Understanding 2 speed AC motor

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This last winter my hot tub had to be drained as it blew a fuse and froze up the lines. Spring is here and I am rummaging through some old motors I have removed from other hot tubs over the years.

My question is the high and low speed on this 220VAC motor. Using 220V on pin1 and pin2 gives you low speed and pin1 and pin3 gives you high speed. Only thing is, both ohm readings are the same 2.1 ohms. So high speed and low speed use the same amount of power? or is it because the winding on one is smaller diameter wire and allows 1/2 the current?

I did learn today though, the 4 wires Black,Red,White and green (Factory wiring with an AMP socket) are not connected as I originally thought, White actually goes to pin1 and black goes to pin2, red to pin3 and so I understand I smoked the low speed winding and i am sure killed a perfectly good motor. So I decided to take apart the motors that had bad bearings and it looks like all I have to do is buy a wheel puller and replace the bad bearings so I actually have 3 motors and I don't have to spend 600 bucks.

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For the price of bearings, I'd be buying new ones - they're probably only $5-15 each. The bearing puller will probably cost a lot more. Warm the new set of bearing up to around 60-100C and they should drop onto the shaft. They will shrink when they cool.

As for the motor speed - depends on the type of mtor. If it is a universal type (like in a power drill) and has brushes, then it is a matter of more magnetic field. If it is a synchronous type, then you can have two windings - one gives you another set of poles. Twice the number of pole, twice the speed.

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Not bearing puller, I mean wheel puller, the aluminum face plate is stuck to the bearing. If the liquid wrench doesnt work I will heat that up.

Soindeed a 2 speed ac motor with 2 windings could have different number of poles for two speeds and use the same amount of power. I did not know that.

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Twice the number of pole, twice the speed.

Right in the ball park, but the wrong way, twice the poles, half the speed.
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Srpm=120*f/Np

I assume motor speeds are related by a factor of 2. Ie in Australia with 50Hz. mains we would have 750 & 1500 (ignoring slip) with 4 & 2 poles respectively.

Charles Darwin, Lord Kelvin & Murphy are always lurking about!
Lee -.-
Riddle me this...How did the serpent move around before the fall?

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Thanks for the correction Lee. I know a little about a lot of things- sometimes too little!

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I assume motor speeds are related by a factor of 2. Ie in Australia with 50Hz. mains we would have 750 & 1500 (ignoring slip) with 4 & 2 poles respectively.

Actually, multi-speed induction motors are usually much stranger. The lower speeds are usually small reductions from the "full speed". Tricks are played with the windings but not by factors of two. A 3-speed blower motor may go from 1000 to 1380 rpm, for example.

Tom Pappano
Tulsa, Oklahoma

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The only thing I'm curious about is to the 220V system....
You state your are a US citizen. Then you have 110V mains in stead of 230V (europe) do you use a voltage doubler of some kind to get to 220V ???

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We have two legs of 110V with 180 degree offest. So when 1 leg is -110 to the second at +110 gives you a 220VAC 60 hz. One leg to ground is 110V for most AC stuff. I can tell you , I am glad too as 220 makes a hell of a bigger spark especially when blowing up motors by connecting them as a direct short, 50 amp circuit breaker but it did melt some #10 wire, arc welding style.

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The main breaker to the house is usually 100A 240VAC. This runs the oven, clothers dryer, air conditioner, water heater, heating strips at 240. Everything else runs from one 120V leg or the other.

Imagecraft compiler user

Last Edited: Wed. Apr 20, 2011 - 12:11 AM
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So you get two phases! Or a Single phase relative to earth.

In Europe, we get a single phase for domestic houses.
Industrial users get 3 phases 120 degrees apart.

Whether you get one or two phases, I really cannot believe that you can have two 'live' wires 180 degrees apart. From what I have seen of U.S. HV transmission lines, you have 3 phases and 'star' point wire.

David.

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Whether you get one or two phases, I really cannot believe that you can have two 'live' wires 180 degrees apart.

Not that strange, really. Homes and businesses that do *not* have three phase are typically supplied by a 240v center tapped transformer with the center tap earth grounded and used as the 'neutral'. Each leg to ground/neutral is 120v.

Three phase customers can have a variety of arrangements

Tom Pappano
Tulsa, Oklahoma

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The center tap on the secondary on the 'pole pig' transformer is the earth ground.

Imagecraft compiler user

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david.prentice wrote:
So you get two phases! Or a Single phase relative to earth.

In Europe, we get a single phase for domestic houses.
Industrial users get 3 phases 120 degrees apart.

Whether you get one or two phases, I really cannot believe that you can have two 'live' wires 180 degrees apart. From what I have seen of U.S. HV transmission lines, you have 3 phases and 'star' point wire.

David.

Almost every house in Canada (and USA) is supplied with two phases which are 180 degrees apart. With this we can get 240volts across both phases, or use a neutral (center tap) to get 120 volts.

Chief Tinkerer

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Isn't the correct term 240v/120v split-phase? There is really no two phase about it. Just a secondary winding with a center tap which is both ground and neutral return for the two 120v legs

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Does every house get a transformer ?
If it is only cookers that use both 'phases' then each household is going to use one half of the transformer (except at tea-time).

In Europe, a neighbourhood will get red, white or blue phase distributed fairly evenly so that the 3 phase load is reasonably balanced.

An industrial 3 phase customer is obliged to be 'reasonable' too.

David.

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Quote:
Does every house get a transformer ?
If it is only cookers that use both 'phases' then each household is going to use one half of the transformer (except at tea-time).

Usually in neighborhoods, each transformer will serve more than one house. A "pole peg", depending on its size, might only supply two to four. With underground utilities it seems larger transformers are used which serve a larger cluster of houses. Out in the country you might have your very own. In the US, 240v usually powers your electric oven, range, electric clothes dryer, air conditioning equipment and if you have them, electric water heater or electric comfort heating. The 120v wall outlets, lighting fixtures and smaller appliances are divided approximately evenly between the two 120v legs to evenly load the transformer secondary. The neighborhood transformers are ultimately fed from high voltage three phase, but sometimes an entire street will be fed from one three phase leg, or, all three phases may run down the street and smaller numbers of transformers might be fed from each phase.

Tom Pappano
Tulsa, Oklahoma

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Tom , I assume that clothes dryers are not hardwired to the switchboard, but have a plug & socket.
Are you able to take to take a couple of photos of single phase (110V) & two phase(220V) plugs & sockets.

Charles Darwin, Lord Kelvin & Murphy are always lurking about!
Lee -.-
Riddle me this...How did the serpent move around before the fall?

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Two phase is those god- awful twist lock plugs?

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This plug goes from the 240V socket to the clothes dryer
http://www.homedepot.com/webapp/...

Imagecraft compiler user

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Thanks Bob,
So you also have two different wall sockets in your homes. One for single phase & one for two phase. I guess you must have the odd person who connects 220V to 110 V equipment!
I reckon the US should upgrade to metrics & 240V mains. The rest of the world has.

Charles Darwin, Lord Kelvin & Murphy are always lurking about!
Lee -.-
Riddle me this...How did the serpent move around before the fall?

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Again not 2 phase, split-phase:

http://en.wikipedia.org/wiki/Spl...

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A split phase electricity distribution system is a 3-wire single-phase distribution system...

...it is sometimes incorrectly referred to as "two-phase".

...it is appropriate to call this power distribution system a 3-wire, single-phase, mid-point neutral system.