3 Phase For Shop?

[Larry Caldwell]

I have a line on a milling machine that has two 3 hp. 3-phase motors. There is no 3-phase power to my property. I have a 400 amp 1-phase service split 200 amps to the house and 200 amps to the shop.

I'm looking at several solutions:

- Solid State phase converters. Expensive, and you lose 1/4 of the motor horsepower.

- Rotary converters. Even more expensive.

- 3-phase generators. My tractor would swing a 21kw generator head, if I could find one. A 15kw would do what I need. Unfortunately the milsurp generators all seem to be way bigger, a 15kw runs about $1k, plus frame, sheaves, belts, etc.

Or I could just see about replacing the motors with 1-phase motors. A single 50a circuit should run it, but the motor mounts are heavy castings and modifying them without cracking them would be tricky.

The last option is to pass on this one. That hurts, because the guy only wants $1000 for a big old 12" by 48" floor machine. But hey, farmer tools, ya know?

Anybody have any ideas? Sympathy?

 

[Tractor Seabee]

I have a line on a milling machine that has two 3 hp. 3-phase motors. There is no 3-phase power to my property. I have a 400 amp 1-phase service split 200 amps to the house and 200 amps to the shop.

I'm looking at several solutions:

- Solid State phase converters. Expensive, and you lose 1/4 of the motor horsepower.

- Rotary converters. Even more expensive.

- 3-phase generators. My tractor would swing a 21kw generator head, if I could find one. A 15kw would do what I need. Unfortunately the milsurp generators all seem to be way bigger, a 15kw runs about $1k, plus frame, sheaves, belts, etc.

Or I could just see about replacing the motors with 1-phase motors. A single 50a circuit should run it, but the motor mounts are heavy castings and modifying them without cracking them would be tricky.

The last option is to pass on this one. That hurts, because the guy only wants $1000 for a big old 12" by 48" floor machine. But hey, farmer tools, ya know?

Anybody have any ideas? Sympathy?

Set up a 3 winding 3 phase transformer as an open delta setup for just the motor. You feed it with single phase on the primary. There is some loss but increase size to compensate. Are you doing your own wiring? Google "open delta transformer wiring" and it will have a wiring diagram and the loss factor. A floor or wall mount you will have to make sure all the winding leads are available in the J box to accomplish it. If the motor is 460-480 you can boost the 240V up to the 460-480V. Power companies used to do this to provide 3 phase power in residential areas w/o 3 phase primary. No moving parts and economical.

Ron

 

[pmsmechanic]

This looks interesting.

 

[Larry Caldwell]

Set up a 3 winding 3 phase transformer as an open delta setup for just the motor. You feed it with single phase on the primary. There is some loss but increase size to compensate. Are you doing your own wiring? Google "open delta transformer wiring" and it will have a wiring diagram and the loss factor. A floor or wall mount you will have to make sure all the winding leads are available in the J box to accomplish it. If the motor is 460-480 you can boost the 240V up to the 460-480V. Power companies used to do this to provide 3 phase power in residential areas w/o 3 phase primary. No moving parts and economical.

Ron

Thanks for the info. It looks like it might serve the purpose.

 

[sandman2234]

I run my 2Hp Bridgeport on a little converter that was cheap when I got it. The power loss usually isn't noticed.
David from jax

 

[newbury]

I have a line on a milling machine that has two 3 hp. 3-phase motors. There is no 3-phase power to my property. I have a 400 amp 1-phase service split 200 amps to the house and 200 amps to the shop.

I'm looking at several solutions:

- Solid State phase converters. Expensive, and you lose 1/4 of the motor horsepower.

- Rotary converters. Even more expensive.

- 3-phase generators. My tractor would swing a 21kw generator head, if I could find one. A 15kw would do what I need. Unfortunately the milsurp generators all seem to be way bigger, a 15kw runs about $1k, plus frame, sheaves, belts, etc.

Or I could just see about replacing the motors with 1-phase motors. A single 50a circuit should run it, but the motor mounts are heavy castings and modifying them without cracking them would be tricky.

The last option is to pass on this one. That hurts, because the guy only wants $1000 for a big old 12" by 48" floor machine. But hey, farmer tools, ya know?

Anybody have any ideas? Sympathy?

There are several options, all viable. and a lot dependent on your respect for electricity.

I'm in a similar situation - I bought a little bit of 3 phase equipment for $800 years ago -

Mainly for the planer.

But have put off getting a power source, it seems I've always more important projects. So it sits in my shop and get's sprayed with Fluid Film occasionally.
My viable options are:
As Seabee wrote static is simplest, there are many you-tube vids of a guys with set ups they start with a rope, a belt, etc. But that always looks dangerous.
VFD (Variable-frequency drive) is another route and is dropping in price and with 3HP motors might be viable and safe. They used to be EXPENSIVE.
I'm trying to go the RPC (Rotary phase converter) route, I bought a 10HP 1760 RPM motor and a son is buying/scavenging the remaining parts (capacitor, enclosure, etc.). I mainly wanted the RPC because I have at least 6 different motors to run, which would require 6 VFD's. ( And would like to buy mor 3 phase.)

For your situation VFD's might be a sweet spot if you are only worried about 2 motors. Ebay sells a lot of good ones, and a lot of cheap ones, and from reports on Practical Machinist SOME cheap ones that are good. Just do your internet research and get good ones.

 

[sandman2234]

Anyone near Florida looking for a used 10hp motor to build a RPC with, let me know.
David from jax

 

[Mendonsy]

You can buy a 3hp VFD that will accept 230v single phase and output 3 phase in the $250 to $300 range. Two of those would probably be the easiest solution and would give you the additional benefit of having adjustable speeds for the motors.

 

[RNeumann]

I wouldn’t switch the motors to split phase. It introduces all sorts of other issues with speed control and replacement parts down the road. This video should provide some guidance. The big decision will be how much 3 phase do you want- just enough for this tool or loads of it for this and future tools (seems a lot of 3 phase tools come up used and fairly cheap!).

Static Phase Converters -vs- Rotary Phase Converters -vs- Variable Frequency Drives - YouTube

 

[mikester]

I have a line on a milling machine that has two 3 hp. 3-phase motors. There is no 3-phase power to my property. I have a 400 amp 1-phase service split 200 amps to the house and 200 amps to the shop.

I'm looking at several solutions:

- Solid State phase converters. Expensive, and you lose 1/4 of the motor horsepower.

- Rotary converters. Even more expensive.

- 3-phase generators. My tractor would swing a 21kw generator head, if I could find one. A 15kw would do what I need. Unfortunately the milsurp generators all seem to be way bigger, a 15kw runs about $1k, plus frame, sheaves, belts, etc.

Or I could just see about replacing the motors with 1-phase motors. A single 50a circuit should run it, but the motor mounts are heavy castings and modifying them without cracking them would be tricky.

The last option is to pass on this one. That hurts, because the guy only wants $1000 for a big old 12" by 48" floor machine. But hey, farmer tools, ya know?

Anybody have any ideas? Sympathy?

Im not sure about losing 1/4 of the rated motor HP on solid state units. Not an issue for me.

Ive been running one of these on my CNC for 10+ years with zero issues and I have no problem recommending them.
Phase Technologies - A world leader in low harmonic and phase converting technologies

This unit provides clean balanced power to the CNC which is susceptible to power problems. Ive never had any trip outs on this system due to dirty power or excessive THD. VFDs have been less robust in this situation.

Rotary units are noisy. VFD might work nicely for your situation as you have small motors. If you are looking at a manual mill Id suggest going VFD to start. If your mill has CNC or a lot of sensitive electronics then solid state is the only way to go.