Talk:Electric motor

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Contents 1 Electric vehicle mass production 2 This moves contents box to top 3 Synchronous Condensors 4 Three Phase Rotating Field Diagram 5 Question about steppers 6 Reducing the armature current 7 Jedlik, 1830 8 Common concepts between single-phase and three-phase headers 9 Number of poles 10 RPM= 11 Few things to add... But where? 12 Thomas Davenport was an American blacksmith and inventor who invented the first DC electrical motor in 1834 13 DC motor equations 14 Planetary Electric Motor? 14.1 Deleted Section 14.2 History 14.3 Comments 15 Do universal motors self-destruct from overspeed when operated on AC? 16 hack....why not? 17 Tesla's Three-Phase electric motor 18 Textbooks 19 limits to efficiency 20 Switched or variable Reluctance motor? 21 Repulsion motors and other types 22 Nano motor 23 does horsepower really equal 750 watts? 24 Comparisons between US and UK domestic electrical installations 25 material used to manuf. brushes used in a.c & d.c. rotating machine 26 Question on Dates 27 Citation needed 28 AC motors and DC motors 29 Torque: current or voltage dependent?

[edit] Electric vehicle mass production

You may have seen the Tesla electric sportscar http://www.teslamotors.com

You may have even seen the T-Zero electric sports car http://www.acpropulsion.com/acp_faqs/faq...

These two cars show that it is now possible to build electric cars that can out-accelerate a Ferrari, and go 250 - 350 miles on a single charge. But both these cars are very expensive.

So who else is working on electric cars?

Would you believe China? They have to work on EVs. There won't be enough oil to support China's future economic growth.

I drive an old electric vehicle. I also have friends with electric vehicles. Some of them have recently been able to buy some amazing, cutting-edge EV batteries from China - example:

http://www.everspring.net/product-batter...

These batteries are better, and cheaper than the ones in those $100,000+ sportscars above. If you look at the chart, you'll see they are as cheap as lead-acid batteries, and they hold up for 1100 charges, twice as many charges as the other LI-Ion batteries on the chart.

Now, look at this car:

http://www.milesautomotive.com/products_...

It's a Chinese electric car, which will be imported into the USA next year. The driving range is almost as good as those sports cars above. But it only costs $28500. And that price could get a lot cheaper.

[edit] This moves contents box to top

I have edited the last paragraph in the Single Phase Motors section in an effort to make the language a bit more clear. I agree with User Mrlennar's comments in that this article needs more work. Someone has put significant effort into the artilce so far with neat looking pictures and a good outline. I am a brand new user to WIKIpedia so I'm reluctant to do too much more editing without comments from other interested users. I suggest we look for good motor relatred links to add to this article - perhap, Baldor.com or Reliance.com. Both companies have significant online resources for users interested in electric motors. I'm not yet familiar with the copyright rules here, so would refrain from uploading some of my motor related pictures from various web sites. --King144 05:23, 29 Sep 2004 (UTC) -9/28/04

I think this article should be made more systematic. IMHO the difference between the various motor types is not made clear enough in this article. I think I may even have the skills to do it.

I would prefer a subdivision in the following types.

• Motors with an armature with coils and a commutator. This is the classic DC motor. The stator can have permanent magnets or electromagnets as well. In the latter case there is the distinction between series and shunt motors, both can run on AC as well as DC.
• AC motors either with a permanent magnet rotor (synchronous) or a so-called squirrel cage rotor (asynchronous or induction motors).

Someone with drawing skills could add a diagram to show how either of these motors works.

Discuss briefly the number of poles and the number of phases of an AC motor. Explain why the one-phase AC motor needs a startup winding or a shaded pole.

Discuss that brushless DC motors and stepper motors are constructed similarly to a permanent magnet rotor AC motor, but that they are driven by switched DC currents instead of AC. The existing info on stepper motors is a good starting point.

The electrical generator article needs even more work I think. At least it should be mentioned that most electric motors can be used as a generator and vice versa. Principal construction of both is the same. Mrlennart 10:23 Apr 26, 2003 (UTC)

The sentence that starts "In order for it to operate it must always run slower than the frequency of the power supply feeding it causes the magnetic field in the motor to rotate,..." is not grammatically correct, but I am not sure how to rewrite it properly. Nanobug 12:15, 5 Aug 2003 (UTC)

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I have removed the following section as Michael Faraday demonstrated the electric motor in 1821 and discovered the dynamo effect in 1831. Maybe somebody could check the Maxwell quote.

== Some history and interconnection ==

"The construction of an electric motor is very similar to that of a dynamo. In fact, a machine can be built that acts as either a motor or a dynamo. Historically, the electrical generator (dynamo), came before the motor. It was not until a workman mis-wired a generator, that the public came to understand that mechanical motion could be generated from an electrical source. James Clerk Maxwell called the electric motor the single greatest invention of his time." Tiles 07:05, 15 Oct 2003 (UTC)

I am gratified that I reproduced similar information and quote, 2.5 yrs later, on another talk page. My source was IEEE Spectrum, in the 1970s. --Ancheta Wis 09:58, 21 March 2006 (UTC)

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I've uploaded a photo of a DC motor in a model railroad that maybe some of you could find interesting, here's it: Image:Motor-dc.JPG

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I would like to see a better explanation of three-phase motors, hopefully with a diagram. I can't find any information on these systems on the internet. Perhaps a different term is more appropriate?

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Technical problem : brushless can't be DC motor !! all the brushless engine have a electronic module to convert the DC to 3phase AC !

From a purely technical point, that may be true, but the universal convention is to refer to these motors as "brushless DC motors", doubtless because the power fed to them is DC. The internal workings of the motor are a black box as far as most folks are concerned.
Atlant 16:54, 6 Jan 2005 (UTC)

[edit] Synchronous Condensors

As far as I know, Synchronous Motors have a theory of their own and the main application is power factor correction which is not mentioned any where. Have a look at Synchronous Motors. --Electron Kid 13:43, 30 October 2005 (UTC)

All motors and generators have a lot of theory in common, but the theory divirges as you get into the details. In engineering texts on rotating machinery, a common approach is to start with synchronous machines and then move on to induction machines and then to DC machines. In each case, the machine can operate as either a motor or generator, but generator controls differ from motor controls, and machines are usually designed for optimum performance as either a motor or generator. Induction machines are not designed for use as generators, but induction motors often serve a dual purpose as either motors or brakes/generators. Induction motors are used for most applications because they are the most simple in their mechanical construction and in the usual start/stop control system. That makes them less expensive. Above 1000Hp or so, synchronous motors are used for more application because they are more efficient and some aspects of construction and control begin to favor them or at least not disfavor them. I don't think that a majority of synchronous machines are used strictly for power factor correction, but that application still deserves to be mentioned. As far as I know, AC machines intended to be only generators are always synchronous. --65.26.227.118 16:26, 30 October 2005 (UTC) I didn't mean to be anonymous. --C J Cowie 16:29, 30 October 2005 (UTC)

[edit] Three Phase Rotating Field Diagram

The excelent animated picture of the rotating field in a three phase machine needs to be located with the relevant paragraph. If nobody objects, I'll shift it (unless someone beats me to it. 86.132.205.37 16:35, 2 June 2006 (UTC)

[edit] Question about steppers

An anonymous editor (68.165.190.225) left the following message in the article:

But how do you wire it?

(referring to stepper motors and digitally controlled servomechanisms, I think). --Heron 12:41, 20 Oct 2004 (UTC)

[edit] Reducing the armature current

An anonymous editor (User:163.1.179.126) has inserted the following text:

Quite counter-intuitively, reducing the armature current will usually make the motor turn faster

I think this is wrong. It is the reduction of FIELD current that causes the motor to run faster (owing to a reduction in the generated counter-EMF with the reduced strength of the magnetic field produced by the field coils).

Which is correct?

Atlant 21:39, 6 Mar 2005 (UTC)

(Apparently, someone else agrees with me since they reverted the new statement out.)

Atlant 13:21, 7 Mar 2005 (UTC)

[edit] Jedlik, 1830

You know...?

http://www.tar.hu/fizfoto/fotok/fizf0575.jpg

gg630504

[edit] Common concepts between single-phase and three-phase headers

Someone just edited valuable data into the "Three-phase induction motor" head, but the text is equally applicable to the earlier "Single-phase induction motor" heading. Shall we just move the new text up there (so "Single-Phase..." continues to be a kind of master description? Or shall we do more-radical surgery, perhaps creating the following headers:

• Induction motors (general concepts of the rotating magnetic field and induction into the armature/rotor)
• Three-phase induction motors as the obvious real-world simple implementation of the theoretical induction motor
• Single-phase motors as a special case with the need for starting provisions

And then, of course, a similar new alignment for synchronous motors:

• Synchronous motors as a variation on how to use the rotating magnetic field
• Three-phase synchronous motors (and the need for starting provisions compared to induction motors)
• Single-phase synchronous motors

Thoughts anyone?

Atlant 20:19, 14 May 2005 (UTC)

[edit] Number of poles

I was taught that the number of poles of a motor is *always* even - every N must have an S. Before I change the article back, can someone point me at an example of an ac induction motor that has an odd number of poles? I can't visualize it... how does the flux get back? If a winding has one end, it has two ends...where's the other end of the winding? --Wtshymanski 22:59, 1 Jun 2005 (UTC)

You're not thinking in "three-phase terms"; in a three-phase world, there's more than a single North and South involved. While it's true that a a) motor must always have a number of poles that is a multiple of the phases and 2) a motor must always have at least two polls, there's no requirement that there be an even number of poles. For example, in my office, I have four different samples of dc brushless motors (which, for operational purposes are really three-phase synchronous motors) and they are all nine-pole motors. (Three of them are small CD-ROM spindle motors and one is a large fractional-horsepower motor from a photocopier.) The use of odd poles is especially common for external-rotor designs where the flux flows through the middle (the merger) of the stationary field coils (as compared to internal-rotor designs where the flux flows through the circumference of the field-coil laminations).

(This has also been discussed on my "talk" page at User talk:Atlant#Electric motor poles.)

Atlant 00:48, 2 Jun 2005 (UTC)

Five and three pole DC-motors on this pic: http://www.floodland.nl/trein/info/digitaal_6_2.jpg --Pjacobi July 4, 2005 18:34 (UTC)

The number of poles is always even... just the number of "physical" poles may not be! This is what's called a "consequent pole motor". You can have a three phase motor with just six physical wound coils in it so they are, say, all North poles. But these types of motors allow more spacing in the iron between the physical poles so the consequent South pole may form between the North poles.--Steve2000 01:49, 28 June 2006 (UTC)Steve2000

[edit] RPM=

What about that equation? RPM = 120F / p works for single phase. Maybe RPM = 180F / p for three-phase. Meggar 2005 July 4 01:00 (UTC)

No, it's always 120 F/p independant of the number of phases; each phase winding has its own poles (though a winding will have the phase belts overlapping). And the number of poles (in an induction motor) is always even, dag nabit...every N has to have an S! See for example Harold J. Herbein Rotating Machinery (1971),Rinehart Press, San Francisco, or any book on ac motors. --Wtshymanski 4 July 2005 03:22 (UTC)

You can "dag nabit" all you like, but the criterion isn't that a motor must have an even number of poles; the criterion is that for each phase, the (vector?) sum of the various poles contributing to the field produces a north and a south pole aligned through the center of the rotor. The nine-pole external-rotor motors that I've described have no trouble meeting that criterion.

I guess I'll have to get my camera and post a picture. :-)

Atlant 4 July 2005 18:02 (UTC)

Alright, it is always 120F/p. The trick is in how they are counted. A three-phase two-pole motor actually has six poles, but two per phase. That is unless it has three physical poles in which case we imagine the nonexistant ones for the count. Meggar 2005 July 4 18:30 (UTC)

[edit] Few things to add... But where?

Nowhere in this article are cars mentioned. I myself can't do the change since I don't know what kind of electric motors are usually used in cars (but I guess I could find out if anyone already knowledgeable isn't available). Moreso, there are no mentions to new electric motors like this one. Raser Technologies has another high-efficiency motor in production already. --Kim Hokkanen

The usual blower, fan, window, etc. motors in cars are quite standard shunt field or permanent-magnet motors. Cranking motors are series-wound motors. Electric motors have never been the main problem holding back electric cars. It's always been *batteries* - if you could store 10 kWH in something the size and cost of a conventional cranking battery, the IC engine would be a curiosity relegated to aircraft and similar applications. If someone has a lot of good text on automotive propulsion motors,it might well be worth an article by itself, but otherwise I'd like to see the main article as general as possible and not turn into a catalog of motor applications. --Wtshymanski 6 July 2005 17:47 (UTC)

Sounds like we need an "Electric motor applications" sub-article! You've already given us a pretty good outline for the "#Automotive applications" section.

By the way, I think the "shunt field DC motor" is probably nearly dead for auto applications; permanent magnets have just become too powerful for electromagnets to compete. I *THINK* I've even heard that cranking motors now use permanent magnets (but I haven't taken a starting motor apart for a few decades).

Atlant 6 July 2005 21:35 (UTC)

Might be - like I said, I don't know much about these yet. The team in Wales claimed that their motor doesn't have any permanent magnets and very few moving parts. So my question becomes: what kind of motor are they talking about and should it be featured in the article? --Khokkanen 7 July 2005 14:29 (UTC)

I added some material related to motor applications to the motor controller article. I was thinking that material might belong here, but it includes some material that is more appropriate for motor controllers.

C J Cowie 16:33, 6 October 2005 (UTC)

[edit] Thomas Davenport was an American blacksmith and inventor who invented the first DC electrical motor in 1834

This web page indicates that Thomas Davenport invented the first DC electrical motor in 1834. http://chem.ch.huji.ac.il/~eugeniik/history/davenport.html

Thomas Davenport was an American blacksmith and inventor who invented the first DC electrical motor in 1834 and made a small model of electrical railway in 1835. He patented a device for "Improvements in propelling machinery by magnetism and electromagnetism" in 1837 (his electric railway). Davenport used his DC electrical motor to power shop machinery, it was the first practical application for the electric motor. Davenport later started a workshop in New York City and published a journal on electromagnetism.

[edit] DC motor equations

If we've got the equation for speed of an AC motor, why not the equation for the speed of a DC motor? I'd add it myself, but I don't know it. --24.163.161.47 18:36, 20 November 2005 (UTC)

[edit] Planetary Electric Motor?

[edit] Deleted Section

Image:PEM.jpg

A recent innovation in motor technology has been the development of the Planetary Electric Motor by VibraQ Corporation in Perth, Western Australia.

The technology is designed to deliver a two dimensional planar motion and utilises the fundamental principle of transverse flux where a current carrying conductor within a magnetic field creates thrust. Oscillatory motion is produced through the electric control of the currents and their phasing within the coils.

The Planetary Electric Motor represents an elegant and unique solution to the problem of creating a planar orbital or variable oscillatory motion, without the use of gearboxes or cranks. Motors can be designed to accommodate required application and are easily scaled.

The energy transfer within this technology is controlled through power electronics and therefore is capable of producing different patterns of motion. It uses controlled flow in a magnetic field set up by permanent magnets, which makes the motor inherently more efficient than a conventional rotary motor.

[edit] History

Above section added: November 30, 2005 User:Vidmes

Reverted: December 1, 2005 User:Wtshymanski (rv - PEM image missing, and in bad place, copy sounds spammish and doesn't really explain the concept, plus I've never heard of it except here on Wikipedia.)

[edit] Comments

What is this exactly? JDR 20:42, 2 December 2005 (UTC)

The web site link does not really explain the concept either and neither does other material (apparently from the same source) that can be found with a Google search. My interpretation is that this is a vibrator that works on the same principle as a tattoo machine or engraving tool. This device appears to add several innovations. It uses both permanent magnets and coils. It uses several magnetic fields and an arrangement for constraining the motion that allows motion in any direction within a plane. The currents in the electromagnets are controlled electronically to cause a pattern of vibratory motion, specifically an orbital motion. The pattern of motion is probably similar to the motion of an orbital wood-finishing sander. Referring to the picture, I suspect that the inner circle moves in an orbital pattern with respect to the outer diameter of the "motor." C J Cowie 01:07, 3 December 2005 (UTC)

[edit] Do universal motors self-destruct from overspeed when operated on AC?

A recently added comment suggests that universal motors can self-destruct from overspeed if operated unloaded. While it's true that powerful DC series motors can definitely self-destruct if operated unloaded, I've never heard of an example of a universal motor self-destructing from overspeed when operated on AC. I've always assumed that it was the inductance of the motor acting to limit the current that prevents the destruction, but I've never actually seen any supporting data one way or the other. Certainly household universal motors (such as blenders, Dremels, power drills, and the like) seem to live just fine loaded only by the friction of their bearings and brushes.

Your thoughts?

Atlant 12:34, 26 January 2006 (UTC)

The problem with DC motors is primarily with complete loss of field current in unloaded shunt and separately excited motors. With series motors, there could be a problem if the load characteristics and the motor's speed-torque curve are such that loss of load could allow a destructive speed. With a series motor, there will always be field current as long as there is armature current. Products like blenders, Dremels and drills are designed to run without an external load. An important part of the internal load is windage. Some of these products have a little fan on the motor shaft to cool the motor. Even without a fan, the windage torque likely exceeds the brush and bearing friction. Altering the design of the product by removing the fan or gearing could conceivably cause a destructive overspeed. Blocking the airflow in a vacuum cleaner certainly unloads the motor considerably and allows a speed increase. I suppose that could lead to failure especially if the fan is already damaged or unbalanced due to vacuuming up rocks or some such thing. --C J Cowie 16:19, 26 January 2006 (UTC)

[edit] hack....why not?

If I have

| NS<rotor>SN|

basically 2 current carying coils fixed in space and magnets mounted on the rotor (such that the polarity facing the coils is the same), is it not a brushless DC motor which doesnt need induction or stepper drive?...and if no, why not? The idea simply is to remove the magnet from the outside onto the inside and rely on the fact that the fixed in space current carrying coil induces a force on the magnet which is mounted on the rotor.--alokdube@hotpop.com

Your rotor will probably rotate 90 degrees and then stop. All electromagnetic motors depend on some arrangement that either:

1. Creates a moving magnetic field (as in induction motors, synchronous motors, and brushless DC motors), or
2. Has some switching arrangement to keep the magnetic fields fixed in space but at a position where they can impose a continuous torque on the rotor (as in commutator DC motors).

Atlant 13:58, 17 February 2006 (UTC)

Please note the following in the above a. the current is in the same direction in both the coils on either side of the magnets b. the magnetic polarity is always the same when facing the current coils c. the current carrying coils are fixed so as seen from above if the current flows upwards in the "fixed" coils, we get the flux into the page, on the Left side and outside the page on the right side. Hence the torque does not balance out. if u want u can always insert 2 more coils on the front and back side. This is being tested right now. A simple way to imagine this is, think of Oesterd's experiment, place a back to back magnetic needle/annular ring magnet in a mesh of wires where the current always flows in the same direction/up to down etc. more like: | | | N--S-rotor-S--N | | |

--alokdube@hotpop.com

It's a little hard to follow your description, but I think what you might be describing is like a squirrel cage motor, but with the difference that the rotor field is generated by passing a current through the squirrel cage between permanent magnets. I can't see how this would rotate, since the field isn't rotating. What is going to set up a torque? Maybe I've misunderstood your description.Graham 06:39, 21 February 2006 (UTC)

Thansk for your comments, I do know what a squirrel cage motor is. This is not the same thing. the torque could be setup as the pole, say north is closer to the current carrying wire as compared to the south consider this

<wire current flowing into page> N-----|-S <wire current flowing into page>

in other words the magnetic needle is hinged at a point closer to one of the poles.

The other arrangement could be is to make the magnets outside (like the outer rotor fan) and ensure that the coil inside carries current in the same direction.

Image:Field plot.jpg

is an example of the field plot

the Blue circles are the coils carrying current into/out of the page and perpendicular to the plane of the page The rest of the circles and dots indicate points with equal magnitude of B

[edit] Tesla's Three-Phase electric motor

A model of a synchronous 3 phase electric motor in my project is here, so it is OK it could be released under GFDL, as far as I am concerned.

The problem was I was not sure which background to choose, and which version of rendering, and whether the image quality satisfies article at all, compared to DC motor rendered in Blender.

3-phase engine is rendered in POV-Ray, and it is easily customizable in regard to number of R rotor poles, S stator poles, other parms, and N the number of wires in each coil. I can easily modify POV-Ray 3D model according to your suggestions.

Here are the images:

Please choose the variant, or propose suggestions. I think three-phase engine is not clearly explained with just a photo of a motor that is not even opened (which is also an option with POV-Ray!!!)

I hope to get some feedback.

There were ideas to clarify rotating magnetic field with a series of pictures showing how vectors of phases add into a single rotating vector - or a movie could do. I just need to convert what was done from Quicktime to MPEG or Ogg. (Recommend a tool?)

Greetz all. -- Mtodorov 69 07:54, 10 March 2006 (UTC)

- i'd go with the third one, it's more defined.

[edit] Textbooks

The Bedford & Hoft text was originally cited as "Bedford and Hoft, unnamed book on power electronics, outdated." I assumed it is the same book that I have and put in a complete citation for it. It is only indirectly related to this article. It should be a reference for Variable Frequency Drive. --C J Cowie 17:33, 12 March 2006 (UTC)

[edit] limits to efficiency

Heat engines have both the Carnot efficiency and a practical upper limit due to heat transfer. Some people claim that Carnot's cycle does not apply to electric motors. I'm wondering if there is any theroetical limit to efficiency and whether this corresponds to a temperature (T_hot) with some physical interpretation (say ionization temperature of the windings). What stops us making a 100% efficient electrical motor? --njh 18:43, 12 March 2006 (UTC)

The Carnot cycle describes a process by which a heat engine converts energy in the form of heat stored in a working fluid to mechanical energy. An electric motor converts electrical energy to mechanical energy in a manner that is quite different from a heat engine.

What prevents us from making a 100% efficient electrical motor is mostly friction. There is mechanical friction due to moving parts sliding against each other the just as happens in a heat engine. There is something similar that happens when electrons flow through an electric wire. The electrical resistance of the wire works against the flow of electrical current and causes electrical energy to be converted to heat. Changing magnetic fields also cause heat in the iron parts of the motor. Any electrical energy that is converted to heat reduces the efficiency of a motor below 100%. With today's technology, large 3-phase AC motors are often 96% efficient. Using superconductors it may be possible to make motors that are quite close to 100% efficient.

Although electric motors are quite efficient, most electrical power is generated using heat engines or by other means that are less efficient than electric motors. There is also energy that is lost as heat is transmitting electricity from the power station to the electric motor.

C J Cowie 21:51, 12 March 2006 (UTC)

I think the true answer is deeper than that. There are many examples of energy conversion that at first glance seem to avoid carnot's cycle, yet when deeper analysed reveal that thermodynamics is hard to escape. (I suspect, though nobody has given me reasons either way, that carnot applies to every energy transformation)

Some examples are fuel cells, solar panels and direct nuclear radiation power conversion. All of these at first glance appear to avoid carnot efficiency (for example, a fuel cell might get 85% efficiency operating at 600K, when the carnot cycle might seem to imply 50% as an upper limit. In fact the cycle is operating from the flame temperature or something.)

All electric motors become less efficient as they get hotter, which might be a symptom of a hidden cycle (or just coincidence).-- njh 00:00, 13 March 2006 (UTC)

(I suspect, though nobody has given me reasons either way, that carnot applies to every energy transformation)

Your suspicion would be wrong, sorry.

Atlant 00:46, 13 March 2006 (UTC)

Could you give a reference that covers this? --njh 01:04, 13 March 2006 (UTC)

Pretty much any good electrical engineering reference on rotating electrical machinery should make this clear to you, but you might want to consider the efficiency of motor-generator units. They can move a surprising amount of electrical power through them (with a full conversion from electrical power to mechanical power and back to electrical power) with a relatively small development of waste heat.

Atlant 01:32, 13 March 2006 (UTC)

That doesn't prove anything, it just shows that the likely Thot is very hot. --njh 09:40, 13 March 2006 (UTC)

As I wrote above, the Carnot cycle describes a heat engine process. An electric motor clearly does not involve a heat engine process. An important Carnot principle can probably, in some sense, be applied to many if not all energy conversion processes.

In Cengle & Boles Thermodynamics an engineering approach, it is stated: "Factors that cause a process to be irreversible are called irreversibilities. They include friction … electric resistance …. The presence of any of these effects renders a process irreversible. A reversible process involves none of these." and the Carnot principle: "The efficiency of an irreversible heat engine is always less than the efficiency of a reversible one operating between the same two reservoirs."

The process of an electric motor is reversible except for mechanical friction, the friction between moving parts and air, electrical resistance, magnetic losses and perhaps some other small items. It is only these items that prevent an electric motor from achieving 100% efficiency.

Increasing the operating temperature of a motor increases the electrical resistance of the copper and aluminum conductors. That would tend to reduce the efficiency. Temperature changes also change mechanical clearances and the dimensions of air gaps in the magnetic circuit. Hard telling what effect that has.

C J Cowie 01:58, 13 March 2006 (UTC)

Thats all very nice, and I am quite aware of that, but it doesn't answer my question. I spoke with a physicist today and he was of the opinion that there was more to it than these surface issues. One interesting thought experiment occured to me: imagine a heat engine driving an electrical generator which heats the hot side of the engine. So the question then becomes one of what the highest temperature achievable with an electric source is (which is certainly very high!). MHD has been shown to do work to at least 15 million K. I shall go digging. --njh 09:40, 13 March 2006 (UTC)

[edit] Switched or variable Reluctance motor?

Sure Ive heard of such a beast- but its not mentioned in the article. Is this just an omission?--Light current 05:26, 31 March 2006 (UTC)

Are these the same as stepper motors?--Light current 08:36, 31 March 2006 (UTC)

I think switched reluctance motors are a variety of stepper motor (with an unmagnetized rotor).

Atlant 14:03, 31 March 2006 (UTC)

OK. Shouldn't these types be put in the article?--Light current 17:32, 31 March 2006 (UTC)

[edit] Repulsion motors and other types

Thank you very much for all the hard work you put in on the repulsion motor section of electric motors. Great addition to the article. Pcb21 Pete 07:24, 12 April 2006 (UTC)

And on that note another "missing topic" that I am trying to find a home for is reluctance motor. As Electric motor is our main article in this area I would like to redirect there, but I don't want to do such a ham-fisted integration job as I did with repulsion motor. Are you able to help out? Pcb21 Pete 08:27, 12 April 2006 (UTC)

If I have time, I will look into that. See also discussion above. There are probably other types of motors, design variations and motor related terms that should be considered for inclusion in this article. --C J Cowie 15:52, 12 April 2006 (UTC)

[edit] Nano motor

I think that consideration should be given to moving this section to one of the nanotechnology articles. It isn't totally out of place in this article, but it is quite different from the types of motors described here. There is already a nanomotor article, but what is described there may not be the same as the nano motor described here. There is also something like this described in the micromachinery article. See also: list of nanotechnology topics and Category:Nanotechnology. --C J Cowie 00:47, 17 April 2006 (UTC)

Well it IS a motor, and what a beautiful animation! It would be a pity to lose it to another page.--Light current 00:55, 17 April 2006 (UTC)

[edit] does horsepower really equal 750 watts?

I have a 3.5 "horsepower" chainsaw which only draws 12 amps at 110 volts. I don't see any discussion of horsepower in this article but elsewhere I have seen that at 100% efficiency 1 HP would be 750 watts. I doubt that 100% efficient motors exist, but perhaps this definition is arbitrary and there are others, perhaps in terms of torque or something. I doubt even marketers could get away with a bold face claim of 3.5 horsepower that violated the laws of physics.--Poodleboy 19:55, 23 April 2006 (UTC)

Used to be about 746 W per horse when I went to school (mind you, horses were big in those days). You have measured it on no load havent you? Try cutting a tough trunk and then measure the current!--Light current 19:59, 23 April 2006 (UTC)

No, I haven't measured it at all. 12 amps is just the UL rating on the device. It is a Remington 3.5 horsepower electric.--Poodleboy 09:13, 24 April 2006 (UTC)

For UL listing, the design engineers (not those devious marketing people) provide ratings on the motor for real world sustained operation. You can calculate sustained horsepower from Hp = (Volts X Amps X Efficiency X Power factor)/746. Estimating efficiency and power factor at 0.8 each, a 12 amp motor will produce about 1-1/4 Hp. (Power factor tells us how much current is used to pproduce power as opposed to magnetizing the motor).

Marketers are clever and devious. They don't usually actually lie, but they often resort to rather obscure versions of the truth. Horsepower advertised for consumer products is usually the "peak horsepower." That is the absolute maximum power that the motor can deliver for a very brief time. Peak horsepower is often measured by increasing the load torque applied to the motor while plotting a graph of the torque vs. speed. The motor's speed decreases as the torque increases and the motor quickly comes to a stop or "stalls" when the peak torque is reached. The peak power is calculated by HP=torque*RPM/5252. Don't try this at home. The manufacturer likely performs this test on the motor alone not the assembled chain saw. Their power supply is capable of safely supplying more current than the typical household outlet can supply. --C J Cowie 21:24, 23 April 2006 (UTC)

A horsepower is an amount of Mechanical work equivalent to 33,000 foot pounds per minute. It dates back to actual horses and I guess your standard nag could be counted on to, for example, raise a 330 pound weight 100 feet in one minute. And yes, it's roughly equivalent to an energy input of 746 watts.

Chain saws, vaccums, and other home appliances that make exagerated claims of horsepower while running off of (say) 15 Amp 120 volt circuits (where the circuit breaker trips somewhere just north of 1800 watts) are, basically, lying, although they'd probably claim they're merely describing the hypothetical peak power of the mechanism.

Atlant 12:32, 24 April 2006 (UTC)

Maybe these ratings are peak horsepower? I've searched the internet, and there are concepts such as service factor and uprated motors, etc. While I found some authoritative discussions of the concepts on commercial site, I haven't found any standards, although the service factor concept seemed to come from some standard. Wikipedia probably could help by filling this void. Here is a link to a pool spa site for gosh sakes, that was about as authoritative as any [1]. Is "peak horsepower" really as useless as some internet articles say? My concept so far, is a little analogous to momentum, a free wheeling motor suddenly brought to a stop, might be applying larger amounts of force that it could continuously, that that peak of power might be useful. For instance, in a chain saw working with a dull chain having trouble cutting a log, it helps to let it rev-up and then the high initial speed has a little more cutting power for an instant, until the chain slows. There are probably analogous examples in other applications, but I don't know if this concept can be made rigorous. Another example, a motor used for pulling something, might be able to use peak horsepower for an instant to get the object moving, overcoming the co-efficient of static friction, and then complete the pulling operation for however long it takes within its standard or brake horsepower rating. Given two motors with the same brake horsepower rating, one with a higher peak rating might be able to get this task started and complete it, while the one with the lower peak rating wouldn't be able to get it started. However, using peak horsepower this way makes it seem a lot like torque?--Poodleboy 09:27, 4 May 2006 (UTC)

I believe what was stated here right above us: These peak horsepower numbers are derived by operating the motor briefly on an (essentially unlimited) power circuit. In that way, for the few seconds before the motor reaches its thermal limits, the vendor can claim truthfully that the motor was developing the claimed five or six horsepower. Of course, because of excess heating, this power level can only be maintained briefly and in the real world, it might well trip the circuit breaker, and there's no way to load your (e.g.) vacuum cleaner to actually require five or six horsepower, but it sure makes a great advertising claim, no ;-) ? At least in your chain saw example (or in traction motors), there's some basis whereby you could actually use this amount of peak mechanical power. But the vacuum cleaner claims are just silly.

Atlant 12:06, 4 May 2006 (UTC)

What limits their power draw on a 15amp circuit? Is the test performed with some kind of limiter removed?--Poodleboy 09:34, 5 May 2006 (UTC)

The circuit breaker or fuse is the main limiting factor. In addition, the high current will probably cause the voltage to drop a little. Even when the current is available, it is difficult to hold the motor at the peak torque point because the slightest increase in the load above the peak capability will caus the motor to stall. The peak torque point on the torque vs. speed curve is not a stable operating point. --C J Cowie 13:10, 5 May 2006 (UTC)

It must be something short of the circuit breaker, because that is not tripping, and it only limits by tripping.--Poodleboy 14:53, 7 May 2006 (UTC)

The motor will only draw high current and trip the breaker if it has a heavy load. The test to determine peak horsepower requires a load that can be carefully controlled and adjusted and measuring equipment that records torque and speed data as the torque and speed change rapidly. Once the torque and speed data has been recorded, horsepower is calculated. Because of the difficulty of controlling the load and making the measurements, it is generally not possible to perform this type of test on an assembled saw, vacuum cleaner of whatever. Only the motor is tested. --C J Cowie 20:24, 7 May 2006 (UTC)

[edit] Comparisons between US and UK domestic electrical installations

Yeah. I was wondering about that!. How much current can you get out of a US wall socket at 110V? 120V (Ie nom rating, not cable frying, fuse busting current)--Light current 21:35, 23 April 2006 (UTC)

In bathrooms, kitchens and dining rooms, 20 amp circuits are required. I believe that 15 amp circuits are permitted everywhere else. The nominal voltage is 120 volts. Circuit breaker and fuse ratings are the same as the nominal circuit service current ratings. --C J Cowie 21:56, 23 April 2006 (UTC)

Bathrooms??? You dont allow mains outlets in bathrooms do you? V. dangerous when your in the altogeher and wet you are a very good conductor!!--Light current 22:02, 23 April 2006 (UTC)

Bathroom, kitchen and outdoor outlets are required to be protected by ground fault interrupters. Hand-held hair dryers now often have GFI protection built into the product. --C J Cowie 22:06, 23 April 2006 (UTC)

Aha. We have solid cross bonding of all accesible conductive parts in bathrooms to create an equipotential zone and no sockets allowed. Even the light switches have to be outside or cord pull types if inside.--Light current 22:35, 23 April 2006 (UTC)

The GFIs are quite effective, but bathrooms here had outlets before GFIs were invented. Installations are supposed to be brought up to code when repairs or improvements are done, but there are lots of unprotected outlets in older buildings. Switches and lights are not usually on GFI protected circuits, but any metal that is not part of the circuit is grounded with a separate ground wire that does not carry current. --C J Cowie 22:34, 23 April 2006 (UTC)

What current are your GFIs set at, and can you survive this current for the time it takes to trip out?--Light current 23:21, 23 April 2006 (UTC)

I believe that they are very effective at preventing death by electric shock. I don't know the specifics for USA designs, but I suspect they are similare to the EU designs. Look at the Residual-current device article. --C J Cowie 23:41, 23 April 2006 (UTC)

We brits are about the only country in the world that don't accept sockets in bathrooms (at least in our accepted standard BS7671, however i know of at least one person who got a schuko socket wired to german regs past building control). Most countries assume that people have enough common sense not to use hand held appliances while in the bath! Plugwash 23:48, 23 April 2006 (UTC)

Whats a schuko? Most countries must have more intelligent people than we have here!(Drying your hair whilst in the bath uused to be a favorite)--Light current 23:57, 23 April 2006 (UTC)

BTW Plugwash, I think this talk could be moved to a more suiatable page. What think? Can you name one?--Light current 23:58, 23 April 2006 (UTC)

Schuko is the manufacturer of a common European plug/socket family.

Atlant 12:26, 24 April 2006 (UTC)

Shucks!--Light current 14:38, 24 April 2006 (UTC)

[edit] material used to manuf. brushes used in a.c & d.c. rotating machine

Hi

Can anyone tell me what is the most common material used to manufacture brushes used in a.c. and d.c. rotating machines —The preceding unsigned comment was added by 84.68.243.36 (talk • contribs) .

Carbon or a Carbon/Copper composite, I think.

Atlant 17:56, 2 May 2006 (UTC)

i think carbon wit copper cos carbon might detoirate fast but in my text it says only carbon brushers by yunusmecci@hotmail.com

Here's what looks like a good reference:

http://www.repcoinc.com/carbon_brushes_fld/reference.asp

And it looks like most brushes are varieties of carbon but yes, some are loaded with metal powder, especially where the lowest resistance is required.

Googling for "brushes carbon commutator material" produced lots of data.

Atlant 15:19, 3 May 2006 (UTC)

When motors and generators first appeared, the brushes really were brushes of copper wire. They were carried on a moveable ring with a handle. The handle moved the brushes around the commutator and the aim was to find the position of minimum sparking (the process was known as 'rocking the brushes'). As the load changed, the brushes needed to be moved to minimise the sparking once again. As motors developed, 2 systems were developed to avoid the need to rock the brushes. One was interpoles between the field poles (the article doesn't mention them). They were wired in seies with the armature and arranged such that they reversed the distortion of the field caused by the armature's own field. The second development was 'high resistance brushes'. These were now made from a formulation of carbon and copper and even though they present a resistance measured in milliohms, they were high resistance compared to the original copper wire brushes. This 'high' resistance limits the spark caused as the brush breaks contact with a commutator segment by effectively raising the resistance of the contact as the segment moves beneath it, rather than suddenly breaking connection. On some particularly high current/low voltage motors, such as automotive starter motors, the brushes contain more copper than carbon, to the extent that they almost look like solid copper.

[edit] Question on Dates

The article refers to Faraday and Maxwell in the 1820s. Maxwell was born in 1831. I didn't want to just take the sentence out... Kephart 05:47, 10 June 2006 (UTC)

Thanks for noticing. I reworded the sentence. --Heron 11:11, 10 June 2006 (UTC)

[edit] Citation needed

This is highly dubious. Removed till a citation is provided.

[rotating magnetic field principle] was employed by scientists such as Michael Faraday in the 1820s and later James Clerk Maxwell

204.56.7.1 15:40, 28 June 2006 (UTC)

[edit] AC motors and DC motors

Could someone split up AC motors and DC motors? This articles is huge! Just wondering. 134.193.26.56 18:48, 30 June 2006 (UTC)

43 kilobytes long : Wikipedia:Article size; > 30 KB May eventually need to be divided (likelihood goes up with size; this is less critical for lists). Thanks. 134.193.26.56 18:50, 30 June 2006 (UTC)

[edit] Torque: current or voltage dependent?

This page says " So what voltage should you operate at? Well, unless you have a battery voltage/current/power limitation, you should operate at 6V. This is simply because DC motors have higher torque at higher voltages."

The article says "Generally speaking the rotational speed of a DC motor is proportional to the voltage applied to it, and the torque is proportional to the current."

I'm confused. --CAD6DEE2E8DAD95A (hello!) 13:46, 4 July 2006 (UTC)

Ohm's Law is the problem. A motor coil acts like a resistor, so you cannot increase JUST the voltage. If you increase the voltage across the motor coil, you also increase the current, and that increases the torque. Torque is proportional to current, not to voltage, but because of Ohm's law, current is proportional to voltage. --Wjbeaty 17:51, 4 July 2006 (UTC)

As Wjbeaty says ohms law comes in, a stalled motor driven by DC essentially acts like a resistor with current proportional to voltage. So the higher the voltage the higher the current and the higher the starting torque. Plugwash 16:59, 1 September 2006 (UTC)

Why is saturation mentioned no where??