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othello · 06:06 PM

>Why do brushless motors have a best efficiency range under a given load?

The number of turns for a given motor will influence how thick the copper wires can be. A smaller copper wire has more resistance (resulting in a bigger voltage drop) and will heat up quicker at a certain amperage when compared to a thicker wire. While the wire heats up resistance also rises. So for a given copper wire you will only be able to flow a certain current before heating it up too much. This is one part of the equation why a motor might be more efficient at 50A then at 100A.

A Neu 1515/2Y (1100kv) for example has thinner copper windings then a Neu 1515/1Y (2200kv). Optimum efficiency for the 2Y (2 turns) might be reached between 10-50A. When flowing more then 50A over those thin windings, those windings will heat up too fast (resistance is 0.019 ohm). The 1Y motor only has a resistance of 0.006 ohm. This is why you can flow a lot more current over its windings before they will heat up too much. And this is also the reason why it will suck more current then the 1Y motor.

If you would apply say 30V to those motors while you block their rotor then theoreticaly they will suck up to:

Neu 1515/2Y (0,019ohm): 30V/0,019ohm=1578A
Neu 1512/1Y (0,006ohm): 30V/0,006ohm=5000A

Also explaining why you will need much better batteries with a higher C rate for a low turn motor.

Other efficiency losses do come from bearing friction, hystheresis ... all this will be part of the overall efficiency at a given load.

>My guess is that startup of a brushless motor means a high current draw to initially get moving. Once you are already moving though, it takes a fraction of the current to keep the motor going, and it also takes a fraction of the startup current to go from say 30,000 RPM to 40,000 RPM. Am I on to it or no?

Normally, with perfect grip under constant acceleration amp draw will get higher and higher while revving up. Shortly before top speed when acceleration gets slower and slower your amp draw will get less. While holding top speed you normally will need less Amps when compared to accelerating.

	(#6)
othello HV basher Offline Posts: 392 Join Date: Jun 2007 Location: Austria (Europe)	03.31.2008, 06:04 PM >Why do brushless motors have a best efficiency range under a given load? The number of turns for a given motor will influence how thick the copper wires can be. A smaller copper wire has more resistance (resulting in a bigger voltage drop) and will heat up quicker at a certain amperage when compared to a thicker wire. While the wire heats up resistance also rises. So for a given copper wire you will only be able to flow a certain current before heating it up too much. This is one part of the equation why a motor might be more efficient at 50A then at 100A. A Neu 1515/2Y (1100kv) for example has thinner copper windings then a Neu 1515/1Y (2200kv). Optimum efficiency for the 2Y (2 turns) might be reached between 10-50A. When flowing more then 50A over those thin windings, those windings will heat up too fast (resistance is 0.019 ohm). The 1Y motor only has a resistance of 0.006 ohm. This is why you can flow a lot more current over its windings before they will heat up too much. And this is also the reason why it will suck more current then the 1Y motor. If you would apply say 30V to those motors while you block their rotor then theoreticaly they will suck up to: Neu 1515/2Y (0,019ohm): 30V/0,019ohm=1578A Neu 1512/1Y (0,006ohm): 30V/0,006ohm=5000A Also explaining why you will need much better batteries with a higher C rate for a low turn motor. Other efficiency losses do come from bearing friction, hystheresis ... all this will be part of the overall efficiency at a given load. >My guess is that startup of a brushless motor means a high current draw to initially get moving. Once you are already moving though, it takes a fraction of the current to keep the motor going, and it also takes a fraction of the startup current to go from say 30,000 RPM to 40,000 RPM. Am I on to it or no? Normally, with perfect grip under constant acceleration amp draw will get higher and higher while revving up. Shortly before top speed when acceleration gets slower and slower your amp draw will get less. While holding top speed you normally will need less Amps when compared to accelerating. Brushless 1:5 custom 4wd Baja based on 1:8 truggy chassie Jazz 55-10-32, Neu 1515/2Y (1100kv), 9s2p A123 (27v), up to 3.1KW Latest video with eagletree Data inserts: Run on asphalt Last edited by othello; 03.31.2008 at 06:06 PM.