# Permanet magnet motors VS field wound



## icebeater (Jan 21, 2009)

UQM makes the motor you're looking for - it's a thing of beauty - but you'll need very deep pockets. These motors are seeing commercial interest so they may get economies of scale in a year or 3. www.uqm.com - check out the power & torque / weight ratios on their 125KW and 150KW motors. 

After the disappointment of a quote from UQM I realized the two things I want a PMDC motor for are regen and motor-reverse (my donor car has a huge complex gearbox that I want to drop.) Zero-maintenance is a luxury vs. replacing brushes. 

Here's what I'm thinking of doing - run two of the etek PMDC motors for reverse and regen - on a low (wheel) speed chain drive as a pony system with 1 or 2 9" DC motors for drive. The other interesting thing about this setup is that the PMDC's could work nicely as a series PHEV by strapping them to one of these honda engines.


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## Bowser330 (Jun 15, 2008)

icebeater said:


> UQM makes the motor you're looking for - it's a thing of beauty - but you'll need very deep pockets. These motors are seeing commercial interest so they may get economies of scale in a year or 3. www.uqm.com - check out the power & torque / weight ratios on their 125KW and 150KW motors.
> 
> After the disappointment of a quote from UQM I realized the two things I want a PMDC motor for are regen and motor-reverse (my donor car has a huge complex gearbox that I want to drop.) Zero-maintenance is a luxury vs. replacing brushes.
> 
> Here's what I'm thinking of doing - run two of the etek PMDC motors for reverse and regen - on a low (wheel) speed chain drive as a pony system with 1 or 2 9" DC motors for drive. The other interesting thing about this setup is that the PMDC's could work nicely as a series PHEV by strapping them to one of these honda engines.


UQM is a joke...theyve been around for years and have always had those rediculous prices...nothing thats going to assist the grassroots market..no one wants us...they always go after the big fish first (like deals with the department of defense, licensing deals, etc)


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## saab96 (Mar 19, 2008)

The iMiev uses a permanent magnet motor. I wonder where that originates?


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## Guest (Jan 23, 2009)

Well since no one else will pipe up and explain maybe I can put in a bit. I think that most large PM motors are not used because of HEAT. Heat and magnets don't get along well. Get a magnet too hot and it looses it's magnetism and you loose your field vs powered electromagnets used for the field. You can also control the power of the electromagnet field where you have no control over a PM field. You only have control over the armature. The electromagnet field is stronger than with a PM. Small format PM motors are doing a fine job but I think the larger you go the less efficient they become. Magnets are not getting stronger. 

Pete




Georgia Tech said:


> It seems as if these guys are not used much in EV applications? I think I have my good reasons as to why, but I want to see what other motor heads out there think....It seems the best PM motors, I'v seen, don't even compare to the worst Field wound motors?
> 
> 
> Also does anyone know of any GOOD PM motors out there besides the pancake motors? e.i. Mars, Perm, ect..
> ...


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## JRP3 (Mar 7, 2008)

My understanding is that since permanent magnets are expensive the motors that use them are expensive as well. At that point you may as well go with AC induction motors.


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## Guest (Jan 23, 2009)

Expensive is an understatement. I agree with this too. I also agree with going AC Induction. Controllers anyone? Until then DC brushed it is. 

Pete : )



JRP3 said:


> My understanding is that since permanent magnets are expensive the motors that use them are expensive as well. At that point you may as well go with AC induction motors.


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## Georgia Tech (Dec 5, 2008)

thanks guys..


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## unclematt (May 11, 2008)

gottdi said:


> Well since no one else will pipe up and explain maybe I can put in a bit. I think that most large PM motors are not used because of HEAT. Heat and magnets don't get along well. Get a magnet too hot and it looses it's magnetism and you loose your field vs powered electromagnets used for the field. You can also control the power of the electromagnet field where you have no control over a PM field. You only have control over the armature. The electromagnet field is stronger than with a PM. Small format PM motors are doing a fine job but I think the larger you go the less efficient they become. Magnets are not getting stronger.
> 
> Pete


I posted this in another thread, but a new PM is in the works that will handle these heat issues easily. Here is my former post about this:

Here is an article about a new manufacturing method for Samarium Cobalt magnets that is going to reduce their cost and increase availability in a big way. When these go on sale we should do a serious analysis of neodymium vs Samarium Cobalt magnets. If their cost comes down as much as is claimed, they might displace neodymium in most electric motors.

LINK


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## JRP3 (Mar 7, 2008)

They still will not address the control issues gottdi mentioned. Here's a good explanation of PM motors vs. induction:


> In an ideal brushless drive, the strength of the magnetic field produced by the permanent magnets would be adjustable. When maximum torque is required, especially at low speeds, the magnetic field strength (B) should be maximum – so that inverter and motor currents are maintained at their lowest possible values. This minimizes the I² R (current² resistance) losses and thereby optimizes efficiency. Likewise, when torque levels are low, the B field should be reduced such that eddy and hysteresis losses due to B are also reduced. Ideally, B should be adjusted such that the sum of the eddy, hysteresis, and I² losses is minimized. Unfortunately, there is no easy way of changing B with permanent magnets.
> 
> In contrast, induction machines have no magnets and B fields are “adjustable,” since B is proportionate to V/f (voltage to frequency). This means that at light loads the inverter can reduce voltage such that magnetic losses are reduced and efficiency is maximized. Thus, the induction machine when operated with a smart inverter has an advantage over a DC brushless machine – magnetic and conduction losses can be traded such that efficiency is optimized. This advantage becomes increasingly important as performance is increased. With DC brushless, as machine size grows, the magnetic losses increase proportionately and part load efficiency drops. With induction, as machine size grows, losses do not necessarily grow. Thus, induction drives may be the favored approach where high-performance is desired; peak efficiency will be a little less than with DC brushless, but average efficiency may actually be better.


http://www.teslamotors.com/blog4/?p=45


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## Qer (May 7, 2008)

gottdi said:


> Expensive is an understatement. I agree with this too. I also agree with going AC Induction. Controllers anyone? Until then DC brushed it is.


My understanding, after studying motors of all kinds a lot lately, is that brushed DC-motors only have two big primary advantages; price and simplicity.

Many have converted their cars based on second hand truck motors and it's easier (not easy though) and cheaper, to build a PWM-controller for brushed DC-motors than it is to build an controller for brushless DC- or AC-motors. There's also the fact that it's possible to do a general controller for all kinds of brushed DC-motors while brushless controllers needs to be more specialized to fit the motor in question.

Disadvantages then? Well, several. But not bad enough you can't live with them.


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## unclematt (May 11, 2008)

JRP3 said:


> They still will not address the control issues gottdi mentioned. Here's a good explanation of PM motors vs. induction:
> 
> http://www.teslamotors.com/blog4/?p=45


I agree with your technical analysis, but please show me the available, affordable, series motor AND controller that is available to the public TODAY. There are NONE.

Not from Raser Technologies (who has a very advanced series wound design), not from AC Propulsion (who are laughably overpriced), not from ANYONE. Its all fine and good to have a concept, or even a working motor, but if it is not produced for sale to the public at a reasonable price, it will remain a toy for rich people.


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## JRP3 (Mar 7, 2008)

http://www.diyelectriccar.com/forums/showthread.php/new-ac-motor-available-24498.html
I may be using this in my Fiero conversion.


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