Cost to convert three phase motor to one phase

[Rob Calkins]

I am looking at an powermatic 8" jointer in three phase. Does anyone have a ballpark figure what it would cost to change the motor to a one phase? I would like to use a Baldor motor.

Thanks,
Rob

[Greg Peterson]

There is no straight answer on converting a three phase motor based machine.

You can get a conversion kit (for lack of a better description) that will allow the three phase motor to run on single phase wiring. Cost? Somewhere less than $100~. You can also make one if you're handy with a soldering iron and can read a schematic.

Couple things to consider if you plan on installing a single phase motor.

1. Is the mount for the motor propietary or can any 'generic' single phase motor be mounted to the unit?
2. Is the price on this piece of equipment so low as to offset the expense of converting the motor? Especially since you express an interest in Baldor. If this machine is going to see alot of constant use, daily, then going with a Baldor motor is probably a good idea. But you also might be bumping into that whole false economy issue again. The conversion to single phase with a quality motor might not put you all that much further ahead when it's all said and done. Really going to be a matter of how good of a deal you get on this peice of equipment.

[Bart Leetch]

I changed my old Delta Unisaw from 3 phase to 1 phase but didn't use Balder or Delta I used a Grizzly motor that bolted right in & works just fine. Cost $200. You can see it on my web page.

[Chris Rosenberger]

The frame size should be listed on the motor tag. Get a 1 phase motor with the same frame size as the 3 phase motor. Baldor will have the highest cost but are good motors. New 2 HP Baldor is about $300.

[Alan DuBoff]

One consideration is that you may need a new starter/switch also, since most of them are either single or 3 phase. You could sell the motor and starter to recover some costs, but you'll only get about $10 per HP (at least that is about going rate).

As far as the conversion, it's not that difficult for machines that have belt drive on them, but for direct drive motors it's requires the exact same frame, which are typically very hard to find on older machines, but a PM 8" jointer should have a belt I believe, I'm not sure which jointer you're talking about.

The other consideration is to get a phase converter to use with it. There are 2 ways to go on that, you can get a static converter which will run you from about $100 - $200, and you need to make sure that it matches up for the motor it's being used on. I know that I have a phase-a-matic 3HP - 5HP static phase converter which came with the table saw I bought which is 3 phase. With a static converter you will only get 2/3rds the rated power from the motor. Something to keep in mind.

The other type of converter is a rotary phase converter, which is like a static phase converter, with a 3 phase idler motor. The idler motor uses the static phase converter to start itself, then the running motor supplies the 3 phase power to the other machines that need to start on the same circuit. You can run 3x the reccomended power. So, the way it works is like this. My 3HP - 5HP phase converter would use a 5HP 3 phase motor. You could run any motors that were 2/3rd of the 5HP idler, which is about 3 HP. You could run 3x the amount of HP on that RPC, which would be 9HP at once.

Check this document for more info on using a static phase converter to build a rotary phase converter, from the phase-a-matic site. There's a lot of info in there about phase converters as well.

Static Phase Installation (Method 2 is using one for a rotary phase converter)

3 phase machines are much cheaper, and the motors can be picked up for much less, since most folks don't have 3 phase power in their homes, and want to do as you are intending, buy a single phase motor. I have two 3 phase motors I bought from folks that did exactly just that. A 2HP Reliance I paid $20 for, and a 5HP Dayton I paid $60 for.

[Craig Zettle]

I am going through the same thing with a shaper. It is a Delta 3phase 5hp and I can't decide if I want to buy a 5hp single phase motor, which will run at full power, or a static phase converter and run at 2/3 power. I can get a 6 to 10 hp static phase converter from grizzly for $229 or a 5hp motor for about a hundred more. Rotary is out of the question because you end up spending more than if you just bought single phase to begin with. (I know you can "build your own with a flea market motor", but if I knew enough to do that I would not be asking the question to begin with). I too was wondering if the motor was just a bolt on, as long as the holes all lined up, or if you needed to buy additional electrical parts.

This question keeps popping up in one form or another, and the answers usually include amazingly complex dissertations that are way above my head. I am sure all most guys want to know is can you do it, what do you need to do it, and what are the drawbacks.

I'm leaning toward Bart's route right now, because for the small extra outlay of cash it just seems to make more sense to me to be able to run at 100% power with no extra elecricals to wear out (another drawback I have heard of with static converters).

Craig

[Bob Wilkerson]

If it's going to be the only machine you ever buy that's 3ph I'd just use a VFD rather than a static converter. VFD's will give you full power. OTOH if you get into more machines it'd be worth having a rotary phase converter. I run all 3 configurations in my shop (1ph, 3ph rotary and VFD's) and no longer worry about the motor design. I like 3ph motors for their durability and lower costs.

Bob

[Rob Russell]

Craig,

One thing to check is the wiring in the machine. 3-phase motors draw less current (lower amps) than equivalent HP single-phase motors. It is possible (although probably not that likely) that you'd have to replace some conductors.

An example would be if the 5HP 3-phase machine was wired with #12 but the 5HP single phase machine draws 25+ amps and needed #10 wiring internally.

Rob

[Craig Zettle]

Thanks Rob, I will check the gauge of the wire.

Bob, what is VFD???

[Timo Christ]

VFD = Variable Frequency Drive
best option, IMO.
T

[Rick Christopherson]

You are not likely to find a VFD in this size range that takes single-phase input and provides 3-phase output. Even if you did, the price would be higher than buying a new motor.

Even though I have an article on how to build a balanced static phase converter, it was not until recently that I discovered that off-the-shelf static converters completely cut-out once the motor is running. In my opinion, this is extremely poor and will damage a motor.

For your application, you could build a static converter for less than $50 and it will rival a store-bought unit. I would not waste my money on a converter that cuts out when the motor gets to running speed. These store-bought units are nothing but a pull-string in disguise.

[Ed Breen]

Along these lines, and talking about phase converters, I read on the two I use that it produces 2/3 hp after about 15 minutes, or when run for considerable time. Most of my run times are under 1 or 2 minutes. Am I wrong in my reading?
Ed

[Rick Christopherson]

Along these lines, and talking about phase converters, I read on the two I use that it produces 2/3 hp after about 15 minutes, or when run for considerable time. Most of my run times are under 1 or 2 minutes. Am I wrong in my reading?
Ed

I don't know the source of this assertion, but it is not correct. After about 1-2 seconds, everything is stabilized and does not change. In other words, there is no difference between 3-seconds and 15 minutes. Once the motor is up to speed, a store-bought static converter drops out and does not impact the motor any further.

[Rob Russell]

I don't know the source of this assertion, but it is not correct. After about 1-2 seconds, everything is stabilized and does not change. In other words, there is no difference between 3-seconds and 15 minutes. Once the motor is up to speed, a store-bought static converter drops out and does not impact the motor any further.

Rick,

It's my understanding that some of the "high-end" static convertors (now that's an oxymoron - "high-end static phase convertor"!) do have run caps which would increase the overall efficiency of the convertor and improve the voltage stability of that wild leg. I don't remember a specific brand. The cheap ones are definitely nothing more than start caps.

Rob

[Bob Wilkerson]

Hi Rick,

My response was aimed at Rob's need to run an 8" jointer which I'd assume is only 1 hp or so. I've purchased a few VFD's in the 1 or 2hp range for less than $150 over the last few years using them on lathes, etc. I like them for the added benefits as well as just 3ph generation. I use one on my lathe which is a 4-speed Powermatic 45.

I'd guess that you were referring to the 5hp shaper response from Craig. I tend to keep 3ph machines 3ph for simplicity and lower costs. FWIW, I do have a 5hp capable VFD on the shelf ready for a project machine that I plan to use on a table saw that will be at a different location. Fortunately I was able to get a NIB unit for less than $200 on ebay.

Most of my larger machines run from a RPC that I've wired througout the shop using a 3ph panel.

Bob