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^{Identify your original capacitors}!

What is polarity? An electrical condition determining the direction in which current tends to flow. Hence, negative (-), positive (+).

What does "almost always" mean? There are always exceptions. You may find one marked differently, who knows!!

What Exactly Is A Capacitor? How Do We Read Theses Things?

   The basic unit of capacitance is the Farad. Named after the inventor. Capacitance is usually measured in microFarads, abbreviated µF, or picoFarads (pF). The unit Farad is used in converting formulas and other calculations. A µF (microFarad) is on millionth of a Farad (10^-6 F) and a pF picoFarad is one-millionth of a microFarad (10^-12 F).

     A capacitor is a device that stores an electrical charge or energy on it's plates. These plates, a positive and a negative plate, are placed very close together with an insulator in between to prevent the plates from touching each other with some type of dielectric. A capacitor can carry a voltage equal to the battery or input voltage. Usually a capacitor has more than two plates depending on the capacitance or dielectric type.

Capacitor Codes
    

     I guess you would really like to know how to read all those different codes. Not to worry, it is not as difficult as it appears. Some capacitors just tell you right out. Take your electrolytic and large body types of capacitors: these usually have the value printed on the body of the cap. For example,:100µF 250V, or something like that would be imprinted right on the body. It would also have marks pointing to the negative end of the capacitor. For more information about this CLICK HERE.

Start here for the smaller non-polarised and old type capacitors!   

           It's mostly the smaller caps have two or three numbers printed on them, some with one or two letters added to that value. Take a look at the table below.


   As you can see it all looks very simple. If a capacitor is marked like this 105, it just means 10+5zeros = 10 + 00000 = 1,000,000pF = 1000 nF = 1 µF. And that's exactly the way you write it too. Value is always in pF (PicoFarads). The letters added to the value is the tolerance and in some cases a second letter is the temperature coefficient mostly only used in military applications, or industrial componenets.

   So, for example, it you have a ceramic capacitor with 474J printed on it: 47+4zeros = 470000 = 470,000pF, J=5% tolerance. (470,000pF = 470nF = 0.47µF) The only major thing to remember here is to move the decimal point back six place for (uf) and three for (nf). Below in table A, is a simple version for direct conversions to make it easier for you.
   

TABLE A 

 coded-decypher-value(pf)-value(nf)-value(uf)......coded-decypher-value(pf)-value(nf)-value(uf)

   Other capacitors may just have 0.1 or 0.01 printed on them. If so, this represents the value in µF. Thus 0.1 means just 0.1 µF. If you want this value in nanoFarads (nf) just move the decimal three places to the right which makes it 100nF capacitor. Some caps will have a value then a letter. For example .068K, in this case its a .068uf 10% capacitor. Again just take a look at FIG 2. 

 The chart below is a simple conversion chart. It will help you understand how we convert uf to pf and nf.

Converting uf-nf-pf

 Decoding the Old Capacitors

This chart will help figure out those codes on the Mica molded type capacitors. However they rearly go bad. I don't think I ever found a bad one myself. Keep in mind this translates them to pf or MMF. Don't worry they both mean the same thing. This example below would translate to 47pf, or 47MMF.

In the picture below you will see two of the most common types of mark ups. In the top picture the 1st digit can also be silver or black. This is done so you know the proper orientation before you decipher the value. In the lower picture the two N/A positions can be blank (no color added).

Plastic or bakelite round capacitors (bumble bee)

 By this time you should realize the color code is pretty universal. Decoding may change from device to device. These read a lot like resistors. Keep in mind, like before this decodes to MMF and is equal to PF.

I find most of these in televisions and amplifiers. Sometimes in foreign radios. However the format is always the same. Other round plastic or bakelite capacitors may have the value printed right on the body. We have all seen these. There is no decoding them. Some have a white band on one end, and like these that defines the negative or outside foil connection.

Well that's it. I want to keep it simple and informative. I hope you found it to be both. Now you can use this guide to insure you install your caps correctly. Keep in mind this coves only some capacitors. Since I specialize in antique radios I stuck with the most common types.

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PLEASE feel free to email me with additional questions about this article.

08/03/07