VFD for a Brown and Sharp Universal Mill?

Iam in a bit of a quandary. I've found three different mills - two nice old Van Norman 12's and a brown and Sharpe 2L Universal Mill for sale. But none of the three can be powered up due to no three phase at their present locations. Oh we just moved, brought it home from the shop, etc...

Well, I want to hear it run before I buy anything, so am thinking maybe be proactive and buy a VFD that can be wired up to existing 220 single phase and get the machine in operation for a proper inspection.

Problem is, the Brown and Sharpe has three motors - a 3 hp spindle motor, and two smaller 3/4 hp motors for the feed and coolant pump. VN the same I think.

Is It possible to use a VFD to provide three phase input power to the machines? Each machine runs the three motors off the same power input, via a relay...

Thanks much for any advice you can offer...

Glenn

For testing, probably. Just understand that if you feed the VFD into the main power source, ALL of the motors will run the same speed, and the VFD will not like having motors turned on and off while it is already running. So if the controls allow it, (i.e. manual controllers) have all of the motors in the Run state BEFORE energizing the VFD, then let it ramp them all up to speed. If the controls use mag starters, you will have to separate out the control power and feed it from another source, then close all of the contactors BEFORE energizing the VFD. If there are any other controls on the machine, separate the control power out no matter what, VFD outputs should not be used on anything but motors.

Just make a homemade RPC and be done with it... For about 200.00 you can buy a good control panel and then all you need is a used three phase motor. I bought a 10 HP motor for about 125.00... They are simple to wire up and you can even mount both the motor and box on a make shift stand of some sort, mount a cord that will plug into a dryer or range outlet and test the machines easily.

I not too sure I would let someone mess around in my electrical boxes but I would have no problems letting them plug into the dryer or range plugs..

Then take it too your shop and mount it and use it to power your whole shop....

Thanks again, Swatkins! I think I will try the homemade RPC idea. Seems the simplest solution.

The main motor being 3 hp, and the others smaller, you would probably get away with a 7.5hp VFD and start the small motors one at a time after the big one. A 5 p would be marginal but might be ok too. Might not be rated for single phase in, which means you might need a bigger one just because of that

Problem is starting current surge. VFDs tend to have a "hard" limit on current, if you go over that they shut off. You can generally get 150% of full rated current for a reasonable time, many seconds, perhaps a minute. With some, 200% for a couple seconds,which will start a motor.

Problem is that its a lot of VFD to have just for testing. And the next test might need more current.

Even bringing up all motors slowly, you will need a fairly large VFD, and you will probably need to pull the control fuse, and block closed the contactors. So you are not testing the controls.

Same issue with an RPC , and they are a LOT heavier. Plus bôth may pull more current at max output, than the available supply can provide (outlets within reach are 120V, etc). Then you are still stuck.

Sometimes you have to go on other data and not run the machine. At least then you have an arguing point to reduce price, you have no idea if or how well they run. And if that is not accepted by the seller, your best weapon is your feet on their way out the door. That can be very effective in reducing the price to compensate for an assumed amount of needed repairs.