#### liveforphysics

##### 100 TW

kiwifiat said:liveforphysics said:Try thinking of what generates the field in terms of amp-turns.

If the tooth has 10 turns with 1 amp of drive current, or 1 turn with 10 amps of drive current, the field in the tooth is 10 amp-turns either way.

Niether Kingfish or I are debating the fact that copper losses between equal fill winding options are equal, the proof is trivial.

John in Cr says this:

"Saying that a slow wind motor makes more torque at the same current is irrelevant, because in that comparison the slow wind makes more heat to produce that greater torque. Apples and oranges comparisons simply don't cut it. Your understanding is incomplete, because you can't ignore copper losses."

And that is misinformation, the copper losses are identical.

His statement is correct. If both motors have identical copper fill, whichever happens to be producing more torque will be the motor generating more heat. This is true regardless of the kV (and hence torque/amp.)

An example of misinformation/myth would be something like Kingfishes lines here:

Kingfish said:21. If Power (P) is the same, we can demonstrate that higher current is less beneficial than higher voltage by using the formula P = I * V = I^2*R = V^2 / R,

22. Therefore higher Current (I) produces more Heat (Q) as loss than can be recovered by other mechanisms within the System, leading to a total loss in efficiency.

23. Therefore motors with faster winds (and having fewer turns) are inherently less efficient than slower winds (and having more turns)…

...

29. In conclusion, the statement “POWER is the same for the same sized WHEEL, spinning at the same SPEED with the same LOAD, for ALL WINDS” is inaccurate and can never exist.

kiwifiat said:We all agree that 10 amps into a 1 turn motor will yield the same torque as 1 amp into a 10 turn motor all else being equal. However in the context of speed/torque characteristics it is not correct to say that the motors are the same, if the torque constant is different how can you claim they are the same?

If you took a pair of coils, and arranged them in series, and powered them so each coil gets say 10A, or arrange them in parallel and drive it so each coil gets 10A, the motor has no way of knowing the difference. The kV shifts 4x up or down, the performance capabilities of the motor remain identical.

kiwifiat said:In terms of system efficiency the higher turn lower lower current wind wins every time.

This is not correct.

kiwifiat said:I assume we all acknowledge that the batteries have internal resistance. We all acknowledge the switching semiconductors have resistance. Is anyone going to provide a proof that a system consisting of a power source,wiring, controller and motor that requires 10 amps to provide X tractive force at the wheel can do so more efficiently than the system that requires only 1 amp? Particularly in the context of the vast majority of ebikes that are constrained in Voltage and the maximum continuous discharge current. So given those real world constraints a higher wind motor will deliver more torque, more tractive force at the wheel, better acceleration, better hill climbing ability and better overall system efficiency than a lower turn count motor when constrained by the power supply.

Myth and nonsense. Learn about how a buck-converter works, the motors windings serve as the inductor in the buck converter.

kiwifiat said:There is a very good reason why the engineers who are responsible for designing the tractive systems for the currently available electric cars have not gone with low turn count low voltage high current solutions but rather high voltage high turn count motors and that reason is system efficiency.

BS. Its because lossy IGBTs were once the only practical game in town for switching high power.