Originally Posted by
unime
No. That's not what is going on with multiple windings. When you connect several identical windings on the same core in parallel, the inductance doesn't change. That's because the same magnetic flux (flowing through the core) is generated by a given current flowing through one winding as (1/n)th the current flowing through n windings.
Honestly, I don't know what the RC car folks are talking about. Multiple windings shouldn't make much of a difference unless they are changing the total amount of copper. I'm not impressed by claims made on a random web site. I do know Maxwell's equations, but I don't see how they might explain those claims.
I just don't understand why you aren't getting this...
Using the
SAME amount of copper you can change the inductance and "effective" resistance by the choice of series or parallel. I mean this is basic stuff here. In order to achieve the same current through each wire (given the same voltage) you need to apply more current from the battery. Every time you divide the copper into more and more individual winds it reduces the resistance that the battery sees. The net effect is to make a 48 volt battery seem to act like a higher voltage battery.
It's just basic series verses parallel stuff...
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Try to explain to me
WHY you think that this isn't valid in some other terms than that you just don't want it to be.
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The different motor options that Unite has all share more or less the
SAME core. The only differences are the wiring patterns and the thickness of the copper. Some have more "Turns". Some have Single winds and others have Double winds. In the end the motor behavior is defined by this mixture of properties.
They don't do Double winds just because they were too lazy to choose a larger gauge wire.
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From what I've read the thinking goes like this:
Inductance makes a difference at the low end of the powerband because the PWM controller can maintain the magnetic field longer. Remember how these controllers work... they are sending pulses out at differing widths depending on the throttle setting and the current limiting that is being used. As the rpms rise to the third quarter of the power band the other forces within the motor tend to dominate and the inductance reduces as a factor. It's at these higher rpms when the BackEMF starts to become the dominant factor and not the inductance and a lower resistance (due to things being in parallel) means the battery can supply the needed current more efficiently.
What is happening with the Double wind is the lower rpms are being given less attention so that the higher rpms (where all the real horsepower is found) are enhanced. The BackEMF is the constant that you can't get past because that's the relationship of the permanent magnets to the magnetic field you are generating. The maximum rpm ends up the same, but the motor is more efficient up top with the Double and the Single is stronger down low.
The RC folks are pretty smart people...
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One last thing to ponder.... as the rpm rises the current actually DROPS with an electric motor. So while the Double, Triple and Quad looks like it should promote an "uncontrolled meltdown" of excessive current with rising rpm it really doesn't. You have to think:
Low rpm - Inductance is the dominant factor
High rpm - BackEMF is the dominant factor
...so the multiple winds are just "shifting" the motors powerband to the right and optimizing for a more narrow (higher power and efficiency) region of the motor.
A Double can make a 36 volt battery "behave" like it was 48 volt as far as power and efficiency, but at the expense of the low rpm compared to the Single. You don't get something for nothing, but you do get the best parts of the higher voltage without needing to use a higher voltage. The Double is just a better wind in many cases. Also, by choosing a Double wiring over a Single the top speed of the motor is the same... in many cases overvolting can mean that you change the top speed so that you spend more and more time in it's lower rpm region and that hurts the efficiency even more. It's sort of a trap when you go up in voltage because the heat goes up along with such a change.
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