Why does the torque output of a DC motor decrease linearly with RPM?
Why does the torque output of a DC motor decrease linearly with RPM?
(OP)
I know this applies to brushed DC motors and I think it applies to brushless as well?
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Why does the torque output of a DC motor decrease linearly with RPM?
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RE: Why does the torque output of a DC motor decrease linearly with RPM?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Why does the torque output of a DC motor decrease linearly with RPM?
It represents a counter voltage developed by the spinning armature.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Why does the torque output of a DC motor decrease linearly with RPM?
V = Ke*w + R*I
where:
V is the voltage across the leads (constant applied in your case);
Ke is the back-EMF constant of the motor (volts per unit speed);
w (omega) is the angular velocity;
R is the resistance;
I is the current
The higher the motor speed, the more of the supply voltage is "used up" by the back-EMF term, and the less is available to drive current through the motor. Since torque is proportional to current, as your speed increases, your torque generation capability decreases linearly.
RE: Why does the torque output of a DC motor decrease linearly with RPM?
RE: Why does the torque output of a DC motor decrease linearly with RPM?
T=Kt*I where Kt is same thing as Ke but in different units (torque/amp)
So studying them together one can see as the voltage is used up to make speed, less is left over to make I (V/R).
So as Curt showed, the faster you go with a constant voltage applied, the less is left over to make current in the motor resistance, hence less torque as u go faster.
So you see you stated it backwards by now; torque does NOT go down as speed goes down, but rather as it goes up.
RE: Why does the torque output of a DC motor decrease linearly with RPM?
RE: Why does the torque output of a DC motor decrease linearly with RPM?
So how about brushless DC or PM AC motors? Is it the same deal?
RE: Why does the torque output of a DC motor decrease linearly with RPM?
Just to toss in a little more the Horsepower is a direct function of the speed times the torque.
Keith Cress
kcress - http://www.flaminsystems.com