vfd question

I thought the normal rating was something like 150%. Thus a VFD rated for

Another thing to look at is braking. Does the unit provide braking, or do you care if the VFD can brake the motor. Other than that a lot of the more expensive VFDs have fancy controls, user interfaces, different inputs, etc, that may or may not be needed in your application.

For what it is worth VFDs are plentiful on ebay. I picked up a $1300 Siemens unit for ~$150. It was a 3 phase only VFD though. I do think the single phase to 3 phase converters do go for more, for obvious reasons.

Otherwise good luck.

Hmm, that's going to pull 36+ amps with a poor power factor if you load the motor fully. I'm not sure running a 10 Hp motor from a single-phase source is such a great idea, if you really are going to draw full power.

Jon

I have two "3 phase only" VFDs in my shop running on single phase power. I have a 1 Hp Magnetek GPD-333 (made by Yaskawa) running my 1 Hp. Bridgeport with no problem. Had I known about the derating at the time, I might have gone for a larger unit, but it seems to work fine.

I have a 15 KVA Toshiba runing a 7.5 Hp lathe, and of course it works fine, too.

Jon

Make sure the VFD of choice will run on single-phase. Some have phase loss detection which shuts down the unit if a phase goes down.

Randy

Is that a parameter that can be changed through programming?

According to ATP* :

Probably not -- but you can often fool it by strapping the one unused phase to the nearest of the other two. It is not checking whether it is different from both of the others, but rather whether there is something there -- so it can safely shut down when being used at full rating if one phase of the power feed is lost.

Enjoy, DoN.

It's a pretty unusual feature on small (

I have a 25 HP and a 45 HP VFD for future projects. They are the ones I'm concerned about. I'll try Don's suggestion if there's a problem.

Ned, Why are small of the smaller VFDs rated for single phase? I do know that the used VFDs that are rated for single phase seem to be going for a premium. Are you saying that any smaller VFD will convert single phase to 3?

Ned sez:

"It's a pretty unusual feature on small ( 20+ years of building and working around industrial

So, see Ned, how you've cut through tons of technical BS and gotten right through to the central (and simple) theme of the subject at hand. Hey! No reading of spec sheets for you - you made an assumption and acted on it. It sorta stands to reason if a 3-phase motor can run on single-phase juice then so can a VFD. So simple! We doesn't need no stinkin' spec sheets!

We have an award for folks like you. It is offered to those that somehow cheat "Darwin" and continue on to unheralded fame. It gives me great pleasure to award you the first ever "IGGY". Picture it! Cute little statue . . . somewhat grotesque though, of a little idiot standing with one foot on his tongue and the other on his dick.

Bob Swinney

Don't all VFD's work by converting DC to synthesized 3-phase AC?

With rectified 3-phase there is no need to store energy because full-wave rectified AC never goes below 86.6% of peak line voltage. With rectified single-phase, some capacitive storage is necessary so there is always DC available to synthesize all three phases.

So, it would seem that any VFD should be able to run on single-phase if sufficient capacitive storage is present.

All that I'm familiar with, yes.

The capacitance also serves to absorb energy when the drive is decelerating the motor. Many (all?) VFDs will disable the motor if the bus voltage goes out of range. Some can be configured to display the bus voltage, which can be useful when setting the accel/decel parameters and for determining if a braking resistor may be required.

Which is why I referred to lost phase detection as a "feature". If a drive can detect a lost phase condition then it seems to me that capability is intentional, not a necessary consequence of the design.

Ned Simmons

Did you mean to say "Why are *some* of the smaller VFDs rated for single phase?"

I can only speculate why some mfrs don't put single phase ratings in their literature - perhaps they perceive it as a small and potentially troublesome market. If you actually ask the applications guys they'll give you a recommendation, which usually involves derating the drive by some factor, most often to 1/2 to 2/3 of it's three phase rating. I personally think that derating a drive that sees light and intermittent use by 1/2 is very conservative.

Ned Simmons