electric motors

First, what does 'split phase' mean on the tag of an electric motor?

Second, why does a low rpm motor (1725) have 2 or 3 times the torque of a 3450 rpm motor of the same HP?

How do they make a motor high rpm and another low rpm..... what's the internal differences?

thanks.

Just for laughs, I wired a motor with 8 poles once just to see how it would do. It ran fine, but never found a use for it. I imagine it's still in a pile of motors I left at the farm when my brother took over.

All single-phase motors require some sort of starting circuit to create a rotating field. (Starting circuits are not required for three-phase motors.) In a split phase motor, the starting circuit is just an extra winding that shifts the phase of the input power. On some motors, you can see the split phase winding when you disassemble the motor.

As B&D said, HP is a function of torque and rpms, but there's more to the story. Different types of motors have different torque characteristics. Most ac motors are induction motors once they're at operating speed; an induction motor must actually run slightly less than its rated "no load" speed to produce torque. A synchronous motor (such as in a clock) always runs at its rated speed, regardless of torque.

One last comment: The brush-type motors used in power tools aren't really ac motors. They're dc motors that don't care if you hit them with ac. So you can run most hand power tools off of 110V DC power. Brush-type motors have high starting torque, don't require starting circuits and can be run at variable speeds.

Three phase uses three live lines at 208,480 or 600V. Higher the voltage, the smaller the size of copper wire or the longer the power supply cable can be.

HP = torque in lb. ft X RPM divided by 5252. On 60Hz power a two pole induction motor tries to run at 3600rpm, four pole 1800 rpm, six pole 1200rpm, eight pole 900 rpm etc.

On the contrary, your posts make it clear you are highly knowledgeable or expert in a wide range of areas, definitely expert in matters concerning electronics, motors, electricity, house wiring, etc. A BS'er you're not, certainly not on this forum, and I suspect not anywhere else, either.

Don't be shy. You can tell us where you come by your knowledge. We'll still respect you if you're educated---you're Canadian. It's only educated Americans we Americans don't respect.

All the best, Stan

Wow! What an education.....I could read this stuff all day...because you fellows break it down so a person like myself can understand it. Thank you again.

So, I understand that the difference in a 3450 rpm motor and a 1725 is probably 2 pole versus 4 pole..correct in my assumption?

Now a for instance: I went to Baldor's website and read the performance data for a couple 1.5 HP motors....only real difference was one was 3450 rpm, the other 1725. The slower motor produced about 3 times the torque of the 3450 rpm motor.....I don't recall the exact figures.....but it was like 5 ft.lbs (3650) vs. 15 ft.lbs. for the 1725 rpm motor. Therefore, I would also assume the 1725 rpm motor will start a heavier load...much heavier in fact. True or false?

Thanks.

Starting torque for an ac motor has less to do with the rated torque and more to do with the type of motor. Split-phase motors have low starting torque, capacitor-start motors have high starting torque. For example, single-phase air compressors almost always use capacitor-start motors.

I put a 3/4 HP SPLIT PHASE 1725 rpm motor on my JD hand crank corn sheller and was....well PO'ed, because it wouldn't start the contraption. Now, after your disseration, it is obvious as to why. I was also dissapointed because it would stall under a load. being the elctrical idiot I am...I was stumped.

So, I decide to buy myself a new motor and away to Ebay I go. I decided to buy a 1.5 horse motor..which of course is a capacitor start type. I was confused as whether to get a 1725 rpm or a 3450. I decided on a 3450. Then after I spends my money...I go look at Baldor's website and go to checking the performance figures and thought...oh crap.....the 1725 has 3X the torque the 3450 does.

But today, I had a brain fart, and yanked the 1 horse capacitor start, 3450 rpm motor from my table saw and try it. WOW! I was astonished and tickled pink to see how well it worked...it was like yanking out a 4 cylinder and dropping in a Hemi. Automatically, I was happy I had bought a 1.5 horse cap. start 3450 rpm motor. However, I am satisfied with the 1 horse now on the sheller and will use the 1.5 on the table saw. By the way.....the motor is a GE, made in the States.

My hat is off to you guys for your kind help and great knowledge of electrical things. Thanks very much for sharing.

Amps are a far better indication of power than stated HP. For 1 HP use 12 Amps at 110V for or 6 Amps at 220V. Apparently manufacturers are lying about HP ratings in two ways, assuming their motors are 100% efficient They aren"t. 60%-65% is more like it. They also are using the amount of power consumed when the lights go out rather the the operating power consumption to rate their motors. It boils down to 1.5 true HP is the practical max on a 20Amp 110V circuit.