# Convert my mill to variable speed?



## cmacclel (Mar 8, 2009)

I have an RF-31 is there any VFD's that do single phase output??? Would I have to buy a new motor??

Barry HELP 


Mac


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## gadget_lover (Mar 8, 2009)

As a mater of fact, there is such a thing. Now I have to look into it too!


http://www.anaconsystems.com/text/opti_e2.html


Daniel


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## PEU (Mar 8, 2009)

pricey but interesting nevertheless.


Pablo


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## cmacclel (Mar 8, 2009)

gadget_lover said:


> As a mater of fact, there is such a thing. Now I have to look into it too!
> 
> 
> http://www.anaconsystems.com/text/opti_e2.html
> ...


 


*Non-compatible Motors
*Anacon drives are not compatible with switched-cap (cap-start or cap-start/cap-run), or "split-phase" AC induction motors. (Why?) Anacon drives are also not intended for brushless DC or switched-reluctance motors.


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## StrikerDown (Mar 9, 2009)

I might be full of poo, but I think the cap start circuit disengages when the motor revs up to normal rpm, if rpm slows the start circuit may try to re-engage or if rpm does not build up to begin with the start circuit would never disengage. Maybe!


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## will (Mar 9, 2009)

StrikerDown said:


> I might be full of poo, but I think the cap start circuit disengages when the motor revs up to normal rpm, if rpm slows the start circuit may try to re-engage or if rpm does not build up to begin with the start circuit would never disengage. Maybe!



Cap start does in fact disengage when the motor gets up to speed. This creates a phasing, which causes the armature to start spinning.


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## precisionworks (Mar 11, 2009)

Hey guys, I've been off the grid for a few days. Trying to catch up with email & forums & most anything else:thumbsup:



> any VFD's that do single phase output?



VFD output is always three phase, although input can be either single phase or three phase. There are electronic ways to give variable speed to a single phase motor, but they are either very pricey or terribly inefficient. Most single phase motors that need to have variable output speed are coupled to a variable reduction gear box. 

Single phase motors, by their nature, are less than smooth running. This waveform shows why:







With single phase input, the polarity reverses 60 times per second (USA) or 50 times per second (the rest of the planet). Either way, the motor sees positive voltage half the time, followed by negative voltage the other half the time. They turn OK for most jobs, but smooth they are not.

The three phase wave form is much different:






Because there are three overlapping phases, the motor windings have only slight voltage dips, and speed is almost perfectly maintained - which minimizes vibration. Three phase motors are always the motor of choice, as long as three phase power is available. Also, since they need no capacitor to start, the windings heat up less with each restart.



> Would I have to buy a new motor?


Yes. But they are common as can be, always lots on eBay, usually a bunch on Craigslist. I've bought 4 new Baldor 3 hp motors, new in box, and never paid over $100 including shipping. Used ones can be had for less.

When you are considering a VFD conversion, you want to look at the physics involved. The first consideration is what size motor to use.

Say that your machine came with a 1.5 hp motor. That motor always runs at nameplate rpm (full rpm), so it makes 1.5 hp -- never more, never less. Step pulleys are used to lower rpm, so 1.5 hp is available at all times.

If you replace the single phase motor with a same size three phase motor, you still have 1.5 hp at 60 Hz. But, with the VFD, you may want to run the motor at half speed (30 Hz = .75 hp), or one quarter speed (15 Hz = .38 hp). Staying with the same size motor is not a good idea because you'll soon have too little for all but the tiniest tools.

In the market today, 3 hp is the largest "inexpensive" single phase to three phase drive. You can find drives up to 10 hp that will accept single phase input, but the price penalty is extreme. Very nice vector drives are available from many makers for under $275 in a NEMA1 (open) enclosure, or about $350 in a NEMA 4x (sealed) enclosure. My last two drives are AC Tech, SMVector, and they are easy to install & easy to program. I've installed & programmed most of the other common drives (Hitachi, TECO, Siemens, Allen-Bradley, Telemechanique, Woods, etc.) and the SMVector is easier than most to set up. Great factory support too.

Bottom line is that you'll need a three phase motor (roughly $100), plus a drive (roughly $300), plus $25 or so for a disconnect & wiring. Three of my shop machines are now set up this way, and I'd never go back to a single speed motor.


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## will (Mar 12, 2009)

Just a quick note about 3 phase. Most residential areas do not have 3 phase available, you need to get a motor/generator set. In some areas you might be able to get the power company to run 3 phase to the home ($$$$$)


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## Mirage_Man (Mar 12, 2009)

will said:


> Just a quick note about 3 phase. Most residential areas do not have 3 phase available, you need to get a motor/generator set. In some areas you might be able to get the power company to run 3 phase to the home ($$$$$)



This is true but since we're talking about a VFD then single phase input is all you'd need to run the 3-phase motor. 

Concerning running 3-phase off single phase... If you're not concerned with variable speed for a 3-phase machine then a rotary phase converter or static phase converter for some machines will work as well. I opted to go the RPC route for my lathe because I really didn't like the idea of re-wiring the lathe.


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## wquiles (Mar 12, 2009)

I already started shopping for the parts to convert and re-wire my lathe using a 3HP 3PH motor and a VFD (with help/advice from Barry!), so I will post "a few" pictures and detailed how-to as I go along in this "project". Good thing is that this type of conversion has been done before by many, so I will not be breaking any new ground (no pun intended!) :devil:

Will


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## precisionworks (Mar 12, 2009)

> Concerning running 3-phase off single phase...



The cheapest way to make a three phase motor run is to use a static phase converter. It converts single phase into two phase. Since it makes only 2 of the 3 phases needed, the motor makes 2/3 of nameplate horsepower. More three phase motors have been killed by static converters than by any other method.

A rotary phase converter (RPC) is a three phase motor adapted to work as a three phase generator. Since it makes all 3 of the needed 3 phases, the motor makes full hp. Commercial models are available, or they can be shop built using a three phase motor that's twice as big as the largest single motor you need to start - if your lathe is 7.5 hp, you'll need a 15 hp motor. You'll have to provide a way to start the idler motor, and you'll have to balance all three phases within 5% of each other. If a voltage regulation circuit isn't provided, they can provide over voltage for smaller motors.

Solid state phase converters produce perfect power, comparable to utility supplied three phase. The price is stiff, but they generate clean enough power for even the most picky CNC machine. The are regulated so that there's no over voltage or under voltage, which drive CNC machines nuts. Phase Perfect is the best known brand. http://www.phaseperfect.com/

Those first three devices serve only one function - they start & run a three phase motor at nameplate rpm.

The VFD provides additional functions, which are user programmed. Variable speed is the biggest draw, and current drives will keep a motor running at the slowest speed you want. They also allow overspeeding the motor, and it is common to run a motor at 150% of nameplate rpm. This wide speed range makes any machine more versatile. Soft start is also built in, as is dynamic braking.

For most users who have single phase available, either the RPC or the VFD is chosen. The RPC provides three phase power, the VFD provides three phase power plus additional control functions.


*Controlling a 3 hp wire brush machine*






*Internal connections*


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## wquiles (Mar 12, 2009)

From the little I have read, it is not good enough to simply connect the VFD at the output of the single phase that goes to the motor, since doing that turns completely ON or OFF the VFD "and" the motor, thereby loosing all of the advantages of the VFD like dinamic braking, etc.. Barry, the question I have is how to re-wire the lathe's controls to allow for all of the safety stuff to work, including the jog function (if possible - very useful!)

Will


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## precisionworks (Mar 12, 2009)

> how to re-wire the lathe's controls to allow for all of the safety stuff to work, including the jog function


In the second photo, terminals 1 through 17 are the control terminals. The lathe or mill control switches are connected to the terminal strip, so pushing the START button on the lathe/mill is the same as pushing the START button on the drive. You reprogram the drive so that the keypad is no longer active, and the drive now accepts commands from the terminal strip. You can reprogram for a remote speed pot, as well as a jog switch.

You can also add an E-stop, which is the large, red button on my machine. Bumping that kills VFD output, but does not power off the VFD.


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## wquiles (Mar 12, 2009)

precisionworks said:


> In the second photo, terminals 1 through 17 are the control terminals. The lathe or mill control switches are connected to the terminal strip, so pushing the START button on the lathe/mill is the same as pushing the START button on the drive. You reprogram the drive so that the keypad is no longer active, and the drive now accepts commands from the terminal strip. You can reprogram for a remote speed pot, as well as a jog switch.
> 
> You can also add an E-stop, which is the large, red button on my machine. Bumping that kills VFD output, but does not power off the VFD.



Ahh - this is definitely easier than I though then - good to know. I definitely want to do (somehow) a remote speed pot at a minimum. I am now even more convinced about doing the re-wire job :devil:

Will


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## PEU (Mar 12, 2009)

may sound like a stupid question, but here it goes anyway: the VFD allows to run the motor in forward AND reverse?


Pablo


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## precisionworks (Mar 12, 2009)

> the VFD allows to run the motor in forward AND reverse?


That's correct. All three phase motors are reversible, and swapping any two of the three leads changes rotation. The VFD electrically swaps two of the three leads whenever you hit the reverse button - some drives require that you hit reverse plus a confirming button to prevent accidental reversal.


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## SafetyBob (Mar 14, 2009)

Nobody has said it yet so I will be the stupid one......the better VFD's are 220 or 240VAC single phase input right? I thought the 115VAC ones were horribly restricted on the size motor you could slap on your equipment, right? 

When you get your stuff together Mac, please tell us exactly what part numbers and stuff you used. Never hurts to have good part numbers around!!

Bob E.


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## precisionworks (Mar 14, 2009)

> the better VFD's are 220 or 240VAC single phase input right?


According to every tech I've spoken with, stay away from the 120v units. They are available, but their track record is spotty.


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