serial or parallel coils

[Q]

On a 9 arm stator we have three phases with each three coils. When we wind each phase with one wire, we have all the coils in series. Now if I would wind each coil with a separate wire, I could put them in parallel.
Would this be benificial? and if so, for what type of motor?

[LBMiller5]

I am assuming that you are considering using the same wire gauge in both cases. If you did that you would increase the current draw to incredibly high levels, and place the full input voltage across each and every tooth in the stator. Let's assume for a minute that the winding of 1 stator tooth of wire has a resistance of .1 ohms. When you wind them in series, the total resistance of the phase is 3 times the resistance of each tooth, for a total of .3 ohms. If we had 9 volts applied across the combined total, each tooth would see 3 volts, since the voltage divides equally across each stator winding. In this case, the locked rotor current would be 9 divided by .3 or 30 Amps.

Winding them in parallel would give a total resistance equal to 1/3 the value of each individual stator tooth, giving a total resistance of 0.0333 ohms, and each stator tooth would have the entire 9 volts input across it. In this case the locked rotor current would be 9 divided by .0333 or 270 amps, which is 9 times the current of the series configuration. Obviously, the speed controller would either fold back into over-current mode or burn up under these conditions, and the battery would not be capable of putting out these kinds of current for more than a few seconds if at all.

This configuration could be used if the wire gauge was increased (IE Smaller wire) so that each tooth had a resistance of 3 times the original value. This would require that the gauge size increase by 4 or 5 numbers. 4 gauge numbers would increase the resistance by a factor of 2.53, and 5 gauge sizes would increase the resistance by a factor of 3.19.

Since the current would be 1/3 the amount, you would need to wrap 3 times as many turns of wire per pole to get the same number of amp-turns of magnetic flux. You could do this, since the smaller wire fits better on the stator, but it would be a lot of work, since you would have to keep track of 18 wire ends, and you would be winding a lot more wire.

This procedure would work best in the "Hot Wind" motors where only 5 or 6 turns of very large wire is used. For example, instead of using 6 turns of 18ga wire, and winding the stator teeth in series, you could put around 15 or 16 turns of 22ga wire (since 6 x 2.53 = 15.18 turns) and wind the stator teeth in parallel to get a similar performing motor. It would be much easier to fit the 22ga wire on the stator that the 18ga since it bends around the corners easier, and stacks together neater than the larger wire.

Good thinking outside the box Q, this kind of information interchange only helps to improve on the motors we use for the hobby. It would not surprise me at all if design engineers for AXI and HI-MAX and Hacker and the like snoop into this site looking for "Good Ideas" to improve on their products! :wink:

Let me know what you think of my appraisal of this question.

Lucien

[Q]

I know Ohm's law, so I'm not really surprised by your answer. :-D

I just wanted to ge a conversation going in regard of the 4 arm stators. You know, the ones from the PC fans. Steve suggested stacking three of them giving a "virtual" 12 arm stator, using one stator per phase.

Now because of this concept we have quite a lot of iron available. The easy winding allows a VERY easy connecting of all the coils. The stacked stators allow you to build a pretty lnog motor which, in combination with the high RPMs, is perfect for EDF. :-D

A motor like this would certainly need a triple bearing. The third bearing is needed to stabelize the bell. At 60K rpm we don't want ANY vibrations!


And in regard of your apraisal, Lucien: you guessed perfectly why I posted the question in the first place. :-D

[bz1mcr]

RYSIUM posted results at RCGroups for several motors he connected this way. I am not sure, but I think in the end, he determined it was not an advantage to connect coils in parallel, and went back to conventional windings and connections.