Is VFD Good or Bad for Old 3 Phase Motors - Woodworking Talk - Woodworkers Forum

 
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post #1 of 6 Old 04-20-2017, 01:24 PM Thread Starter
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Is VFD Good or Bad for Old 3 Phase Motors

I have been looking at a couple of power tools that have a 220v 3 phase motor. I was wanting to avoid having to install a rotary converter. But I have been told the VFDs that some folks use are bad for older motors and can ruin them. Can you share any insight into this? Thank you in advance.
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post #2 of 6 Old 04-20-2017, 06:03 PM
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The ideal motor for an inverter will have class F insulation on the windings it will tell you what class of insulation the motor has on the data plate, there might be a few that don't but 99% do

If you are going to use the machine non stop it could impact the insulation, but I have had quite a few that ran many hours with no problems, and are still running fine

Also you don't want to go below 20 CPS running the motor, or it can pit the bearings, but that is fairly rare and it you do it would be a good idea to install an Aegis ring to ground the shaft to the body of the motor to stop any pitting

If you find a 3ph machine at a bargain I would go for it. I did many times and have yet to get bit.

One other thing, some people will tell you you need to go to the next higher HP rating on the inverter, unless you like to waste money, just get the appropriate size, and sometimes you can get by with a smaller rarted inverter if you size it by amo draw, the motor rating it kind of a guide.

All of what I posted was taught in classes by Westinghouse/TECO, Square D, Emerson, Allen Bradley, ABB, Baldor, etc
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post #3 of 6 Old 04-20-2017, 06:42 PM
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I can't see how running a VFD would have any impact on an older motor, good or bad. So long as the voltage is right, they don't generally care what the frequency is. I have heard that running a 3 phase motor as certain frequencies on the low end can cause issues with the bearings, but if memory serves that only happens at the really low speeds that aren't very likely to be used.

I should mention, I can't remember what I had for breakfast this morning, so make of that what you will

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post #4 of 6 Old 04-20-2017, 07:29 PM
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Quote:
Originally Posted by lukebarber View Post
I have been looking at a couple of power tools that have a 220v 3 phase motor. I was wanting to avoid having to install a rotary converter. But I have been told the VFDs that some folks use are bad for older motors and can ruin them. Can you share any insight into this? Thank you in advance.
Actually any phase converter is bad for the motors but a VFD is closer to actual three phase than anything you can do.
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post #5 of 6 Old 04-21-2017, 10:39 AM
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digital VFD create square wave voltage, not sine wave voltage, and that is "harder" on windings/conductors/terminations.

older motor where the insulation may be weaker or breaking down may be pushed to burnout.
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post #6 of 6 Old 04-21-2017, 11:20 AM
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Actually the inverters operate a 3 ph AC motor in pulsating DC. Bearing pitting can be pretty much cured by line reactors and the carrier frequency, but an Aegis rub ring will cure them the easiest, and they finally mode split rings so you don't even have to pull off the drive on the motor
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