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Old Jun 22, 2007, 09:58 PM
Don Young
Don Young
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Re: Single phase electric motor problem


"jlh45" <jlh45.2sls4n@rcgroups.com> wrote in message
news:jlh45.2sls4n@rcgroups.com...
>
> Although this is not strictly an engineering problem, I hope there is
> someone who can point me in the right direction to solve a strange
> problem I have with an electric motor.
>
> For about 25 years I have had an Elektra Beckum table mounted 12 inch
> circular saw which for several years has been used rarely, maybe only
> one job in a year. The motor is a 2.2 kw, 2,800 rpm capacitor start
> single phase induction motor, which is rated at 11.5A.
>
> Recently I needed to use the saw, but when I pressed the start button
> the motor started in reverse - not what you want with a circular saw!
>
> It has never done this before and there is no reverse option on the
> no-volt switch.
>
> The next time I attempted to start the saw it was obvious that it
> didn't 'know' which way to rotate and blew the 13amp fuse - it has
> blown fuses ever since I've had the saw but not often enough to warrant
> any serious investigation.
>
> At the next start up I spun the saw blade in right direction and then
> pressed the start button, whereupon the saw ran perfectly.
>
> I have used the saw frequently over the last ten days and have found
> that I have to spin the blade to ensure the motor starts in the right
> direction. It has been cutting long lengths of timber with no signs of
> distress. If I don't spin the blade the motor will mostly start in the
> wrong direction, very occasionally in the right direction, and has also
> blown another fuse.
>
> Before I pull the motor to pieces does anyone have any ideas why this
> is happening and what to look for when I get inside the motor?
>
> Thanks.
>
> John
>
>
> --
> jlh45
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>

I would check capacitor, internal starting switch, and start
winding/connections in that order. I suspect a shorted capacitor might
possibly cause reversed starting, all could cause failure to start and
blowing of fuse.

Don Young, Alabama USA