Static Phase Converters - Anybody use them?

[Bill Dufour]

A vfd has one feature not available on a static or rotary. They can safely run a motor bigger then their design size all day long. My lathe came with a 1hp VFd supplying a 3hp motor. It had limits set so the motor actually only made 1hp but it was full rpm and not noticeable except on big heavy cuts where it bogged down. I eventually replaced it with 3hp VFD and used the older unit to run my 1hp mill/drill.
Most home shops will never need more then 3hp except maybe on a wide belt sander.
Bill D

[Bradley Gray]

The simplest converter I ever saw was a friend who ran 20 or so machines on an idler motor. 220 single phase to 2 legs, 3rd leg generated by the idler. He used his foot to spin the idler up to speed.

[Malcolm McLeod]

Malcolm,
I thought derating the vfd was only needed at above above 5hp? And also isn’t it really all about amps? How many amps the vfd can output (10.5A for the FM50 IIRC) and the motor tag on the machine’s motor tag.

Dennis, sorry if this is hijacking your phase converter thread.... Throw a rock at me and I'll crawl back in my hole.

Matt, power in must equal power out (ignoring losses/inefficiency). And you're correct it IS all about amps (again, think wire ampacity). For a given 3ph power output drawing X amps, you'll need ~1.7X amps as the input when its derived from a 1ph source. So, you need a relatively larger input section (bigger 'wire') to support that.

As for where de-rating needs to begin, I can't speak w/ any great knowledge. That;s for the manufacturer to specify. It depends on the specific manufacturer and the components they select in building a given VFD. They may pick 'over-sized' input components as a matter of routine - - They cost not too much more? They don't impact warranty issues? They allow bulk buying for use in a wide range of VFD sizes? By using a larger-than-necessary input section, it may open up new markets? (Here we are talking about them! Probably not 10 used by SMCers 10 yrs ago.) ...Maybe this parts economic changes at 5 HP VFDs?

Or, maybe manufacturers realize that most 1ph residential services in the USA just aren't built to effectively/economically supply a 7.5 HP or larger motor? Your guess is as good as mine. (I just use 'em; I don't build 'em. And I don't use 'em in 1ph applications, so take this for the $0.02 its worth. Currently, I have 3 teams commissioning a total of about 1000 Hp / week. Little ones are 480V; big ones are 4160V.)

[Larry Edgerton]

I may be wrong but it was my understanding that the units designed and sold as an option for phase conversion are rated at the specified HP, but it is when you use a unit that is 3ph/3ph you then need to de-rate.

[Mike Delyster]

I may be wrong but it was my understanding that the units designed and sold as an option for phase conversion are rated at the specified HP, but it is when you use a unit that is 3ph/3ph you then need to de-rate.

This is the way I understand it as well. I'm no export though.
I would suggest to the OP to contact Jack Forsburg he's a member here. He will be able to answer all your VFD questions.