Single phase variable speed output?

ronlyke · Oct 26, 2014

Can a VFD do this?
115v input, 115v single phase variable speed output to a 1/3hp motor.

I want to control the speed of my new die filer.

Or should I look for a small 3 ph motor?
Cheap.

greenbuggy · Oct 26, 2014

You don't need a VFD to do so - you can do so by varying voltage using a variac or PWM using something like a "router speed controller" since you are only feeding single phase and not 3 phase power to your motor.

Edit: MLCS 9400 Standard Duty Router Speed Control - Router Accessories - Amazon.com no affiliation with this brand it was just one I found via a quick google search

Sea Farmer · Oct 26, 2014

I mounted a small DC motor and speed controller on my die filer to slow it down. A forum search will show that several other members here have gone that route.

I am pleased with the results.

See this thread: http://www.practicalmachinist.com/v...s-vfd/variac-control-tool-motor-speed-157488/

ronlyke · Oct 26, 2014

Well that was simple.
Thanks.

9100 · Oct 26, 2014

greenbuggy said:
You don't need a VFD to do so - you can do so by varying voltage using a variac or PWM using something like a "router speed controller" since you are only feeding single phase and not 3 phase power to your motor.

Edit: MLCS 9400 Standard Duty Router Speed Control - Router Accessories - Amazon.com no affiliation with this brand it was just one I found via a quick google search

Not if it is an AC induction motor. Varying the armature voltage while keeping the field voltage high works well on a DC motor but a VFD varies the frequency of the output voltage, true whether it is a single or three phase motor. A single phase motor will probably have issues with the starting winding on a low frequency, so something like a DC motor or conversion to three phase is a better bet.

Just lowering the voltage on an AC motor, single or three phase, will usually have poor results. The motor will try to run as close to synchronous speed as it can until it gives up and drops to a much lower speed.

Bill

extropic · Oct 26, 2014

9100 said:
Not if it is an AC induction motor. Varying the armature voltage while keeping the field voltage high works well on a DC motor but a VFD varies the frequency of the output voltage, true whether it is a single or three phase motor. A single phase motor will probably have issues with the starting winding on a low frequency, so something like a DC motor or conversion to three phase is a better bet.

Just lowering the voltage on an AC motor, single or three phase, will usually have poor results. The motor will try to run as close to synchronous speed as it can until it gives up and drops to a much lower speed.

Bill

The OP's 1/3 HP motor is probably an induction type motor, so what Bill has written is good advice (and true).
However, just to be clear, variable speed can be safely achieved using AC motors with brushes (mechanically commutated) using a Variac or speed controller as referenced in #2 above. Think of any plug in power tool with variable speed.

greenbuggy · Oct 26, 2014

9100 said:
Not if it is an AC induction motor. Varying the armature voltage while keeping the field voltage high works well on a DC motor but a VFD varies the frequency of the output voltage, true whether it is a single or three phase motor.

I did say that you could vary the voltage using a variac or using PWM, usually PWM arrangements modify on-off time (or time on past zero crossing) without influencing voltage.

A single phase motor will probably have issues with the starting winding on a low frequency, so something like a DC motor or conversion to three phase is a better bet.

While I can't dispute the technical correctness of what you've posted here, it seems unnecessarily complicated given the application the OP is talking about. If you can't start it at a low enough frequency, voltage or cycle time, crank the dial up till it starts and dial it down til it runs where you want it to.

Jraef · Oct 27, 2014

Is this a bench top filer or are you referring to a hand held die GRINDER? Different beasts. A hand-held die grinder would have a high speed universal motor

Most of the bench top die FILERS I have seen come with standard off-the-shelf single phase AC induction motors that are capacitor start, I have never seen one that uses a universal motor. If so, you cannot use any sort of speed control on those motors without damaging them, sorry. You could possibly replace that motor with a PSC (Permanent Split Capacitor) type, and there are 115V single phase VFDs that work on those, but those VFDs are typically MORE expensive than 3 phase output VFDs so if you have to change the motor anyway, just get a 3 phase motor.

Bottom line though, when dealing with controlling speed on any kind of single phase motor, you must first ACCURATELY determine which of the half-dozen different KINDS of single phase motor you have. No guessing, no ASSuming.

Sea Farmer · Oct 27, 2014

To the OP, here is one of several threads that discuss changing a die filer to variable speed: http://www.practicalmachinist.com/vb/general/die-filing-machine-144118/

9100 · Oct 27, 2014

greenbuggy said:
I did say that you could vary the voltage using a variac or using PWM, usually PWM arrangements modify on-off time (or time on past zero crossing) without influencing voltage.

While I can't dispute the technical correctness of what you've posted here, it seems unnecessarily complicated given the application the OP is talking about. If you can't start it at a low enough frequency, voltage or cycle time, crank the dial up till it starts and dial it down til it runs where you want it to.

Whether it is being fed from a Variac or PWM, the effective voltage is flipping back and forth 60 times per second and the motor is going to try to go that fast. It never quite gets there because it has to have some slippage to generate the armature current, but when its speed gets very far away, it is going to give up. Even if you find a speed it will run at, it probably will drop off as soon as you load it. Then if it gets slow enough for the starting winding to kick in, things will get really weird. The idea is nothing but trouble.

As Jraef says you may be able to run some single phase motors off a variable frequency supply, but not many and probably not very well.

Bill

JST · Oct 27, 2014

Cost-wise, there isn't any point in discussing the matter when talking about used.... it's whatever you pay...

If you get a cheap DC motor, get a KB controller or similar. If you find a cheap 3P, you can get a half horse capable VFD for around $100to $150 from such sources as Dealer's electric. In fact, D E MIGHT even have a single phase VFD, but then you need to come up with a PSC motor.

Dealer's electric etc have overstock stuff, discontinued etc, so that stuff is cheap. Otherwise, those sources sell full pop new stuff as well. Make sure you know where you are on their site, and have some clue what it ought to cost as overstock "distressed merchandise".

New cost-wise, the DC motor will be the most, the 3p plus VFD may be the least, and the single phase and 1p VFD in the middle. All will be expensive-ish. DC motor probably the most because they are the most complex to make.

ronlyke · Oct 28, 2014

This is a bench top die filer. Butterfly model H-14 by Harvey manufacturing.
Is the motor shown a candidate for a router type speed controller or one of the cheap ones discussed earlier, or is it not going to work?

(If I understand the posts by Jraef and Thermite, I think I'm out of luck, right?)

Thanks

9100 · Oct 28, 2014

ronlyke said:
This is a bench top die filer. Butterfly model H-14 by Harvey manufacturing.
Is the motor shown a candidate for a router type speed controller or one of the cheap ones discussed earlier, or is it not going to work?

(If I understand the posts by Jraef and Thermite, I think I'm out of luck, right?)

Thanks

Right. I would go for a three phase motor and VFD because it should be more stable speedwise. You should be able to find a drop in replacement. On the positive side, it looks like a nice machine worth an investment. I have often wished I had one.

Bill

Sea Farmer · Oct 28, 2014

That's the same motor I removed from my Keller die filer. A Variac didn't slow it down nearly enough before stalling. I debated the DC vs 3P/VFD issue and went for the DC, but it was a toss-up as to cost, I don't think there's a clear hands-down winner between the two. Couldn't scrounge anything used so went with new, and up to 1/2 HP based on what I read in the other threads.

Low speed torque is the principal requirement to use these toys effectively. I kept the original pulleys and 3V belt, but can probably gain a bit more by going up in belt/pulley size if its ever necessary. The 1/2 HP motor will accommodate that.

I don't use mine very often, but when the job calls for filing to a scribed line its perfect.

jim rozen · Oct 28, 2014

That's a capacitor-start induction motor. Don't run it off a variac, it won't work well.

My bet is convert to a similar frame 3~ motor and add an small VFD.

ronlyke · Oct 29, 2014

I don't know anything about DC motors, like what to ask for that would have similar power, and I know even less about controls, so I guess it's 3ph & a VFD. I use those on one of my lathes & my mill. I really didn't want to spend much money on it, though. Does anyone have a suggestion for inexpensive VFD's? I found a Teco for $115.00. Is that as low as they get?

ronlyke · Oct 31, 2014

Thanks to all of you.

Ron

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