Changing 3 Phase for Single Phase - How Easy?

[Dean Ousterhout]

Hello all, I am thinking about some tools that are fairly new, within the last 30 years, that have been used in a commercial setting, but most have 3 phase.

I happen to have one 2 hp motor 1 phase sitting around from a dust collector that I dismantled and I am thinking it would work well on an 8" jointer, or perhaps a 20" bandsaw?

I just wondered if there are problems swapping motors? Are there problems with the motor mounts and the holes not aligning properly? Do you have to get new motor mounts?

Needless to say some of these machines are way less expensive than new, or ebay, or craigslist...

Thanks for any insight...

[Van Huskey]

Motors use standard form factors BUT there are several different form factors, these are NEMA #s like 56 etc. You can run into different shaft sizes and have to change pulleys which is easy and cheap except for a few oddballs. In the end if you are getting multiple 3 phase machines it maybe cheaper and easier to provide 3 phase power with a rotary phase converter or if a single machine a VFD.

[Stephen Cherry]

it maybe cheaper and easier to provide 3 phase power with a rotary phase converter or if a single machine a VFD.

Plus three phase motors are more reliable (no start capacitor, etc). In my opinion, you would be pretty crazy to switch a bandsaw from three phase because you can ged a small vfd for about 150 dollars (factorymation.com), and the drive provides variable speed, controlled acceleration, as well as phase conversion. Some of the drives will allow for a resistor to be added for braking.

[Mike Ruggeri]

I've done it a few times and it hasn't been that big of an issue. As Van said, the motor will tell the mount # and it is easier if your replacement motor is the same mount type. I did it on a 3ph bandsaw and just swapped out the old 3ph motor with a single phase version of the same mount #. I also did it on 2 shapers and on those I had to drill new holes in the mounting plate as the shapers had a different mount # and I could get a more common #56 for considerably less money (I was lucky that I could just drill new holes as opposed to having to come up with a new mounting plate). You may also have to change wiring in the switch/starter depending on how it is set up. Lastly, I agree with Van that if you are doing a mutiple 3ph machines, a rotary phase converter might start to make sense.

Mike

[Carroll Courtney]

Going to a 2hp single phase may require a starter which has overload protection.I don't know if you can fine a switch (on/off) that will handle the startup amps and then the running amps RLA's.Larges motor for a (double pole single throw) is rated at 1hp.As for the mounting,most motors have slots to give alittle wiggle room.Post some pics of this badboy,love to see it---Carroll

[Van Huskey]

I think we are hitting most of the points just remember it will be easy to do but maybe not 100% simple, if that makes sense. Further there are so many variables it will be better when you can give a specific example ie: I have X shaper with a Y hp 3 phase motor in it, I want to put Z single phase A hp motor in it, what are my options.

My bottom line is do not "fear the phase".

[george wilson]

You can buy those variable frequency converters so cheap these days,you might think about putting on one of those. Then you can have 3 phase motors and variable speed. I bought a 1 h.p. unit for about $80.00 a while back. Easier than trying to make a different motor fit,and having to deal with making the pulleys work,depending upon the installation.

[Chip Lindley]

Dean, there is a fairly steep learning curve concerning motor electricals, going from zero to 60. In the beginning there are many questions and discoveries that will become elementary knowledge later.

First of all is the physical swapping of the motors. Yes, motor mounts may have to be adapted. Replacement 1ph motors should be the same RPM as the original. And, the motor shaft diameter would have to be same to use the original pulley.

Second is electricals. A 1ph motor of the same Hp. can draw twice the amps of an equivalent 3ph motor. Your 1ph 2Hp motor draws around 12A. A 3ph 2Hp motor draws around 6A. The existing manual or magnetic starter of a 3-phase machine may not be rated for a same-Hp single-phase motor. Wiring also must be heavier for same-Hp. single-phase. These considerations cannot be ignored.

It is an enjoyment for me to deal with these motor things. I gained basic knowledge from reading. There was no Google in the '80s and '90s. Magazine articles from Fine Woodworking and Home Shop Machinist were crucial to gaining understanding. Younger guys don't know how lucky they are to have more knowledge than they can possibly read, right at their fingertips!

[Matt Meiser]

I think it depends widely on the machine. A 3HP vfd for a TS might not make much sense. My 6" jointer just needed a 3/4HP motor which I bought from a friend for $35. No reason for variable speed there either. For a drill press or a lathe it might be preferable to have 3 phase and a VFD.

[Dean Ousterhout]

So it sounds like 3 phase are "better" than 1 phase... although better is one of those interesting words...

But.. I suppose there must be a lot of good reasons why commercial operations use so much hardware that is 3 phase.

So... it sounds like I should consider wiring up some 3 phase. Although, I think I will wait till I have a 3 phase machine. I just won't shy away from buying one if I find a good price.

Chip... about the learning curve... welcome to life? I had to laugh about the internet and a reference to "younger" folks... hahaha.... I also (at 57) very much appreciate, no, revel, in how wonderful it is to find information... of course... there is also a lot of mis-information that must be sifted through. The loudest voice is not necessarily the most accurate.

So... lets say I have multiple 3 phase machines but I only use one at a time and I have limited space on the breaker panel. Can I wire a bunch of 3 phase machines so they are all on the same line? Or, have a 3 phase extension cord that plugs in whatever machine I need to use?


Thanks for all the advice... it is greatly appreciated...

PS... I finally got my Clearvue wired and a temporary input line so I could "vaccum" the garage floor... hahaha... what an expensive vacuum... ... More permanent ducting is forthcoming.. But I can say that this is one nice compliment to the shop(ok... not a real shop yet... just a bunch of machines in the garage, but there is a plan )

[Mike Hollingsworth]

I suppose there must be a lot of good reasons why commercial operations use so much hardware that is 3 phase.

#1 reason is the power itself is cheaper. Motors also.

[Rod Sheridan]

#1 reason is the power itself is cheaper. Motors also.

I'm an Electrical technologist and I haven't seen any rate differences between single and three phase power in any of our locations in Canada.

Single phase motors can have high efficiencies and power factor, almost as good as premium 3 phase motors.

Single phase power provides 2 "pushes" per cycle to the motor rotor, compared to 6 "pushes" per cycle for a 3 phase motor.

Obviously the motor has to maintain a reasonably consistent shaft speed, so single phase motors will be limited in their maximum power ratings, without being enormous to have enough flywheel effect.

It's very unusual to see single phase motors past about 10 HP, 3 phase motors go into the tens of thousands of HP.

Single phase motors also require a starting winding to establish a rotating magnetic field, 3 phase motors provide this through their design, no starting winding required.

If it were me and I wanted to run a 3 phase machine at home, I would use a VFD to drive the 3 phase motor. If I needed variable speed, I would have that as an added bonus.

You can use a phase converter to run a 3 phase motor from single phase power, however it is expensive to do that if you want true 3 phase power.

Many schemes exist to start the 3 phase motor then run it on single phase power. That's a terrible thing to do a three phase motor, and the motor runs at much reduced power.

More expensive converters produce real 3 phase power with balanced voltages, that's much better for the motor, yet much more expensive.

Me, I would probably replace the motor with a single phase unit if possible, or add a VFD as option #2.

The add an expensive converter and provide a second power system to my shop would be way down the list for a hobby use.

Regards, Rod.

[Chip Lindley]

Everyone has different priorities AND budgets in their shop. I was lucky to find at auction, several 3-phase bargain machines during the '80s and '90s at obscenely low prices. Powermatic Model 26 5hp shaper. Moak 3hp spindle shaper, Northfield 12", 3hp jointer. I also came by a commercial ARCO 5hp Roto Phase RPC to run them with. All four together cost me only $500! That was the start of my affair with 3-phase.

Cost of installing 3ph power from utility companies is completely prohibitive. Even for existing buildings with 3ph power, I understand there is a hefty "minimum" charge whether any power is consumed or not. Many shops with commercial 3ph power have switched to RPCs for converting single-phase to their 3ph needs. Since each 3ph machine adds some 3ph amperage to the system, several machines can be run at once; cheaper than using commercial power. My 5hp ARCO could run machines totalling 15hp, if started one at a time. All this on a 30A 230V single-phase breaker. Go figure! I never ran over two motors at any one time; a 5hp shaper and 2hp DC. The RPC handled both together easily. A heavy 10/4 extension was run to the shaper, (or any other machine up to 5hp) and the DC was hard-wired to the RPC.

If luck presented you with a lone 2hp 3ph machine, and you seriously doubt other 3ph machines will be in your shop, by all means the VFD is the way to go. But, each machine must have it's own VFD, sized for that machine's motor.

True that 3ph motors are simpler and more reliable than many 1ph motors. But, the main attraction is that 3ph machines can often be bought for pennies on the dollar--dirt cheap compared to the same machine with a 1ph motor. Many garage woodworkers shy away from 3ph machinery, thinking it cannot be run in a home shop. Their ignorance is Our Bliss, and the machines sell accordingly.

[Van Huskey]

Powermatic Model 26 5hp shaper. Moak 3hp spindle shaper, Northfield 12", 3hp jointer. I also came by a commercial ARCO 5hp Roto Phase RPC to run them with. All four together cost me only $500! That was the start of my affair with 3-phase.

I am running and telling Keith. This is a family friendly forum and that is positively OBSCENE!