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Hi,

I have an AC motor with a power rating of 65 watts at a rated speed. Can this power increase if I am going to increase the load that will cause to change the motor's rated speed?

Any suggestion please... tnx....

Can anybody help me to compute for the power input of the motor with varying speed?

An AC induction motor will not typically slow down when load is applied (unless it is an extreme load, i.e., typically greater than 125% of its rated power). Power, for a three phase motor is calculated by the formula: sq root of 3 x volts x amps x cos theta. I suspect that your 65 watt motor is single phase, so you need to drop the sq root of 3 part of the calculation. However, the tough part for your calculation is knowing what cos theta is. This is the phase angle between the voltage and current vectors and an angle that varies with motor load. Power will increase as more load is applied. You cannot accurately determine load my simply measuring motor current as this changes very little until there is 65% or more load on the motor (as compared with its rated power). So in conclusion, you can apply more load, the motor should not slow down providing you stay within its 65 watt rating and power will increase as you apply more load.

Take a look at power monitors and get back to me if you need help in finding one.

Hope this helps.

Paul,

Great explanation. As a temporary measure do you think connecting to a KWh meter and timing the disk rotation would give a reasonably accurate low-cost measure? They are usually easy to get your hands on.

Roy