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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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    seems odd. Is the bearing a bronze bush knock-on or a ball or roller race ? sometimes things would be put on warm. I have used offcuts of glass fibre PCB material with the copper all etched to clear on both sides as a paxolin/tufnol substitute in cases needing a bit more strength.  While it is a bit odd the online PCB places are quite happy to do PCB cut outs in funny shapes without any copper.just needs to be drawn as a gerber outline.

    Mike.

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  • 0

    seems odd. Is the bearing a bronze bush knock-on or a ball or roller race ? sometimes things would be put on warm. I have used offcuts of glass fibre PCB material with the copper all etched to clear on both sides as a paxolin/tufnol substitute in cases needing a bit more strength.  While it is a bit odd the online PCB places are quite happy to do PCB cut outs in funny shapes without any copper.just needs to be drawn as a gerber outline.

    Mike.

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