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View Full Version : 3-phase motor to single-phase?



Johnnyreich
10-14-2013, 05:58 PM
There's a Bridgeport mill available in my area with a 1-horse 3-phase motor. I have no capabilities for 3-phase at my location. I do have single-phase 110 and 220.

Why not just repower the unit with a single-phase 220-volt motor? Does this make sense or is the installation of a phase converter the only route to take? I have no experience of any kind in this area, so your advice is highly appreciated.

Thanks,
Johnny

winchman
10-14-2013, 06:09 PM
If you have 220-volt available, the best route to go for a single 3-phase machine is a VFD. I got mine from Automation Direct.

http://www.automationdirect.com/adc/Shopping/Catalog/Drives/GS1_%28120_-z-_230_VAC_V-z-Hz_Control%29

thebigron
10-14-2013, 06:24 PM
A real good reason is that once you take a close look at the motor in question, you will discover that it is an oddball and a single phase one to fit the mounting will cost you the price of half a dozen VFD's. Do what winchman suggest for less than a couple hundred bucks. You will be proud and welcome to the forum.

kitno455
10-14-2013, 07:21 PM
VFD, without a question. Even good ones like Hitachi are so cheap now, that I've been ripping single phase motors out of my stuff, and putting 3 phase motors in!

allan

KiddZimaHater
10-14-2013, 07:24 PM
Keep the 3-phase motor. Buy yourself a VFD (Variable Frequency Drive) rated for 1-horsepower.
The VFD will convert 220 single phase power into 220 3-phase power.
It also serves as your on/off, speed, and fwd/rev functions.
You'll love it

The Artful Bodger
10-14-2013, 07:28 PM
My knee mill is single phase and the motor is heavy, it is also very difficult to change the belt position. Needless to say there is always a strong temptation to run the spindle at whatever speed is already set rather than to match the job.

How much useful speed variation could I get with a 3 phase motor and a VFD? -50% to +100%?

Johnnyreich
10-14-2013, 07:36 PM
Thanks to all. I had not even thought of a VFD and had no idea they were so inexpensive.

Willy
10-14-2013, 07:39 PM
Like everyone else says, run your 3-ph motor with a VFD.
Why have a perfectly good motor laying around doing nothing? The cost of the VFD will be less than a good quality replacement motor.
Being able to run a 3-PH motor with single phase is just the tip of the iceberg as far as operating features that a VFD will give you. Smooth ramp up and ramp down, reverse rotation, adjustable overload protection, etc, etc.
3-phase motors equipped with a VFD is the way lathes, milling machines, and drill presses is should come from the manufacture.

KiddZimaHater
10-14-2013, 08:12 PM
How much useful speed variation could I get with a 3 phase motor and a VFD? -50% to +100%?
On my lathe with VFD I get -100% to 100%
In other words, I can turn it all the way down to zero RPM, and up to 100% of whatever pulley speed I have it set on.
I can always go down to zero, but in order to go faster, I need to go up to the next higher pulley.
If I'm belted to the fastest pulley, then I have full range of speeds.

Leadfootin
10-14-2013, 08:15 PM
My 600V Bridgeport is set up with a cheap 600 to 240V transformer to boost the voltage to a 600V VFD. Works excellent and plugs into a 240V wall outlet.

Peter

SGW
10-14-2013, 08:23 PM
With my VFD, which does not have the latest bells and whistles for torque at low speeds, I find that the useful lower limit is about 20Hz. If pressed, I have run it at 10Hz but torque is very marginal at such a low frequency. On the high end, 120Hz is no problem. I don't think I've tried going beyond that.

Wayne Sippola
10-14-2013, 08:47 PM
I built a power feed unit with a 1hp motor and VFD. On the slow side, I run it at .6 hz which conveniently gives .6 inch per minute. I push a button to give 60 hz for rapids. The motor pulses when using the lowest setting, but not so much that it's a problem with small endmills. At a couple hz, the pulsing is no longer noticeable. This is using an older AC Tech VFD.

Wayne

MrSleepy
10-15-2013, 06:04 AM
I built a power feed unit with a 1hp motor and VFD. On the slow side, I run it at .6 hz which conveniently gives .6 inch per minute. I push a button to give 60 hz for rapids. The motor pulses when using the lowest setting, but not so much that it's a problem with small endmills. At a couple hz, the pulsing is no longer noticeable. This is using an older AC Tech VFD.

Wayne

Sounds like a great way to cook a motor :).

The cooling fan will also be doing 0.6Hz....but the current in the coils will be essentially the same as when run at 60Hz.

Something to watch for.

Rob

Forrest Addy
10-15-2013, 06:19 AM
Sounds like a great way to cook a motor :).

The cooling fan will also be doing 0.6Hz....but the current in the coils will be essentially the same as when run at 60Hz.

Something to watch for.

Rob

There's a huge "yabbu" that needs to be examined. Induction motors do not draw nameplate current full time; they only draw the power needed for a particular load. Below a certain load current the motor can dissipate heat without the need for a fan. While that load current is certainly variable motor to motor a light load application like a 1 HP motor intermittantly driving a feed train is likely pretty safe without a fan. But the need for a separate cooling fan really does need to be watched for.

YMMV acccording to application of course, but the load/current/duty cycle/ambient air temp/cooling requirements for any motor/load combination have to be assessed before one sweats the need for a cooling fan. A threshold RPM does not automatically indicate the need for supplelental cooling unless the duty cycle is such that motor operating temperatures approach the temp rating for the motor insulation.

A biscuit fan zip tied to the motor's fan housing may not be enough. Gotta think it through, engineer style.