ECN Forum Forums General Topics of the Trade General Discussion Area Motor help

I been told that back before rotary phase converters were available, a lot of old timers that lived out in the boonies would run three phase equipment in their wood shops by making a static synchronous phase generator using a second junk three phase motor and connecting one winding that was out of phase with the drive motors enough to create the third leg.
I have no idea if this is allowed anymore, or what it does for power factor, motor heating, etc., but met a guy from Vermont probably 15 years ago that did just this in his woodshop.
Since this was probably once a fairly common practice, maybe you could find an old timer industrial electrician in your area to help you hammer out the details to do it safely.

The static phase converters that I've used have a note on the door that the motor only develops 2/3 of it's rated h.p. if your 5 hp motor will only do as much work as a 3 hp, is it still worthwhile?

Phil,
My advice before you do anything with this motor, is dismantle it and have a good look at the seals,bearings and armature.
You say it has run before, but it is not clear when.
Bearing races can get distorted if left in the one place for any length of time, this can affect how well the armature turns within the narrow gap between the rotor and the stator and that gap is not that much.
To merely run the thing is inviting disaster.
The other thing that concerns me a tad, is that using an older type motor, the power factor of that motor isn't going to be that great, motors have improved considerably over the years.
The actual in-rush current would be a lot larger, than for a modern motor of the same rating.
Personally, I wouldn't use a phase converter on any motor unless it was the last resort, the reason for that being, converters have a habit of inducing harmonic currents into the lines supplying them.
What I would go for is a new motor and a Variable Frequency Drive, built for your voltage and load in mind.
No use mucking around, mate, it would save tears in the end.
Just my $0.02 worth.

Ausador....If what you say is true, knowone should give any advice on this forum. This is a discussion forum and knowone can be singled out for giving good information or bad information. It is what it is, a forum. Most of the members are proffesionals.

VFD's are no harder to program than connecting the motor. Some VFD's are challenging, but for most it is very simple. I have had many customers that were afraid to try VFD's. To show them how easy it is to set up, I told them I could teach anyone that spoke english and had fingers, could program the VFD to start, stop, ramp up and ramp down in a matter of minutes.
I have never failed with this approach. Also, I am more than happy to assist in programming here on this site. All I need is the brand and model number.

Regardless of your doubts it is a viable option that should be considered.



"Most Correct"????

That is strictly a matter of opinion.

Either replacing the motor or producing a third phase are 'correct' answers and I bet there are other correct options as well.



No, but advising to change the motor is no different from advising to produce a third phase. Either method can be done wrong and result in injury.




That is one opinion, John is also entitled to his.

In general I am a keep it simple guy and think VFDs are being overused but that is just my humble opinion.

Thanks Bob.