3ph Generator head for Phase Converter

wetoddid · Jul 28, 2014

Gents,

I have just procured a 3 phase Stamford 480 generator head. It is useless to me the way it sits, and I didn't plan on attaching an engine to it. Is it possible to use a single phase motor to swing this generator head to create 480V 3ph where there is none? I realize that I am unlikely to find a single phase motor big enough to drive it to its capacity, but with a derated motor, it seems plausible. I apologize if this has been discussed before, I did a search and didn't find anything.

Kevin

DaveKamp · Jul 28, 2014

wetoddid said:
Gents,

I have just procured a 3 phase Stamford 480 generator head. It is useless to me the way it sits, and I didn't plan on attaching an engine to it. Is it possible to use a single phase motor to swing this generator head to create 480V 3ph where there is none? I realize that I am unlikely to find a single phase motor big enough to drive it to its capacity, but with a derated motor, it seems plausible. I apologize if this has been discussed before, I did a search and didn't find anything.

Kevin

Theoretically, yes, it is certainly possible, and plausible. It would not be extremely efficient, and in end result, it may not work very well, but it'd work.

Reason why it wouldn't be extremely efficient, is because it requires a certain amount of input power just to excite the field, and depending on how BIG the generator head is, that excitation load may be a big enough chunk of your input motor's budget to take away from effectiveness in your 480v 3ph output.

How big is the Stamford (in KW or KVA?). Is there a tag that identifies the exciter's output?

For example, my 35kva Kato's exciter generates around 1100w just for excitation current... and it doesn't matter wether it's running at no load, or full load, the excitation demand is there... so the engine is putting (1100/742=) ~1.5hp just to spin the exciter... and then you're spinning the generator's cooling fan, which was designed and sized to move enough airflow to cool the full load continuous-duty rating of the machine (and it's presenting that much static drag even if the generator isn't under a high load)...

So what's the Stamford's ratings, how big a motor were you planning on using to drive it, and what were you planning on powering in terms of a load?

wetoddid · Jul 29, 2014

The head states 40 volts x 2 amps so 800 watts. There might be hope if that is the major variable. It's a 28.5 KVA amp 480 head. I'm not too familiar with what large capacity single phase motors there are out there but seems like it will require a big one to make it worth your while.

jakefreese · Jul 29, 2014

One thing that will be an issue driving that generator head with a electric motor is you will not be able to make 60hz out of it due to motor slip from the prime mover. Best you would see would be about 58hz. Synchronous motor would be the only way to make 60hz. All the voltage regulation and frequency control becomes more challenging as you prime mover is fixed, you don't have a gas pedal to adjust for load changes.

wetoddid · Jul 29, 2014

My power requirements are nil at the moment, as I'm just starting to build my shop...at a glacial pace. My main goal was to not have to pass on 440 machines due to lack of power available. I can only assume that my requirements will not surpass 10 HP at any time. I understand this generator head is overkill, but my other hobby is tinkering.

A cursory search online finds plenty of 10HP single phase motors, but I am unable to find anything bigger. I have 200A 1ph service available.

The more I think about it, the more I realize I need to bone up on my electrical knowledge, or lack thereof. Ugly's book is now in the Amazon cart :eek:

Screen Shot 2014-07-29 at 6.23.36 AM.jpg

wetoddid · Jul 29, 2014

jakefreese said:
One thing that will be an issue driving that generator head with a electric motor is you will not be able to make 60hz out of it due to motor slip from the prime mover. Best you would see would be about 58hz. Synchronous motor would be the only way to make 60hz. All the voltage regulation and frequency control becomes more challenging as you prime mover is fixed, you don't have a gas pedal to adjust for load changes.

Would the same scenario be created if one was using a rotary phase converter? The only reason why I would pursue this was to alleviate slip from one leg of the system. Would it be correct to assume that slip on all phases is better than slip on one?

I guess the better question is: Can this system be made to work any better than a "standard" RPC with step up transformers and capacitors all over the place? Money is not the issue here as the generator head fell in my lap.

9100 · Jul 29, 2014

You possibly could use it as an RPC with a transformer to feed it 480 volt single phase. It would need a way to get up to near synchronous speed. You might be able to short the armature winding to make it act like a regular induction motor, then apply a DC voltage to lock it in. You could also use a pony motor. I asked about doing that in this thread, but didn't really get answer.

http://www.practicalmachinist.com/v...ry-idler-motor-really-different-motor-258055/

If you drove it with a single phase motor as a motor-generator, you could belt drive with pulleys adjusted to make up for the slip in the drive motor. If you are sufficiently adventurous, you could make a Reeves drive with a servo system to adjust the ration for varying loads, but I doubt that you want to go to that much trouble. It probably wouldn't work that well, anyway.

Bill

Vernon Tuck · Jul 29, 2014

DaveKamp said:
Theoretically, yes, it is certainly possible, and plausible. It would not be extremely efficient, and in end result, it may not work very well, but it'd work.

Reason why it wouldn't be extremely efficient, is because it requires a certain amount of input power just to excite the field, and depending on how BIG the generator head is, that excitation load may be a big enough chunk of your input motor's budget to take away from effectiveness in your 480v 3ph output.

How big is the Stamford (in KW or KVA?). Is there a tag that identifies the exciter's output?

For example, my 35kva Kato's exciter generates around 1100w just for excitation current... and it doesn't matter wether it's running at no load, or full load, the excitation demand is there... so the engine is putting (1100/742=) ~1.5hp just to spin the exciter... and then you're spinning the generator's cooling fan, which was designed and sized to move enough airflow to cool the full load continuous-duty rating of the machine (and it's presenting that much static drag even if the generator isn't under a high load)...

So what's the Stamford's ratings, how big a motor were you planning on using to drive it, and what were you planning on powering in terms of a load?

Yet another example of physics pissing on our plans. When will this tyrrany end?

;o) VT

Tony Quiring · Jul 29, 2014

Called a dynamotor and was very common.

But lots of work and losses.

Most motors have multi voltage motors so rewire most of the time is good.

motion guru · Jul 29, 2014

15HP single phase motors are about as big as I have ever seen - Baldor makes one

peterh5322 · Jul 29, 2014

"Best you would see would be about 58hz. Synchronous motor would be the only way to make 60hz."

So, you drive the generator belted, with a 58:60 step-up, which is 1.03 to 1, or so, using a Browning (or equal) adjustable diameter sheave on the induction motor end.

jakefreese · Jul 29, 2014

peterh5322 said:
"Best you would see would be about 58hz. Synchronous motor would be the only way to make 60hz."

So, you drive the generator belted, with a 58:60 step-up, which is 1.03 to 1, or so, using a Browning (or equal) adjustable diameter sheave on the induction motor end.

That would work but slip will vary with load. You still have the problem of no gas pedal on your prime mover.

As for using it as part of a RPC will less than ideal as the design is essentially opposite of a motor in regards to current is opposite of the two. With proper Dee rating I could see it being done. But you could probably sell it and buy the parts for an RPC that you would have a better system in the end.

DaveKamp · Jul 29, 2014

Vernon Tuck said:
Yet another example of physics pissing on our plans. When will this tyrrany end?

;o) VT

--- !!!! STOP PLATE TECTONICS !!!!

and...

Law of man says Jaywalking sometimes gets you a $20 dollar citation that you MAY be able to contest and beat.

Law of nature says Jaywalking gets you the death sentence with trial on-the-spot, where jury and executioner are a garbage truck.

DaveKamp · Jul 29, 2014

peterh5322 said:
"Best you would see would be about 58hz. Synchronous motor would be the only way to make 60hz."

So, you drive the generator belted, with a 58:60 step-up, which is 1.03 to 1, or so, using a Browning (or equal) adjustable diameter sheave on the induction motor end.

Or same size belt pulleys, and apply several passes of electrical tape to the motor-side sheave groove... (banjos playing in the background)

JST · Jul 29, 2014

These things are indeed common, or were... In the form of the "dynamotor", they were a one-piece, and you would have a two-piece, which will probably work BETTER. Each part is better optimized.... the real dynamotor used one rotor for everything.

At the old work, we had a set made JUST like you suggest, but belted to provide 50Hz output at 10 kVA. Worked fine, and slip was never an issue of consequence.... it might at full load have been a 2 Hz change.. They can be bought from several companies even now. Most use a synchronous motor drive, but I know at least one motor repair guy who had a 7.5 or so HP setup that he used for testing, single-phase induction to 3 phase genny. He actually direct-coupled his, but I think I would belt-up for slip.

I know you will get the finest 3 phase balance you can expect from a setup like that..... Far better than an RPC.

Garwood · Jul 30, 2014

I bought a commercially made one of these off craigslist, it was even a Stamford head.

It had a 10HP Baldor single phase motor belted to the generator. I was told it was originally sold for running 50HZ radio equipment on 60HZ power. I switched it up to run 60 HZ and it worked fine for running small machinery.

I ended up switching it back to 50HZ speed and leasing it to a company that sold electronic equipment to Europe and had to load to test the equipment. They ended up getting more orders and made me an offer I couldn't refuse to buy it outright.

I would save the coin it would cost to make one and buy a Phase Perfect if I wanted clean power.

nsaqam · Aug 5, 2014

As Tony said above, an easier, cheaper approach to using 460v machinery might be to rewire the motors and change a few overload heaters to accommodate the 230v 3ph you may already have.

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