3-phase woodworking machine question

[Jason White]

I see a lot of used woodworking machines on Craigslist that are 3-phase electric. As such, they seem to sell for less money because there's a smaller pool of people interested in them.

I know you can get a phase converter, but can't you also just swap out the 3-phase motor with a 1-phase motor? Or is there more to it than that?

- Jason

[Myk Rian]

Just swap it out.

[Jason White]

Will the existing power switch work, or will I need to change that, too?

[David Kumm]

When you go to single phase you are doubling the amp draw so depending on the electrics you might need to do nothing or swap out the mag starter, or at least change the heaters. Not a huge deal although I would not change over a three phase motor. Once you get into industrial machines you will get to like them and look for a permanent solution. VFDs, RPCs, or Phase Perfect. Dave

[Keith Bohn]

It depends on the switch (motor control) but typically yes/just use two legs instead of three. If it has heaters there may be some diddling with that.

[Jeff Monson]

When you go to single phase you are doubling the amp draw so depending on the electrics you might need to do nothing or swap out the mag starter, or at least change the heaters. Not a huge deal although I would not change over a three phase motor. Once you get into industrial machines you will get to like them and look for a permanent solution. VFDs, RPCs, or Phase Perfect. Dave

I think that is the best advice, I have 3 different 3 phase machines in my shop now, all run off a RPC which came with my 1st machine purchase. 3 phase is easy to wire also Don't let 3 phase intimidate you, its not a big deal IMO.

[Bruce Page]

I wouldn’t change out the motors. I have two 3phase machines that run off a single Phase-O-Matic converter. I’ve had this setup for over 20 years and never had a problem with it.

[jack forsberg]

Jason

You would think that that all it takes is to switch out the treefaze motor for a singa faze. and in some cases that is the easiest to do if its a light little machines that were offered to the market in single phase options. you know the consumer grades like Delta ,grizs ,powermatic.

here are the issue as i see them. First not like you going to be able the switch out a RAS motor or a direct drive mortiser motor for single phase at a cost that would make it worth it. Two the motor control are general of the more industrial kind and some are not single phase compatible and so you will need a new switch$$$$$$. Three some single motors wont fit into the opening/motor mount because of the start capacitor humped up on the motor gets in the way(three phase motors are generally smaller). forth motor rotation can be a problem as not all single phase motors are reversible and three phase are so machine with forward and reverse can be a challenge.. fifth single phase motor only come in 2 voltages (120/240) where as 3 phase more come in many and you can not use motor starer that are of a different voltage because of sizing in some cases. lastly understand that a single phase motor the same HP will draw more amps than its three phase counter part and this may mean rewiring all the electric in the machines.

If a machine you are looking at is 240 volts and under 3 hp is will cost way less to use a VFD IMO
VFD are so easy to wire a monkey could do it.

Don't be put off to keep a machine 3 phase as it is in more cases a better chose for braking speed control and so many other things.ever wounder why the industry uses 3 phase? And everyone knows real machines are 3 phase.

My opinion is swamping the motor for single phase is the most expensive way to go .

jack
English machines




I see a lot of used woodworking machines on Craigslist that are 3-phase electric. As such, they seem to sell for less money because there's a smaller pool of people interested in them.

I know you can get a phase converter, but can't you also just swap out the 3-phase motor with a 1-phase motor? Or is there more to it than that?

- Jason

[Stephen Cherry]

Three phase machines are like Utz Potato chips, if you have just one, you want them all.

[jack forsberg]

Three phase machines are like Utz Potato chips, if you have just one, you want them all.


And then there are the voltages that are like all the flavors. way be 2 dimensional when you can be 3?


jack
English machines

[Peter Quinn]

Jason

You would think that that all it takes is to switch out the treefaze motor for a singa faze. and in some cases that is the easiest to do if its a light little machines that were offered to the market in single phase options. you know the consumer grades like Delta ,grizs ,powermatic.

here are the issue as i see them. First not like you going to be able the switch out a RAS motor or a direct drive mortiser motor for single phase at a cost that would make it worth it. Two the motor control are general of the more industrial kind and some are not single phase compatible and so you will need a new switch$$$$$$. Three some single motors wont fit into the opening/motor mount because of the start capacitor humped up on the motor gets in the way(three phase motors are generally smaller). forth motor rotation can be a problem as not all single phase motors are reversible and three phase are so machine with forward and reverse can be a challenge.. fifth single phase motor only come in 2 voltages (120/240) where as 3 phase more come in many and you can not use motor starer that are of a different voltage because of sizing in some cases. lastly understand that a single phase motor the same HP will draw more amps than its three phase counter part and this may mean rewiring all the electric in the machines.

If a machine you are looking at is 240 volts and under 3 hp is will cost way less to use a VFD IMO
VFD are so easy to wire a monkey could do it.

Don't be put off to keep a machine 3 phase as it is in more cases a better chose for braking speed control and so many other things.ever wounder why the industry uses 3 phase? And everyone knows real machines are 3 phase.

My opinion is swamping the motor for single phase is the most expensive way to go .

jack
English machines


Uh.....what he said. It's a rare machine where you can find a cheap easy bolt on 220V replacement. If there were only one motor mount in the world things would be easier. Sure you can machine your way out of many situations, but time has an expense too. Three phase motors are always smaller at the same HP rating. No caps, no start windings....just smaller, so single phase motors wont always fit in the given space. A good industrial 3 phs motor could run virtually forever, much simpler than single phase. And often the starter circuit really is wired in a much lighter gauge wire than single phase will require, so you would wind up rewiring the starter, maybe replacing a mag starter too. I found for my shop that once I got a 3 phase circuit running via RPC, three phase machines became much easier to acquire. I got one great deal that made it worth it to get the RPC, not an easy machine to swap motors, the single phase motor was actually going to cost me more to install than doing the phase conversion soup to nuts. So yes, you may find an occasional cheap motor swap situation, and if you have a pile of 220V motors around, or you only want one such machine, go for that. But honestly, once you get used to 3 phase industrial equipment, you want more, and its almost definitely going to be more expensive/difficult to convert a variety of machines. Easier to get one good phase convertor, deal with all 3 phase. I can only run one machine at a time, but its a one man shop, so unless I grow two more hands, thats not a problem.

[Steve Kohn]

I've learned that one huge benefit with 3 phase and a converter is the ability to make any machine variable speed. On some machines this doesn't matter, however on sanders it can really help prevent burning and allow much more control. I recently restored a combination sander that was 3 phase. The variable speed option is the main reason I'm hanging onto it. It is really much more useful for both wood and metal. I'm even considering converting my single phase edge sander over to 3 phase by changing the motor out and putting a converter on it.

[jack forsberg]

here is a simple 3 phase Drill press i got for $95 that cost $130 to convert with a VFD to run on 120 volts single phase house hold power.

tell me if you think i got more than a single phase motor change would have given me?
this video show the VFD upfit.
http://www.youtube.com/watch?v=6UsuoWTe7xs

this its it finished

http://www.youtube.com/watch?v=eIEwVt3kswU


jack
English machines

[Peter Quinn]

here is a simple 3 phase Drill press i got for $95 that cost $130 to convert with a VFD to run on 120 volts single phase house hold power.

tell me if you think i got more than a single phase motor change would have given me?
this video show the VFD upfit.
http://www.youtube.com/watch?v=6UsuoWTe7xs

this its it finished

http://www.youtube.com/watch?v=eIEwVt3kswU


jack
English machines

I'm loving that drill press. The foot pedal looks pretty handy, variable speed on the fly is great. To me it actually make more sense to buy single phase machines and replace the motors with 3 phase than the other way around in some cases....such as anywhere variable speed is useful. Kind of gives you a mini bridgeport there. Throw a XY milling table on there and I'm in drill press heaven. Now I'm on the mental lookout for a 3 phase DP!

[Larry Fox]

I agree with other posters have said about NOT changing. My tablesaw is 3-phase and runs off of a large RPC. It did take a while to get all the wiring done as I added a new single phase and 3-phase sub panel but now that I have it, I love it because of the opportunities it presents me for other machines. One thing to keep in mind though is that 3-phase electrical equipment like breakers and panels tend to be more expensive than their single phase counterparts but eBay is rife with listings.

[Charlie Velasquez]

. . . . . lastly understand that a single phase motor the same HP will draw more amps than its three phase counter part . . .



When you go to single phase you are doubling the amp draw . . .

Several responders mentioned this. Could someone explain this?
I thought 1hp ~ 745watts; watts = V x A.
So on a 2hp motor: 2 x 745w ~ 1490w
220 volt single phase: 1490/220 = 6.8A

How is this different on 220V three phase? (Assuming most people with a rpc convert 220 single to 220 three phase)

[jack forsberg]

Several responders mentioned this. Could someone explain this?
I thought 1hp ~ 745watts; watts = V x A.
So on a 2hp motor: 2 x 745w ~ 1490w
220 volt single phase: 1490/220 = 6.8A

How is this different on 220V three phase? (Assuming most people with a rpc convert 220 single to 220 three phase)


Very easy

a single phase motor 240 volts feed the amps to the motor with 2 legs. a single phase motor 120 volts feed the amps with one leg but at 2 times as much as 240. watts is volts x amps. watts is power

three phase motor get feed the amps with 3 legs so it takes about 1.75 amps of single phase power for every amps of 3 phase power because there are only 2 legs in single phase at 240 to feed the watts/power. The motor wire in single phase motors needs to handle 1.75 time the amps/watts each leg needs as it has one less leg than a 3 phase motor /winding does of the same HP.

In the end they use the same amount of power both single and 3 phase motor for HP rating though 3 phase has less lose(power factor). its all in how the amps are feed. One leg 120 volts single,2 legs 240 volts single and three phase 3 legs 240 volts.
jack
English machines

[Rick Fisher]

Great explanation Jack.

The math to calculate watts for a single phase motor is Watts = Amp x Volts x E
E is the Power Factor of the motor, which is usually on the label
For a 3 phase motor its Watts = Amps x Volts x E x 1.73

3 phases of power are basically 120 degrees apart on an electric motor. If you picture a triangle forming a circle, each leg is 1/3 the way around the circle.. Therefore, no two legs are as far away from each other as possible. If they where, they would be 2 ... because they are 120 degrees apart, they are 1.73 apart..


In your analogy,

A 15 amp 120V motor would draw 1800 watts.
A 7.5amp 240V motor would draw 1800 watts
A 4.3 amp 240V PH-3 motor would draw 1800 watts ( Because 4.3 amps x 1.732 x 240 volts = 1787 watts )

3 motors, same power ..

1.732 is basically the square root of 3 .. or the square root of 3 phase..

[David Kumm]

Although 1.73 - 1 is the mathmatical conversion, three phase motors are typically 10-20% more efficient than single phase so at least in my head you need to double the amps to bring the same hp to the work. Another reason for three phase. Dave

[jack forsberg]

Rick
I was so trying to put it down in laymen terms with out the math as this is what confuses most new to the game. Thanks for the run down as it is clear to me and others. In the end motors are dumb and you would be surprised what they will run on. Even 3 phase motor will run on single phase power and a pull rope. After all that's all a RPC is. 3 phase motors are a dime a dozen too. I could buy 10 three phase motors for the price of a new single phase motor and used single phase motor don't come up much and are a lot more money. One other thing to add is single phase motors are limited to about 10 hp after that it get real hard to start them and they are so so much money. no limit on 3 phase motor HP.



jack
English machines

[Aleks Hunter]

If the choice is between getting a rotary converter and doing a little wiring and putting a single phase motor on an industrial grade machine, Go with the converter. 3 phase is better than single.
Having a three phase power source opens all sorts of doors to acquiring better machinery for less cost. As you pointed out there is far less demand for 3 phase equipment, and the 3phase stuff is true industrial equipment unlike stuff from companies that put "industrial" in their name.

[Rick Fisher]

In practical terms.. the number is usually about 1.75 ..

Modern Single phase motors, especially like the Baldor Super E series are more efficient than older 3 phase. The difference is really small...

[John Downey]

At the risk of being horribly pedantic....

There is no 240 volt 3 phase, it is 208 volt. Each phase is 120 degrees from the other two, either leading or trailing. Sine(120) X 240V = 208V

When you measure any one phase to ground or common you get 120V, but there is no way to measure peak to peak on three phase, at any time in the cycle there is always only 208V between any two phases.

That drill press is just the thing Jack. Three phase motor and a VFD is the way to go. I'm almost hoping the single phase motor on mine goes out so I can set up a VFD :D

[Steven Wayne]

That is not correct. I have four wire three phase 240 in my shop.
A-B = 240v
B-C = 240v
C-A = 240v
A-N = 120v
B-N = 208v
C-N = 120v

Polyphase AC quantities (voltages and currents) are represented as vectors (aka phasors). Ie a magnitude with a direction (phase angle). The square root of three is not because there are 3 phases. It is because of the angular relationship between phase-to-phase and phase-to-neutral voltage or current, which boils down to trigonometry.

In a wye connection phase-to-phase current = phase-to-neutral current and phase-to-phase voltage = phase-to-neutral voltage * sqrt(3).

in a delta connection phase-to-phase voltage = phase to neutral voltage and current is times sqrt(3).

theres a lot of partially correct info in this thread. I do three phase power for a living and am happy to answer questions.

I hope this helps.

[Jim Neeley]

Steven,

I agree with everything you have said but would like to add one point of expansion for clarification.

Many commercial buildings (at least here in Alaska) are wired with 208V 3-phase in a Wye configuration which leaves you 120V from any phase to neutral. This is *a* way but not the only way to provide electrical service.

This in no way negates what you've said about 240V although most of what I work with is industrial where it's 277/480V. (root 3 variance).

Jim in Alaska

[John Downey]

You are correct of course Steve, it was getting late and I was thinking only of the 3 wire set up that rotary converters attempt to replicate. I'd forgotten about high leg delta systems.

[Rick Fisher]

I have a Phase Perfect and it measures 240, 240, 242.

The legs of the single phase ( voltage ) don't match what is produced by the converter, which would indicate some type of voltage correction.

There is no neutral .. IMO that would mean Delta configuration.

[jack forsberg]

theres a lot of partially correct info in this thread. I do three phase power for a living and am happy to answer questions.

I hope this helps.


OK I got a question

there a code here in Canada that states that the the voltage to ground can be no more the 150 .


"2-106 Circuit voltage-to-ground – Dwelling unitsBranch circuits in dwelling units shall not have a voltage exceeding 150 volts-to-ground except that, where the calculated load on the service conductors of an apartment or similar building exceeds 250 kV•A and where qualified electrical maintenance personnel are available, higher voltages not exceeding the voltage-to-ground of a nominal system voltage of 347/600Y shall be permitted to be used in the dwelling unit to supply the following fixed (not portable) equipment:
(a) space heating, provided that wall-mounted thermostats operate at a voltage not exceeding 300 volts-to-ground;
(b) water heating; and
(c) air conditioning."


how would you ground a RPC feed 240 single from the main and then stepped up with a delta to delta trans 600/240 feed backwards?

jack
English machines

[Brian Brightwell]

My homemade RPC. It works well. I used surplus scrounged parts for not a lot of money. I have five three phase machines now. Ten horsepower is the largest. I put the RPC outside the main shop walls so I don't have to listen to it.
http://i773.photobucket.com/albums/yy11/bebrightwell/Shop%20Photos/th_P1010015.jpg (http://s773.photobucket.com/user/bebrightwell/media/Shop%20Photos/P1010015.jpg.html)

http://i773.photobucket.com/albums/yy11/bebrightwell/Shop%20Photos/th_P1010013.jpg (http://s773.photobucket.com/user/bebrightwell/media/Shop%20Photos/P1010013.jpg.html)

[David Kumm]

Phase Perfect is wired 240 Delta although I believe you can specify wye configuration. The manufactured leg is 208 to ground. Dave

[Stephen Cherry]

My homemade RPC. It works well. I used surplus scrounged parts for not a lot of money. I have five three phase machines now. Ten horsepower is the largest. I put the RPC outside the main shop walls so I don't have to listen to it.
http://i773.photobucket.com/albums/yy11/bebrightwell/Shop%20Photos/th_P1010015.jpg (http://s773.photobucket.com/user/bebrightwell/media/Shop%20Photos/P1010015.jpg.html)

http://i773.photobucket.com/albums/yy11/bebrightwell/Shop%20Photos/th_P1010013.jpg (http://s773.photobucket.com/user/bebrightwell/media/Shop%20Photos/P1010013.jpg.html)

I like that bandsaw!

[jack forsberg]

I like that bandsaw!

bandsaw?

jack
English machines

[Stephen Cherry]

bandsaw?

jack
English machines

click on the pixture, then scroll with the right and left arrow key

[jack forsberg]

click on the pixture, then scroll with the right and left arrow key


wow left handed too.

jack
English machines

[Gus Dundon]

What's that band saw?

[Brian Brightwell]

That bandsaw is a Cresent. It was made it the 1930's I think. I bought it from a machinist I used to work with,( I am not a machinist). His asking price was $250. I didn't try to get it cheaper!