I haven't done it. A friend is an electrician & self taught machinist. He uses a rope around the shaft to start a three phase motor on single phase. This is pretty lame power source. He then switches other motors on using the first as power supply. A bare minimum of three three phase motors must be run idling to supply a third phase & ultimately supply the lathe, or mill you hope to supply. He estimated the motor doing the work to produce 1/2 the torque & horsepower it should.
It causes several problems in the loaded motor, is not a perfect system.
An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.
I’ve seen motors that can be wired for 460/230 three phase
or 230 single phase. Not sure if stator has anything unique
about it allowing it to be used on single phase.
When used on 230 single phase,start and run capacitors
and voltage sensing relay are needed and HP of motor is derated.
Never seen such a motor, nor can I wrap my head around the concept. Motors need additional windings to be used on either phase. I can't figure where there would be room inside the motor frame for a second set of windings. Wouldn't be very efficient.
An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.
Back to the basic question can it run off a add a phase or rotary phase maybe if you have a big enough one which goes back to the feasibility it probably runs on 35 to 40 amps so gonna take 60 amps to start it ! So for a short duration you need a lot of amps
can you run it dropping one leg probably but your going to be derated!
Can you add capacitors and etc , etc ,etc , yes maybe but the average guy at home isn’t going to do that the feasibility of it is not there
Feasibility , reliability and the ability to do some of that restricts the average user
I also will bring up one point that all of that brings up questions if the insurance man comes and looks things over
If it was feasible everyone would do it because there are a lot of those old motor Generators around they wouldn’t be going to the junkyard
My point is we shouldn’t be telling people it can be done if you don’t have one sitting in your shop working telling somebody who is new at this that it can be done in theory isn’t the best practice .
It just how motors work.
Most do not know single phase capacitor start and or run motors are 2 phase motors.
The capacitor shifts the phase.
Dave
I think you are a little confused. The start winding is very different in induction from the run. It is this fact cures the indecision of which direction to turn. The large induction pulls voltage timing out of alignment with current peak. Energy is wasted in the form of extra heat. Each capacitor serves the same purpose, correcting the timing so voltage & current peak simultaneously. Start winding for torque, run winding for efficiency & motor life.
An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.
You using the capacitors to shift the phase. The start capacitor is only for starting. The oil capacitor is for running to keep power up.
Using capacitors is about 99% efficient and if all you have single phase it works great.
If you three phase use it.
Dave
Originally Posted by Willie B
I think you are a little confused. The start winding is very different in induction from the run. It is this fact cures the indecision of which direction to turn. The large induction pulls voltage timing out of alignment with current peak. Energy is wasted in the form of extra heat. Each capacitor serves the same purpose, correcting the timing so voltage & current peak simultaneously. Start winding for torque, run winding for efficiency & motor life.
You using the capacitors to shift the phase. The start capacitor is only for starting. The oil capacitor is for running to keep power up.
Using capacitors is about 99% efficient and if all you have single phase it works great.
If you three phase use it.
Dave
Thank you. I will go on using three phase motors on three phase power sources, or in special circumstances, I'll use a phase convertor. In no circumstance will I connect a three phase motor doing a job to a single phase power source.
I commend you for having a secret I never learned in 53 years in the trade. I sure wish you would share your secret.
An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.
I looked while I was at the shop today I have a old Airco { Hornet I think } motor generator it takes 32 amps to run it so 50 amps to start it and it runs at 3500 rpm so like sberry said earlier maybe for a hobby guy the biggest problem with the motor generator is they are very noisy and they only have one purpose and that is to stick weld and they are great to air arc with
You using the capacitors to shift the phase. The start capacitor is only for starting. The oil capacitor is for running to keep power up.
Using capacitors is about 99% efficient and if all you have single phase it works great.
If you three phase use it.
Dave
I have not been able to achieve this efficiency with capacitors. No where close. But it does work
I built a 10HP rotory phase converter a long time ago and its not very good, it has a capacitor start
, you switch it on and hold down a button until the 10hp idol motor is at speed, I was running a 2.2KW motor but it would bog down and stall some times.
Here’s one configuration I found yesterday for running a
three phase motor on single phase. No capacitors on this
one.
Not exactly sure how that start relay works. I’m thinking
it closes on high current, making the two “U” windings
only for starting. It must be considerably less efficient
than running it on three phase. I know HP is derated
for single phase.
Miller a/c-d/c Thunderbolt XL
Millermatic 180
Purox O/A
Smith Littletorch O/A
Hobart Champion Elite
I agree with sberry why does everyone want to reinvent the welding machine ?
All of you that have never run a motor generator go run one somewhere before you gobble up a bunch of junk for something that might not work anyway ! Go buy a welder you can plug into the wall and use
I agree with sberry why does everyone want to reinvent the welding machine ?
All of you that have never run a motor generator go run one somewhere before you gobble up a bunch of junk for something that might not work anyway ! Go buy a welder you can plug into the wall and use
They should have to listen to one howl too. I've been in a shop with a couple of SAE 400's and they were more than loud.
Everyone stressed to me they are good, its like a locally made Ac arc welder with its wooden transformer frame, I thought it would be horrible but it welds really well
Those old "bullet" welders run beautifully, I've used them before. Also an older Hobart 600 amp torpedo. Both machines were loud, much like the turbine whine of an airplane spooling up. I would take one if it was very cheap or even free, but I sure don't have the power to run it. Never seen one that would run on less than 50A of 3-phase. Instead I do have a lathe and the know-how... to hook it up to an engine. It would probably be quieter, and give another 50+ years of fantastically smooth DC. IRC Lincoln was marketing theirs at high-end TIG shops back in "the day".
They should have to listen to one howl too. I've be.
especially when u had much too drink the night before. my 250 is quiter than most, i havent had the power to run it in ages. some are noisier than others, maybe bearings or something arent as tight anymore
Originally Posted by SOHC
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