Phase Converters and Variable Frequency Drives

      50 hertz, 60 hertz ... single-phase, three-phase ... here's some info on the gizmos you need to run motors on a different kind of power. February 4, 2011

Question
A friend of mine in Ireland recently burned out a motor on a single phase 220 v Powermatic table saw. The problem was the difference in hertz - the saw is 60, and in Ireland it's 50. I went to the tool nut in Porchester to try and buy a converter, but no one had an idea. I asked a few electricians - same result. Any thoughts?

Forum Responses
(Solid Wood Machining Forum)
From contributor L:
Buy a 50 Hz motor.



From contributor A:
You can buy a converter, however the cost would be prohibitive for a 3hp motor. Buying a 50 hz motor would cost less and would last longer. You can get a converter to run a portable tablesaw for under $100 on the net. Real motors draw a lot of power.


From the original questioner:
Cheers for the advice! I sent a lot of small tools home two years ago and my Dewalt chopsaw doesn't run right. One of those converters might be the trick.


From contributor R:
Since a new motor is already needed, get a used 3 phase motor and a VFD. The VFD doesn't care what the line frequency is and it can convert that in any frequency 3 phase power you want. The total cost should be less than the cost of a single phase motor.


From contributor A:
Basically you need to calculate watts based on amperage for the requirement. This 2000 watt unit will handle a 15 amp 110v portable continuously. Not that you would ever use it that way.

My local motor shop (awesome guys) claimed that you can run a 60 hz on 50 hz power without much trouble. They've done it here in special applications. Their definition of continuous is all day. Not one hour running a wood planer. I'm bringing a couple of pieces of equipment (planer, jointer, big drill press) with me and I currently don't have enough cash to swap motors. I'm going hobbyist for a few years anyways.



From the original questioner:
Thanks again lads. What is a VFD and what difference does a 3 phase make? More power? My problem is the hertz. I'm not good when it comes to electric, plus before I started buying my own machinery my electrician told me to buy single phase. I know plenty of woodworkers that sent back saws that had no problem. I rang Delta and they don't make a 50 hertz motor. Where do I go for used stuff?


From contributor R:
A VFD is a variable frequency drive. Oversimplified, it generates 3 phase power from 1 phase. It also allows you to change the speed of a motor by changing the frequency of the power it generates.

VFDs have been around for at least 20 years and like most technology, it takes about 20 years before it becomes ubiquitous. This technology is reasonably cheap. A 3 hp VFD can be bought for $185.00. Used 3 phase motors can be had for under $50, sometimes for free.



From contributor G:
A VFD alone will not generate three phase power from single phase. As its name suggests, it will vary the frequency (hertz). A "phase converter" is what generates 3 phase from single phase. The proper phase converter is needed. The correct converter will be configured to receive the existing incoming power (phase, voltage and amperage) and put out the same as needed. By nature of design it costs almost nothing to add a VFD to a motor controller (which can contain both a VFD and a phase converter), so many units have both and can be programmed to your requirements. I am by no means an expert in this area, but this has been my recent experience.


From contributor W:
A VFD can convert single phase to 3 phase - check out the specs for one from ABB:
ABB AC Drive, 230V 1 / 3 PH Input, 230V 3 PH Output, 4.3FLA, IP20
*This unit has a continuous output current rating up to 4.3 amps
* 200-230VAC 1 / 3 PH Input, 50/60Hz (Voltage +10% to -15%, Frequency 5%) Input
0-230V, 3 PH Output
1 Analog Input (0-10V, 4-20mA, 0-20mA)
2 Programmable Multi-function Inputs
2 Operation Control Inputs (FWD/REV)
1 Analog Output (0-10VDC)
1 Multi-function Output Relay
3 digit, 7 segment LED display
150% rated current for 1 minute
200% instantaneous overcurrent
Electronic overload protection and stall prevention
Ground fault and short circuit protection
UL 508 / cUL / CE

You can buy these on EBay and use them to control the speed of 3 phase motors using standard single phase electricity.



From contributor G:
What you are referring to is not just a VFD. It is a motor controller, also called a motor drive, or in your description, an AC drive. It is obviously capable of many more functions than just varying frequency. Maybe you can't even buy a unit that is only a VFD anymore, I don't know.


From contributor R:
A modern VFD performs many functions. Some of the functions are:
3 phase power generator/inverter
motor controller
motor overload
ground fault detector
Some even take in 120 volt single phase and produce 230 volt 3 phase power.


From the original questioner:
Thanks - ye have been a great help and have saved me a lot of time searching. Really appreciate it.

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