Farads, Micro and Pico - Short #180

In this short episode, Bryan explains the fundamentals of capacitance, focusing on the unit of measure: farads, including micro and pico.

Farads are named after scientist Michael Faraday and measure capacitance; one farad represents the capacitance of a capacitor in which one coulomb of charge causes a potential difference of one volt across the plates. Farads measure the storage of electrical energy and indicate the capacitor's ability to create a phase shift.

Since farads are large units, our capacitors are rated in microfarads (1/1,000,000 farads). Bigger capacitors have higher microfarad ratings and store more charge.

Capacitors create a phase shift and limit current on the start or auxiliary winding. (You'll read less current across the start winding than the run winding or common when a run capacitor is in the circuit.) The start winding helps get a single-phase motor up and running (but it isn't present on all motors). Three-phase power has three windings, and it has three sine waves 120 degrees out of phase with each other, all of which can apply directional force. A single-phase motor has two windings and only one sine wave, so it doesn't have that phase difference, making it difficult to start a motor. Capacitors charge and discharge at a different point of the sine wave, causing a phase shift.

A picofarad is 1/1,000,000,000,000 farad, which is smaller than the microfarads we use. However, our meters can auto-range into the picofarad scale if they read a very weak capacitor. You'll have to make sure your meter is reading in the microfarad scale, not the picofarad scale.

 

Learn more about the 5th Annual HVACR Training Symposium at https://hvacrschool.com/Symposium24.

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.”

Subscribe to our YouTube channel at https://www.youtube.com/@HVACS. 

Check out our handy calculators HERE or on the HVAC School Mobile App (Google Play Store or App Store).