# Probably a stupid question



## major (Apr 4, 2008)

Winfield1990 said:


> In an electric motor instead of using turns of wire , if I had a cast sleeve to replace the windings.
> 
> exactly what would happen.


Well we had a bad start, didn't we? Lots of different kinds of motors out there. I have no idea what kind of motor you're talking about. But the cage induction motor rotor is cast in one piece instead of being wound. And homopolar* motors use a copper disc for the armature.

I don't know "exactly" (that is pretty demanding of you), but vaguely, you get lower generated voltage due to fewer turns.

Regards,

major


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## frodus (Apr 12, 2008)

Not likely going to work at all

A coil has an entry and exit for current.... so how does a cast piece put current into and out of the coil? Its just going to look like a short circuit.

Also, the copper coil, is actually a really long piece of copper wire with a thin insulator on it. Its not conductive on the sides where it touches the winding next to it. 

Also, If you had a rotor with 100 windings, it would use less current and higher voltage than something with 1 winding (cast piece) for the same amount of "flux".

Plus, in order to generate the magnetic flux, you need a circular path for the current, and just 1 huge winding isn't going to be enough to really generate that without having a HUGE amount of current. 

There's LOTS of information out there on motors, how they work, how they're build....etc. Maybe you're just not looking in the right place..... I'd recommend going to a library, there's TONS of books on motor theory. Motors are what, 100+ years old? There's plenty of info out there on every different kind of motor, try the library first, if not, barnes and noble.


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## major (Apr 4, 2008)

Winfield1990 said:


> but you said I would get lower generated voltage due to lower turns *so a less powerful motor* , since the amount of copper being used even though there are less turns is the same. Would that still be less power?


Hey Winfield,

Just as you put inferences in your questions before, you now do it to my answers. I did not say "less powerful", did I? What I said was lower generated voltage due to less turns. And that relates to the volt/amp ratio. So you could get the same motor output in your example from the "solid coil", which would relate to a half turn, if you had a supply voltage of a very low potential and high amperage. So such a motor design may be reasonable for a supply of say 0.1 volts and 1000 amps for a 100 watt motor. 

Regards,

major


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## major (Apr 4, 2008)

Winfield1990 said:


> Information just seems to be very limited.


Hey Winfield,

Just point at "major" in the upper left of this post and click. Then go to past posts. Take an hour or two and read my past posts on motors. I've covered it quite extensively. Showed the basic equations, how to use performance plots and even coil turn modifications. And then you have me here to ask about it. All I want is an intelligent question from you 

Regards,

major


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## major (Apr 4, 2008)

Winfield1990 said:


> You didt have to say it so hurtful  will do.


Sorry Winfield,

I put the smiley after it. 

From my prospective, I see the same questions over and over and somehow I try to reply with the same answers said differently. Often I can refer back to previous post. But most times it is quicker just to compose something. And then my macabre humor can get into the mix.

Sorry again and hope you can find what I have thrown out there useful.

major


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## icec0o1 (Sep 3, 2009)

Winfield1990 said:


> As for connection the cast would be made with wires built into the mold so they would come out with their own connections. The molten metal would fill the tube openings of the cast so whe the cast is pulled apart it has the connecting wires also.
> 
> So the loops are there to be able to create a stronger field with less volts going through the wire but more amps , so less loops I just have to use more volts and less amps to achieve the same thing?


The second paragraph is the opposite of what would happen. You could cast a single U cast of copper for a single loop. Since the "wire" would be thicker, you could pass more current through it. The voltage is kind of irrelevant as it only applies to the maximum speed of the motor. 

So 10V and 20A will give you 200 watts to a motor with a, let's say theoretical speed of 1000rpm where torque = 0 (so it can't accelerate any faster) and 0.2ft/lb torque at 500rpm. 
20V 10A will also give you 200 watts but for the same motor, theoretical speed would be 2000rpm and you'd get 0.1ft/lb at 1000rpm. If you have a 2:1 gearbox, you'd get 0.2ft/lb at 500rpm so the same amount of power, except for the losses in the gearbox. 

Most importantly, a single loop will not be efficient at all as a larger portion of the current will be converted to heat as opposed to a magnetic field. There is a certain amount of turns for the maximum efficiency possible of a motor for certain applications and if you go into the physics of it, you can calculate it.


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## major (Apr 4, 2008)

Winfield1990 said:


> Major I read all of your past posts , I dont feel they helped me at all your posts topics and answers to those topics are totally different from the info ive been looking for.


So the basic motor equations for voltage, speed, torque and amps are of no interest, or maybe you knew that. Oh well. Good luck with what ever it is you want to find.


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## icec0o1 (Sep 3, 2009)

Winfield1990 said:


> "So 10V and 20A will give you 200 watts to a motor with a, let's say theoretical speed of 1000rpm where torque = 0 (so it can't accelerate any faster) and 0.2ft/lb torque at 500rpm.
> 20V 10A will also give you 200 watts but for the same motor, theoretical speed would be 2000rpm and you'd get 0.1ft/lb at 1000rpm"
> 
> I understand what watts are and how to get them I sometimes confuse volts and amps from one another but so.
> ...


The theoretical motor at 1000rpm will have a back emf of 10V so you wouldn't get any current going through it. If you want to go faster than 1000rpm, you'd have to increase the voltage.

So technically, the motor spinning at 1000rpm will consume 0 amps (0 watts) if you provide 10 volts and something like 5 amps (100 watts) if you provide 20 volts.


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## icec0o1 (Sep 3, 2009)

Winfield1990 said:


> your values are different than your last example thats whats confusing me.
> 
> 10v x 20a = 200watts = 1000rpm / 0torque
> 20v x 10a = 200 watts = 1000rpm / 0.1torque
> ...


20 amps is what your battery can supply. At 0rpm, you can push all of those 20 amps through the motor. Once the motor starts going, it produces back emf or resistive voltage. At 1000rpm, your battery is trying to push current with 10v potential but the motor is pushing back with 10v so no current flows. At 999rpm, you'll have ~0.00001 torque. Of course, the motor will never reach 1000rpm but will get infinately close as time goes on, provided you're feeding 10v. If you increase the potential to 20volts, now the battery pushes electrons stronger and current can flow again. 

The 200 watts are a maximum figure. That's why the motor winding resistance and coils is very important and the optimum varies with different projects. 

Getting back to your original question, a single casted copper loop will have very, very little resistance. The motor would have incredible low end torque as it'll allow you to pass hundreds of amps at very low voltage. It'll probably have efficiency in the 10% range however and you would need a massive cooling solution.


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## major (Apr 4, 2008)

Winfield1990 said:


> Are the back EMF's a curve or a linear increase


Hey Winfield,

It depends on the flux. If you're looking at Permanent Magnet (PM) motors, the flux is constant, until you get into high armature demagnetization or temperature extremes. So the generated voltage (what you call back EMF, I think) would be linear WRT speed.

Here are a couple of paste jobs from prior posts of mine showing the equations using this.



> Actually the number of armature conductors is the important factor in the performance of the motor. But the motors you speak of use a single turn wave wound type armature. So the number of conductors in the armature is twice the number of comm bars, or one turn per bar.
> 
> Eg = K * Wa * Flux
> 
> ...





> The motor is not just resistive. There is the back EMF (BEMF) or as I prefer to call it generated voltage (Eg). This is a potential (voltage) which opposes the applied voltage (battery, or Vb). Motor resistance (Rm) is very small, as is battery resistance (Rb) and lead resistance is so small it is usually ignored.
> 
> So the voltage equation for the motor circuit is:
> 
> ...


Regards,

major


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## icec0o1 (Sep 3, 2009)

Winfield1990 said:


> What defines the maximum amps that the motor is able to push as long as the EMF's are not limiting them and also the batteries?
> 
> Is it the heat being produced in the coils?


If you're talking about a wind turbine or regenerative breaking as in the motor producing energy, the maximum it can push depends on the flux or the strength of the magnets used. 

If you're talking about how many amps you can feed to a motor at lets say 10rpm where EMF is negligible, it would depend on the AWG or thickness of the copper wires in the motor's coils. The thinner they are, the faster they'll overheat and burn up.


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## Woodsmith (Jun 5, 2008)

Winfield1990 said:


> I know theyve been around for a long time , but I just cant seem to find really good info over the net atleast from my sources is all I was meaning from mainstream.
> 
> You can easily type in about an IC engine how they work and find much more detailed information about them than electric motors.
> 
> I guess alot of that has to do with ICE's are really really simple though. Electric motors are more complicated unless only just because education now days sucks


One of the issues with answering your questions, IMO, is that sometimes you need to have a better understanding of how a thing works before you try to understand how modifying the thing would work.

For example, as you say, you can get a lot of information on the net about how ICE works. ICE had more moving parts but is fairly simple to understand the basics of as you can see the moving parts and the stuff that makes it move.
Electric motors have fewer moving parts but rely on something much more complicated to understand in how it really works.

It's like you are kinda asking if an ICE would work if you made the cylinder head out of a solid lump instead of a thing with holes and fiddly moving bits in it when you don't yet know what is inside an ICE nor understand the Otto cycle.

Replacing a field coil with a solid cast lump of copper is a bit like suggesting replacing your central heating plumbing system at home with 3' of 8" sewer pipe on the end of the boiler. It would probably hold the same amount of water but what purpose would it have?


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## Woodsmith (Jun 5, 2008)

That was where I was a few months back, I hadn't much of a clue.

I've done a lot of reading since then.

Have a look at this thread, there is a link to a free book on motors you can down load.
The direct link is here:
http://greenev.zapto.org/electricvw/Electric_VW/PDF_Books.html

I have read the whole book now but I had to print it out in sections and turn it into an A5 book that is over an inch thick.


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## major (Apr 4, 2008)

Woodsmith said:


> One of the issues with answering your questions, IMO, is that sometimes you need to have a better understanding of how a thing works before you try to understand how modifying the thing would work.


Hey Wood,

Wise opinion, IMO  I hope you don't mind if I quote you on that.

Regards,

major


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## Woodsmith (Jun 5, 2008)

You're welcome to the quote Major, I use it a lot when I am teaching. 
Some of my students design the most fantastical pieces of furniture and yet haven't learnt the basics of how wood behaves as a material. Then they don't understand why I tell them that either it won't work that way or won't survive beyond a few weeks of changable humidity.

Winfield, the book is a big read.
I printed it out in 10 sections of 40 pages, double sided, A5 booklet format and then assembled it as a bound paperback. Great bedside reading for an autistic person.
It is mostly ac motors with a section on dc but it is all relevent as it will tell you of the different types and how and why they work.


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## Woodsmith (Jun 5, 2008)

Try some of these at a much more basic level.

http://electronics.howstuffworks.com/motor.htm/printable
http://www.explainthatstuff.com/electricmotors.html
http://www.phys.unsw.edu.au/hsc/hsc/electric_motors.html
http://video.google.co.uk/videosear...sult_group&ct=title&resnum=4&ved=0CB0QqwQwAw#


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