DC vs. AC motors

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masonsteele
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DC vs. AC motors

I saw that REVA in India is switching over to AC motors, and that a lot of people were excited about it. Why is that? What are the benefits of using an AC motor over a DC one. I was thinking about getting an ETEK DC for a motorcycle project. How would that compare to their cheaper AC motors?
thanks,
m

NickF23
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I don't know very much about

I don't know very much about this and would love to know more about AC motors in general. Here's what I know so far:

3 kinds of motors for EV's

brushed dc
brushless DC
AC motor

AC motors have more torque than either brushed or brushless DC motor. They are also more efficient over a wider RPM range. Their downside is they're more expensive, i think its the controller that costs more. All the high spec EV's I've heard of have them

goodnslo
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Correcting 3 types of motors

The three types are:
PM (permanent magnet) motors
DC motors (windings only)
AC motors

Anything else is a variation of these.

goodnslo
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DC vs AC

This means as compared to PM DC motors
1. the price of the motor will be cheaper because it will not be dependant on the cost of the rare earth magnets. An AC motor only has windings
2. the weight of the motor varies with the windings and the weight of the material
3. torque is dependant on poles and windings, i.e. the design and type of AC motor

masonsteele
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I'm confused by this page

I thought I was looking at an AC and a DC motor on the electric motorsport inventory page (http://www.electricmotorsport.com/PARTS/parts.htm). However, the AC motor is listed as a Perm magnet 3 phase motor. If I understand, AC's don't have perm magnets. Am i mistaken?
thanks,
m

Max
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Perm Motor GmbH is a

Perm Motor GmbH is a company, so the expression Perm does not necessarily mean
permanent magnet motor! Visit their homepage and you'll see they are also making
alternative current motors. Anyhow, the PMG132 of Perm is a permanent magnet motor (DC).
I found this document by chance with some basic explanations of the different motor types and their main characteristics/components. Power.pdf
Unfortunately I can't remember where I saw a great overview of the different motor types some time ago. Here are some more explanations of electric motors: overview

Cheers

Max

masonsteele
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I was referring to Etek's, but thanks for the info

I was referring to the Etek listed on the elctricmotorsport parts page as an AC Motor. Thanks for the info on Perm tho. I'm getting more and more interested in using two of those, despite the prohibitive costs. I can't believe they are so much more than the Eteks. Thanks for the links you provided. good stuff. I found a good overview at wikipedia as well (http://en.wikipedia.org/wiki/Electric_motor). If you remember your source, please shoot me an email.
thanks,
M

Max
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Etek

What electricmotorsport is calling the brushless Etek is an AC motor from Mars Electric LLC
The normal Etek is using the same design than the Lynch motors, see agnimotors.com.
Also the Perm PMG motor series is using the patented design of the Lynch permanent magnet
motors.
BTW, wikipedia is always a good source for some information!

Max

masonsteele
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I love the Agni motors!

Thanks for the info. Just wrote to Agni Motors regarding purchase. Do you know of anyone who has used one?
thanks,
m

Max
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AgniMotors

If I had known you are interested in their motors I would have posted two replies from them
regarding to their motors and prices. I'm sure you'll get a pretty helpful and friendly answer of them!
The AgniMotor is the most efficient DC permanent magnet motor I know (up to 93%). It's nearly the same motor than the Lynch motors but with some improvements and made in India by Agnimotors where Cedric Lynch is now working. However the motor is pretty expensive, about 700GB pounds (~1350USD) excl VAT and shipping. The PMG132 is pretty similar and priced arround 800USD.
I think the Agnimotor is a quality product and the high price is due to low quantities.
If you browse the web you should find some information or user reports relating to the motor.
BTW, what are you planning to use the motor for?

Regards

Max

masonsteele
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dream machine

That's a bit expensive. I was trying to save over the PMG.
I started out wanting to build a three-wheeler, but ran in to chassis design problems. So I opted instead to convert a small Japanese car; however, the hassle of getting it to the US and registered was more than I could deal with. My current plan is to buy a GEM NEV, modify it to a three-wheeler with one wide wheel in the rear, and then give it some oomph with 2 new motors and a controller. That way I can avoid the entire chassis construction for now, and still have a vehicle that can be registered a a motorcycle.
sound round-about? We'll see where it goes from here. I found some relatively cheap Gem's in the san francisco area.
M

Max
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sounds good!

sounds good what you are planning there.
I'm in favour of three wheeled vehicles.
Particularly on a two wheels in front and one rear wheel design.
For the reason that you mentioned things like "building your own chassis" you maybe want
to read some documents about three-wheel vehicles.
If you go to Robert Q. Riley Enterprises, LLC
In the section downloads you can find documents like this (very interesting) one:
Primary Factors That Determine
Handling & Rollover Characteristics

Do not forget to post about your vehicle in the appropriate section on this board (if you really get it)

Max

masonsteele
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cool. will do.

Those nev's are moving off of craigslsit pretty quick. I get back to the US on the 27th; hopefully I'll be able ot find one then.
I love RQRiley's site. I been all over that stuff since I was a kid in a barber shop and first picked up an issue of pop-sci with one of his creations in it. can't even remember which one. the guys a visionary.
thansk for the support,
m

andrew
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Re: I was referring to Etek's, but thanks for the info

The etek you see is a brushless DC motor or BLDC motor which is very different from an AC motor, and requires a very different controller. Just thought you should know...

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chas_stevenson
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Re: Correcting 3 types of motors

Funny, I thought there were only 2 types of electric motors, AC and DC. A PM(permanent magnet) motor as you call it must use either AC or DC to operate. I'm not fully versed on motors but I thought if it was a permanent magnet motor it used DC. So I only know of 2 types.

Confused?
Chas S.

goodnslo
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Re: Correcting 3 types of motors

it becomes all mechanical supplied by a mechanical motion until all motion stops. Very limited and not very useful. There used to be a movie of an aluminum disc spinning as a result of a spinning magnet on the earlier site, although demonstrating something else, it is a prime example of what I mean.

chas_stevenson
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Re: Correcting 2 types of motors

From "Webster's Online Dictionary"

Main Entry: 1mo┬Ětor
Pronunciation: 'mO-t&r
Function: noun
Etymology: Latin, from movEre to move
1 : one that imparts motion; specifically : PRIME MOVER
2 : any of various power units that develop energy or impart motion: as a : a small compact engine b : INTERNAL COMBUSTION ENGINE; especially : a gasoline engine c : a rotating machine that transforms electrical energy into mechanical energy

Using the definition from the "Webster's Online Dictionary" what you describe "all mechanical supplied by a mechanical motion" is the opposite of a motor. A motor by the definition is what supplies the motion and what you are describe requires the input of motion so how can this be a motor? If there is a motor out there that doesn't use batteries then lets put one of those on a bike. This would eliminate a great deal of weight, from batteries, and solve the range problem.

Your explanation "aluminum disc spinning as a result of a spinning magnet" leaves a lot to be desired. What caused the magnet to spin?

I want one,
Chas S.

Fechter
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Re: Correcting 2 types of motors

I think you guys are confusing a permanent magnet AC motor, which is the same as a brushless motor, with an induction motor. The aluminum disc spins because the rotating magnetic field is inducing current in it. Induction motors are very common in industrial settings, and have no permanent magnets.

It takes a special controller to run an induction motor. Sometimes this is called an inverter.
Induction motors are very simple and robust. Just a pair of ball bearings, a rotor, and a stator.
Here's the one that Electric Motorsport used on the GPR:
http://hiperformancegolfcars.com/

They were also experimenting with the Mars motor, which is an Etek sized permanent magnet brushless motor.

goodnslo
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Re: Correcting 2 types of motors

Chas, Instead of limiting the definition on an EXAMPLE, maintain its broad definition of 1 : one that imparts motion; 2 : any of various power units that develop energy or impart motion:
So by the same definition, the example I had cited imparts motion. Using another simple science experiment to illustrate, placing magnets on the rotor and another magnet in close proximity as the stator still imparts motion; its just not very useful. I am not advocating free energy, but maintaining the broader definition.
Remember "c : a rotating machine that transforms electrical energy into mechanical energy" is an example. It is not the end all and be all, it allows exceptions and additions.

Fechter, the original example I was speaking of is a science experiment that spun a magnet with the poles alternating between facing the aluminum piece. Yes, it does induce a current and it does spin. It just doesnt use AC current. It is used to illustrate the Lenz effect.

chas_stevenson
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Re: Correcting 2 types of motors

goodnslo,

I think we have both been talking about 2 different things. I have been trying to understand how there is another motor that does not use AC or DC since the topic of this thread is "DC vs. AC motors" I guess we are both off topic. Thanks for trying to explain the science experiment but I don't see how it is relevant to electric vehicles.

Fetcher,

You seem to have a good grasp on motors. I understand AC motors are more efficent than DC motors but DC motors can produce more torque in a smaller package. Is this correct? What are the pro's and con's of each type?

Thanks,
Chas S.

Fechter
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Re: Correcting 2 types of motors

As far as I can tell, a permanent magnet brushless (BLDC) motor will give the highest efficiency. If you look at the specs on the Hiperformance AC motor, it outperforms the series-wound DC motors it replaces. I think it comes close to a BLDC motor.

The primary advantages of an induction motor are simple construction (theoretically cheaper) and the max RPM is not really a function of battery voltage, so it has an extended operating range. Induction motors lose efficiency in smaller sizes, so they are only practical for larger applications.

BLDC and induction motors require fairly complex 3 phase controllers, which may cost more than the motor itself. Induction motor controllers are the most expensive.

Brushed DC motors are reasonably efficient, the least expensive and can use very inexpensive PWM controllers.

Here's a good technical reference for brushed DC and induction motors:
http://www.reliance.com/mtr/mtrthrmn.htm

Here's an explaination of brushless motors:
http://www.servomag.com/flash/4-pole/smi-motor007.htm

NickF23
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Re: Correcting 2 types of motors

Interesting writeup on brushless DC vs AC induction.

http://www.teslamotors.com/blog1/?p=45

andrew
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Re: DC vs. AC motors

EDIT: Referring to this article: http://www.teslamotors.com/blog1/?p=45

Good article, but some claims are wrong.

Back when I had hair on my head and carried a slide rule, there were lead acid batteries, DC brush motors, and contactor controllers. Today, none of these remain

Thats funny... I didn't know I bought 170lbs of lithium batteries for my motorcycle, labeled lead-acid.

The only notable uses of induction drives have been the General Motors EV-1; the AC Propulsion vehicles, including the tzero; and the Tesla Roadster.

He did not mention the Ford Ranger EV.

Permanent magnet (PM) rotors are also difficult to handle due to very large forces that come into play when anything ferromagnetic gets close to them.

This is not necessarily a problem, as rotors can be assembled in a demagnetized state.

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abcd
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Re: DC vs. AC motors

I think there is only one DC motor. It is kinda strange and is only used for
special uses, where very high power is needed as it uses very high current and low
voltages it doesn't work well with normal consumer uses.

All other motors normally called DC motors are Ac machines.

This has some thing to due with how normal motors that run on DC
convert it to AC using brushes or in busshless motors, special chips.

abcd
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Re: Correcting 3 types of motors

http://en.wikipedia.org/wiki/Homopolar_motor this is a DC motor.

It also could be called a PM motor since it has a magnet, however it might not need a magnet but could use an electo-magnet I guess.

Although not thinking about this someone might run the electo- magent with ac, and the motor its self with ac and call this an ac motor instead of the DC motor.

So I beter require it to use the magnet,

hope this explains things more. :)

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