[GETRIDAONE]

I am restoring an old (1945) Walker Turner floor drill press. I wanted an original motor to go on it and found a guy that sells parts and restores motors. He has a 3 phase motor that he is working on for me. I want to get a VFD to control the speed and convert from single to 3 phase at the same time. My question is what happens if the VFD you are using is just marginal for the motor amp rating. I know there is some lose in HP rating after conversion. Will the drill just have no torque and slow down ??
The price difference for a 1 HP and 2 HP is going on double. Its like a car, you spent more than it is worth.

[Cammer-6]

VFDs are rated on HP and efficiency
Youll probably never need 100% of your HP.
Yes the drill will slow down and stop,
after all the smoke is let out of the VFD.
Its amazing what a good VFD can do.
We installed some large high voltage ones on the 4000 HP chillers at EPCOT.
We went from 6% voltage drop across the whole incoming utility line to 3%
and helped with the life of the chillers too.
Did you see the pics of the Rockwell bandsaw speed controller I rebuilt?
It used a vacuum tube and rheostat to vary the voltage at the clutch
which determined the amount of slip it got.Pretty cool design by Eaton.
As far as the 3ph to single ph conversion,I know of no VFDs that do this,
perhaps a stand alone unit will work but keep in mind it will reduced HP.

[Jim Scites]

I remember from the one VFD class I took that you probably need an inverter duty motor. Most of the older electric motors were not capable of inverter duty. They make a lot of noise when you run them on a VFD and don't last very long.

[Cammer-6]

Originally Posted by Jim Scites

I remember from the one VFD class I took that you probably need an inverter duty motor. Most of the older electric motors were not capable of inverter duty. They make a lot of noise when you run them on a VFD and don't last very long.

good point

[Stuart]

VFDs typically have a current trip set point, so if the motor draws too many amps it will simply shut down.

[Cammer-6]

my point at satire was to say that if nothing else you need to oversize the VFD not undersize it.
Kinda like saying I want to go drag racing with an 800HP car but have a trans thats only up to 300HP.

[GETRIDAONE]

Thanks for the replies, I didn't get any reply notices on my E Mail.
The motor is a 3/4 HP 220/440V 3 phase so the amp draw shoiuld be low. I found a website for shop tools and there are people using the small VFD's with no problem or loss of performance. The drive was the same model as he suggested I use and has had other people use on their restored old motors. Continuous output amps on the small VFD is only 4.5 but will take double that for about a minute before shutting off. You can adjust the ramp up speed so it comes on slow and sets to speed you want.
We shall see if it is as easy as it sounds

[stags]

I can't help with the VFD but - nice drill press.

I've owned several W/T machines from that era and really liked them. Good luck with it.
Mark O.

[Stuckinda60s]

I don't see the advantage for a small unit which already utilizes a pulley drive for varying speed. You're not going to use it enough to recognize much in the way of savings. So, you're not going to get any return on your money.

As far as converting to 3-phase, I have to question that for such a small unit, as well. The amp-draw for 240V, single-phase, will be quite low for that unit, also.

[bjacobs41042]

Originally Posted by Jim Scites

I remember from the one VFD class I took that you probably need an inverter duty motor. Most of the older electric motors were not capable of inverter duty. They make a lot of noise when you run them on a VFD and don't last very long.

Jim is absolutely right on this point. The phase paper in the old motor will not tolerate the spikes in the digital wave form for very long, and you will fry the motor. Any premium efficient motor will be acceptable for use, and inverter duty will be needed if you wish to generate full torque for extended periods at more than a 3:1 turndown (20hz or less)

VFD's can take 240VAC single phase and output 240VAC 3 phase, no problem, but you will definitely want one that can output as much or more amperage as the nameplate calls for. Most 1 hp drives will go 4.2 amps @240 VAC, but a 3/4 HP motor should not need that much.

HTH,
Bill