Is it possible to measure power consumption of an electronic device by using a Voltmeter.?

Question

If so, how would it work exactly? Would I need an external battery source and measure the voltage/amperage from there? Or can I just use a wall outlet for power and measure?

Also, do I subtract the measured voltage from the original battery voltage to get how much voltage the electronic device uses?

Thx.

Answer 1

No, you have to be able to measure current as well. If it's AC, you need more information (phase).

No, the voltmeter measures deflection, there is no offset for the internal battery.

Answer 2

No, you can not. The voltmeter has no way of measuring current through the device under test. Remember, P=IE. Spelled out, that is Power is equal to Volts Multiplied by Current (Amps). Now, If you do not have an Amp-meter, or there is not a scale for that built into your voltmeter, then put a low value resistor in series with the Positive power supply lead. A 0.1 ohm resistor of at least 2 watts should do just fine. Measure the voltage across that resistor with the device turned on. Now, I= E/R, so divide the voltage read across the resistor by the value of the resistor. That will give you a good first estimate of the current being drawn, and with the voltage being delivered to the device, you can figure out the power being drawn by the device.