On 30 Oct 2020 at 16:42:02 GMT, "R D S" wrote:

On 30/10/2020 16:06, Fredxx wrote:
Just because two transistors let go doesn't mean they were the fault.

They are just as like to be the symptom of another fault.

Precisely my concern.

Is the inverter being used because you don't have a 3-phase supply? If
you do have a 3P supply can you wire it directly to make sure the motor
is good?


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?

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.

--
Roger Hayter