VFD for a single Phase motor!!

[Yepez]

Hi!!!
I wonder if is posible to control the motor's speed with a Variable Frecuency Drive, I allready know it is posible with a 3 phase motors, but I can't finde a VFD to works with a Single Phase (110V) AC motor.

What I want to do? I have an ordinary 1HP Single Phase 110V AC motor, 3400rpm, 60Hz, 7Amp, and I want to control the speed to use it as a milling spindle.

The problem is all VFD I saw, have an output of 3 phase or 2 phase. Actually I have one YASKAWA Mini VFD, but in the specifications of the drive say it is for a 4Hp 3phase motors. It have 3 phase AC input (400V) and have a 3 phase output, so, my question is can this control my 1 phase motor?
If not, how could I do that?


THANKS!!!!

[HuFlungDung]

No, it is impossible because the operational principle of a 3 phase motor is different than a single phase (the way they're wound is different).

But it is possible that you could purchase a 3 phase motor to replace your single phase motor.

[Al_The_Man]

Although there are single phase VFD's http://www.anaconsystems.com/text/singleov.html
They have usually very severe limitations on some motors, especially at low rpm, and as HU said the recommended way is to switch to a 3 phase motor which will give you much better control at low rpm etc, also you mention it is a 400v VFD so you would not be able to use it for your 120v motor. It will require 400vac input.
If you are limited to single phase 120/230 the common solution is to obtain a 230 volt VFD that you can operate on single phase in, this will give 230v 3ph out to operate a 220/230v three phase motor.
Al

[aghobby]

It's possible but only if you have a brushed type motor.

Low end router like Dewalt, Porter cable and Dremel are brushed type. You can easily vary the speed of them using a triac speed variator in woodworking equipement.

Take a look at this inexpensive one: http://www.jointability.com/s/dynami...ail.cfm?pid=54

[gmac]

yes, you can use that 400V VFD to control your motor. it will cost a lot more money and be very impractical but those limitations are imposed by the choices you have made. its a lot more expensive than buying another motor that works every bit as well as the 120V motor you have, but you can do it the way you said you wanted to. you will need to McGyver a bunch of items to work together and its up to you to get the many details correct. it is NOT safe todo this so you take your own life in your hands when you attempt this kind of thing. you will void every equipment warranty on all of the items when you do this and there willbe no liability for anybody but yourself. think about that when you make your choices and limit your options. the person that pays for your mistakes will be YOU.

the following description is NOT a course in electrical engineering, its a description of the tasks involved. there are a number of particular items of information and methods and you will need to learn how to do all of these things but its your ballgame- you decided what you wanted to do so here's what it takes to make it happen. YMMV and Im not responsible for any reslts good or bad. as a matter of fact I think the tooth fairy published me this recipe so sue her if you get hurt doing things like this. McGyver never got insurance either- if you are that type then you would already know all of what is said here.
heres what you need to do:

1. provide the drive with a 400V input power source, thats up to you to find one. if you are installing this at a factory that has 480V three phase power there then you already have a good place to start.
2. using the drive's settings and software, set up the drive to provide up to its rated output current for a 4 hp motor. turn off and lock out all of its protective functions for undercurrent and underload protection, phase loss, phase unbalance, differential, and phase reversal. you will probably need to simply turn off all of the protective functions for the drive, this application is way off-base for most drives so its not agood application but its will work if you do all the parts correctly.
3. find a three phase transformer that has the ratios to transform the 400V line-to line volatge output to 120V. this is actually not too hard, you can use a bank of three control power transformers that are available at a wide range of input and output voltages.
you will be using only two legs of the drive to power the transformer if its a single-phase transformer, three legs if its a three-phase transformer.
4. following explanation is for the single-phase two-leg approach only.
5. provide a protective fuse for the motor- rated for motor duty at about 115% to 125% of the motors rated FLA. wire the motor leads to go thru thei fuse and to the 120V output of the transformer.
6 provide a dummy load on the drive loose leg. this will be about half of the load of the motor full load. do some math and figure out what to use. connecting four 100-watt 120V lamps in series gets you 400 watts at 480V series voltage, thats about a half horsepower. if one of them blows out, the drive may shut down if you dont have all the unbalance and phase loss protection turned off .

7 start the drive up and put an ammeter on the leads driving the transformer. set the speed to run at 100%- that will be 60 hertz frequency. the motor shuold run at nearly its rated speed if you did everything correctly and the drive should be putting out about 1/3 or so of its rated current, maybe a bit less. you can use the speed control on the drive to turn the motor speed down but it will lose power very quickly because the motor is not magnetically or electrically designed to run this way.

the drive can burn the motor up by running it this way, but it IS running it. the motor can also go to maybe 120% of its normal speed but again- power falls off VERY fast as you increase speed. you are fighting the transformer curve losses of efficiency as speed changes as well as the motor loss curve so expect the normal results. the ability of this clusterboink arrangement to work as a mill spindle is almost zero, due to the problems in keeping it running and all the hodgepodge of connections and equipment. YOU asked for it- there is the answer on how to do it. Now go ahead and do it and tell us how much fun you had and how well it works..