# Different amperage with a normal and a hook Multimeter?

I am measuring the electric power (P = VI) in a gear-motor. I measure it of two ways. One way is measure with a multimeter the resistance of the motor, then with V=RI, I measure the current, then I multiply that by the voltage and a obtain something near 2000 watts. In the other hand I have a multimeter hook that measures high values of current, but with it I obtain a different amperage and that leads to an electric power near of 600 watts. Why is this? I think is a big difference, which is the real one? Since I am controlling it with AC current, Is AC resistance or amperage Different than DC? Thanks in advance

• V=IR doesn't account for back EMF. So it is only accurate when the motor is stalled. When it's running unloaded, it generates enough voltage to cancel most (possibly 90-95%) of the source voltage and takes 5-10% of the stall current. If it's taking 30% of the stall current it's quite heavily loaded, running about 70% of its nominal speed (maybe 75% of its unloaded speed) – Brian Drummond May 9 '16 at 18:22