Inverter gone bang!

Precisely my concern.

Yeah, but the machines were supplied like that. Designed to plug into 13A but with 3 phase motors.

They've definitely been modded and might have run on 3 phase once but had their internals replaced, but surely it would be cheaper to change a motor than fit an inverter?

Or is there an advantage to 3 phase motor on an inverter over a single phase one?

.023k = 23 ohms

I have a friend who suggests that all semiconductors with more than 2 legs driven from the mains are only sophisticated fuses, since you seldom see a fuse in the circuit!

Brian

That computes perfectly to me. Do all the windings read the same. Can you rotate the motor manually and see if anything alters? I have had motors where an armature has been gently hitting the coils with eventually fatal results!

Brian

If he had one why bother with the device, unless its some kind of slow starter circuit to lessen the load at start up.

Brian

Because they enable you to vary the speed of an induction motor with something like its normal torque and no need for changeable belts and suchlike.

autocorrect seems to have preferred overcorrect to overcurrent.

Lots. Lighter motor for same power. Better starting torque. No need for a capacitor - a major point failure. (Other types of single phases motors are possible especially for very small ones.) More choice of number of poles, hence speed. More efficient.

And of course a variable frequency inverter can alter motor speed.

It is used bt all 'brushless DC motors', be one in yer Dyson cordless. It replaces a mechanical commutator.

It happens that Brian Gaff (Sofa) formulated :

Maybe to be able to vary the motor speed?

Or he might have access to 3-ph, though no 3-ph on the site where the motor is.

All electric motors are in the end synchronous AC motors. In a typical DC motor or 'universal' AC/DC motor the synchronous AC is created by a mechanical commutator. This commutator may be replaced at some gain in efficiency by an electronic inverter, either controlled by a sensor on the motor or by sensing voltage and current in the windings.

A normal synchronous 3 phase mains AC motor suffers from the inability to deliver decent torque at anything except its rated RPM. The use of a variable frequency electronic inverter removes this limitation.

Of all the motors you choose to compare the induction motor is an entirely different beast. It relies on a rotating field, and a rotor where currents are induced in empathy with the field, that effective drag the rotor up in speed towards that indicated by the rotating field.

There is therefore no need for a commutator. It is never quite synchronous in that there is always an element of slip.

A deep bar rotor can overcome much of the poor starting torque limitation.

Crawling/cogging is just as an important feature in these motors; where the rotor locks to a sub-harmonic of the rotating field frequency.

It's usually something obvious isn't it?

Upon closer inspection having removed the motor to have it tested, the cable was out of the gland/grip and there was damage to some insulation where it had rubbed against the side of the housing, probably during a recent move where it was unceremoniously dragged up a flight of stairs. (Presumably the same debacle causing the earth to come off it's connector at the other end of the cable.

Anyway, another lesson learned, periodic checking of such things, especially after moving stuff around.