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-   -   protecting motors when power turns on (http://www.diychatroom.com/f18/protecting-motors-when-power-turns-36094/)

jim.seattle 01-16-2009 07:48 PM

protecting motors when power turns on
 
I have several expensive air filters and with most motors that run at different speeds it turns on full (high) then to medium and then to low. Turning the motor on by plugging it in while the switch is in med or low will damage the motor.

So, I'm concerned if I leave the motors running at medium or low & then the power goes off AND THEN comes back on again.

I'm looking for something to plug the filter into so that if it senses the power going off it will turn itself off so that when the power returns the filter will not go on.

Any ideas?

I do not want to run them at high speed all day or use a UPS.

Thanks,

Jim

nap 01-16-2009 08:15 PM

You kind of lost me on some of what you said but if you want something that is running to not restart once power is lost until you take some other action, you simple need a relay wired that it holds once it is energized but requires some action by you to re-energize it once power drops out. Actually a really simple thing.



what does this mean:

Quote:

have several expensive air filters and with most motors that run at different speeds it turns on full (high) then to medium and then to low. Turning the motor on by plugging it in while the switch is in med or low will damage the motor.
why will the motor be damaged if starting on med or low? Most multi-speed motors I deal with can be started in any speed. Most motors actually prefer a slow start. It causes less stress on everything.

KE2KB 01-16-2009 09:09 PM

Like Nap, I cannot understand why the appliance would be damaged in the situation you describe.
Any manufacturer who designs a reasonably reliable product is going to protect the equipment against uncontrolled power loss and restoration. After all, power outages happen all the time, everywhere on Earth!

I have such a device that will indeed trip out and require manual reset after power has been removed. It is a portable GFCI device. It is intended to protect the operator of portable power tools from dangerous ground-fault currents. This particular one I own will always reset to OFF/Tripped when power is removed from it.

You should not require something like this, but if you want, I can give you the info on this device.

AllanJ 01-16-2009 09:50 PM

Do the motor instructions say not to plug it in with the switch in low, or is it just hearsay?

I am guessing that the knob is labeled off-high-med-low because most people want the fan on high and for them they will then only have to turn the knob a little ways.

I have been in buildings where the main disconnect has to be turned on manually each time after a power failure.

J. V. 01-17-2009 12:06 PM

I would not lose any sleep over this.


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