OK my version of back EMF. In general I see it applied to motors, particularly DC motors and it can get confusing.
Take a typical DC motor with a winding resistance Rw.
That DC motor when driven mechanically will produce a voltage proportional to speed. In fact it can be used as a tachometer.
When you start to load that motor we now have V = Vm - (Im * Rw), since we are drawing current. I is non zero. the current is actually in the SAME direction, but it's OPPOSITE to what's being applied. It doesn't reverse polarity. The current does because it' being generated. So this generated current happens because the motor is moving drops across the resistance of the motor.
I*R is and EMF or V and -(Iw*R) is opposite to what's being applied. But the sign of the current is what changed,
You can design a speed regulator by maintaining the calculated terminal voltage using the current and the constant Rw (winding resistance). In theory the resistance changes with temperature a bit.
Take a typical DC motor with a winding resistance Rw.
That DC motor when driven mechanically will produce a voltage proportional to speed. In fact it can be used as a tachometer.
When you start to load that motor we now have V = Vm - (Im * Rw), since we are drawing current. I is non zero. the current is actually in the SAME direction, but it's OPPOSITE to what's being applied. It doesn't reverse polarity. The current does because it' being generated. So this generated current happens because the motor is moving drops across the resistance of the motor.
I*R is and EMF or V and -(Iw*R) is opposite to what's being applied. But the sign of the current is what changed,
You can design a speed regulator by maintaining the calculated terminal voltage using the current and the constant Rw (winding resistance). In theory the resistance changes with temperature a bit.