How to test a capacitor while ac is running

[dannoland]

Here is an explanation of why this method works. Capacitive reactance is equal to 1/(2 x pi x f x C), where pi is the number 3.14, f is the frequency of the power supply in hertz, C is the capacitance in farads. In the USA, the frequency is 60 hertz. Like resistance in an electric circuit, capacitive reactance impedes the current in an ac circuit. Just as resistance is the quotient of voltage across the resistance divided by the current through the resistance, capacitive reactance is the quotient of voltage (V) across a capacitor divided by the current (I) through the capacitor. Therefore, capacitive reactance (1/(2 x pi x f x C)) is equal to V divided by I. Now, algebraically rearrange the equation to get capacitance, C, alone on one side to the equal sign. The equation would look like this: C = I / (2 x pi x f x V). The capacitance here is farads. Multiply by 1, 000, 000 to change farads to microfarads. Thus, for C in microfarads, the formula looks like this: C (uF) = (1, 000, 000 x I) / ((2 x 3.14 x 60) x V) = (1, 000, 000 x I) / ( 377 x V) = (1, 000, 000 / 377) x (I / V) = 2652.6 x (I / V).

[rello]

I appreciate the video really helped and worked!

[realSamAndrew]

It's efficient for routine maintenance, but not for troubleshooting if the unit won't run. Then you still need to test it offline.