Static Phase Converters - Anybody use them?

[Dennis Peacock]

I am finding way too many good deals of old 3 phase power tools for crazy cheap prices at times. What's the trick to using a static phase converter with power tools? I've looked at rotary but boy are they pricey!

Inquiring minds want to know. :)

[Allan Speers]

These days, good VFD's are so cheap, there's very little reason to consider a rotary converter, let alone a static one.

For under $300 you can get a 3HP, tried & true TECO. It gives you vari-speed, soft-start, dynamic braking, overload protection, and re-start protection. (In other words, you don't need a mag starter.)

The only difference is, you ideally want one VFD for each motor.

[Bruce Page]

I have been running my lathe & mill off a single Phase-O-Matic static converter since the mid 90's without any problems. I would have gone with a VFD but I don't think they were around at the time.

[John TenEyck]

VFD's are a good choice up to 3 HP motors. Above that, though, they go up in price dramatically, at least from what I saw when I was looking for one that could handle 5 HP. So we ended up using a static phase converter on it and the owner has had no problems in 2+ years. You will lose 1/3 of the power, so if that's important don't use one. In our case it was going on a jointer and 3+ HP is still plenty. The static phase converter was custom built by a local company (Sanborn, NY), and cost just over $100. The only downside with SPC's is they are not meant to be cycled very often; max. 10 on/off cycles per hour to avoid premature failure.

John

[Matt Day]

For under $300 you can get a 3HP, tried & true TECO.

I think you mean under $200 for the FM50-203-c.

For my stationary machines that are three phase i’ve got a VFD/machine, such as TS, jointer, bandsaw, and planer (whenever I get around to restoring it).
For the other few 3 phase machines (spindle sander, grinder/buffer, and soon to be disc sander, I’ve got a 2hp VFD “sub-station” setup. Since these machines are used less frequently, I plug and unplug both the switch and power for each machine as needed. Settings are shared between the machines as far as accel/decel times.

[Allan Speers]

I think you mean under $200 for the FM50-203-c.


Wow, they've really dropped in the last few years!

Well, there you go.

[Dennis Peacock]

So, I'd need to get a VFD for a 3 HP motor and that VFD would operate my 3 HP 3PH motor on a TS for example...without any other hardware? Sorry, but I'm just now researching this stuff and having to learn as I go.

[Mike Delyster]

One thing I haven’t seen mentioned yet. The cheaper VFDs that everyone so far is talking about will run a 240 volt 3 phase motor. When you get into different 3 phase voltages the cost goes way up. A lot of the 480-460 volt motors can all so be wired to run on 240-220 volt power, but some don’t.

[Brian Holcombe]

These days, good VFD's are so cheap, there's very little reason to consider a rotary converter, let alone a static one.

For under $300 you can get a 3HP, tried & true TECO. It gives you vari-speed, soft-start, dynamic braking, overload protection, and re-start protection. (In other words, you don't need a mag starter.)

The only difference is, you ideally want one VFD for each motor.

I have three machines which run on one rotary, one of which has a dust collector which is also 3ph running at the same time, it's now a considerable cost savings to individual VFD's.

Rotary also offers the advantage of not needing to control the machine any differently than you would otherwise, with machines that are on and off a lot, this is handy. I run a milling machine with a VFD and winding it up and winding it down at the start and stop of every cut is a PITA when you're doing certain tasks. If I ran my slot mortiser that way it would drive me nuts, same with the Maka. I have no idea how a Maka would run with a VFD.

So, don't be so quick to write off the rotary. :D

[Malcolm McLeod]

So, I'd need to get a VFD for a 3 HP motor and that VFD would operate my 3 HP 3PH motor on a TS for example...without any other hardware? Sorry, but I'm just now researching this stuff and having to learn as I go.

Make sure the manufacturer specifically states it will handle your specific conditions; in this ^^case^^ 3 HP with 230V/1ph input. Or you should de-rate the VFD you purchase.

The one thing that seems to throw most folks is 'de-rating' a 3ph VFD to use 1ph input power - -
- 3HP/230V/1ph motor typically pulls around 17 FLAmps.
- 3HP/230V/3ph motor typically pulls around 10 FLAmps.

If you want to power a 3HP/3ph motor, the output of the VFD must be sized to deliver 10 Amps. However in typical residential use, the input side of the VFD has to 'make' this 3HP from a 1ph supply, which requires 17 Amps. So, the VFD sees 17 Amps input and 10 Amps output - both equaling 3HP - and just like wire, it must be sized for this amperage.

Many manufacturers have begun advertising their VFDs to handle a particular HP WITH 1ph input/3ph output, but if they don't, then prudence dictates you de-rate the VFD.

In the above case you'd need a 5HP VFD to power a 3HP motor, since a 5HP/3ph VFD can handle 15-16 FLAmps at its input terminals (17A is just a tiny O'Load, and probably well within the safety margins of the manufacturer). So, you have 'de-rated' a 5HP VFD to 3HP.

I hope my explanation is clear and concept may seem confusing, but don't get lost in the details.

[Jim Becker]

Dennis, relative to rotary, if I'm not mistaken, you can reduce the cost by building your own since getting a functional, big and older three phase motor to do the work can be pretty inexpensive. There are articles "out there" that say how to do this. They are probably just fine for common tools, but not recommended for machines like CNC because the more crude DIY rotaries do not provide balanced power output on all the phases.

[Carl Beckett]

I ran a 10hp widebelt sander off a phase-o-matic static converter for years. I know it means less than max HP, but it turns out I didnt need max hp and it worked perfectly fine. The converter I picked up used (10 to 15hp range I believe it is rated for), for $150. Hard to beat for 10hp (even if only 6.66hp)

A couple years back I was able to get a 10hp rotary PC for $500 (again used). This I acquired at the same time as a new/different widebelt. So now I use that.

But to be honest, there was no difference in performance for me. (static vs rotary).

I tried selling the static converter a couple times but no interest, should put it up for sale again. I toyed with the idea of getting a used 3 phase motor (they are cheap on CL) and coupling with the static converter - making it a rotary converter. Figured that would give about a 10hp RPC with less than $300 in it. But I got a different one now so dont want another project. Someday. Maybe.

A lot of positive experiences with VFD and not much love for the static converters by the purists. But my experience was 100% positive and no need to over think it, the static converter worked fine even at the larger HP. VFD gets $$ as you increase HP.

[Jerome Stanek]

Way back when phase converters were not supposed to exit we got one from an electric motor place we got a static converter for one motor but later added a floating motor to run several different motors.

[Bruce Wrenn]

Ten years ago, I built a rotary phase converter for neighbor for his machine shop. Used a salvaged three phase motor, coupled to a Herbish dryer motor. The Herbish dryer motor has a lead that line voltage appears upon when it reaches operational speed. Household dryer motors have the same feature. It prevents the heating element from running if fan isn't turning. The line voltage allowed for a relay to pull in and excite the three phase motor. Put a magnetic starter of whole shebang, so if power went out, and then returned, system wouldn't self destruct by letting "magic smoke" out. Web site "Practical Machinest" has many different shop made RPC's on it. With a RPC, you have two choices to get it running, either a pony motor, or relay and capacitors.

[Matt Day]

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.

[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.... :o 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.