Test for my logic on phase converters

[Steve Mathews]

I've searched, researched and read so much about phase converters here and elsewhere that I'm blue in the face. Being new to woodworking and after purchasing a used Jet 5hp, 3-phase cabinet saw I find myself faced with having to get a phase converter. The question has been which one; static, rotary or digital. The direction that I'm leaning to now is the static converter for the following reasons.

The cost for the static converter is obviously cheaper.
Since the 3-phase motor is 5hp the static converter would only degrade the power to about 3.3hp, still better than if the saw had a 3 hp, single phase motor.
The resulting power is probably more than adequate for my needs as a beginner.
The static converter is easy to hook up and doesn't require any changes to my table saw.

Well, that's my logic. Any suggestions would be appreciated.

[Richard Coers]

The one consideration you should add in the equation is, Will I ever buy another 3 phase machine? A static will on work on one machine, unless of course you add an outlet and then change the hookup with the different machines each time you use them. A properly sized rotary will power the entire shop. All of them are easy to hookup, so throw that out. You won't be a beginner of long, so throw that out. Heavy starting load machines are not well suited to a static. I blew up a homemade static with the first bandsaw I tried to use it on. Of course starting a 32" bandsaw is a lot different that a 14". What is the price difference between the static and a replacement 5hp motor. Don't get a Jet price unless you have to. You should be able to find motor places that will sell you a exact replacement for less money.

[David Kumm]

There are plenty of cheap ways into a rotary converter. Do it right and have something you can always use and grow with. Static is like a cheap blade on a nice saw. You only feel good until the first cut. Dave

[Brian Brightwell]

I agree with these two gentlemen. I built a rotary with a used 10 Hp motor and scrounged parts. I now have five three phase machines.

http://i773.photobucket.com/albums/yy11/bebrightwell/th_P1010015.jpg (http://s773.photobucket.com/user/bebrightwell/media/P1010015.jpg.html)

http://i773.photobucket.com/albums/yy11/bebrightwell/th_P1010013.jpg (http://s773.photobucket.com/user/bebrightwell/media/P1010013.jpg.html)

[Steve Mathews]

My first thought was to just replace the motor but finding something that would fit turned out to be a chore. Apparently the motor frame and mounting are unique to the Jet cabinet saw. At least I was never able to find a replacement without having to do a lot of modifications to the mounting, etc. I also understand that if I changed to a single phase motor the magnetic starter would also have to be changed.

Again, I know that there is some power loss using a static converter but again, wouldn't a 5hp 3-phase motor (powered through a static converter) perform better than a single phase 3 phase motor?

[John McClanahan]

I had the same problem. I bought a used Powermatic 66 with a 5 hp 3 ph motor. I wasn't too thrilled with needing to have a separate rotary unit for just 1 tool. A VFD to convert single phase to 3 phase for a 5 hp motor is expensive, plus it maxed out the power to my garage. Static converters are the cheap way out, but if the motor runs near its rated (de-rated) power, motor heating can be a problem.

I was eager to fire it up, The Powermatic uses a C frame motor, so I made a motor mount adaptor so I could use a more common T mount 1 1/2 hp motor to get by for awhile. Its been 2 years now and I have been happy with the 1 1/2 hp motor.

John

[Rod Sheridan]

Steve, I would buy a VFD for the machine since you're happy with 3 HP.

It will replace the old starter, provide soft start for the saw, and will be much better for the motor than single phasing it.

Regards, Rod.

[Stephen Cherry]

I agree with these two gentlemen. I built a rotary with a used 10 Hp motor and scrounged parts. I now have five three phase machines.

http://i773.photobucket.com/albums/yy11/bebrightwell/th_P1010015.jpg (http://s773.photobucket.com/user/bebrightwell/media/P1010015.jpg.html)

http://i773.photobucket.com/albums/yy11/bebrightwell/th_P1010013.jpg (http://s773.photobucket.com/user/bebrightwell/media/P1010013.jpg.html)

That's what I did also. Used rotary phase converters do come up used, also.

[Glenn Ancona]

Steve - the inverter we used in our shop was a rotary before we got 3ph.. A 10 hp ran a 7.5 hp. panel saw for years. I would think a 5 hp. would be more than enough. The rotary was hooked up w/o changing anything on the saw. You should be able to find one cheap

[ian maybury]

I got lots of help here - really appreciated - and ended up with a rotary on a big bandsaw, and for shop 3 phase supply; and a VFD on a Pentz/Clear Vue dust system. Both situations took advantage of their different pros and cons - and both have so far been trouble free.

Another rotary fan here where converters are concerned unless maybe the load is basically steady state - better quality output power than a static, normally enables use of machines own switches etc (just plug in to the converter as normal), well able to handle a bandsaw with heavy wheels (if properly set up), reasonable control of start up current if your supply is of limited amps, runs multiple loads simultaneously/as switched on up to rated kW (good basis for a whole shop system), minimal inconvenience in use (just switch on), easily linked with a transformer to deliver 400V 3 phase if required, reliable if a good one.

VFDs control start up current even better (you can make the ramp as slow as you like), and offer a gazillion control options (inc easy to hook up to a remote) - but are a bit more more awkward to wire and set up. They need shielded cable, basic programming, the manuals can be a pain (so much detail), have to be connected directly to the motor to be powered (replace the machine's own switches etc), run only one machine at a time, are typically limited to 230V 3 phase etc., may/may not depending on your application deliver all the torque required. (should be fine on a saw given the highish RPM and low inertia - Felder use them all the time)

Etc

ian

[Mike Heidrick]

The reality is a static will work just fine. And you can also add an ideler motor latter. And you can also add caps and balance it latter as well. My 5hp single stage DC has worked great on a cheap static and ideler for 7 years.

[Dave Cav]

Steve, I would buy a VFD for the machine since you're happy with 3 HP.

It will replace the old starter, provide soft start for the saw, and will be much better for the motor than single phasing it.

Regards, Rod.

I'm in the same camp as Rod. I'm running a number of 3 phase machines with VFDs. You don't necessarily need to have a 5 HP vfd for a 5 HP table saw. I have been running a Delta 12/14" table with a 5 HP Baldor 3 phase motor with a 3 HP VFD for a number of years with no problems. The vfd will shut itself down before there are any overcurrent problems. I have ripped 8/4 maple with a heavy rip blade with no problems with this setup.

[Jerome Stanek]

Does it have a magnetic starter switch on the saw.

[Steve Mathews]

Yes. It's the same starter that came with the saw originally. Here's a picture if it helps.
259927

[David L Morse]

I've been running my 70 year old shaper with it's original 3 phase motor for 15 years with a static converter and have had no problems. Just remember that a static converter is not really a phase converter. What it converts is a 3 phase motor into a capacitor start single phase motor at slightly more than 2/3 the 3 phase HP rating.

[Michael W. Clark]

I too have a static on my 3ph 5hp tablesaw. No problems with power or bogging down. I think it would be at least equal to the power of a 3hp 1ph tablesaw. I don't know much about phase converters, but like Mike said, I think you can add an idler motor to it later essentially making it a rotary.

[Steve Mathews]

If I went with a rotary what hp rating would be appropriate, 5hp for 5hp saw? I'm assuming that the converter would only be used for the saw.

[John McClanahan]

I'm in the same camp as Rod. I'm running a number of 3 phase machines with VFDs. You don't necessarily need to have a 5 HP vfd for a 5 HP table saw. I have been running a Delta 12/14" table with a 5 HP Baldor 3 phase motor with a 3 HP VFD for a number of years with no problems. The vfd will shut itself down before there are any overcurrent problems. I have ripped 8/4 maple with a heavy rip blade with no problems with this setup.

Dave, Will the VFD shut down, or does it limit the amps to the motor, thus limiting the horsepower?

John

[Steve Mathews]

This is what I'm thinking now. The rotary would be a good choice (for me) if the hobby took hold and more 3-phase tools were on the horizon. It also makes sense to take advantage of all the power of a 5hp motor. But, if my understanding is correct, a static converter will at least provide the power of a 3hp single phase saw. If I were to buy a new saw or even a replacement motor my choice would probably be a 3hp single phase. So, what am I gaining or losing? Others seem to be quite happy with a 3hp saw. Also, I have no guarantee that the existing motor is working (haven't seen it run) or will last (it's a Taiwanese motor). If the motor is bad or fails it seems to make sense going with something single phase. And if the saw doesn't get much use or I get bored with the hobby the most I've lost is the price of a static converter. I guess the direction I'm leaning toward now is a static converter. Am I missing anything? I have to say this whole exchange has been very helpful. All of the comments and suggestions have been great. Thanks!

[Mike Heidrick]

What you will get with just a static converter is unbalanced voltages on one of the three legs with a static converter. It will run just fine but is not teh best setup you can have.

If you size a RPC, for full 5hp, choose a 7.5hp sized RPC (or ideler).

Add caps to the run circuit to balance the voltages on all three legs if you decide to add an ideler motor and want to balance it like a good RPC should do.

If you buy a 5hp single phase input rated VFD it will deliver a full 5hp on a sigle phase input. If the RPC is not rated for single phase input you will derrate the VFD if you use single phase input.

[Rich Riddle]

Steve,

I run a rotary phase converter for my one three-phase machine, but it has an "outlet" in which to plug any future three-phase machine. That set-up seemed to make the most sense, but I had a free idler motor available and simply spend a hundred dollars on parts to make the converter including a shut-off control box. I will post pictures for you tomorrow.

[David Kumm]

RPC size depends on the brand. Kay and Arco are the most heavily built and they size by the largest motor the unit can start. Most others need to be oversized. I've seen 5 hp RPCs in the 300-350 range for Kay and about the same for 7.5 others. Keep in mind a RPC that will start a table saw might not start a band saw with the same motor or even a shaper so a little extra capacity is a good thing if you have the amps to support it. Look at the frame size of the idler motor as it tells you how robust the unit is. The mag starter needs to be bypassed for a vfd but no big deal. Dave

[Andy Pratt]

Another vote for using a VFD. I'm not an expert but i recently did a lot of research on them and they are a slam dunk compared to the other phase conversion options in my opinion. Even just looking at the phase conversion feature you will usually find that the vfd will come out on top in terms of price/functionality. When you add in all the extra things that the VFD can do for you, and how it eliminates the need for most of the other electronic components on a machine (capacitors, contactors, reversing switches, overload protection, speed control) they become the best solution by far.

John, I know that my VFD is programmed to cut power to the motor if there is over-amperage for a set period of time (which is based on a amps over/time curve and can be user defined as to sensitivity). I don't think they ever turn themselves off, but they effectively do by not sending power to the motor anymore.

[ian maybury]

Not to be contentious, but it seems to me there are definite (and significant) pros and cons to both types of unit - that which suits will depend on the scenario. There's potentially a wide range of applications which either can handle, but there are some definites where you need one or the other....

ian

[Tom Clark FL]

A five horse 3ph motor should have a 10 horse static to be trouble free. I have a 5 horse rotary for my 3hp mill and 3hp lathe that has been trouble free for the last 22 years. A friend tried to run a 10 hp lathe on a 10hp static and had tons of problems until he purchased a 15hp static. Then it ran OK.

[Erik Manchester]

I recently picked up a used 15 HP RPC that comes with a built in remote starter and can provide up to 45 HP in total which will address all of my 3 Ph needs for a long time. I had looked at the static option and VFD but the RPC provides me with more options. Heavy suckers though, mine weighs close to 400 lbs.

[David Kumm]

Erik, about 80 amps input to start it? Dave

[Michael W. Clark]

How does a 15HP RPC run 45HP worth of equipment?
Not doubting what Erik is saying, it is probably a ratings/nomenclature thing that I don't understand.
Mike

[David Kumm]

Michael, RPCs are often rated to run three times the largest motor the converter can start as the motors will share some power and it is assumed that all will not be pulling fully loaded amps. A 15 hp converter puts out about 60 amps so it can run more than you would guess once started. Dave

[Michael W. Clark]

Thanks David,
I think I understand the rating now. How do you determine the output amperagae and the supply amperage (circuit size required)?

To the OP, I apologize for the off topic questions.

Mike

[Jerome Stanek]

I would get a rotary phase convertor and wire it into a panel for future tools.

[David Kumm]

Thanks David,
I think I understand the rating now. How do you determine the output amperagae and the supply amperage (circuit size required)?

To the OP, I apologize for the off topic questions.

Mike

Go to Kay Industries website and look at their installation instructions. They give sizes for various converters. Basically a 15 hp will create output amps on the manufactured leg about equal to the amperage of the two input legs. 60+ amps input makes 60 amps output. L1 and L2 come from the panel or if going first to the converter, then directly to the machines or three phase panel the wire must be rated for 250%. The drawing makes it clear which sizes are needed. Dave

[Christopher Clark]

I vote for the VFD. They get better all the time. Recently, I'm seeing cheap VFDs from TECO. I would call TECO and talk to a tech support person and explain your requirements. They would suggest the appropriate model number. When you have that info you can search for the lowest price.

[Chris Fournier]

Which are you a fan of? RPC or VFD? Same question really. As someone who struggles with both every day I''l say this: a well set up fuel injection system will be more efficient and outperform a well set up carburetor every time. the trick is "well set up". Personally I'd go VFD. Look for the appropriate unit used and it is dirt cheap.