Help with reading a voltmeter

[Shinok87]

So I bought a voltmeter and I hooked it up to a electric motor. I want to see how much power the motor can produce in Watts. The voltmeter reads .5 in the 20V DC mode. How much power, in Watts, is this?

[swansont]

P=IV You need to know the current. That will tell you what the motor is drawing. The output will be somewhat less (maybe 90%)

[jian]

Maybe you need insert an ammeter in the circuit to get the power which is drawn by the motor. However, you still need to know the efficiency of motor. The simplest way is just read these information from its name plate. Usually, the name plate will specify the normal working voltage, and out power under normal working conditions.. As long as your motor is under normal conditions, the power can be directly read from the name plate.

The other way is to conduct a simple experment to calculate the power output like lifting an object with mass m. The gravitational energy gained of the object per unit time equals to the power output if the mass is approriate enough to maintain the motion under constant speed.