Simple motor question from newbie

[onemegresistor]

I know almost nothing about electric motors so I'm sure this is an easy question for some of you to answer. I have a treadmill that I would like to use for something else, but I'm worried about how much electricity it will use. My question is does it use less electricity when on slower speeds than higher speeds? I would assume so, and I guess that would mean it would draw less amps when on slower speeds? If so, how can I figure out approximately how many amps I'm drawing???

Thanks...

-Ryan

 

[aolalde]

A tread mill is a constant torque load for a given weight. The friction force (Fr) developed is proportional to the weight (N) and the friction coefficient (u).

Fr= u*N
The Torque will depend of the roll radius (R).
T = Fr * R
And the power consumption (HP) is proportional to the speed (rpm) and torque(T).

HP = T*rpm/5252

For constant torque, the power (HP) increases or decreases following the speed.

The motor current (I) will increase if the motor has to develop more power (HP) and decrease if the power demand is reduced, but it depends too on the line voltage (Vl), Efficiency of the motor(EFF) and the motor power factor (PF).
For a single phase motor:

I = HP*746/(Vl*EFF*PF) (amperes)

As you can see the ease way to know the current consumption is by measuring it with a clamp-on ampere-meter, rather than calculation.