I don't see a off topic board, am I going to get spanked??
- Thread starter LorenC
- Start date
TheOtherZilla
Pull my finger
Not an engineer, but I am a professional electrician..
LorenC
Keep trying for better, or get out of the way.
Making a rotary phase converter by running a 20hp 3ph. motor on single phase input, while it generates the 3rd leg. That motor is started using a small single phase shaft couple thru a sprag for no drag once it's power is shut down and the 3ph is running. The single phase drive motor is not involved in this wiring exercise.
Do I size the wiring for the largest load the generator will see(60-75% of generators 3ph motor depending on loads starting amps) or do I size for the 20hp motor 3ph amps, or even 20hp single phase amps?
Do I size the wiring for the largest load the generator will see(60-75% of generators 3ph motor depending on loads starting amps) or do I size for the 20hp motor 3ph amps, or even 20hp single phase amps?
TheOtherZilla
Pull my finger
So basically you are using a single phase motor to turn a 3 phase motor? And the three phase motor is connected single phase? Seeings as to how a 20 HP 3-phase motor will probly only draw ~25 amps @ full load and that requires #10 copper, I would calculate the largest load and use that.. A 20 HP single phase 220 volt motor probly draws ~70 amps.. From memory 70 amps needs #4 copper wire I believe.
I am not quite picturing what you described..
Here's a link to wire size chart that should tell you what you need to know.
http://cerrowire.com/ampacity-charts
I am not quite picturing what you described..
Here's a link to wire size chart that should tell you what you need to know.
http://cerrowire.com/ampacity-charts
LorenC
Keep trying for better, or get out of the way.
Found this chart listing 220v 20hp 3ph at 52 amps. http://www.hvacwebtech.com/motoramps.htm
A 3ph. motor will run on 2 legs, but won't start itself that way. So starting it with a shaft coupled, small, single phase motor is a cheap method if a suitable motor is at hand, which it is. A sprag between the two lets the single phase stop after turning off the power. So, turn on the single phase, it spins both up to rpm. Turn on the 3ph. and it continues to run since 2 legs are powered, turn off the single phase, it coasts down and stops. The 2 legs of 220v single phase run to the 3ph motor and on to a breaker panel, 3rd leg from the 3ph motor is now generating power, it goes to the same breaker panel with a 3ph breaker of suitable size. You now have 3ph power supply as long as the generator/motor is running. Available load amps to use is less than the generator/motor depending on the starting amps on those motors. 2 downsides to this method is you are using power to idle the 3ph. generator/motor, and that new 3rd leg is low on voltage. I'm thinking if I size the 220v for the largest load I'll be using, plus a bit, I should be fine? 40amp breaker and #8 wire for 15hp load? The current largest load I have is a 10hp lathe so for now I'll be under the 15hp plan even.
A 3ph. motor will run on 2 legs, but won't start itself that way. So starting it with a shaft coupled, small, single phase motor is a cheap method if a suitable motor is at hand, which it is. A sprag between the two lets the single phase stop after turning off the power. So, turn on the single phase, it spins both up to rpm. Turn on the 3ph. and it continues to run since 2 legs are powered, turn off the single phase, it coasts down and stops. The 2 legs of 220v single phase run to the 3ph motor and on to a breaker panel, 3rd leg from the 3ph motor is now generating power, it goes to the same breaker panel with a 3ph breaker of suitable size. You now have 3ph power supply as long as the generator/motor is running. Available load amps to use is less than the generator/motor depending on the starting amps on those motors. 2 downsides to this method is you are using power to idle the 3ph. generator/motor, and that new 3rd leg is low on voltage. I'm thinking if I size the 220v for the largest load I'll be using, plus a bit, I should be fine? 40amp breaker and #8 wire for 15hp load? The current largest load I have is a 10hp lathe so for now I'll be under the 15hp plan even.
TheOtherZilla
Pull my finger
Ok,I assumed 480 3 phase as that is what I work with all the time.. 52 amps on 220 3P is about what I expect.. I have never used 3 phase 240.. I think you need #4 copper as in my other post.
While it might look good on paper I have my doubts.. Once you start using only the 3 phase motor with 2 legs it will be in what is called a single phase condition and will draw much more than the 3 phase amps [52]. If I were attempting this I would size for the 20 hp 220 single phase motor.. or #4 copper..
I am researching this as I have never heard of this conversion.
K I found this site and it has wire size info specific to your project
http://www.metalwebnews.com/howto/ph-conv/ph-conv.html
And another
http://dcacmotors.blogspot.com/2009/04/running-3-phase-motors-with-1-phase.html
While it might look good on paper I have my doubts.. Once you start using only the 3 phase motor with 2 legs it will be in what is called a single phase condition and will draw much more than the 3 phase amps [52]. If I were attempting this I would size for the 20 hp 220 single phase motor.. or #4 copper..
I am researching this as I have never heard of this conversion.
K I found this site and it has wire size info specific to your project
http://www.metalwebnews.com/howto/ph-conv/ph-conv.html
And another
http://dcacmotors.blogspot.com/2009/04/running-3-phase-motors-with-1-phase.html
Depending on what you are trying to run you may have to boost the generated phase to make it clean. There are kits you can purchase and phase converters are used by many where 3 phase power is not available. Its been a while since I did any hard wiring but in your case the single phase load on the converter would determine wire ampacity for the line side. Ugly's reference book should tell you what you want to know.
Loren,
I couldn't take it, I went out into my shop, and gathered up some parts laying around.
I got a Magnetek 1.0 h.p 3 phase motor, 3450rpm, wired for 220 3 phase it draws 3.0 amps f/l
This will be my phase converter motor.
I also grabbed a 1/2 hp GE 3 phase motor, 1725 rpm, 2.2 amps f/l
and I grabbed a 3 phase contactor with a 115 vac coil
I wired the converter motor from a 220 switched outlet on my test bench then paralleled those two legs to A&C phases on my contactor and onto the 1/2 h.p motor I want to run, I then wired B phase through the contactor and onto the 1/2 h.p motor. B phase being my extra or third leg coming out of my converter motor.
I then wired the 115 volt contactor coil through another switched outlet.
I turned the converter on but it wouldn't start so I wrapped a rope on the shaft and turned it back on and pulled on the rope,....it fired up. I was pulling 2.6 amps on both legs at the converter, I measured voltage on the contactor and A to C was 240volts, A to B was 212volts and B to C was 223volts, since true three phase power is 120 degrees apart phases and this set up isn't I could see the difference in voltage between phases. I turned the contactor on and the 1/2 horse motor took right off, I took a amp reading there and this was the findings,...A phase was 2.0 amps and motor is good for 2.2 Phase C the same but B phase was only .3 amps.
I now measured at the source of the single phase power again and it had raised to 4.8 amps so there pulling both motors since there paralleled off each other.
SO,.....your going to have to run wire to handle the F/L current of your phase converter motor plus the F/L current of the motor or motors to be used, you will also have to fuse accordingly
Also to do it right you should use motor starters for each motor with heaters sized for each motor.
It only took me about 30 minutes to build it and I played with it for about a 1/2 hour and it has took me a hour to write this and it is still running and both motors are running cool, although there not doing anything, I hope this will help you some.
Take note I don't know what your local codes are and I didn't look into the National Electrical code book I just hooked it up and it will work, so if you want it leagal you need to do your own homework on that,...run big enough wire, I always like to be on the plus side, set your heaters to protect your motors and fuse to protect your wiring.
Wayne
I couldn't take it, I went out into my shop, and gathered up some parts laying around.
I got a Magnetek 1.0 h.p 3 phase motor, 3450rpm, wired for 220 3 phase it draws 3.0 amps f/l
This will be my phase converter motor.
I also grabbed a 1/2 hp GE 3 phase motor, 1725 rpm, 2.2 amps f/l
and I grabbed a 3 phase contactor with a 115 vac coil
I wired the converter motor from a 220 switched outlet on my test bench then paralleled those two legs to A&C phases on my contactor and onto the 1/2 h.p motor I want to run, I then wired B phase through the contactor and onto the 1/2 h.p motor. B phase being my extra or third leg coming out of my converter motor.
I then wired the 115 volt contactor coil through another switched outlet.
I turned the converter on but it wouldn't start so I wrapped a rope on the shaft and turned it back on and pulled on the rope,....it fired up. I was pulling 2.6 amps on both legs at the converter, I measured voltage on the contactor and A to C was 240volts, A to B was 212volts and B to C was 223volts, since true three phase power is 120 degrees apart phases and this set up isn't I could see the difference in voltage between phases. I turned the contactor on and the 1/2 horse motor took right off, I took a amp reading there and this was the findings,...A phase was 2.0 amps and motor is good for 2.2 Phase C the same but B phase was only .3 amps.
I now measured at the source of the single phase power again and it had raised to 4.8 amps so there pulling both motors since there paralleled off each other.
SO,.....your going to have to run wire to handle the F/L current of your phase converter motor plus the F/L current of the motor or motors to be used, you will also have to fuse accordingly
Also to do it right you should use motor starters for each motor with heaters sized for each motor.
It only took me about 30 minutes to build it and I played with it for about a 1/2 hour and it has took me a hour to write this and it is still running and both motors are running cool, although there not doing anything, I hope this will help you some.
Take note I don't know what your local codes are and I didn't look into the National Electrical code book I just hooked it up and it will work, so if you want it leagal you need to do your own homework on that,...run big enough wire, I always like to be on the plus side, set your heaters to protect your motors and fuse to protect your wiring.
Wayne
TheOtherZilla
Pull my finger
Velly intellesting. I guess the big question is how many amps are we sizing for?
LorenC
Keep trying for better, or get out of the way.
Man I like that! A guy that just gets things DONE! LOL
So I think I'll limit the load motors to 15hp on this system, as from what I've heard it sounds like a good safe point when starting with a 20hp idler. 15hp looks to be 42 amps on 230v, add some for the idler and a 60 amp breaker looks like a good place to be? That's 4ga. then, right? Too many dang charts and options on the web, want to confirm what I think I'm seeing.
So I think I'll limit the load motors to 15hp on this system, as from what I've heard it sounds like a good safe point when starting with a 20hp idler. 15hp looks to be 42 amps on 230v, add some for the idler and a 60 amp breaker looks like a good place to be? That's 4ga. then, right? Too many dang charts and options on the web, want to confirm what I think I'm seeing.
TheOtherZilla
Pull my finger
You could get by with a #6..
TheOtherZilla
Pull my finger
As far as I know a #10 should work, Here's a conductor chart that may help
http://www.electrician2.com/calculators/wireocpd_ver_1.html
And another simpler one.
http://www.controlmart.com/equipment%20ground%20calc.html
http://www.electrician2.com/calculators/wireocpd_ver_1.html
And another simpler one.
http://www.controlmart.com/equipment%20ground%20calc.html
Loren,
I am a little confused as to what your Converter motor is and what your Lathe size is, I believe your using a 20 HP for your rotary phase converter and your lathe is a 10 hp 3 phase motor, if that is the case then here are my recommendations, however you only nee a 10 HP converter motor, hp for hp. Anyway since you have a 20 hp 3 phase motor at 230 vac it draws 54 amps and your 10 hp lathe draws 28 amps which = 82 amps since your paralleling the single phase power to both the idler motor and your lathe you have to protect L1 and L2 from your panel with a 100 amp breaker, and really to be right according to the nec you need over a 200 amp breaker but if you start the idler then the lathe you should be okay with a 100 ampres you will need #3 wire. Now your wires going to your lathe you can easily get by with a #10, you should run three phase wires through a three phase breaker or fuses sized for your 10 hp motor and you should run that through a starter with overload protection, you will need 50 amp dual element time delay fuses or a 60 amp breaker, the 100 amp main WILL NOT HOLD if you try starting the phase converter and the lathe at the same time, you will probably have to go to a 175 amp breaker to do that, the motors both together will probably pull 80 amps or less but the initial start will spike WAYYYY up there and you will need enough breaker to hold it, I re did my table top phase converter I through together last night and added a capacitor and it will start on its own now with out aid of a rope or a pony motor. Now those big breakers are going to cost you some money, so if you know any industrial electricians maybe you can get some used stuff from them that will work, I got my info out of the 2008 ugly's pages 38-40 which comes out of the NEC. Again I urge you to find some body that can get you this stuff and if one of them can get you a 10 Hp idler motor then you can cut your breaker and wire cost in half and that is exactly what I would do, I would at least drop my idler to 15 hp, hope this helps some.
Wayne.
I am a little confused as to what your Converter motor is and what your Lathe size is, I believe your using a 20 HP for your rotary phase converter and your lathe is a 10 hp 3 phase motor, if that is the case then here are my recommendations, however you only nee a 10 HP converter motor, hp for hp. Anyway since you have a 20 hp 3 phase motor at 230 vac it draws 54 amps and your 10 hp lathe draws 28 amps which = 82 amps since your paralleling the single phase power to both the idler motor and your lathe you have to protect L1 and L2 from your panel with a 100 amp breaker, and really to be right according to the nec you need over a 200 amp breaker but if you start the idler then the lathe you should be okay with a 100 ampres you will need #3 wire. Now your wires going to your lathe you can easily get by with a #10, you should run three phase wires through a three phase breaker or fuses sized for your 10 hp motor and you should run that through a starter with overload protection, you will need 50 amp dual element time delay fuses or a 60 amp breaker, the 100 amp main WILL NOT HOLD if you try starting the phase converter and the lathe at the same time, you will probably have to go to a 175 amp breaker to do that, the motors both together will probably pull 80 amps or less but the initial start will spike WAYYYY up there and you will need enough breaker to hold it, I re did my table top phase converter I through together last night and added a capacitor and it will start on its own now with out aid of a rope or a pony motor. Now those big breakers are going to cost you some money, so if you know any industrial electricians maybe you can get some used stuff from them that will work, I got my info out of the 2008 ugly's pages 38-40 which comes out of the NEC. Again I urge you to find some body that can get you this stuff and if one of them can get you a 10 Hp idler motor then you can cut your breaker and wire cost in half and that is exactly what I would do, I would at least drop my idler to 15 hp, hope this helps some.
Wayne.
I read about these home-made phase converters/generators on the PracticalMachinist website, but when the time came to replace the crapped-out chicom 3hp single phase on my JET lathe, I went with a 3hp 3-phase moter, and a VFD to run it. Works great, and also gives me speed control.
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