Where to find capacitors

Yea, I have pretty much stopped that unless it is a last resort. That solder pot must be nice, how much did it run you? It's probably saved me more in beat soldering tips alone by now. I think a metal pot on a heat source would work about as well. That is all mine seems to be there is a heating element under the cup part. Hit a thrift store and get one of them electric burners then put a tuna can on it full of solder. If you want to go top shelf then get a tiny frying pan while you're at the thrift store for a couple bucks more.

My solder pot isn't anything more than that, it is an iron cup with an electric heating element under it. If there is anything more than that going on I can't see it. I will tell you this though it takes my pot about 40 minutes to get molten so be patient. It isn't like popping something in the microwave. Probably, not sure if I'm willing to risk any of my pots. I'll surely try if I come across any old ones though. Well I didn't mean a pot you cooked in. Really a nice big pipe end cap would probably be a good vessel, or a small cast iron pot of some sort.

Or one of the homebrewed crucibles I've seen people make out of a short length of pipe with a plate welded to the bottom of it. Something along those lines. Though honestly I've seen people melt aluminum in paint cans and solder has a lot lower melting temperature than aluminum does. I have air and don't think its so good. If there's a better way of stripping boards I've never heard of it, or I'd have it!

L You are completely right, it is a subject that needs a good explanation. I also have taken apart a lot of old or disfunctional electronincs for parts and have burn some fingers while doing it and as you say it isn't as straightforward as it seems.

And I must say that I now prefer to buy part instead of reusing them with the exception of motors and solar cells and some other bigger and more expensive parts. Some of the standard values are so cheap that isn't worth to heat my solderingiron for it.

And new parts have long leads so they are easier to use when soldering. But that ofcourse is only my humble opinion. Well if you have the means the way I find the best is to use a pick and get under the part to pop it up.

Really depends on the part, sometimes I use pump pliers, and sometimes angled needle nosed pliers work best. But overall I can pop a lot of parts with a simple pick tool.

But you're right, trying to salvage parts with a soldering iron is a waste of time and often destroys parts in the process as well. At some point the capacitor plates will be so full of charges that they just can't accept any more.

There are enough negative charges on one plate that they can repel any others that try to join. This is where the capacitance farads of a capacitor comes into play, which tells you the maximum amount of charge the cap can store. If a path in the circuit is created, which allows the charges to find another path to each other, they'll leave the capacitor, and it will discharge.

For example, in the circuit below, a battery can be used to induce an electric potential across the capacitor. This will cause equal but opposite charges to build up on each of the plates, until they're so full they repel any more current from flowing. An LED placed in series with the cap could provide a path for the current, and the energy stored in the capacitor could be used to briefly illuminate the LED.

A capacitor's capacitance -- how many farads it has -- tells you how much charge it can store. How much charge a capacitor is currently storing depends on the potential difference voltage between its plates. This relationship between charge, capacitance, and voltage can be modeled with this equation:.

Charge Q stored in a capacitor is the product of its capacitance C and the voltage V applied to it. The capacitance of a capacitor should always be a constant, known value. So we can adjust voltage to increase or decrease the cap's charge. More voltage means more charge, less voltage That equation also gives us a good way to define the value of one farad.

One farad F is the capacity to store one unit of energy coulombs per every one volt. The gist of a capacitor's relationship to voltage and current is this: the amount of current through a capacitor depends on both the capacitance and how quickly the voltage is rising or falling.

If the voltage across a capacitor swiftly rises, a large positive current will be induced through the capacitor. A slower rise in voltage across a capacitor equates to a smaller current through it. If the voltage across a capacitor is steady and unchanging, no current will go through it. This is ugly, and gets into calculus.

It's not all that necessary until you get into time-domain analysis, filter-design, and other gnarly stuff, so skip ahead to the next page if you're not comfortable with this equation. The equation for calculating current through a capacitor is:. The big takeaway from this equation is that if voltage is steady , the derivative is zero, which means current is also zero.

This is why current cannot flow through a capacitor holding a steady, DC voltage. There are all sorts of capacitor types out there, each with certain features and drawbacks which make it better for some applications than others. The most commonly used and produced capacitor out there is the ceramic capacitor. The name comes from the material from which their dielectric is made.

Ceramic capacitors are usually both physically and capacitance-wise small. A surface-mount ceramic cap is commonly found in a tiny 0. Through-hole ceramic caps usually look like small commonly yellow or red bulbs, with two protruding terminals.

Two caps in a through-hole, radial package; a 22pF cap on the left, and a 0. In the middle, a tiny 0. Compared to the equally popular electrolytic caps, ceramics are a more near-ideal capacitor much lower ESR and leakage currents , but their small capacitance can be limiting. They are usually the least expensive option too. These caps are well-suited for high-frequency coupling and decoupling applications.

Electrolytics are great because they can pack a lot of capacitance into a relatively small volume. They're especially well suited to high-voltage applications because of their relatively high maximum voltage ratings. Aluminum electrolytic capacitors, the most popular of the electrolytic family, usually look like little tin cans, with both leads extending from the bottom. An assortment of through-hole and surface-mount electrolytic capacitors.

Notice each has some method for marking the cathode negative lead. Unfortunately, electrolytic caps are usually polarized. They have a positive pin -- the anode -- and a negative pin called the cathode.

When voltage is applied to an electrolytic cap, the anode must be at a higher voltage than the cathode. The cathode of an electrolytic capacitor is usually identified with a '-' marking, and a colored strip on the case.

The leg of the anode might also be slightly longer as another indication. If voltage is applied in reverse on an electrolytic cap, they'll fail spectacularly making a pop and bursting open , and permanently. After popping an electrolytic will behave like a short circuit. These caps also notorious for leakage -- allowing small amounts of current on the order of nA to run through the dielectric from one terminal to the other. This makes electrolytic caps less-than-ideal for energy storage, which is unfortunate given their high capacity and voltage rating.

If you're looking for a capacitor made to store energy, look no further than supercapacitors. These caps are uniquely designed to have very high capacitances, in the range of farads. High capacitance, but only rated for 2. Notice these are also polarized. While they can store a huge amount of charge, supercaps can't deal with very high voltages. This 10F supercap is only rated for 2.

Any more than that will destroy it. Super caps are commonly placed in series to achieve a higher voltage rating while reducing total capacitance. The main application for supercapacitors is in storing and releasing energy , like batteries, which are their main competition.

While supercaps can't hold as much energy as an equally sized battery, they can release it much faster, and they usually have a much longer lifespan. Another common capacitor type is the film capacitor , which features very low parasitic losses ESR , making them great for dealing with very high currents. There's plenty of other less common capacitors. Variable capacitors can produce a range of capacitances, which makes them a good alternative to variable resistors in tuning circuits.

Twisted wires or PCBs can create capacitance sometimes undesired because each consists of two conductors separated by an insulator.

Leyden Jars -- a glass jar filled with and surrounded by conductors -- are the O. Finally, of course, flux capacitors a strange combination of inductor and capacitor are critical if you ever plan on traveling back to the glory days. Much like resistors , multiple capacitors can be combined in series or parallel to create a combined equivalent capacitance.

Capacitors, however, add together in a way that's completely the opposite of resistors. When capacitors are placed in parallel with one another the total capacitance is simply the sum of all capacitances. This is analogous to the way resistors add when in series. Much like resistors are a pain to add in parallel, capacitors get funky when placed in series. The total capacitance of N capacitors in series is the inverse of the sum of all inverse capacitances.

If you only have two capacitors in series, you can use the "product-over-sum" method to calculate the total capacitance:. Taking that equation even further, if you have two equal-valued capacitors in series , the total capacitance is half of their value.

For example two 10F supercapacitors in series will produce a total capacitance of 5F it'll also have the benefit of doubling the voltage rating of the total capacitor, from 2. There are tons of applications for this nifty little actually they're usually pretty large passive component. To give you an idea of their wide range of uses, here are a few examples:.

A lot of the capacitors you see in circuits, especially those featuring an integrated circuit , are decoupling. A decoupling capacitor's job is to supress high-frequency noise in power supply signals. They take tiny voltage ripples, which could otherwise be harmful to delicate ICs, out of the voltage supply.

In a way, decoupling capacitors act as a very small, local power supply for ICs almost like an uninterruptible power supply is to computers. If the power supply very temporarily drops its voltage which is actually pretty common, especially when the circuit it's powering is constantly switching its load requirements , a decoupling capacitor can briefly supply power at the correct voltage. This is why these capacitors are also called bypass caps; they can temporarily act as a power source, bypassing the power supply.

Decoupling capacitors connect between the power source 5V, 3. It's not uncommon to use two or more different-valued, even different types of capacitors to bypass the power supply, because some capacitor values will be better than others at filtering out certain frequencies of noise. In this schematic , three decoupling capacitors are used to help reduce the noise in an accelerometer's voltage supply.

Two ceramic 0. While it seems like this might create a short from power to ground, only high-frequency signals can run through the capacitor to ground. The DC signal will go to the IC, just as desired. Another reason these are called bypass capacitors is because the high frequencies in the kHz-MHz range bypass the IC, instead running through the capacitor to get to ground.

When physically placing decoupling capacitors, they should always be located as close as possible to an IC. The further away they are, they less effective they'll be.

Here's the physical circuit layout from the schematic above. The tiny, black IC is surrounded by two 0. To follow good engineering practice, always add at least one decoupling capacitor to every IC.

Usually 0. They're a cheap addition, and they help make sure the chip isn't subjected to big dips or spikes in voltage. Diode rectifiers can be used to turn the AC voltage coming out of your wall into the DC voltage required by most electronics.

But diodes alone can't turn an AC signal into a clean DC signal, they need the help of capacitors! By adding a parallel capacitor to a bridge rectifier, a rectified signal like this:. Capacitors are stubborn components, they'll always try to resist sudden changes in voltage. The filter capacitor will charge up as the rectified voltage increases.

When the rectified voltage coming into the cap starts its rapid decline, the capacitor will access its bank of stored energy, and it'll discharge very slowly, supplying energy to the load.

The capacitor shouldn't fully discharge before the input rectified signal starts to increase again, recharging the cap. This dance plays out many times a second, over-and-over as long as the power supply is in use. An AC-to-DC power supply circuit. The filter cap C1 is critical in smoothing out the DC signal sent to the load circuit.

If you tear apart any AC-to-DC power supply, you're bound to find at least one rather large capacitor. Below are the guts of a 9V DC wall adapter. Notice any capacitors in there? There might be more capacitors than you think! The big, yellow rectangle in the foreground is a high-voltage 0.

The blue disc-shaped cap and the little green one in the middle are both ceramics. It seems obvious that if a capacitor stores energy, one of it's many applications would be supplying that energy to a circuit, just like a battery.

The problem is capacitors have a much lower energy density than batteries; they just can't pack as much energy as an equally sized chemical battery but that gap is narrowing! The upside of capacitors is they usually lead longer lives than batteries, which makes them a better choice environmentally. They're also capable of delivering energy much faster than a battery, which makes them good for applications which need a short, but high burst of power. A camera flash might get its power from a capacitor which, in turn, was probably charged by a battery.

Capacitors have a unique response to signals of varying frequencies. They can block out low-frequency or DC signal-components while allowing higher frequencies to pass right through. They're like a bouncer at a very exclusive club for high frequencies only. Filtering signals can be useful in all sorts of signal processing applications.