PM DC motors 1

[paulmars]

Are all PM motors DC? Are all DC mtrs PM? I know its basic questions, but searching the web did not give me an answer.

 

[BobM3]

Not all DC motors are PM. Not sure about the other direction.

 

[davidbeach]

No to both.

 

[waross]

To protect the guilty and confuse the innocent, brushless DC motors are actually PM AC motors.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[paulmars]

ok, here is the question I really should have asked first. I have about 100 motors. AC, DC, 3ph. How do I know which are PM?

 

[davidbeach]

From that you don't. Looking at the nameplate of each motor may be your only choice.

 

[paulmars]

so DC, AC single and 3ph can all be PM?

 

[davidbeach]

Probably not AC single phase, not AC induction motors, but DC could as could any AC synchronous motors. Or you may not find a single PM motor in the whole lot.

 

[itsmoked]

I can't say I've heard of an AC single phase PM motor. So you could say, "any single phase AC motors are not PM".

Keith Cress
kcress -

http://www.flaminsystems.com

 

[davidbeach]

Single phase synchronous clock motors are a good candidate for a single phase AC PM motor.

 

[itsmoked]

OK you got me there. A few ancient non-shaded pole style eclectric clocks. Yep the ones with the little mangled disks spinning under the cover with the tiny window in it. I do remember those.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[DickDV]

A DC motor with a PM field will be distinquishable on the nameplate by having no field data and in the junction box by having no field leads (F1 and F2 or S1 and S2).

The vast majority of AC motors are induction motors and do not have permanent magnets. Those with PM's will not have any slip, ie, the rpm at 60hz will be exactly 3600/1800/1200/or900 etc.

Servo duty motors, whether AC or DC, will not have a kw or hp listing on the nameplate and will generally say "servo" somewhere. Most but not all servo motors have permanent magnets, whether AC or DC.

 

[paulmars]

can only pm dc be used in wind turbines? Excepting, of course, the AC ones that use a ac to dc converter.

 

[itsmoked]

Sure. Induction generators. They are often used in wind and have nothing 'permanent magnet' about them.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[paulmars]

Let me re-phrase my q: can only pm dc MOTORS be used in wind turbines? Excepting, of course, the AC ones that use a ac to dc converter.

I have sold many DC mtrs to ppl making turbines and I learn what I need as I go. I now have someone who needs a PM DC mtr to make a wind turbine.

Also, none of my Bodine gear mtrs say PM, buy they also dont have field date, so are they PM?

 

[waross]

Before the advent of high strength, permanent permanent magnets, DC generators were all self excited. No permamnent magnets, just enough residual magnetism to bootstarp the generation.
That would be almost all automotive generators from the Ford Model A up to the mid 50s and into the early 60s.Also, the original Winchargers cerca the 30s and 40s did not have permanent magnets. Self excited shunt generator that bootstrapped from residual magnetism.

http://www.wincharger.com/

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

But why PM DC with brushes when you could go PM AC synchronous and not require any brushes? It would seem to me that DC anything would be the last thing I'd want in a small wind turbine. Big enough that you'd have a nacelle, perhaps, but if brush service is either on the outside at the top of the tower or by bringing the machine to the ground it seems like a lot of unnecessary and/or hazardous work.

 

[paulmars]

so, the magnets are just used to start the motor? Please excuse my ignorance.

 

[davidbeach]

All motors require a field to run. If the field is provided by a PM, then it is always provided by the PM. If it isn't a PM field, then the field is provided electrically. Induction motors induce the field, synchronous motors have fields supplied by separate connections to slip rings, and DC motors may or may not have separate field terminals. But the field is needed always.

 

[paulmars]

thanks. Someone is telling me, that mtrs need to be PM to be used as generators. True or False?