Old Unisaw and 3phase conversion?

Re: Old Unisaw and 3phase conversion?

I am not an expert in this and hopefully you will gets some more knowledgeable responses but this is my take on it:

Normally when there is a single-phase source to a 3-phase load an often good solution is a VFD for the conversion. I don't think this works in your case because you also need to boost the output voltage and I don't think that works. You need to double-the output voltage plus a bit more, not just a few percent. If I'm right you would need a transformer and that gets costly. A rotary phase converter may be able to do it but it would be costly for a single machine.

Your best bet might be to swap out the motor for a 220V single-phase.  Motor rewinding to 220V would be an option but may also be expensive. 3-phase motors are often stated to be easy to find and cheap so pairing a 220V one with a VFD to get the 3-phases may be an option but you are still likely looking at a couple of hundred or so for a VFD - there is a huge range of prices.

For a 220V 3-phase motor there is also the option of what is called a static converter (I believe) which is a cheaper but not as good method.

Bill

Re: Old Unisaw and 3phase conversion?

I would jump on that saw in a heartbeat.

Only trouble is the color!  Get some nice grey paint and a 3hp or 2hp Leeson replacement motor.  I have the same vintage saw that had a single phase repulsion-induction motor which eventually failed.  Modern Leesons are a direct replacement, only thing I had to do is swap the little junction box from the old motor to replace the taller one on the Leeson, it prevented full tilt of the arbor.  I did that instead of modifying the saw cabinet, but that would be the other option.

If you want to fund the motor, take that motor cover off and sell it on ebay.  People pay crazy money for them.

Re: Old Unisaw and 3phase conversion?

That's a $500 saw in my opinion. Check the play in the gear assemblies that raise/lower, and tilt the blade. The first old timer I bought, the gear on the  elevation shaft was worn so much, the teeth came to a point. Loosen the motor and belt, and spin the arbor to check the feel of the arbor bearings and side to side play.

Re: Old Unisaw and 3phase conversion?

First of all, a 3 phase converter takes more power into to it, to get the rated power that the motor needs.  I'd say replace the 3ph motor with a 3 or 5 hp single phase...now a new Baldor will be over $750...if your lucky you can find a cheap one on ebay for if your lucky for $300.  You'll also probaby have to replace the on/off switch, with a switch rated for the HP amps/volts your new single phase motor.  The reason 3ph motors btw, are prevalent is that they are cheaper to make..no need for a cap start, and therefor a cap cutout switch once up to speed.

Re: Old Unisaw and 3phase conversion?

I’m with Dick on the value, and would look for a deal on a 3hp single phase. 

As for the starter, I think you can probably use it. It depends on the coil voltage requirements. I think they usually only have two wires through the coil,

while there are 3 contacts actuated. It should tell inside the starter cover, or maybe right on the coil.

Also overload protection change

The current in the 220V motor would be a lot higher so overload protection heaters would have to be changed to maintain operation/safety. This assumes the protection is part of the starter switch.