High and low speed motor.

[Jraef]

Just a little friendly advice on forum posting. You are getting yourself in too deep too fast and mixing things up. You need to slow down and stick to one thing at a time.

1 phase motors, as you described in the beginning, are very different from 3 phase motors.

Using VFDs is very different from using 2 speed motors. You cannot use VFDs on 1 phase motors for the most part.

The only kind of 1 phase motors that can change speed by reducing voltage only are Shaded Pole motors and Universal Motors. For any other type, reducing voltage causes an overload.

If you have "windings" in the rotor of a motor, you either have a Wound Rotor Induction Motor, a Synchronous Motor or a Universal Motor. These are altogether different again from the other things being discussed earlier.

Since this thread started out as a question about a 1 phase 2 speed motor, it's best to finish that out and start a different thread to discuss the other issues, otherwise the responses will get confusing to you since different people may end up responding to different questions on different subjects.

Motor speed is a function of the applied frequency and the number of magnetic poles. 1 phase 2 speed spa pump motors change speeds by using 2 different sets of windings to create two different numbers of magnetic poles in the stator. It's called "2 Speed 2 Winding". In your spa controls then, there is a switch that switches the 120VAC to one set of windings or the other. If you download this booklet, it explains it.

 

[ActionDave]

I knew you guys with better typing and English skills would not let me down.

I believe the typical two-speed motor reduces speed by simply powering less windings, not fewer poles, thus reducing torque.

In other words, it's not a synchronous motor.

Larry, would this be the way a two speed furnace motor would work? I think it does, however I thought the lower speed powered more windings.

 

[LarryFine]

I knew you guys with better typing and English skills would not let me down.

Thanks. I think.

Larry, would this be the way a two speed furnace motor would work? I think it does, however I thought the lower speed powered more windings.

I think so, too, same as 3-speed blower motors. But, fewer windings would result in a weaker magnetic field. I think.

 

[kwired]

Thanks. I think.

I think so, too, same as 3-speed blower motors. But, fewer windings would result in a weaker magnetic field. I think.

And more speed but less torque.

 

[LarryFine]

And more speed but less torque.

So, how would the speeds under load compare?

 

[ActionDave]

Thanks. I think.

Absolutely, your welcome. I wish Goggle would come up with a translator that could interpret the thoughts in my head without me using words.

I think so, too, same as 3-speed blower motors. But, fewer windings would result in a weaker magnetic field. I think.

And more speed but less torque.

That's what I was told. Now the big question- Why would a weaker field translate to more speed?

 

[kwired]

Have you ever noticed a direct drive fan that runs at 3400 RPM (2 pole) motor takes longer to accelerate from stopped condition than similar fan with a 4 or 6 pole motor?

It is because the high speed motor produces less torque.

I don't know if there is necessarily weaker field in a 2 pole motor but there is more distance between fields They are 180 degrees apart vs 90 degrees in a 4 pole motor.

This would likely be the reason for more torque in the 4 pole motor also. The fields in the rotor are interacting with the stator fields 90 degrees sooner.

 

[rcwilson]

It is because the high speed motor produces less torque.

This would likely be the reason for more torque in the 4 pole motor also. QUOTE]

HP= [Torque (Ft-lb) x rpm] / 5252.

A 10 HP, 1800 rpm 4-pole motor has to produce twice the torque as a 10 HP, 3600 rpm, 2-pole motor to put out the same shaft horsepower.

 

[G._S._Ohm]

So, how would the speeds under load compare?

Water pump speed probably depends on power^3, so 10% more hp into the pump = 33% more speed.

 

[dkarst]

Water pump speed probably depends on power^3, so 10% more hp into the pump = 33% more speed.

Are you sure you don't mean that required power depends on the speed^3 (affinity law of a pump) --> to increase the speed of a pump by 10%, you require (1.1)^3 = 33% more shaft power ?

 

[G._S._Ohm]

Are you sure you don't mean that required power depends on the speed^3 (affinity law of a pump) --> to increase the speed of a pump by 10%, you require (1.1)^3 = 33% more shaft power ?

I can't believe some of the mistakes I'm making lately. . .