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Fixing a small motor

Chris Pearson

I want to fix an ancient 1/8 hp motor (Carter Electrical Co Ltd). As far as I can tell, the centrifugal switch has worn out, so that will be fun making a new one.

My question is what resistance seems reasonable for the coils. IR is good (well into the tens of megaohms) but they are a little dark and I would like to be confident that there has been no internal shorting.

The main coil is about 18 ohms and the starting coil 33 ohms. My maths tells me that the running current should be around 0.4 A. I cannot remember a lot about motors, but I realise that the impedance of the coils will be higher at 50 Hz than the (DC) resistance and that back EMF reduces the current. I hope therefore that the resistance values are about right.

Grateful for any reassurance!

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    Gentlemen, thank you - I am reassured.

    Here are the two parts of the switch. The depth of field is poor, but I think that you can see the wear on the fixed side of the switch. The range of travel of the 3 pawls (or at least one of them) is limited and I think that it no longer makes contact adequately.

    The switch connects (and disconnects) the starting coil. No capacitor.

    The motor powers a Tiplap lathe tool grinder - Google it to find out more.

    ee467a937d54d90cc3d3015cee3d87c7-original-20210809switch.jpg
Reply
  • 0

    Gentlemen, thank you - I am reassured.

    Here are the two parts of the switch. The depth of field is poor, but I think that you can see the wear on the fixed side of the switch. The range of travel of the 3 pawls (or at least one of them) is limited and I think that it no longer makes contact adequately.

    The switch connects (and disconnects) the starting coil. No capacitor.

    The motor powers a Tiplap lathe tool grinder - Google it to find out more.

    ee467a937d54d90cc3d3015cee3d87c7-original-20210809switch.jpg
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