Capacitors 218


Capacitors are components of electrical and electronics that store electric charge. They are mostly used in smoothing, filtering and timing circuits. They smooth circuits because they store charge, they filter circuits because they allow a.c and block d.c and finally they are used to time since a capacitor takes up time to fill up.

CLASSIFICATION OF CAPACITORS

  1. Polarized
  2. Unpolarized

all of these have two conductors one positive and one negative spaced by a dielectric material  that is used as an insulator.

TYPES OF DI-ELECTRIC MATERIAL

  1. Polyester – gives good quality capacitor,gives a working upto 750v d.c, a tolerance of negative or positive 20% & is suitable for high frequency use.
  2. Poly-carbonate – values from 0.01-10 microfarrads,a working voltage upto 680V d.c and a tolerance of positive or negative 20%.
  3. Mica – it is the most acurate di-electric material, ranges from 2-1000 picofarrad. a working voltage upto 350v d.c,Tolerance of negative1% but the downside is its rather costly
  4. Electrolytic – used when large capacitance is required. value upto 100,000 microfarrads, has high di-electric strength, working voltage upto 450v d.c and tolerance of negative -25% and positive 100%.
  5. Air – used as di-electric in variable capacitor and tuning capacitor in radios and televisions

TYPES OF CAPACITOR

  1. Electrolytic capacitor– This are polarized i.e they have polarity and should be connected in the right way. They are of axial and radial type. They have printed value of capacitance and voltage rating. 
  2. Tantalum bead capacitor – they are small and are used where great capacitance is needed in small sizes. voltage, capacitance and polarity are printed in full. some older versions had two stripe color codes just like a resistor but in this grey is 0.01 & white is 0.1 so values less than 10 microfarrads are shown.A third color close to the leads shown voltage where:-     yellow = 6.3V, black= 10,green = 16, blue = 20V, grey = 25V, white = 30V,pink = 35V. please note that the positive lead is to the right when a spot is facing you.  the above two are polarized capacitors and below are the non-polarized capacitors.
  3. Mica capacitor – are made of mica di-electric and its qualities ara as explained above.
  4. Paper capacitor – This are made by paper di-electric and properties are as explained above. 
  5. polystyrene capacitor – its qualities almost similar to poly-carbonate. 
  6. Polypropylene Capacitor- properties is almost similar to poly-carbonate 
  7. Polyester capacitor – properties of this are as above.
  8. Trimmer capacitorThis are adjusted when machine is serviced to give specifically set capacitance.  they are like mini variable capacitors.
  9. variable capacitor – in this a one a capacitance can be adjusted by a knob. they are used for tuning circuits.

NUMBER CODE

The number code is used when print work is kind of difficult as above in smds.

  • 1st number = 1st digit
  • 2nd number = 2nd digit
  • 3rd number = no of zeros to give capacitance in picofarrads
  • Any letters indicate tolerance and voltage rating

i.e  422J means 4200picofarrads ( J= 5% tolerance)

COLOR CODES

The color code resembles on in resistors and was used in now antique polyester capacitors and is no longer used. The top three colors giving value in picofarrads, the fourth is the tolerance and the fifth is voltage rating. i.e

brown, black, red means 1000 picofarrads.

DISCHARGING A CAPACITOR

In this u can use depending on the capacitor a 100W bulb with wires soldered into it connected to the capacitor leads. if there a charge the bulb will light up and after it discharges it goes off. Some used a screw driver to short circuit the leads which is not recommended or as high voltage wire wound resistor.

TESTING CAPACITORS

Bad capacitors often bulge, blow, change color or let out a liquid that is usually a technicians eye and call. But this is still not 100% prove that a capacitor is bad a faulty capacitor may look just okay. in this case u may use a digital capacitance meter, a  capanalyzer 88a series ii, or a capacitor& inductor analyzer since a normal multimeter wont work efficiently.

 

 


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