3 phase motor on 220 volts single phase- % horsepower decrease?

[slowzuki]

I bit the bullet and got a single phase 10 hp for my mill. If I did it again, I would have put 2x 5 hp motors instead. Cheaper, easier to start (lower peak inrush). The 2.5 hp carriage advance motor I have is 3 phase but I put an ebay vfd on it. Don't need a single phase rated inverter, you can just derate them.

 

[LD1]

I am not sure, but I think he only means screwing up stuff you are feeding with the phase converter???

I agree that the best "low cost" solution would be a rotary.

A 3 phase motor will "actually" run on 240v, it just wont start.

A rotary converter uses capacitors to "start" the motor, and then it runs on 240 single phase through two of the three sets of windings in the 3PH motor. Induction causes power to be created and sent out that 3rd leg.

Due to the inefficiency of that process, the converter is usually upsized one. So if you want to power a 7.5HP motor with a rotary, the base motor for the rotart should be a 10HP.

And while they are close, the voltage on the 3 legs (two from your 240 supply, and the one created) are not exactally equal. This will screw with electronics like lathes and mills that have certain features.

But for what you want, a rotary should work just fine:thumbsup:

 

[LD1]

I bit the bullet and got a single phase 10 hp for my mill. If I did it again, I would have put 2x 5 hp motors instead. Cheaper, easier to start (lower peak inrush). The 2.5 hp carriage advance motor I have is 3 phase but I put an ebay vfd on it. Don't need a single phase rated inverter, you can just derate them.

I was replying while you must have been typing that:confused2:

That should work just fine:thumbsup:

 

[zzvyb6]

My 50kw Winpower pto generator has 3 phase taps on it. It was only $900. You have a tractor, eh?

What about converting the bandsaw to tractor powered by rigging up a belt or chain drive to the pto directly? There is a sawmill that I go to a few miles up the road that uses a JD 4430 to drive a huge circular sawmill blade with its pto output. That baby cuts thru 30" oak and hickory logs without a single smoke puff from the governor (or the Attorney General).

 

[Craig Clayton]

I wanted to give you a quick wiki about VFD,s. This teck is newish.

Variable-frequency drive - Wikipedia, the free encyclopedia

It will control the inrush on motors.

Craig Clayton

 

[Tractor Seabee]

Ron- are you saying that when I have this 3 phase motor turned on, I am altering the wave form for all of the circuits supplied by this transformer?

So, while I am running this motor off a circuit in the garage, electronic equipment in the house might also be affected?

Yes, everything on the output side of the utility company transformer on the pole, could be affected, depends on how good the items filter system in its power supply. Depending on the vintage of your phase converter the tgransients fed back could vary a lot. That is one reason why commercial and industrial buildings have seperate transformers for lighting/plug and motor/power loads other than different voltages.

Bottom line, if it all works don't worry about it. If there is an interference problem this info can give you a clue why and where it comes from. 3 phase motors cost a lot less than single phase and are more effecient. We always specify motors and other power loads 1 HP and larger as three phase when 3 phase is available.

My brother-in-law has a big farm in Oregon where there is no three phase utility power; nhe tried to get them to do a seperate open-delta system for pumps and stationary machines and they refused. No reason except they never do anymore, they bwanted $15K to run 10 miles of wire to give him regular 3 phase. He declined and uses all single phase motors. I offered to do the seperate transformers on his side of the meter which would have included a isolation transformer ahead of the open delta ones but he did not want to bother at that time. That would have been around $3K for the loads he planned.

No, I am not an engineer or an electrician, just a guy with a lot of practical experience working around motors.

Ron

 

[5030]

30% useable power reduction with static conversion. That's 30% nameplate horsepower reduction, and starting torque (because an electrical motor produces maximum torque at stall).

What occurs is the capacitor bank provides the T3 current and electromechanically excites the T3 windings when starting.

All 3 phase motors regardless of winding style will self excite the T3 leg after reaching rated rpm. (Wye or Delta wound)

Rotary conversion is much better (and more expensive) because a slave motor provides the necessary T3 excitation and running current. It's quite possible to spin an old 3 phase motor with a single phase motor (induction-repulshon 3 phase motor) and pull the generated T3 leg to run your 3 phase motor efficiently at rated nameplate power. Just keep in mind that the T3 motor you use a slave motor must have a higher nameplate power rating than the motor(s) you wish to run, however, 3 phase motors are stackable, that is, multiple motors at running RPM will generate the T3 leg in enough amperage to run additional motors (so long as your wiring is of sufficient gage to carry the amperage).

I use dedicated rotary conversion in my shop because, one, it creates less internal heat in the motor, two, no loss in starting/running power and three, I need true 60hz power to run my frequency controlled machines.

 

[KYErik]

What about converting the bandsaw to tractor powered by rigging up a belt or chain drive to the pto directly?

My bandmill has a moving carriage/blade assembly (log is stationary), so designing some sort of 13 foot sliding driveline would be tough.

Here is the thread that I posted (with pics) when I finished building the mill about 6 yrs ago: http://www.tractorbynet.com/forums/build-yourself/74963-home-built-bandsaw-mill.html

 

[KYErik]

Yes, everything on the output side of the utility company transformer on the pole, could be affected, depends on how good the items filter system in its power supply. Depending on the vintage of your phase converter the tgransients fed back could vary a lot. That is one reason why commercial and industrial buildings have seperate transformers for lighting/plug and motor/power loads other than different voltages.

Bottom line, if it all works don't worry about it. If there is an interference problem this info can give you a clue why and where it comes from.

The static phase converter is at least 40 years old. The capacitors are stacked inside a grounded metal box. This static converter starts up the motor nicely, but sparks literally fly/arc between the caps when the power to the motor is shut down.

Is it possible to detect any interference/transients using a digital voltmeter? (I don't have an oscilliscope).

 

[KYErik]

30% useable power reduction with static conversion. That's 30% nameplate horsepower reduction, and starting torque (because an electrical motor produces maximum torque at stall).


Rotary conversion is much better (and more expensive) because a slave motor provides the necessary T3 excitation and running current. It's quite possible to spin an old 3 phase motor with a single phase motor (induction-repulshon 3 phase motor) and pull the generated T3 leg to run your 3 phase motor efficiently at rated nameplate power. Just keep in mind that the T3 motor you use a slave motor must have a higher nameplate power rating than the motor(s) you wish to run, however, 3 phase motors are stackable, that is, multiple motors at running RPM will generate the T3 leg in enough amperage to run additional motors (so long as your wiring is of sufficient gage to carry the amperage).

a home made rotary converter- This is what I was considering using the 2 extra 7.5 hp 3 phase motors for (as rotary converters). So if I was to spin up the slave motors (one at a time), then I could gain back the 30% reduction and could run the 7.5 hp bandmill motor at its full rated capacity?

Do you have a guess as to how many amps of single phase your rotary converter uses by itself?

I was just considering how much I'd have to upsize the breaker and wire for this circuit if I was also running the two other 7.5hp motors as slave motors for the one on the bandmill and knowing the slaves' consumption would help me to calculate the increase in electrical load.