I don't see a off topic board, am I going to get spanked??

[bozo699]

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.

Flatlander,
Yes these are very nice, I put one on a gunsmith friend of mines new to him but very old DC lathe, I removed the DC motor and switch gear and installed a new 7.5 HP 3 phase motor and a 10 hp single phase 220vac input 220 three phase output VFD, works like a charm
Wayne.

 

[LorenC]

I guess that's where part of my request for an engineer comes in bozo699.The idler motor won't be at fl amps, so would it really need to be sized for that? And remember there won't be the inrush of amps to start the 20hp since the small single will start that, AND, the loads only start after the converter is up and running.
I have a good chance of getting a higher hp equipment later so that's why I opted for the 20hp. I was looking for a 15hp but the 20 was too good to pass up.

 

[TheOtherZilla]

According to the NEC you will need to size according to the nameplate data. I haven't been to work for the last week so I do not have my code book handy to get specifics on motor hook ups.. I am talking about the starting motor.. If you are going to use a 20hp 220 single phase motor you will need to size things accordingly.

 

[bozo699]

According to the NEC you will need to size according to the nameplate data. I haven't been to work for the last week so I do not have my code book handy to get specifics on motor hook ups.. I am talking about the starting motor.. If you are going to use a 20hp 220 single phase motor you will need to size things accordingly.

Zilla,
on this setup the single phase leads are hooked to both the starter motor and the Lathe, there paralleled off each other there fore share the load on L1 and L2, I know I already set one up in my electric shop on my lunch break and took amp readings, I think there is a section in the code book just past motors on Rotary phase converters, Article 455 I think, now you might be right, there may be some rule on the largest motor or something but the amp meter doesn't lie.

Loren,
Your right your inrush wouldn't be as high when starting with a pony motor starting your idler motor, however motores are designed to run at full load amps so don't think just because your 20 hp idler is just idling along running the 10 horse that it's not pulling it's 54 amps because it will be or close to it.

A side note I read somewhere as long as your idler motor has a S.F (service factor) of 1.15 or 1.25 you can run horse for horse or close to it.
Wayne.

 

[TheOtherZilla]

Bozo, check the links I posted. I remember one of them mentioning the service factor..

 

[LorenC]

Oh by the way zilla, those two links were quite beyond me. I just looked at the pictures. :-\

So bozo, a motor doing no work draws the same amps as one loaded to the max? How can that be?

hth do I get the posting window to be normal page size? it's giant wide, like 3 pages wide. I hit the wrong button somewhere sometime...

 

[bozo699]

Bozo, check the links I posted. I remember one of them mentioning the service factor..

Zilla,
I am really restricted what I can view on the internet at work so I never clicked on the links you provided but I am at home now, really a useful calculator, I have saved it in my favorites, Thank you
Of course when figuring OCPD for a motor you have to go off the table in 430 for the device used, I am only going off memory because I loaned my code books out to a kid going to school, where I work I rarely use a code book, but say a instantaneous breaker you multiply the f/l name plate amps X 800% a inverse time breaker by 250% a time delayed fuse X 175% and one other fuse I forget the multiplication factor. But using the calculator provided I came up with the same answer I gave.

Loren,
Like I said I rarely use a code book, I work in a ammunition's plant and if I need power I always oversize as they change there minds daily on there needs, but I have found the guy's at the local supply houses know more then most engineers and inspectors so if all else fails go the a professional electrical supply house (NOT HOME DEPOT) and tell them what your doing and they will give the information needed.

The one thing I think is being overlooked is the fact were using single phase power for both motors used, or for that matter if we hooked up 10 separate 3 phase motors they all will be pulling off our single phase supply breaker, I may be wrong but I think your all thinking that you supply the 3 phase converter motor and it does the rest for you, but that's not true it's only supplying the third leg, for almost true 3 phase power the single phase wires parallel off the converter motor to the three phase motor or motors being used in this case the 10 hp lathe, so when figuring the wire size from your home 240v panel to your 20 hp rotary phase converter and all motors beyond that from the same single phase line has to be taken into account for OCPD and wire size! Individual motor starters and thermal protection shall be separately sized for each motor used. I may be wrong on this but it is how I have been taught or my interpretation of it, I could easily be wrong as I have been many times and there are many exceptions and rules in the NEC. This much I do know when your all done stick a amp clamp at the end of the line, by your explanation that will be the motor leads to your 10 hp lathe motor, the two single phase lines going to it will give you total amps being used while running, best of luck to you on this build.

P.S when I hooked a capacitor in line the three phase motor started easily on it's own and you would not have to go to the trouble of perfectly aligning your 110v starting motor to your converter and make certain its going in the right direction, but doing it your way will cut down on the inrush current of the initial starting process, just food for thought.
Wayne.

 

[bozo699]

Oh by the way zilla, those two links were quite beyond me. I just looked at the pictures. :-\

So bozo, a motor doing no work draws the same amps as one loaded to the max? How can that be?

hth do I get the posting window to be normal page size? it's giant wide, like 3 pages wide. I hit the wrong button somewhere sometime...

Loren,
Yes the motor amperage will increase some when a load is introduced to it, but it will run idle close to the name plate rating when everything is running efficiently and remember a true three phase motor has three poles 120 degrees apart and a single phase motor has two poles 180 degrees apart or 4 poles 90 degrees apart and then with a home made converter your trying to stick the third led that's at 120 degrees in there somewhere, so in laymen terms it is unbalanced,...runs but is not at 100% efficient.

As far as the wide posting page, the site has done some recent upgrades, try reloading your page with the refresh button, if your problem still persists try looking at this link.
Wayne.

http://forum.accurateshooter.com/index.php/topic,3777308.msg36016749.html#msg36016749

 

[LorenC]

Bozo, check the links I posted. I remember one of them mentioning the service factor..

Zilla,
I am really restricted what I can view on the internet at work so I never clicked on the links you provided but I am at home now, really a useful calculator, I have saved it in my favorites, Thank you
Of course when figuring OCPD for a motor you have to go off the table in 430 for the device used, I am only going off memory because I loaned my code books out to a kid going to school, where I work I rarely use a code book, but say a instantaneous breaker you multiply the f/l name plate amps X 800% a inverse time breaker by 250% a time delayed fuse X 175% and one other fuse I forget the multiplication factor. But using the calculator provided I came up with the same answer I gave.

Loren,
Like I said I rarely use a code book, I work in a ammunition's plant and if I need power I always oversize as they change there minds daily on there needs, but I have found the guy's at the local supply houses know more then most engineers and inspectors so if all else fails go the a professional electrical supply house (NOT HOME DEPOT) and tell them what your doing and they will give the information needed.
The one thing I think is being overlooked is the fact were using single phase power for both motors used, or for that matter if we hooked up 10 separate 3 phase motors they all will be pulling off our single phase supply breaker, I may be wrong but I think your all thinking that you supply the 3 phase converter motor and it does the rest for you, but that's not true it's only supplying the third leg, for almost true 3 phase power the single phase wires parallel off the converter motor to the three phase motor or motors being used in this case the 10 hp lathe, so when figuring the wire size from your home 240v panel to your 20 hp rotary phase converter and all motors beyond that from the same single phase line has to be taken into account for OCPD and wire size! Individual motor starters and thermal protection shall be separately sized for each motor used. I may be wrong on this but it is how I have been taught or my interpretation of it, I could easily be wrong as I have been many times and there are many exceptions and rules in the NEC. This much I do know when your all done stick a amp clamp at the end of the line, by your explanation that will be the motor leads to your 10 hp lathe motor, the two single phase lines going to it will give you total amps being used while running, best of luck to you on this build.

P.S when I hooked a capacitor in line the three phase motor started easily on it's own and you would not have to go to the trouble of perfectly aligning your 110v starting motor to your converter and make certain its going in the right direction, but doing it your way will cut down on the inrush current of the initial starting process, just food for thought.
Wayne.

Nope, fully aware of that.

 

[LorenC]

Ok, well I have a bunch of #2 thhn, looks like I'll work that into the system.

My bold highlight turned into bold type in that last post too, sorry for the "shout".

 

[bozo699]

Loren,
I am sorry for being so long winded I am only trying to help. I actually have learned quite a bit just setting up my own phase converter at work, it was a fun project and I have enjoyed this thread, I hope you post your end results and any failures and what worked best, again I wasn't trying to imply you were stupid or Zilla either, Because of your thread I built a working unit and learned a couple of things and it appeared to me you were thinking only the converter was pulling from the single phase breaker and I wanted that to be perfectly clear that it wasn't so I am glad that your,....fully aware of that,...and still wish you the best of luck.
Wayne.

P.S on smaller motors you will notice with a amp clamp when running idle there close to the name plate rating and the bigger you go the less that seems to be true, I have worked on many motors as big as 500 hp and a lot of 50 too 200 hp motors and they seem to idle way below name plate while a 1 or 2 hp motor will be close to name plate while idling, I didn't get this out of a book, just 20 years working in a sawmill taking readings of many different motors.