3 phase for a tool with 2 motors

[PNW_Guy]

Helping a friend get a mill set up, and he's going to need some sort of phase converter - he has 240v single phase, but the mill is 3 phase.

A RPC would be easy but a used one is hard to find, and the few I've seen are obscenely expensive.

I'm wondering if a VFD would work in this specific situation. The mill has 2 3 phase motors - one for the spindle and one for the power feed. It's an integrated power feed, not an add-on, like a Bridgeport.
I've always heard that you can only run a single motor on 3 phase. Is that true for this case as well? The VFD would no be used for a speed control - it would always run at 60hz.

 

[Larry$]

Before I had 3 phase from the power company, I made my own rotary converter. Really simple and I'm sure there must be some good YouTube how to's now. What it takes: a 3 phase motor, some way to start it spinning ( I used large capacitors that I bought from Grainer) Momentary contact switch and a power switch. There are probably better ways now but that was many years ago. I used that system for at least 10 years. Note that you will not get full HP out of your motor but close enough for most purposes.

 

[Karl_T]

you would need two VFDs. The one for the power feed is going to be really small, like a 1/2 hp. I did this on my mill.

 

[matthewsx]

Unless you want to get into rewiring the mill the easiest/cheapest solution is a static phase converter.

I’ve bought several from

Static Phase Converters

Static Phase Converters A static phase converter is used to generate 3 phase power during the starting of a motor. A static phase converter consists of one or more start capacitors and a start relay. The start capacitors produce electricity across the third winding of a motor during start up,

www.northamericaphaseconverters.com

And been happy with the service and performance.

Yes, he will loose some power but it’s unlikely he’ll notice the difference in a hobby shop. If he wants to go with a rotary converter later all it takes is a used 3 phase motor to convert the static box.

John

 

[Chipper5783]

There are a few approaches, which is best depends on your specific situation. A VFD should only be used on one motor and use the VFD to control the motor (not the existing motor controls). Of course there are people that just use the VFD as a phase converter (the guy I know that did it ended up toasting something - I’m not sure if the motor or the VFD). A VFD has the benefit of giving speed control, regulated starting and stopping (I.e. make it a soft start if you have a weak supply and electrical braking so the machine doesn’t take long to coast down).

A phase converter is great because one device will cover all the motors (assuming you are voltage matched, if you are not - still a simple solution to get a transformer). The more motors in play, more sense a phase converter makes. It is an easy solution because you plug in and go (when you get more machines, just keep plugging them in). I started with one lathe (two motors, the main one is a 2 speed motor) and got a 5hp rotary phase converter - that one converter did me for 35 years and supported the purchase of ~8 more machines (probably 20 three phase motors from very small to 5hp). I retired that RPC because I bought a machine of 15hp.

When looking at phase converters there are a few options. Making your own is very straightforward (lots of online information). I bought mine - 1983, I didn’t know how simple they were, I paid $1700 (quite a bit of money in ‘83), but as a 35 year investment - not really a big deal. With getting an old CNC, I upgraded to a PhasePerfect - and switched the entire shop over to the PP. My only regret was not getting the PP sooner (the PP is on the expensive end of phase converters, but I find it works very well in my application).

I suggest you have a good look at getting some sort of an RPC.

 

[Ulma Doctor]

I real life operation, 2 motors can be run from the same VFD , provided that the capacity of the VFD is sufficient to handle both motor loads. The motors are not going to be able to run at different frequencies as a caveat.

A RPC , is easily constructed from a capacitor, a spare 3 phase motor of sufficient size, a couple monetary switches, and some wiring.

 

[strantor]

If you're going to use a VFD, I would recommend a sine filter on the output. Those smaller motors like for lube pumps, coolant pumps, power feeds, are more susceptible to HV death spikes than bigger motors like spindle motors.

This is advice similar to "if you're going to lay with a professional, wear protection"

 

[Dabbler]

@PNW_Guy You *might* be able to use a VFD, but only in in a very limited set of circumstances. Capacity is not the problem. It is the feedback loop that the VFD depends on, if either of the 2 motors are switched.

-Let me know the current ratings of each of the motors, and I'll look into it for you.

@Chipper5783 How big did you go for your PP? I have a Rotophase 15HP which seems about right for my shop. My largest motor is 7.5HP, with a 1HP secondary motor on the machine.

 

[Ultradog MN]

Helping a friend get a mill set up, and he's going to need some sort of phase converter - he has 240v single phase, but the mill is 3 phase.

A RPC would be easy but a used one is hard to find, and the few I've seen are obscenely expensive.

I'm wondering if a VFD would work in this specific situation. The mill has 2 3 phase motors - one for the spindle and one for the power feed. It's an integrated power feed, not an add-on, like a Bridgeport.
I've always heard that you can only run a single motor on 3 phase. Is that true for this case as well? The VFD would no be used for a speed control - it would always run at 60hz.

An RPC obscenely expensive?
I'm curious where you got that idea?
I built this one for a friend of mine a couple of months ago.
5 hp motor off craigslist $50
A kit with all the capacitors, contactors, etc $75
A 12x15x6" enclosure box $35
Some wire, solderless connectors, scrap metal, welding rod, spray paint, etc $25?
Let's call it a total of $200
The kit was from the link below and came with a diagram that a caveman could follow and I'm no electric guru.
This is my second one.
The one I built for my shop has a 7.5 hp idler and will run any of the seven 3 phase machines I now have including the 2 motors I have in my mill. And it actually cost me less cause I got the motor for free.
Of course I can't run more than one machine at a time - Only have 2 hands - but I have started and idled my 3 hp lathe, 1.3 hp mill (both motors together) and my 1 hp bandsaw - all at the same time.

WNY Supply & Phase Converter Store :: Phase converter kit

www.wnysupply.com

 

[Chipper5783]

@Chipper5783 How big did you go for your PP? I have a Rotophase 15HP which seems about right for my shop. My largest motor is 7.5HP, with a 1HP secondary motor on the machine.

I got a 20hp PP (I don’t think they offer anything between the 10hp and the 20hp). Strictly speaking I don’t have enough power in the service supply (100A residential service) to feed it to full capacity - but I don’t really need the full capacity - seems to work fine.

My RPC (that I don’t use anymore) is a 5hp Willet addaphase, it would start my 5hp air compressor (FLA of 15 amps), but it wouldn’t reliably start the 5hp setting on the lathe (trip the O/L protection in the RPC) - I’d spin it up on the low speed and switch to the higher speed. It was not a big deal because I generally run the lathe on the lower motor speed - the gear box gives a good range selection and the lower motor speed is quieter.