VFD for Power Problem

yes.

right

Yes. You need to select a VFD that is sized 50% higher than your motor

-- so for your 3 HP mill, you would need 5+ HP VFD due to running on single phase.

i

Yes.

Yes.

Absolutely false. Read the specs on the VFD, you're looking for a 3HP rated VFD that is rated for single phase input. You do not have to oversize the VFD if you get one the is rated for single phase input. A VFD that is not rated for single phase input *may* be able to operate from single phase with derating, but some will not operate from a single phase input period.

There are several selections here:

That are 3HP rated VFDs that are rated for single phase input. You'll see that under input they list both 230VAC single phase and 230VAC three phase as acceptable and the output is of course 3HP 230VAC three phase. No derating or oversizing required.

Pete C.

Yes, I agree, there is no need for derating for VFDs that are rated for single phase input -- only for ones that are rated for 3 phase input.

i

That's true, but that wouldn't cause me to shy away from a bargain on a larger drive without a single phase rating.

If there are small VFDs that won't operate from single phase, they're pretty unusual. Do you have any specific drives in mind?

Ned Simmons

The larger drive you buy cheap without checking the specs... Murphy's law.

Pete C.

The Hitachi SJ300 is one. Has a sensor for all three phases that you can't beat. I had to return the unit. Went with SJ100 Hitachi, it does single phase in.

BTW, these are an excellent drive and available from automationdirect.com

Karl

Pretty much so yes. Id suggest getting a 5hp VFD however when running a

3hp motor on single phase, as there are some losses involved when powering off of single phase. Runs between 10-25% depending on the quality of the VFD and so forth.

You can also put a remote control pendant on most VFDs and use it to also control a lathe and other 3ph equipment. So it can power each of many machines in the shop, just not at the same time.

Gunner

Political Correctness

A doctrine fostered by a delusional, illogical liberal minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.

also has inexpensive single phase input vfds. The GS2 and GS1 series, I use them regularly in machine shops

Gunner

Political Correctness

A doctrine fostered by a delusional, illogical liberal minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.

if the mill has three phase coolant and/or table traverse motors, you may want to fit capacitors to them and run them from the single phase supply. This isn't a big job, however.

If you're lucky, you could make enough from selling the rotary convertor to pay for the VFD :-)

Mark Rand RTFM

I had a VFD on my Bridgeport when I first bought it but I replaced with a RPC because the longer motor spinup time drove me crazy. Also be aware you won't be able to power-reverse (which is not a problem unless you tap).

MikeB

I didn't know you can't power reverse with VFD, I do tap holes using the reverse. What size rotary phase do you have?

MiikeB wrote:

The longer spin up is programmable / adjustable on nearly every VFD, just set it to what you like. As for the power reverse, you'll have to find a decent tapping head I guess. An oversized VFD might let you plug reverse from it's control, certainly no VFD will tolerate switching between it and the motor.

Pete C.

I was beginning to think there was no such animal. Thanks for the heads up, Karl.

Ned Simmons

Sure you can, it's one of the nicest things about a VFD on a mill. You can drill at 1000 RPM, replace the drill with a tap, dial the speed down and tap at 100RPM without touching the belts or vari-speed.

I have my mill set up with FWD-STOP-REV pushbuttons. The accel and decel are set at 1 second. At 100RPM the spindle reverses in about 1-1/2 turns just as smoothly and quietly as can be.

Ned Simmons

My RPC has a 5Hp idler & the BPort has a 1 Hp motor.

Also be sure your RPC has enough capacitors on the start windings to help it surge less on startup.

A VFD will usually trip on overcurrent if you reverse before the spindle almost stops.

MikeB

A low rated VFD with no braking resistor might.

I have a 5hp VFD running a 3hp motor on my Gorton Master Mill, and regularly tap with virtually instant reverse at speeds of 150-200 rpm

I should note.it will also reverse with no alarm at speeds up to 4500 rpm as well. I often use it as a demonstration of VFD capabilities.

I do have an outboard 200 watt ceramic tubular resistor mounted inside the Spooge housing.

The Gorton Master Mill spindle.and motor are almost twice the size of the less beefy Bridgeport btw... Double the rotating mass. Decell time I programmed for 1 second. It stops/reverses faster at lower speeds of course.

Gunner

Rule #35 "That which does not kill you, has made a huge tactical error"

...

I should note the SJ300 is not a run of the mill VFD. It is for very precise speed control, includes tuning for no ripple in speed and an encoder input. I had purchased it for the spindle drive on my Hardinge CHNC high precision lathe.

Karl

That is a pretty fancy drive. I've got comparable Mitsubishis on my lathe and mill, but they're running open loop. I've also used some similar Yaskawa vector drives on high speed winding spindles where speed regulation was critical. I don't believe either the Yaskawas or the Mitsubishis can detect a single phase condition - if they can, they don't shut under that condition by default.

Ned Simmons

I have a Grizzly three phase square column mill that I rewired so that the contactors that would ordinarily reverse the motor provide the directional input to the VFD, and I have a nice ramp for backing out of a hole slower than I went in when tapping. Of course, having the speed knob nearby helps a lot, too. You will ruin your VFD by switching the output on and off, or even worse, reversing the motor. Mine faults, but it has to be powered down in order to reset it. PITA.