220 volts Toshiba VFd running a 600 volts 3 phase motor

[DickDV]

Ron, your description of RMS voltage is exactly the definition I use in my classes and I find it is the most understandable, easily. It produces the same heat in a resistor as the same DC voltage and that's because RMS is the measure of the potential for POWER in the AC wave. Actually, it is the intergral of the wave or the area under the wave for the math types but then, its not so understandable any more when you say it that way!

Torque in a motor is determined by the volts per hertz ratio so, if you have a 600V motor and a 230V drive, as I said in my earlier post, the drive can produce full torque in the motor up to the point where the drive output max's out at 230V. Above that, the ratio falls off due to the inability to output more voltage and, since the ratio is falling, so is the ability of the motor to make torque.

So, yes, you can run the motor up to 60Hz but the torque just won't be there due to the lack of voltage.

 

[DickDV]

Oops! Intergral should be integral in the post above. And, yes, Terry, voltage doublers are around in the drive world but I have never seen one for anything other than raising 120VAC single phase up to 240VAC single phase to power a 230VAC three phase output drive.

And, its always on rather small <1hp drives. I suppose that's because the 120V current gets too high too quickly but I wonder if maybe the doubler circuit isn't too efficient either. Some electronic tech will have to tell me about that because I don't know.

 

[Terry Woods]

Voltage Doublers have been used in Television forever.

How do you think they develop such large DC-Flyback voltages(10's of 1,000's) from 120VAC?