Single phase and VFD"s

Please educate me. Still going back and forth on old versus new thickness planer. The used General 130 that I am still considering [Dave Krumm has me second guessing myself] has a 3 phase motor. Checking this AM, with an electrical supplier, I am told that the maximum RPM for any such single phase motor will be approx. 3450 RPM. Now I realize that most on here are using the VFD's to get around all of this. So my question using the VFD is, will I get the recommended 4500 RPM's that General suggests for 3 phase and does the motor run hotter as well?. I'm not sure what the actual General single phase motor replacement RPM rating is. For me , I would totally like to go in the single phase direction. Greg

Greg, the three phase motor on the planer is what rpm? That is a belt drive cutter head so the motor should be standard rpm. The Vfd is only to convert from single to three phase. No speed adjustment should be necessary. Dave

Yep, a three phase induction motor will only run about 3450 RPM on 60 Hz so the additional speed of the head must be realized from different size pulleys on the machine.

It is possible to overspeed an induction motor (run it higher than 3450 RPM) on a VFD but there's a limit to how fast you can go. You lose the constant torque that you get in the lower speeds when you use a VFD to go beyond about 3450 RPM.

Mike

Greg, I'm a huge General and three phase fan but you need to know it is not as simple as plugging the vfd into the wall recepticle and the machine into the vfd. The 220 in the wall needs to be switched so you have an easy way to shut the vfd off. they don't come with an off switch on the input side. The vfd needs to be wired directly to the motor. If the machine has a mechanical switch you can just plug the machine into the vfd but you must always leave the switch on and NOT use it to turn off the planer. If the machine has a magnetic starter it must be completely bypassed. Not difficult or very time consuming but necessary. Read up in this and other forums about use of vfds and feel comfortable before committing. Dave

Thanks guys and sorry Dave for the misspell on your last name. The electrical shop said to get the T-frame #'s from the motor. Should read T182 or 184, so I emailed the seller this AM for that info. The only thing I took from my first visit was that it indeed was a 3 phase. And Mike, thanks, changing the pulley size never crossed my mind. I think the seller only had a couple of us looking. Informed me late last nite that he still had it. I told him I will make an offer. As soon as I'm confident on the electrical end of things. Greg

Hi, as others have said the VFD will be used to produce 60 Hz, 3 phase power for this application.

The planer motor/pulley arrangement will provide the correct speed for the planer head.

The VFD will not be used to overspeed the motor by running it t greater than 60 Hz, all it will be doing is providing soft start, and converting single phase input into 3 phase output for the motor...........Regards, Rod.

The motor on the planer, even though 3 phase, is a standard speed to run on 60 Hz, the vfd simply changes the single phase to 3 phase...
the motor will then be able to run at LESS than the original speed if you want it to... but when the vfd is set to full (max) speed it will be 3 phase 60 hz
and the motor will run at normal speed.... no need to change belts, etc.... simply connect it up and run... you WILL need a switch in front of
the vfd OR use the switch on the vfd to start/stop planer... most vfd's have a way to connect a remote switch to it to start/stop it.. that is what I do..

Rod is correct in what he said......

First of all, it would be possible to turn up the frequency a little until you run out of voltage. Maybe 70 hz? Your power will drop off as the freq increases above 60 HZ.

I think a vfd is always a good idea for controlled acceleration and breaking.

Also, it's possible to use the existing start stop switch and magnetic starter as a run permit to turn the drive on and off. So you would hit the same buttons. Unplugging the machine is the ultimate off switch.

Any specific setup questions? Feel free to ask.

Thanks again fellas for the insight. Going in the VFD direction is totally new stuff for me . My workplace is loaded on 3 phase electrical wiring so its mostly any combination of voltage to work with, obviously. I will make the gentleman an offer in the AM. Time will tell. Greg

OK - I will ask a question (its been a while since being in the motor drive space):

In the old days, many of the VFD's were switching transistors - pulse width modulated - which was evened out via the motor inductance. (and in those days any little thing would blow those dang transistors, which are hard to fuse because there is no better fuse than a transistor! I remember some type of Darlington power transistors.

Are the three phase VFD's the same? Is it then a gang of power transistors, one for each phase? Which might reduce the current needs on each (and reduced cost of the transistor elements).

Quote:

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Originally Posted by Carl Beckett

OK - I will ask a question (its been a while since being in the motor drive space):

In the old days, many of the VFD's were switching transistors - pulse width modulated - which was evened out via the motor inductance. (and in those days any little thing would blow those dang transistors, which are hard to fuse because there is no better fuse than a transistor! I remember some type of Darlington power transistors.

Are the three phase VFD's the same? Is it then a gang of power transistors, one for each phase? Which might reduce the current needs on each (and reduced cost of the transistor elements).

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Carl- todays drives use field effect transistors (two per phase, one positive and one negative, for a total of 6), or FETs, (at least last I have heard). When I was an engineer (10 years ago), I used them alot with very little problem. Now they are cheap, and available. One thing that goes wrong is the filter capacitors, they have a time limited lifespan. The output transistors age with each heating and cooling cycle. It's like bending metal back and forth, you can bend and bend many times until the internal stress builds up and it breaks. It's really a mechanical problem with the materials properties.

As for the cost of the parts, I think that the capacitors may cost more than the FET's, but it is hard to say what a big manufacturer would be paying for anything.

Personally, if I were buying a drive for serious use, I would consider the Hitachi drives that drives wharehouse sells. They are a little more money, but they are a solid industrial product with complete documentation. This is not to say that the cheaper drives are no good, though. But if my buttocks were on the line, I would choose the Hitachi every time.

As far as electrical problems, I wouldn't worry too much; these things are used everywhere with great reliability.