question about starting three phase 25hp moter

I have a question about starting and running a 25 hp 3 phase motor.

I have a small shop beside my home and I have a 20 hp rotary phase converter. I know that this will not start the 25 hp motor on a bullard 42 inch vertical lathe that I have. Is there a way to bump this up without buying a larger phase converter? I also have a house and a mobile home next to my shop all separate sources of power yet comming from the same pole.

One person that I talked to said that I could run two 110 volt lines from my shop power and one 110 volt line from my house or mobile home to run this moter. I wasen't sure about this and wanted to confirm this answer with someone that knew a lot more then I do. Can this be done safely and will it run this motor without burning it up?

Start some other machines running off of the converter and let them idle this will add to the capacity of the converter as any three phase motors running on line act as converters also. Your 20 hp converter should start the lathe anyway if its not under load.
Pulling lines from the house and shop will do nothing to help you most likely don't have three phase on the property you may not even have it at the pole and you would need at least 240 or 480 volt not 110.

Jeff

Jeff

I tried doing what you said and had several machines in my shop running. If I added up the hp between all those machines and my 20 hp phase converter it was 43hp. This still is not enough to start this 25 hp moter It just kicked the breaker out on my phase converter.

Sorry I was not thinking it through when I posted, Your breaker and wiring was probably sized to the 20 hp converter. So I'm guessing your converter has a 100amp breaker not enough to start a 25hp motor, it could be possible to upgrade the breaker and wiring to the converter and use the some other equipment as idlers. One suggestion if I may, do you need 25hp? maybe finding a 15hp motor could be a less expensive approach than a electrical upgrade.
One other possible option maybe you could spin the lathe motor up with a pony motor then start you would not be able to run full load without tripping the breaker or overloads on the converter, but if you don't need to run full load it works if/when you are on the edge of being able to start, it just needs a little help we used to start a large blower for a paint booth that way.
Disclaimer none of the above are correct way of doing this I'm sure you already know this but can get you by at your own risk.

Jeff

I have some large centrifugal blowers I run from a phase converter. I have to use a belt tightener clutch deal to get the mass of weight moving and up to speed after the motor is running. Otherwise, the motor will take out fuses before it is up to speed. That is a 25 hp motor on a 100 amp breaker. Also, a 20 hp on 100 amp fuses. Is there a way to reduce the load on the motor at starting?

I could run two 110 volt lines from my shop power and one 110 volt line from my house or mobile home to run this moter.

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Three power lines do not make 3ph power, unless each is fed from one of three transformers mounted to the pole that feeds your shop.

Can this be done safely and will it run this motor without burning it up?

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That's easy to answer... NO and NO.

As others have said, you'll need either a smaller lathe motor, or a way to reduce inertial starting load, or a RPC of probably 50 hp total (which can be the 20 hp you have now plus another 30 hp idler) ... except you'll have to upgrade the shop wiring.

No free lunch in electricity, especially when the machines get big like your 42" VTL.

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Barry Milton

What size is the service feeding your shop?

Think about a reduced starting voltage set up. There is a electrical diagram posted in this forum. Do a search

CalG

I just wanted to thank all of you for your advice. I suppose that I will have to get a larger phase converter.

I would suggest just adding to your current phase converter. Adding a second idler motor would be your easiest fix. If you have a 3 phase panel using 3 phase breakers, it's really simple. There are a few postings on dual idler RPCs in the archives.

I was finally able to get my 25 hp moter running on what I have. I talked with a person who builds and sells phase converters. He told me to run 2 wires from a 100 amp breaker from my single phase directly to the machine with the 25hp moter and one comming from the leg that produces the third phase on my 20 hp rotary phase converter to the machine. I did this and hit the switch .this did not work. I went to the starter and pushed it in manually which started the moter. At first it was to much and kicked my main breaker out. I let things cool off and tried again pushing the starter in manually and then letting off for a few times untill the moter got up to speed. I do not like to start a moter this way because I feel that it is hard on it and I could possibly burn it up.
Everything seems to run ok. Nothing seems to get hot and the moter runs quietly. I sat a wooden stump on my 42 inch bullard spiral drive vtl and gave it a test run.
The only problem that I had was when first trying to start this machine with the push button switch which made it feel like the machine was jumping all over the place. Now the push button does nothing at all and I have to keep a piece of wood wedged in the electric box holding the starter up. As you can see I have something else to fix. Perhaps one of you can tell me what I need to fix in this electrical box with my starter for the 25hp moter on the bullard. I have checked the wireing and cleaned the contacts off in the push button switch but this has not changed anything. There is a small coil undernieth the starter that I suspect, but when it comes to this kind of stuff I do not know what I am doing or what does what.
At least for now this may get me by so I can do a job on this machine for a customer. Later I want to put a phase converter on this machine from the company who told me how to at least do this much.

adding a input choke in series with the motor will reduce the inrush too; they are typically sold as 3 & 5% impedance reactors. 25hp 3ph unit guess around $ 150. we sell them and can quote if u want (email us!). meanwhile check out concept here:

MTE Corporation - Line/Load Reactors, Line Reactors, Load Reactors- MTE Corporation

Larger motors often have all the coil leads brought out separately. This allows connecting in Y for starting and delta for running. Connecting in Y amounts to dividing the voltage by 1.732. I know nothing about your motor and 25 hp may not be large enough for that treatment, but it is worth looking into because it would make your life a lot easier.

Bill

9100 said:

Larger motors often have all the coil leads brought out separately. This allows connecting in Y for starting and delta for running. Connecting in Y amounts to dividing the voltage by 1.732. I know nothing about your motor and 25 hp may not be large enough for that treatment, but it is worth looking into because it would make your life a lot easier.

Bill

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FWIW, I have a 15HP 3ph motor with seperate leads like that: Y for starting and delta for run...

Years ago before I built my 60 HP converter, I had trouble starting the 25HP motor on my 4 1/2" boring mill with my 25 HP phase converter.

The cold inrush trying to bring this motor up to speed is what kills it. My main vonverter had a belt driven single phase motor to help bring it up to speed, so I figured why not do the saem on this machine.

I wired it into my phase converter as normal, and added a single phase motor to help bring the big motor on the boring mill up to speed and then closed the contactor. It starts just fine and had no issues unless I took and insanely heavy cut and let the RPM's start to fall off.

Stuart Caruk said:

Years ago before I built my 60 HP converter, I had trouble starting the 25HP motor on my 4 1/2" boring mill with my 25 HP phase converter.

The cold inrush trying to bring this motor up to speed is what kills it. My main vonverter had a belt driven single phase motor to help bring it up to speed, so I figured why not do the saem on this machine.

I wired it into my phase converter as normal, and added a single phase motor to help bring the big motor on the boring mill up to speed and then closed the contactor. It starts just fine and had no issues unless I took and insanely heavy cut and let the RPM's start to fall off.

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Just out of curiosity, if you have that much horsepower, why can't you get three phase? I did a couple of dances with the local power co and finally blackmailed them into giving them the line with a 35 hp motor generator. Their rules were 20 total hp and at least one 7 1/2 or larger motor.

Bill

9100 said:

Just out of curiosity, if you have that much horsepower, why can't you get three phase? I did a couple of dances with the local power co and finally blackmailed them into giving them the line with a 35 hp motor generator. Their rules were 20 total hp and at least one 7 1/2 or larger motor.

Bill

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Bill, your PM box is full. I have some questions regarding how this worked with the local power co in east central MO.

Thanks!

9100 said:

Just out of curiosity, if you have that much horsepower, why can't you get three phase? I did a couple of dances with the local power co and finally blackmailed them into giving them the line with a 35 hp motor generator. Their rules were 20 total hp and at least one 7 1/2 or larger motor.

Bill

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I tried getting 3ph at Tx shop years ago, power co did not care what I wanted to run, best they could do was offer a 400 amp single phase service. If I absolutely needed 3ph, they could do it, if I was willing to cough up 20K. Closest place with 3ph is a mile away.

dalmatiangirl61 said:

I tried getting 3ph at Tx shop years ago, power co did not care what I wanted to run, best they could do was offer a 400 amp single phase service. If I absolutely needed 3ph, they could do it, if I was willing to cough up 20K. Closest place with 3ph is a mile away.

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Thats about what ive been told to expect for pricing, and i just need to set one pole. The power is literally right on the other side of a state hwy.

9100 said:

Just out of curiosity, if you have that much horsepower, why can't you get three phase? I did a couple of dances with the local power co and finally blackmailed them into giving them the line with a 35 hp motor generator. Their rules were 20 total hp and at least one 7 1/2 or larger motor.

Bill

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I'd really appreciate your help. If you are listening, dinner of your choice is on me.