A couple of motor questions

Mar 23, 2012 11 Replies

If anyone in here is motor savvy...



I have 2 motors, 0.6hp, 3 phase, 130V, 20,000 rpm (In case any of that matters). They appears brushless, in that I can't see any.



Near the back of the shaft there is what looks like a disc shaped magnet aligned with a housing containing some sensors, I presume this is to monitor the speed. Am I likely to be able to replace this? Cos i've bust one like a clumsy **** while replacing a bearing.



On another motor I have successfully replaced a bearing but it's now a fair bit noisier, I think I have warped the fan at the very back of the shaft, it was held on by a roll pin and was a real pain in the arse to get off. I'm presuming I can get this balanced. Would this be done with the shaft in or out? Would any (or most) motor places be able to do this or is it a specialised job? There is a local motor place but they'd tell me they could do it if they couldn't and still try to charge. And what sort of price?



Ta for any help.


Some pics,

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magnet near the right side of the shaft in the second picture is the bit that I have knocked a chunk out of, it sits in the part in pic 3 when assembled.

I'd have called it an induction motor but here -

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call it a servo motor.

Don't be silly. That's the actual motor speed of many a mains power tool.

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"Bosch GBM 6RE 350w Professional Rotary Drill 230v GBM6RE

Very high speed (no-load speed: 4000 rpm) for small drilling diameters."

It's stated on the label of many.

It's certainly a brushless DC motor of some flavour. These might help:

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planers for example.

Bill

That's the chuck speed. Motor speed likely far higher.

I thought my old angle grinder was rated at 11,000 rpm, and that was after a reduction gearbox with quite some reduction. Is the motor wasn't doing 30-40,000 rpm I'd be very surprised.

optimal power to weight of a fairly dull cheap motor is somewhere in the

20k-40k regime for sort of 2" diameter rotors.

Resistive losses are current related,and torque is current related so until the AC losses - iron/eddy current - and other RPM related losses build, the faster the RPM the more power you get.

So there is every advantage to push RPM as high as the brush bounce and actual rotor integrity will safely go.

And gear the result down.

My small Bosch router runs 33K rpm

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