Author Topic: Which is more efficient? alternator serpentine-coil  (Read 1548 times)

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copilador

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Which is more efficient? alternator serpentine-coil
« on: February 17, 2017, 12:51:00 PM »
Hi.
Which alternator is more efficient? for generator axial eolic, coil or serpentine:



Thanks

joestue

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Re: Which is more efficient? alternator serpentine-coil
« Reply #1 on: February 17, 2017, 02:58:24 PM »
If the coils are the same electrical width, then the coil that has more copper in it is more efficient. (also the coil that fits the same copper in a smaller air gap, due to more compact coil configuration.)

The problem with serpentine coils is the end turns are slightly longer. this may not matter depending on other details. for example the 12 pole 36 slot car alternator, due to the length to width ratio of the coils, it probably wouldn't make a significant difference if it was serpentine wound or if each pole had its own coil.


in the first example, you can see that you can't fit any more copper in the coil structure without making the coil less efficient electrically, that is, making the inside width approach zero. which wastes copper losses because a coil with a width of zero doesn't make any voltage. by volume, the first coil might be half as efficient as a solid plate of copper.

in the second example, it appears you can add about 50% more turns and still fit those coils in place. also the end turns are longer than they need to be. you can make the second configuration with separate coils, you are not stuck with the serpentine configuration.

Warpspeed

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Re: Which is more efficient? alternator serpentine-coil
« Reply #2 on: February 17, 2017, 04:37:20 PM »
Yup, Joe has nailed it.

You want as much copper as you can possibly fit  into the narrowest possible air gap.

The radial part of the turns in each coil are the only part of the winding which develops power. The concentric part of the turns produce nothing but just adds extra wire length and resistance. Obviously there must be a concentric part in order to produce full turns so there is not much you can really do about that.

Looking at those two sets of windings, the first  appears to be a much flatter winding which should enable a narrower air gap.  The second has overlapping full coils that cross over making the winding more bulky and wider requiring an increased air gap to clear the crossovers.

With a radial flux machine its very easy to arrange for overlapping windings by placing all  the bulging crossovers right out of the magnetic path beyond the ends of the rotor.

but with a three phase axial flux machine, you still need crossovers but it needs some thought how best to do that while keeping the windings and air gap as narrow as possible with minimum overall wire length per turn.




joestue

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Re: Which is more efficient? alternator serpentine-coil
« Reply #3 on: February 17, 2017, 04:44:54 PM »
The second has overlapping full coils that cross over making the winding more bulky and wider requiring an increased air gap to clear the crossovers.

but you only have the magnets cover the radial part of the coil, the magnets protrude out of a disk, so the end turns where the wires have to cross over each other, that part can be about double the thickness of the air gap between the magnets for practical purposes.

here's a cross section of what it should look like.
http://motoredbikes.com/attachments/cross-section-png.26611/

in order to pull this off you really need a press to compact the coils while the epoxy or polyester resin cures to get a flat enough coil structure.
« Last Edit: February 17, 2017, 04:50:08 PM by joestue »

copilador

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Re: Which is more efficient? alternator serpentine-coil
« Reply #4 on: February 17, 2017, 09:38:53 PM »
Thank you, for the answers,  it's very good for me.  :)

Adriaan Kragten

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Re: Which is more efficient? alternator serpentine-coil
« Reply #5 on: February 18, 2017, 01:07:33 PM »
It is not only that you have to realise the maximum amount of copper. What is also important that the copper is at the position where it generates the maximum voltage. If you have an armature with for instance 12 poles, the magnet pole angle is 30 degrees. This means that the optimum position of the radial parts of a coil must also make an angle of 30 degrees with each other and that the radial wires must point to the centre of the shaft. For this condition, the left part of a coil produces the maximum voltage when a north pole is passing just at the same time when a south pole is passing the right side of a coil. However, this positioning is only possible for the central wires of the coil. For the inner wires the distance in between the wires is too short and for the outer wires, the distance is too long. The generated voltages are therefore out of phase and the resulting voltage is therefore lower than for the central wires.

The upper photo shows a 1-layer winding with rather thick coils and therefore with many wires which don't have the optimum position. The lower photo shows a 2-layers winding with thinner coils but more wires have a position close to the optimum and therefore more power and a higher efficiency can be expected for a certain rotational speed even if both options use the same amount of copper. But a 2-layers winding has crossing coil heads and is therefore more difficult to manufacture for an axial flux generator. But for radial flux asynchronous motors it is a standard configuration.

In my free public report KD 596, I give the description and a picture of a 12-pole axial flux generator with a 1-layer winding with 9 circular coils. But in chapter 11, I give an alternative 2-layers winding with 18 coils. The generator drawings for the option with the 1-layer winding are given in a separate manual available at the bottom of the list with KD-reports on my website www.kdwindturbines.nl .