Has anyone heard of an application where you input a single phase voltage into a vfd and get 3 phase out with the loss of some HP. Has anyone tried this?

yes i done that allready before and many manufacters did have a statement on running single phase input to reduce the capaicty of the VFD device to prevent overheating.

Merci, Marc

Sure, I've done it. As a result, I was able to control the speed of some air handler motors.

Was horsepower lost? I really don't know. The whole point of the exercise was to NOT use the motors to their fullest extent. The air handler's power requirements dropped from 28 amps to 8 amps, as a result.

Yes, and before they came along we used "phase convertors" on single phase to do such applications as running an elevator(3-phase) in a residential neighborhood church.

They are a bit** to size properly and to get the ahj to authorize...the math is way too complicated for me...but engineers are cheap and slutty if you have cash money now and not the promise of payment on wednesday....(ok cheap shot and too obscure probably.....sigh)

Anyway yes it works fine....but you need engineering supervision.

I'll answer a little differently in an attempt to seem high priced and somewhat selective. The single phase input works via a single phase input rectifier section to provide power to the DC bus. The 3 phase output works via a 3 phase inverter section with suitable drives. You're stuck with the horsepower loss because you will never achieve anywhere near 100% conversion efficiency. If you could the VFD would be very small and require no heat sinking. If you meant deliberately limiting the load's horsepower through the VFD's programming, that is fairly common these days. I'll ask around next time I'm over at the dollar store pickin' up chicks.
Joe

Smaller VFDs are often used that way by home shop machinists so that they can run surplus 3 phase machine tools on residential single phase 240V.

If the 3 phase VFD has 3 input terminals, L1,L2,L3, how do you connect Single phase power? .... L1 to Hot, L2 to Neatral, and L3 nothing?

most small VFD's incomming voltage is typically L to L 240 line to line or 208 line to line as well genrally most VFD useally used the 208 or 240 volts system but very rare but some can take 120 v as input voltage

Merci, Marc

You need to refer to the specific VFD's manual for this info. If the unit is capable of single phase input, then proper connections should be spelled out somewhere. You would want to connect the power to the 2 legs that feed the transformer that provides low voltage power to the drive electronics. On most this is L1 + L2, on others I have seen, L1 + L3. Depends on the manufacturer.

Input power would be 2 hot phases (240VAC), not a hot phase and a neutral (120VAC).

VFDs and UPSs rectify AC into DC, and then create a new AC signal. The output and input are completely independant. Whether it can handle 1-phase at all really depends on the design- specifically, the controls. The guts are simple, they can handle it, but the controls might consider it a fault and shut down as opposed to switched into a derated mode.

If the input is wye, it really doesn't matter hardware-wise if you go L1-L2 or L2-L3, etc, they're all identical.

If you put 1-phase into a 3-phase VFD, even if it's rated for 1-phase use, you're going to introduce extra ripple current onto the DC bus which can may the output a bit dirty. You'll have to derate the VFD, probably to about 57% of its original rating.

Yes, VFD's can be fed with single phase and output 3 phase. Most VFD manufacturers use a derating system to maximize the output current available. Heat is the enemy of a VFD, and proper derating on single phase operated units should be considered.
You will find that most VFD's under 5 Hp have no derate. And VfD's over 5 Hp need to be derated. For example if you have a 7.5 hp three phase motor, you will most likely need a 10 Hp VFD. This is true with most all VFD manufacturers, but not all. So find out. You can look in any motor and drive catalog and it will give you the information you need for single phase operation. Some require only the two CCC's on any off the three input terminals, and some require a jumper to the empty terminal.
Another thing to consider is the motor itself. Is it rated for PWM operation? Is the magnet wire sufficient for VFD application? Internal magnet wire rated above 1600 volts.
Many times people will put a VFD on a motor to find that the motor fails prematurely. This is very common.
All new motors with the exception of single phase incorporate this special magnet wire in production. If your motor is more than five years old it may not have this wire in it. If it is less than five years old it probably has it already. For great prices on VFD's check www.automationdirect.com

For information on VFD's take a look at:
www.baldor.com
www.tecowestinghouse.com
www.wegelectric.com