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NOOB question: how does kV-rating relate to max/min RPM of the motor?

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Henque19
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NOOB question: how does kV-rating relate to max/min RPM of the motor?

I have a (probably basic) question about BLDC motors:

Motor speed is supposedly given by kV * battery voltage. But the ESC determines the motor RPM through pulsing current to the different windings, right?

Is kV*voltage just the max rpm the motor can run at? Or is a motor with too high kV very inefficient at RPM:s much lower than kV*voltage?

I'm confused, grateful for any kind of clarification!

frank
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Basically the copper fill is important. For the motor KV does not matter so much, as long as the same amount of copper is in the stator. Higher KV motors put more strain on the ESC since you push more Amps at a given torque output. As long as the ESC is beefy enough, you can use slightly higher KV motors and have less limits in possible RPM.

Henque19
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Great, thanks!

I think I misunderstood Kv as RPM at a given voltage. But it's rather what voltage will the motor generate when driven at a given RPM.

So if I interperet your reply correctly,  a higher than optimal Kv motor will generate lower voltage (and higher current) when regeneratively breaking. But will it (given similar copper fill) have a comparable efficiency than a lower Kv motor at the same RPM? 

frank
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The motor should be as efficient. However, more Amps create more heat in the ESC. You always need to look at the entire system.

Henque19
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Good point, thanks for pointing it out!