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Old Jun 22, 2007, 06:26 PM
jlh45 is offline
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Joined Oct 2006
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Single phase electric motor problem

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
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