Coiling a motor

Hello everyone,
I recently bought a 1/4hp motor that i want to recoil differently. The rotor contains four electro magnet and the stator contains two. The
metal is about twice on the stator than the rotor. I managed to put 550 turns of 29 gauge wire on the rotor, it gives an somewhat appreciable electromagnetic force. I want to get the same on the stator but I am not getting the results. I first coil with 550 turns of 29 gauge, but twice the metal made it a lot weaker then the rotor and by putting them side by side, they would stick together even if they had a repulsive polarity. I then used 200 turns of 24 gauge wire it did give me a good electromagnet but pulls 4 amps of current, even if i use more turns, it still uses a lot of current. will the rotor never heats up. They are all hooked up to a 12v battery. What are the steps of obtaining the same magnetic field on the stator and the rotor. ? without using too much current on the stator?
thank you
ken
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lerameur wrote:

What were the original turns counts and wire sizes? Does the motor have brushes? Is the rotor and stator connected in series through those brushes?

What metal are you talking about? The core or the windings? Twice what? Mass?

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I received the motor already stripped from its wires, It had been passed in an oven to remove all the copper wire, I got it from a shop where they rebuilt motors.

The mass is the soft metal core, otherwise it would be the coil metal, just referred to as coil windings. The mass i do not know cause the stator are all connected together, The size would be the area of the metal. If you want I can take a picture and post it on a web site.
ken
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lerameur wrote:

That would be very helpful. Bring us a link to the photos.
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Hello,
I added some picture at the following link: http://www3.sympatico.ca/lerameur/coil /
please tell me if more explanation is needed.
Ken
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lerameur wrote:

Are the copper commutator bars under the tape? If not, what do you intend to attach the rotor wires to? Does the motor case include brush holders?
What makes you think that modifying the stator pole pieces as you describe (cutting off the "long legs" and drilling holes will improve the operation of the motor?
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It's been 20 or 25 years since I worked in the rewind shop, but I'll give my 2-1/2 cents worth. Looking at the rotor picture, it is divided into four sections and each section has slots for more than just one coil per section. I think it would accept 3 coils per section. The best picture I can find is here
http://www.maxxprod.com/mpi/tips_files/ss6.jpg
It shows each slot is shared by two coils. I hope you plan on dipping and baking the rotor and stator to secure the windings, it won't last long if you don't. I just went back and reread your original post, you said "I want to recoil differently" so my response may have little relevance. Good Luck Mike
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The original rotor had 2 interwoven coils in each slot using 24gauge wire , I believe the amount of turns was about 50, I get the real number later, but it not relevant in my motor Since I am using different gauge wire and position in my motor, it is totally different, no comparison possible.
Also , yes there is a slip ring where the electrical tape is, it is not shown on the picture because i did not think it was useful for what I am trying to do at this stage. So the two stator coil will be in series and two coils on the rotor will also be in series. the reason I cut the stator core metal was to make wight of both stator and rotor identical. I was hoping to get the same amount of metal with the same numbers of turns. This would of given me two identical electromagnet on the rotor and stator repulsing themselves until the next 1/4 turn. The only different i can see is the waffle layers are thicker on the stator then the rotor.
Ken
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hello,
I worked on the motor all day today. I made an excel sheet and would like to know if my calculations are correct. It seems that no matter how many turns I have, my electromagnet will have the same force but uses more or less current depending the length used. Is this correct? Here is the link of my excel sheet: http://www3.sympatico.ca/lerameur/coil/motor_core_calculations.xls
ken
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lerameur wrote:

No. The number of inches for a single turn will increase after the first layer is wound. You use 8.5 inches regardless of how many turns.
Ed
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Ok but for a ball park figure i guess this is good enough. So if you look at the power consumed P=V*I, There is a lot more power used for a 100 turn then for a 1500 turn, both giving almost the same amp turn. So you can save energy by increasing the number of turn, using less power and still having a motor giving the same mechanical output !?
K
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Ah... um... let me be as polite about this as I can be. It is clear from reading this thread so far that you really don't understand the design of motors very well.
Cutting the 'ears' off of the stator pole pieces was a bad idea. They were there to spread the magnetic field from the poles out so that it would cross as much of the rotor iron as possible to the stator pole piece on the opposite side. Drilling holes in the stator pole pieces just reduces the permeability of the pole piece and reduces the field strength. The total 'mass' of the pole pieces is only vaguely related to how strong a magnetic field it can sustain.
Measuring the strength of the magnetic field when out of the motor frame is pretty pointless. The maximum 'pull' of an electromagnet is a function of the MMF (amp-turns) and the total reluctance of the magnetic circuit. Air is a much poorer 'conductor' of magnetic 'lines-of-flux' then iron. In a proper motor frame, the frame itself completes have of the magnetic 'circuit'. The 'lines-of-flux' come out the pole face, traverse a thin air gap to the rotor iron, flow across the rotor iron (assuming you haven't drilled it full of holes :-( ) across another thin air gap to the opposite pole piece, through that pole piece around the circumference of the motor frame back to the back-side of the first pole piece. Putting more air in this 'circuit' (i.e. drilling holes in the stator pole pieces) will make the reluctance of this higher and *reduce* the total magnetic flux around the rotor's conductors. That will reduce the capabilities of the machine.
The numerous slots in the rotor were designed to carry many small coils as you have deduced from its original construction. This maximizes the number of current-carrying conductors that will be within the magnetic field of the stator at any given moment, thus maximizing the amount of torque. Also having coils in each slot means the torque developed will be much smoother. Your 'four-pole' rotor design will have severe 'cogging' as the rotor rotates around with some positions producing zero torque and others producing maximum.
In your sketch you show the rotor and stator pole pieces directly facing each other. While it is true that the repulsive force will be maximum at that point, you will get *zero* torque at that point. The repulsive forces will push directly toward the rotor's axle and not develop any torque at all. To develop torque you need a force and a moment arm. In the position of your sketch, you have no moment arm.
Using many turns of fine wire for the stator (i.e. shunt field winding) *does* reduce the I^2*R losses in the stator. As you surmised, using large wire means more current but fewer turns, while fine wire means less current but more turns. Either way you get about the same number of amp-turns to generate the stator's magnetic field.
But the amount of current flowing through the rotor coils is more complicated. Not only is there the resistance of the wire, but the fact that the wire is moving through a magnetic field (at least hopefully). So there is a voltage induced in this wire (ala Faraday) that will complicate the current calculation. In fact, in most DC motors this electromotive force is the predominant term and the resistance is a couple of orders of magnitude less significant (i.e. about 100 times less). Without going into all the math, the result is simply TANSTAAFL (There Ain't No Such Thing As A Free Lunch). To get more mechanical power out, you have to put more electrical power in. And electrical power flow in will *always* be higher than mechanical power flow out.
In commercial motors, the many coils on the rotor are usually connected in series or parallel or some combination (google for 'lap-winding' and 'wave-winding' to get an idea how they would be connected). These coils are connected such that the coils carry current almost all the time. Being in a wide magnetic field (owing to those pole tips you've cut off), they have forces acting on them almost all the time and hence produce a nice steady torque. The one instant that a particular coil does *not* have current flowing is when the current is about to be reversed by virtue of the commutator. Curiously, this happens when the coil is located exactly where your sketch shows. At that moment, the amount of electromotive-force induced in the coil is nearly zero and the current can be reversed without excessive arcing as the commutator segments connected to this coil are momentarily shorted out by one of the brushes.
When you mention 'slip rings', you probably mean 'commutator'. DC motors use a segmented ring where each segment is insulated from the others and connected to opposite ends of two coil windings. Thus the brushes can alternately connect to different coils and at different ends of the coils as the rotor rotates so as to keep the current through the coils in the proper direction to maintain smooth torque generation. 'Slip rings' is a term used for a continuous ring that is insulated from the shaft. It would connect one coil connection to one brush all the time and not provide this electro-mechanical switching. You *could* use solid-state electronics to control the current flow through the coils, but you would also need some sort of shaft encoder/ sensor so that your electronics could detect the shaft position and know exactly when to reverse the current.
Better go study some DC motor theory for a while. Or just continue to experiment on your own, that's fine if you want. But chances are if you do your own experiments, you'll start to realize that the 'normal' design of DC motors is the-way-it-is because it works better then all the other designs. Over 100 years of 'experimentation' is how the current design came to be what you see today.
daestrom
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wrote:

daestrom ,
thanks for the theory.
I was told that the more metal used the less powerful the magnet. is this true ? My goal is to make a very simple motor. Once this is turning, I will fill in the void, by that I mean when the motor has no impulse and is just spinning on momentum. I will add mot coil. Tell me something, I put up an excel spreadsheet on an early link. On this, my calculation showed me that even with more turn of a fine (30 gauge wire) I can never make an electro-magnet as power as when I used an 18 gauge wire. is this true? Most DC motor i have seen so far have a permanent magnet. The motor I am using was initially an AC motor, that I am rewinding it in a DC fashion motor. I know it is not going to be as efficient as an overlap winding motor but I want to learn about the winding, gauge wire and metal aspect. I have not found a book speaking about the theory of this. OOoh lots of book on calculations, efficiency and how a motor generally works, but they do not go on details on gauge wires or such things. Any books you recommend on this subject?
ken
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----------------------------

Daestrom has given you good advice. The advice you have re use of more metal- is questionable and not necessarily true(i.e wrapped in "if this, then that" which is meaningless without the "this" and "that"). In a typical motor, in the normal operating region, the air gap is far more important.
The field windings are designed to produce a given flux density at the air gap which depends on the ampere turns. You can use any combination of turns and current to get the desired level (which is limited by iron saturation but mainly determined by the air gap. However, reducing the current and increasing the number of turns runs into problems in that, due to space and economic considerations, the wire size would have to be reduced- so with more turns and smaller wires, the resistance of the field winding increases. It is not a matter of turns or of current but it is a matter of net ampere turns. First figure out the required amp-turns needed to produce the desired flux density in the air gap for the desired pole area. then the problem is to determine the best balance of turns and current for that situation. Whatever the field I^2R loss is- it is only a small part of the total power balance-say 2-5%. so this is a secondary concern. Now, in a typical DC motor, the field pole is quite wide so that it "covers" more of the actual winding. The ideal would be to have half the rotor winding under each pole and these two halves in parallel. Physically this can't quite be done. Curtailing the pole span can reduce field losses but will certainly have an adverse effect on the motor operation which is far more important. Why take a 50% hit on performance to reduce the field loss from 3% to 2.5% ?
Many small motors do have a permanent magnet. However, once you get beyond "small" you will have electromagnets.
Another puzzler is that you are rewinding an AC motor as a DC motor. Somehow this is doomed to failure as a typical AC motor doesn't have a commutator. If the motor you are winding has a commutator -chances are that it is a "universal" or series motor which is essentially a DC motor that can run on AC (actually works better on DC)-so what you are attempting to achieve is a puzzle.
Daestrom suggested that you look at the theory of DC motors. DO THAT. Look for texts on motor design. What these will tell you is what has been found from over a century of practice and theory, is to map out "where there be dragons" and how to avoid them.
--

Don Kelly snipped-for-privacy@shawcross.ca
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essentially, yes.
If the motor is cooled, or only used for short durations you can over-drive it a bit.
Bye. Jasen
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wrote:

Your post doesn't make a lot of sense. Yeah, you may know what you are doing, but anyone reading the post won't
We could make a lot of assumptions from what you post - like presumably this is a DC motor or AC/DC? You don't say.
You shouldn't expect the highly subjective idea of magnetic pull to translate into real world results. It may . . .but don't bet on it.
All engineering is compromise. You need to look at the "ampere turns" of the original, and translate that for the lower (?) voltage. Voltage goes down, wire size and current goes up for the same horsepower output. Don't worry about "pull" or mass of iron involved. Someone more knowledgeable than you, already made those compromises.
Try to match the original for ampere turns if this is DC. Ampere turns translates into magnetic force - directly.
Always post exactly what you have (in generic terms) and what you want to achieve.
And my hats off to you - since you're actually tinkering with it - but the rules do work, so learn them and apply them.
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Would we assume that at max torque, the gauss of the field is equal to the gauss of the armature? Lets say 10,000 gauss in each coil (20,000 total) gives force X. If one coil has 5000 and the other 15000 would the force be 5000? 15000? 20000? Thanks!
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----------------------------

------------------------ No The flux of concern is the air gap flux due to the field. The armature current will produce a flux which is ideally perpendicular to the field flux and is lower because the air gap is larger between poles. This can have a secondary and unwanted effect called armature reaction. Voltage in the armature is due to the flux produced by the field.
Get a text on the operation of DC motors.
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==================================================I ask about force, you babble about flux, and tell me to get a book on oeration of dc motors. ("Hook the red wire to the + terminal, the black wire to the - terminal"). I'd give you an F for reponding to the question. Let me ask it in a different way. A permanent magnet with gauss X can pull Y lbs Z inches from a steel plate. Do 2 of these magmets pull 2*Y lbs at the same distance? If the magnets have different strength, does the force still arithmetically sum? (I suspect that it is 'bad design' to have either the field or the armature a lot stronger than the other. Agree?)
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I am not sure about this, but I think they will cancel. Imagine two people pushing each other, One can push with 200newton and the other can push with only 100newton, the end result would be the same as one person is pushing with 100newton and the other one not pushing at all. Ken
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