Thread: Three Phase Equipment on a Single Phase Supply

Originally Posted by Cliff Rogers

I was complaining about this to an old bloke who had 3 phase in his shed, he said... "you live in a rural area, just buy a 3 phase gen set at an auction, you only have to start it when you want to run the machines"

Made sense, I haven't had a chance to see what sort of money a 3 phase gen set goes for.

Cliff

That is exactly what I had at the old place in a rural area with my nearest neighbour at least a kilometre away. 35KVA with a Perkins diesel. Lovely. Not an option here.

Even there, the pacticality of starting the Genset to run a motor for even five minutes was daunting not to mention being about the worst thing possible for a diesel motor. I would normally find another way if possible and leave the genset option for bigger (longer) jobs.

Hence the quest for an alternative.

Single phase motors available as follows:
4KW 2 pole $500 plus freight, ($55)
3KW 4 pole $440 plus freight. ($48)

Eqvivalent VFDs (4KW) starting from $350 plus freight $50. VFDs sourced from Australia are nearly twice the price. It is true that it is possible to swap the VFD from one motor to another, but in practice it would be a right pain in the ####! A bit like sharing a three pin plug. Not going to happen is it?

Regards
Paul

Originally Posted by Bushmiller

.... it is possible to swap the VFD from one motor to another, but in practice it would be a right pain in the ####! A bit like sharing a three pin plug. Not going to happen is it?

Regards
Paul

Nuh, I don't even swap jaws on my chucks, I just buy another chuck & set it up with the other jaws & swap chucks instead.

am i right in thinking you can run a 4 pole motor at 3000rpm by using a VFD to drive it @ 100Hz?

Hi bonox,

Categorically no, for a couple of different reasons.

Firstly, induction motors rely on slip (difference between synchronous and operating speeds) to produce torque. For 100Hz input to a 4 pole motor, you would typically expect 2800 to 2850RPM for a motor providing usefull output.

Secondly, unless the motor was specifically designed for VFD drive, the iron cores in the windings would most likely not appreciate the higher frequency drive, and would respond with significant iron losses, resulting in overheating and reduced power output.

You were not specific about the motor type, but single phase and VFD are virtually mutually exclusive, due to the presence of start windings, start caps and centrifugal switches in single phase motors. They normally run at a single nominal speed and these devices are 'tuned' to suit that speed.

For the most part, a 2 pole motor would be cheaper or similar in price to a suitable VFD and more efficient.