Circular Saw failure

I pulled my failed circular saw apart to see whether it was repairable.

Seems a rather dramatic failure of the commutator.

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So, no :(

Sylvia.

Reply to
Sylvia Else
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Antifungal cream fixed my circular sore but I doubt it will do much for that commutator.

Reply to
Aussie

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Sylvia Else wrote:

** ROTFLMAO ...

.... Phil

Reply to
Phil Allison

Back in the day we used to repair or replace commutators but not in this day and age especially ones with this method of construction.

I made this one with a lathe and files over 50 years ago as part of a course, bit tarnished wit age.

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Reply to
FMurtz

Are you an armature winder by trade Fred? Maybe an electrical fitter?

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Xeno
Reply to
Xeno

Not an armature winder but have done so.

Reply to
FMurtz

More of an amateur winder then? :-)

Reply to
Clocky

Yup, she's cactus.

Reply to
Clocky

Ahhh the old mica insulation. Things have changed all right.

Reply to
Rheilly Phoull

Very good!

Reply to
Aussie

It was the only reason you would be tinkering with commutators I would have thought. My electrical mate at the railways in Melbourne started in the trade of armature winder (motor winder?) but gravitated to the electrical fitting side of things. That's how he ended up working on the metro trains in Vic. I suppose an electrical fitter would be tinkering with commutators a lot too.

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Xeno
Reply to
Xeno

Especially on the metro trains. Thousands of commutatators using the rail network every morning and evening.

Reply to
Peter

true.

false. ( see "back EMF" )

nope.

you get electric braking, but not electric energy recovery

In general motors are like capacitors, energy goes in and out as currents and is stored as a voltage (called back emf) in a permanent magnet motor back emf is proportional to the spin speed and direction.

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Reply to
Jasen Betts

In general, you are wrong. There are two kinds of stored energy, rotational and magnetic. Different approaches are used to recover them, and depend on the type of motor. For the most common PM type, the armature has enough resistance that you can short it and stop it quickly - which is what Phil was talking about.

With a very high-performance (high L/R ratio) motor, shorting it keeps the current circulating in the motor inductance, not being lost in its resistance, so you don't get strong braking and it won't stop very quickly.

So instead, you short it to allow the rotational energy to pump up the current (against the motor inductance) then switch to route the current into the battery. Because this is pushing current against a significant voltage, it does work (extracts energy) (based on L*I^2), but you're only extracting the electromagnetic energy. So the current falls, and to get more of the rotational energy out, you commutate back to a short circuit until the current rises again, pumping more energy into the magnetic field, which you then extract into the battery.

Regeneration requires this kind of commutation.

Clifford Heath

Reply to
Clifford Heath

Back EMF results from changing magnetic flux as a result of the rotor's motion. It depends on that change, and has nothing to do with the applied voltage. It's only referred to as "back EMF" because in a motor that's running normally, it is opposite to the applied voltage. If you instantaneous reverse the applied voltage, the back EMF doesn't change, because the rotor is still rotating in the same direction. So the back EMF now adds to the applied voltage.

Sylvia.

Reply to
Sylvia Else

Voltage is speed. Current it torque. It stops fast. (this only works with permanent magnet motors)

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Reply to
Jasen Betts

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