Capacitance Capacitance is the ability of a dielectric (insulator) to store an electrical charge Charge = Coulomb = Q = 6.25 X 1018 electrons
Capacitors A capacitor is a component that stores electrical charge Schematic Make up of a capacitor The unit of measurement for capacitance is the Farad + - Non-Polarity Sensitive Polarity Sensitive 2 Conducting Plates Dielectric (Insulator) Note to teacher: charge up a 470 µF cap to 30v and then discharge
Farad 1 Farad: when 1 coulomb is stored in a dielectric with a potential of 1 volt 1 Farad is a very large value Typical values of capacitance are in: microfarads (μF) (10-6) picofarads (pF) (10-12) Higher farad value = more stored charge Note: Charge up 470 μF and 1000 μF to show difference Q C= V Coulomb Farad= Volt 1 Volt 1 coulomb
How Capacitors Work Charging Storing a charge Discharge http://micro.magnet.fsu.edu/electromag/java/capacitor/index.html
Factors affecting Capacitance: The ability of a capacitor to store electrical charge (capacitance size) depends upon Size (surface area) of the plates Larger plate area = more capacitance Distance between the plates Capacitance increases as the width decreases Dielectric Material Air = 1 Paper = 2-6 Ceramics = 80 – 1200 Mica = 3-8 Mylar = 2-3 Electrolytic = 7 http://micro.magnet.fsu.edu/electromag/java/capacitance/index.html 200 μF 100 μF 200 μF 100 μF
Three Important Facts When Choosing a Capacitor Capacitance Value Voltage Rating Polarity
Capacitance Value Rules of thumb (as in 99% of the time) MF or mF on an old capacitor = µF . If a capacitor has a value of 1 µF or more it is usually an electrolytic (canister) capacitor. Conversely, if the capacitance value is less than 1 µF it is usually a disc or chicklet variety.
.047 k .1 Z Capacitance Values of Disc Capacitors The value of the disc capacitors is usually given in one of two methods. The capacitance value is sometimes printed on the face of the disc capacitor like the following. If this is done then the value of the capacitance is given in micro farads (µF).
Capacitance Values of Disc Capacitors The capacitance value is sometimes printed in code on the face of the disc as shown below. If this is the case then the capacitance value is given in picofarads (pF). The code given is the same as the code used to determine resistor values. For example: 102 would represent 1= 1st digit of value, 0 = 2nd digit of value, 2= multiplier (how many zeros) Therefore 102 = 1000 picofarads (pF) or .001 micro farads (µF)
Capacitors in Series and Parallel Capacitors in Series Capacitors in Parallel In series the width of the dielectric is additive 10 μF 10 μF CT = 5 μF Notice that they are exactly opposite of resistors!!!!!!!! 10 μF 10 μF CT = 20 μF In parallel the plate surface area is additive