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Author Topic: 3 phase converters  (Read 7859 times)

gpkull

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3 phase converters
« on: November 01, 2006, 02:53:11 AM »
dont want to start ww3 here but am needing 3 phase for epuip and have to convert or generate as the local utility would want the 4th mortgage. have worked with it for years but all i knew was 3 hot legs is 3 phase. well good and true but i got more interested when i got a lathe w/ a 2 speed motor 3 phase of course. the big Q is rotary vs static. i understand to much to get into trouble bet not enough to help out. this is it correct me if i have  not understood correctly. here goes.  from the static converters so far that i have have seen (motor start relay) and a couple caps and such you de rate your load 1/3 giving you 4 hp from a 6 hp motor. with rotary you use a 3phase motor higher in hp + caps than your load. the prob here is that you are generating a 3rd leg witch has to stay in phase with what you started with. i do understand that a 3 phase motor is basic 3 motors in one. the catch is with any 3 phase converted or not if the voltage differs the motor life is directly realted. ,got all the goods just didnt want to run any chitlins out the drive ways on beggers wein. the girl friend wanted piece in the hood  i told her this is the "BLUE SMOKE TEST" she said u better......    got to  if there is a better im shure yual will post the 7.5 hp is US 1740 9wire from best guess 69-72 the lathe is zubal 70-75 tks all

Jim Mc

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Re: 3 phase converters
« Reply #1 on: November 01, 2006, 04:18:26 AM »
... i do understand that a 3 phase motor is basic 3 motors in one. the catch is with any 3 phase converted or not if the voltage differs the motor life is directly realted. ,got all the goods just didnt want to run any chitlins out the drive ways on beggers wein. the girl friend wanted piece in the hood  i told her this is the "BLUE SMOKE TEST" she said u better......    got to  if there is a better im shure yual will post the 7.5 hp is US 1740 9wire from best guess 69-72 the lathe is zubal 70-75 tks all

Holy Cow!  Is there a question in here somewhere?  If I knew what the heck you were asking, I could help - I have a fair amount of phase converter experience...

Doug

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Re: 3 phase converters
« Reply #2 on: November 01, 2006, 04:40:14 AM »
Yes thats kind of all over the place....

I could help you wire up an induction converter from a free spining induction motor if that what you want.

Doug

rleonard

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Re: 3 phase converters
« Reply #3 on: November 01, 2006, 03:27:33 PM »
I was following along until he got to the chitlins and the girlfriend on the hood? 

I hae been running on rotary converters that I built for over 20 years.  As far as I can tell they work.  I start my 15HP IR air compressor too!  I did have to pull some rabbits out of the hat to make it work.

Bob
Faster - Better - Cheaper  You can have any two, but not all three

gpkull

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Re: 3 phase converters
« Reply #4 on: November 02, 2006, 12:11:21 AM »
there is a question static vs rotary.  the kids were coming over for the candy thing as holloween was last night and if i blew something up the kids would go runing and of course the next is not hard to figure out. i have a 7.5hp motor thats good. the lathe motor is rated 3 hp i believe.  i have a schematic but dont know how reliable it is. it  uses 2 270-324mfd caps in parallel off one of the 2 original legs. that line is energized when the 2 original ones are and then the button is released. does this sound familair?   any help will do

Doug

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Re: 3 phase converters
« Reply #5 on: November 02, 2006, 01:30:39 AM »
Yes I think I understand what your saying....

You want to use two Capacitors for starting and the others for running the converter. Yes some people do it this way but I've also seen timer and AC unit starters do the same.

If you could post a picture of what you want to wire and how your thinking of doing it and I'll see if there is any thoughts I can offer.

Doug

mobile_bob

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Re: 3 phase converters
« Reply #6 on: November 02, 2006, 02:49:15 AM »
you might also jump over to

practicalmachinist.com

they have a section on their forum with everything phase converter, variable freq drives and such.

the coolest one i have seen used a briggs and stratton recoil start adapted to the 3 phase motor, you just flip the mag starter in and connect 2 legs of single phase and give it a yank and off it run's, generating the 3 phase. pretty darn cool, and simple to set up.

also there are those that flip on the power to the motor/converter and kick the pulley with their boot to get it started and off it goes, not recommended but it works evidently.

bob g
otherpower.com, microcogen.info, practicalmachinist.com
(useful forums), utterpower.com for all sorts of diy info

Doug

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Re: 3 phase converters
« Reply #7 on: November 02, 2006, 11:00:47 PM »
You can make them self start Bob, and the addition of extra ballance caps around the shop on other loads will help to keep the voltage on the induced third phase. The more motor running especialy with high intertia loads the better for adding stability and starting current.

Doug

gpkull

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Re: 3 phase converters
« Reply #8 on: November 03, 2006, 03:34:14 AM »
doug  got ya and will try to figure out how to post the schematic that i have . i do understand that the balance of the three legs will decide how long your motor will last. i do think rotary or inductive is the way to go here. bob will check that out also. either way got to get something going need reliable 3ph. the lathe  i have does not run the motor cont. so everytime i want the chuck to turn start the motor do your biz to stop the chuck hit foot bar this drops the contactor.
« Last Edit: November 04, 2006, 11:05:46 PM by gpkull »

gpkull

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Re: 3 phase converters
« Reply #9 on: November 05, 2006, 04:06:13 AM »
still trying to get the schemeatic up. did generate 3 phase but very unhappy with results. the 3 legs feeding the lathe were L1 8amps L2 2amps L3 9amps. just the rotary on the primary side is 15 amps then the lathe with no work is 25 amps prim. the lines are very unbalanced dont know why? a friend said try loading the lathe and see if the legs dont balance out if it does thats no good for a "spring cut" we call that a very light trim. also my inverter motor did not growel before the lathe was energized. have ran into cases were the inverter motor made loud noise until load motor was fired up. the line voltage is 125 a side and have no problem with voltage drop before or after the breakers.

gpkull

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Re: 3 phase converters
« Reply #10 on: November 05, 2006, 04:49:07 AM »
doug odd enough the induced leg is the the leg drawing 2 amps. i have tagged them all. as common w/ 3 phase there is usually either a high or low leg to nuetral and i lucked out with the first go round that my transformer was cleared. there was no gue or smell before  the chuck went into action. yes i did check before as the  4th of july is still a ways away. dont want sparks and cabooms before there time

Doug

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Re: 3 phase converters
« Reply #11 on: November 05, 2006, 04:50:53 AM »
Your not going to get a ballanced three phase out of this rig....

Try adding a little more capacitance to the Lathe.

Do you have any other 3 phase loads you can run with the Lathe?
All lightly loaded motors will contribute some current to fatten up the induced phase.

There are things that can be done like adding an auto transformer to the induced phase But I think you may be able to make some improvements with capacitors alone.

Doug

I need a print of what you built, to see if there;s room for improvement

gpkull

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Re: 3 phase converters
« Reply #12 on: November 05, 2006, 10:14:58 PM »
i just havent managed a print yet but the design is easy. you use caps to start the rotary then drop them when it comes up to speed. the caps are on one leg only when you drop them that leg becomes the third. i have no caps in use after the rotary is up to speed. the only other 3 phase motor i have is a 3/4 hp there is a set up i found to balance the voltage but its 190.00 and no garantee to cure my problem. if the voltage can be corrected with caps will this be constant as the load increases?

Doug

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Re: 3 phase converters
« Reply #13 on: November 06, 2006, 12:03:40 AM »
Try and use some oil caps and leave them in the circut after the converter is running...

This will help.

Doug

gpkull

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Re: 3 phase converters
« Reply #14 on: November 06, 2006, 12:45:48 AM »
doug what uf do you recommend starting with?  do i connect from the generated leg to each of others?  do you think this is the balancing act that i ran into for the pricy unit i spoke of earlier?