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Discussion Starter · #1 ·
Soooo, do you wanna know what happens when a electronic "static phase converter" shoots craps on a three phase machine operating on single phase power ???? Wellll..... I'll tell you what happens: The motor fries quite quickly, the "majic smoke" is released and a fellow finds himself in a pinch. The only picture of the guilty device failed to show up on the camera, so that will have to be added at a later date. What follows is the end result and the resolution that included that jolly robust old fella, Santa Clause !!!!

This little guy is only a one hp 230v three phase motor for what is called a "J-Head" Bridgeport vertical milling machine. But now it is a boat anchor, the windings roasted severely and the bearings locked up. Not finding anyone with a "rewind" shop, I found a new replacement in Conneticutt for $2499.00.... Now that is TWENTY FIVE HUNRED DOLLARS !!!!! Just a little rich for this poor boys blood....

I HATE fuzzy photos.... Anyway, we took a trip to a salvage company about 70 miles away that specializes in parting out these old machines and there was found a new (to me) old replacement motor for an extremely reasonable price by comparison anyway. $125.00 is more like what fits my el cheapo budget. But its still a 3 phase motor and all I have is single phase power and a baaaaaad static phase converter.... and a new one of those will NOT ever be used by me ever again. The power loss is approximately 1/3, plus they are prone to failure according to some guys.

The new "old" motor is installed and waiting for a solution. Having a home made rotary phase converter that works off of relays, timers, capacitors and a pony motor is always an option, but I want a bit of a better solution maybe a little cheaper on operating costs. So a few hints were dropped during Tuesday nite dinners about how nice it would be for Santa to order a specific device from a specific company for a specific project for a specific old guy in the family and it only took......10, maybe 15 suggestions for it to take hold.

Low and behold the kids got ahold of the Jolly Old Buzzard and got him to drop off the exact specific item listed above...right under our Christmas tree !!! Now it only took three months to get around to working on it, but we don't wanna rush into anything too quickly you know.

This little guy is a VFD (Variable Frequency Drive) and it allows a single phase power input to be converted digitally into a three phase output only with slight loss of power to the driven motor. This particular drive has factory parameters set internally to handle three phase motors up to 3 horsepower. There is myriad of points that can be fine tuned if so desired. It will allow infinitely variable speeds (thus the "variable" in the variable frequency drive) with touch of an up or down arrow or by a field installed remote potentiometer. It has a series of "fault" protections like high or low voltage, high current draw, power failure on incoming power line and many others.

Pretty bullet proof.

Mounting seems to be a snap by grabbing a scrap piece of 1 1/2"x 1 1/2" angle iron and a 5/16" bit produce a quick mount for the top of the machine. There's a huge casting behind the vertical head, and 7/32" holed were bored in the top of that and tapped to 5/16" threads....

It didn't take too long to produce a nice secure vibration free mounting bracket for the little VFD with a nice backing large enough to install an enclosure around the device. There will be a main disconnect on the right end of the bracket and a remote dial for controlling the variable speed and a reversing switch on the front of the enclosure. The enclosure ensures no dust, grindings or metal chips will enter the electronics of the Drive. The enlosure will also have to be vented to allow heat to escape.

The little green terminal strip is the connection point for the external controls if configured as such, and also for the reversing switch and variable potentiometer. The larger terminal strip on the bottom is for the input and output voltages.

About 4 years ago a three phase pre wired exhaust fan had to be installed, and the electrician pulled off this prewire 3 phase plus and the 8' pig tail of 12-4 w/ ground "SO" cord and tossed it to the wayside. Now, being the eclectic collector of anything electric OR rusty, this cord found its way to the second level of my shop and has been sitting there reserved for this particular project !!!! Don't need the plug, but the pig tail will work just fine for the 3 phase output of the VFD to the motor.

This will all be totally enclosed (as soon as the enclosure is made) but not for the test firing. May even incorporate an "E" stop (Emergency Stop) button on the front surface of the enclosure for additional safety.

Powered up and configured for keypad control, this little puppy is ready to rock and roll.....well, ready to throw chips anyway !!!! Starting at 000, the "UP" arrow is pushed until you get the optimum speed for the cutter being used, and you are good to go.

Setting it for 40 Hz will make the motor run at 2/3's rpm and 60 Hz will operate it at full rpm. Invinite speeds are achieved in between, as each frequency is divided by 10. Usually the minimum speed should be set at 18 - 20 Hz, and of course the maximum at 60 Hz. Very little power loss is realized with this method and one real cool thing is that with the step pullys on the top of the Bridgeport, cutter speed can be limited by means of their adjustment then more precise control is then achieved by use of the VFD. Its like having two transmissions in series on an old truck or tractor.

There are adjust able "acceleration and decelleration" ramps, that allow the speed at which it attains setpoint to be determined as well as how fast it slows back to zero rpm. The display can be configured in many ways, showing speed by either frequency or rpm and amp draw can also be

So, there you have it....another repair job, this time with the help of Ol Saint Nick....

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Re: Running a 3 ph Motor on Single Phase ???? Answer is With

Wendell, did you ask for a senior discount on that $2500 motor ;)? As far as taking a couple of month to get to it, it's like I told John M, you got to pace yourself :lol:
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