Capacitor Information, technical note.

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Reading and decoding

Polarity Identification

Repairs (filter caps)

Repairs (bypass caps)

 

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, and how do we read theses things?

  The basic unit of capacitance is the Farad, named after the Michael Faraday. Prior to the 1970's, capacitors were also called condensers. Same part, same function, different name. You'll still hear the old name used by some radio technicians. You will certainly see it in old schematics. Capacitance is usually measured in microfarads abbreviated F, nanofarads (nf), or picoFarads (pF). However through the years "uf" had many other acronyms. For example a 40uf may be read as 40 mF, 40 MF, 40 mfd, 40 MFD. The unit Farad is used in converting formulas and other calculations. A F (microFarad) is one millionth of a Farad (10-6 F) and a picofarad (pf) 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 are placed very close together with an insulator in between to prevent the plates from touching each other, and a 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. Once charged the discharge rate can be influenced by another source. This action can create oscillation, or be used for electronic timing. The rate in witch the capacitor charges and discharges can be used to create a filter, or limit unwanted noise. There is lots more we can do with capacitors too.

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. For example: 100F 250V, or something like that would be imprinted in plain text. 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 will 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.

Capacitor Codes
   
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 F. 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 components.

   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 = 0.47F) 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 

102 10+00 =1,000pf  1nf .001uf     333 33+000 33,000pf 33nf 0.033uf
103 10+000 =10,000pf 10nf .01uf 334 33+0000 330,000pf 330nf 0.33uf
104 10+0000 =100,000pf 100nf .1uf 472 47+00 4,700pf 4.7nf 0.0047uf
222 22+00 =2,200pf 2.2nf .0022uf 473 47+000 47000pf 47nf 0.047uf
223 22+000 =22,000pf 22nf .022uf 502 50+00 5,000 5nf 0.005uf
224 22+0000 220,000pf 220nf .22uf 503 50+000 50,000pf 50nf 0.05uf
332 33+00 3300pf 3.3nf .0033uf 504 50+0000 500,000pf 500nf 0.5uf

  Other capacitors may just have 0.1 or 0.01 printed on them. If so, this represents the value in F. Thus, 0.1 means just 0.1 F. 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. 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.

FIG 2:Converting uf-nf-pf

microFarads (F)   nanoFarads (nF)   picoFarads (pF)
0.000001F = 0.001nF = 1pF
0.00001F = 0.01nF = 10pF
0.0001F = 0.1nF = 100pF
0.001F = 1nF = 1000pF
0.01F = 10nF = 10,000pF
0.1F = 100nF = 100,000pF
1F = 1000nF = 1,000,000pF
10F = 10,000nF = 10,000,000pF
100F = 100,000nF = 100,000,000pF

Decoding the Old Capacitors

  This chart will help figure out those codes on the Mica molded type capacitors. However, they rarely 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. I am sure we have all seen these, and there is no need decoding them. Some have a white band on one end, and like these that defines the negative or outside foil connection.

 

Identify your capacitors polarity:

Lets start with two of the most common: Radial (wires coming out the bottom) and Axial (wires coming out the sides)

[Image]      [Image]      [Image]      [Image]

  In the example above you will notice five different ways to show polarity. There are more, but I think this will be enough to get the point. The arrows and stripes are "almost always" present. You will find many variations of this as well. They always depict the negative lead. The fifth way to find the negative is the shorter lead. 

[Image]

  In this example above you will find an added way to figure out the polarity. Remember these are marked with arrows and strips just like the radial caps at the top. Almost always pointing to the negative end. On axial caps though, we can find the polarity just by looking for the aluminum housing. The aluminum housing is almost always the negative end. The other end will have a rubber seal, sometimes epoxy or glass, but always insulated from the housing. If you see no marks, or both sides are insulated, then you may have a non-polarised electrolytic capacitor. You would find these in crossover networks, speakers, and some amplifier circuit boards. Other than that, this should help for 99% of them.

NOW, a couple things about capacitors with out a polarity!

Take a look at these. The first one has no markings at all. This is a normal axial capacitor. This is the most common type found in early radios, and televisions. As well as most early electronic devices. They used paper and oil as a dielectric. The new capacitors use a metalized poly film. Called a dry capacitor. The new one will never dry out on you, will last your lifetime PLUS, and will perform just as good if not better than the original.

[Image]

The next capacitor is basically the same except they do have a mark for a polarity. Not necessarily for Positive and Negative. This mark denotes which side is connected to the outside foil. The mark will be a stripe running all around the body of the capacitor. The reasons for the marking has to do with coupling in Hi Fi amps. If you use these correctly they will cut down noise generated internally in the amp. You would want to connect the marked end in a special way so the out side foil doesn't interfere with another component. Or can help eliminate interference from other components.

[Image]

Most people call these audio caps, because they are primarily used in critical, or high end amplifier circuits.

Capacitor symbols used in schematics 

  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. The photo on the left shows us some examples for the scematic symbol of a capacitor.

Did you know why most Antique Radios fail to work?

  Most antique radio failures are due to dried out CAPACITORS. Most capacitors are made with foil and a dielectric. As time goes by the material used as a dielectric can dissipate from the body of a capacitor, causing it to fail. Sometimes they short causing other failures, but most of them just OPEN-UP, or drift beyond its designed tolerance. In some case the electronic circuit acts as though the capacitor isn't even in the circuit. Just replacing a couple capacitors can repair most antique radios. Most of those are due to FILTER CAPACITORS failing. How many radios have you powered up only to hear a loud annoying hum, or nothing at all? A filter capacitor is a major component used to turn AC current into DC current. I don't know of any radio that actually uses AC current in the electronics! This will explain where the hum comes from, and why. For a couple bucks you can repair this problem yourself!

Example 1.1 shows you a very basic working DC power supply output. Notice the (B+), clean and flat! As it should be!

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This example, 1.2, shows what the output looks like when the capacitor is not there OR when it's OPEN.

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  This condition is called a ripple. The ripple causes the loud hum, because the noise is amplified through the circuit of the radio. Due to its overwhelming characteristics the volume control may not work either! If you hear nothing at all, then chances are the capacitor is shorted and giving you no voltage. In some cases very little.

WHAT ABOUT CAPACITOR VALUES?

  Actually the exact replacement value only has to be close. In most circuits the value can be doubled, even tripled. Too much filtering doesn't hurt in this case. For example, a 12mf (microfarad) capacitor can be replaced by a 10mf or 20mf. I would go with a higher value before a lower one though. Typically your best bet would be to stay within + or - 20% of the original value.

WHAT ABOUT VOLTAGE RATINGS?

  Never replace a capacitor with one rated below the original capacitors voltage! HOWEVER, a replacement rated above the original value is acceptable. That's about it. If the original value is 350 volts, then any voltage rating higher is acceptable. The voltage rating on a capacitor is a maximum value. A 400-volt, 450-volt, or even 600-volt can be used to replace a 350 volt capacitor.

WHAT ABOUT DUAL OR MUTIPLE CAPACITORS?

  Dual or multiple capacitors are capacitors with more than one capacitor inside a single package. BUT, They don't have to be inside a single package. They are used to simplify the manufacturing of the radios. In fact it would be a better bet to replace these capacitors with single capacitors. Multiple capacitors cost more and are harder to find. You will also find that sometimes only one of the capacitors in the package is bad. If you did have single capacitors, you could replace just one at a lower cost. In any case take a look at example 2.1

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  Take a close look at the value and voltage ratings on the replacement capacitors. This is a prime example concerning values and voltages. If there were a forth wire, then you would add a third capacitor. See example 2.2 below. Save yourself the heartache and expense trying to find a replacement.

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LETS USE UP THE CAPS YOU ALREADY HAVE

  Here are a few other things you can do with capacitors. This is great if you have capacitors already and don't need to spend the extra money on more! In example 3.1 you will see how we can make a 50mf cap from two 25mf caps.

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  Notice the voltage values are different. In this case the total voltage can NOT be higher then the lowest voltage value. This is now a 50mf, 160-volt capacitor. Now take a look what happens when we add another capacitor. Example 3.2 is now a 100mf 160-volt capacitor. I guess you got the point by now. This is called a parallel design. Just remember capacitors add up in this configuration.

[Image]

  Now lets make a 12mf out of two 25mf capacitors. What we want now is a configuration that divides capacitor values. Simply put Series configuration. Example 3.3 will show the differences.

[Image]

  Now lets review. Always watch your voltage ratings! Always watch your polarity (notice the + on all my examples) these are called electrolytic capacitors because they have a polarity. Be sure you discharge your capacitors before you handel them. For any questions e-mail me, to order caps CLICK HERE I have limited values to start! I will continue to add stock, and I will continue to ADD technical notes.

Did you know why most Antique Radios fail to work II?

  Most antique radios failures are due to dried out CAPACITORS. Most capacitors are made with foil and a dielectric. As time goes by the material used as a dielectric can dissipate from the body of a capacitor, causing it to fail. Sometimes they short causing other failures, but most of them just OPEN-UP. The electronic circuit acts as though the capacitor isn't even in the circuit. Just replacing a couple capacitors can repair most antique radios. You may hear nothing, or you may experience a loss of selectivity and/or sensitivity. This will help to explain why for a couple bucks you can repair these problems yourself with a few capacitors!

Example 1.1 shows you a very basic working bypass filter. Used here to ensure AC does not get through, but DC does.

This example, 1.2, shows just the opposite. This will allow AC through, but not DC.

  Example 1.2 could be used as an input signal conditioner on an amplifier. Blocking DC, which can damage your speakers as well as your amp. However it will allow AC or audio (AC in many frequencies) to pass. If it were to open then nothing would get through. Or the output may sound weak and distorted. On a very basic scale AC sees a capacitor as a short circuit. DC sees a capacitor as an open. SOOOO, why use capacitors in a DC circuit? One reason we already know. To block AC and or noise. If we read the previous Tech Notes, we also know they are used to filter DC. With a couple more components we use capacitors for oscillators, band pass filters, and so on. We won't go that far. Beside I'm not sure if I can! I want to keep this simple to insure it could aid anyone.

WHAT ABOUT CAPACITOR VALUES

  Actually the exact replacement value only has to be close. For example, a 0.56mf (microfarad) capacitor can be replaced by a 0.47mf, 0.50mf or 0.68mf. Typically your best bet would be to stay within + or - 20% of the original value. Remember the original parts were not very accurate. That's why old electronics has so many adjustments. You could not replace a 0.1 with a 0.01 though. Notice the decimal points. However a 0.15mf can be replaced by a 0.18mf in most cases. If you find a circuit that calls for a certain value with a 5% or better tolerance, then you should get an exact replacement if possible.

WHAT ABOUT VOLTAGE RATINGS

  Never replace a capacitor with one rated below the original capacitors voltage! HOWEVER, a replacement rated above the original value is acceptable. That's about it. If the original value is 630 volts, then any voltage rating higher is acceptable. The voltage rating on a capacitor is a maximum value. A 630-volt, 1000-volt, or even 1200-volt can be used to replace a 600 volt capacitor.

LETS USE UP THE CAPS YOU ALREADY HAVE

  Here are a few other things you can do with capacitors. This is great if you have capacitors already and don't need to spend the extra money on more! In example 3.1 you will see how we can make a 0.1mf cap from two 0.047mf caps. It's simple they add up in this configuration, called parallel. Notice there are no polarities. These are non-polarized capacitors. So the direction does not matter.

  In this case the total voltage cannot be higher then the lowest voltage value. This is now a 0.1mf, 400-volt capacitor. Now take a look what happens when we add another capacitor. Example 3.2 is now a 0.2mf 200-volt capacitor. I guess you got the point by now. Again the total voltage cannot exceed the lowest voltage value capacitor.

  Now lets make a 0.047mf out of two 0.1mf capacitors. What we want now is a configuration that divides capacitor values. Simply put, Series configuration. Example 3.3 will show the differences.

   Now lets review: Always watch your voltage ratings! Use the lowest voltage value when connecting in series OR parallel. Always discharge capacitors before handling them. Capacitors can hold a charge for a long period of time.

   For any questions see my web page www.wjoe.com, to order caps www.wjoe.com/capacitors.htm

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