits there and hums. So I put it on a timer which is not as good as a thermostat.

For testing purposes, connect a drop light with a
incandescent bulb in it on the same circuit that runs the
fan after the SSR. You may only need a small one.

See if the fan will operate with that light also connected to
the same circuit, use a power strip of something that gets powered
via the SSR to make sure you're on the same switched circuit.

Report back :)

Jamie

isw

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May 31, 2015, 11:45:12 PM5/31/15

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In article <7a9cad5f-f783-4bb4...@googlegroups.com>,

Some SSRs are not happy with largely inductive loads (i.e. fans).

Isaac

Jon Elson

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Jun 1, 2015, 5:47:21 PM6/1/15

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These fans have one-time thermal fuses buried in the windings, to prevent
house fires. If you are using this to cool off a hot attic, that may be
getting the thermal fuse too close to the fusing temperature, add a couple
hours of motor on time and the fuse may blow.

Jon

Cydrome Leader

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Jun 2, 2015, 5:38:04 PM6/2/15

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You might try a name brand solid state relay and see what happens. Crydom
is real, silicon cube is not.