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In a way, a capacitor is a little like a battery. Although they work in completely different ways, capacitors and batteries both store electrical energy. If you have read How Batteries Work, then you know that a battery has two terminals. Inside the battery, chemical reactions produce electrons on one terminal and absorb electrons on the other terminal. A capacitor is much simpler than a battery, as it can't produce new electrons -- it only stores them.
In this article, we'll learn exactly what a capacitor is, what it does and how it's used in electronics. We'll also look at the history of the capacitor and how several people helped shape its progress.
Inside the capacitor, the terminals connect to two metal platesseparated by a non-conducting substance, or dielectric. You can easily make a capacitor from two pieces of aluminum foil and a piece of paper. It won't be a particularly good capacitor in terms of its storage capacity, but it will work.
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What use of c in circuits?
C = capacitors. Capcitors can be used to store voltages so that they become voltage sources, or they can be used in mixed A/D circuits as timers, attenuators, filters, etc.
How do capcitors work?
A capacitor is a bit like a battery, but it has a different job to do. A battery uses chemicals to store electrical energy and release it very slowly through a circuit; sometimes (in the case of a quartz watch) it can take several years. A capacitor generally releases its energy much more rapidly-often in seconds or less. If you're taking a flash photograph, for example, you need your camera to produce a huge burst of light in a fraction of a second. A capacitor attached to the flash gun charges up for a few seconds using energy from your camera's batteries. (It takes time to charge a capacitor and that's why you typically have to wait a little while.) Once the capacitor is fully charged, it can release all that energy in an instant through the xenon flash bulb. Zap!Capacitors come in all shapes and sizes, but they usually have the same basic components. There are the two conductors (known as plates, largely for historic reasons) and there's the insulator in between them (called the dielectric). The two plates inside a capacitor are wired to two electrical connections on the outside called terminals, which are like thin metal legs you can hook into an electric circuit.
Why you add the capcitors to motor?
Capacitors are used with motors in two different ways. Sometimes the same motor will have both techniques applied, and be associated with two significantly different-looking capacitors. *When motors with brushes are running normally, the motor brushes produce sparks, which cause noise "from DC to daylight". This has nothing to do with PWM -- it happens even when these motors are connected directly across a battery, without any PWM. If we did nothing, the cable running from the electronics board (or directly from the battery) to the motor would act like an antenna, radiating TV and other radio interference. One way people fix that problem is to attach small ceramic capacitors directly to the motor to absorb much of that noise. b c d e *When using PWM to drive the motor, when the transistors turn "on", the motor may pull a current spike / surge current -- the above noise-filtering capacitors make that current spike worse. When the transistors turn "off", the motor inductance may cause voltage spikes from the motor inductance -- the above noise-filtering capacitors help a little. More complex filters attached directly to the motor can help these two problems. a b *When a motor -- even a motor that doesn't have brushes -- is first turned on at a dead stop, and also when the robot hits an obstruction and stalls the motor, the motor pulls much higher currents than it does in normal operation -- currents that may last for several seconds. This high current may pull down the battery power rail enough to reset all the digital electronics in the system (or perhaps reset just some of the digital electronics, causing half-brain syndrome). One work-around has 2 parts: 1.add large electrolytic capacitors directly across the battery (or across the battery input to the PWM motor driver, or across the battery input to the digital electronics, or often capacitors in all three locations) -- these capacitors work better at supplying high currents for a few milliseconds than the battery does. 2.In the few milliseconds we have before the stalled motor pulls all the energy from those big capacitors and then pulls the power rails low enough to start resetting things, program the digital system to somehow recognize that the motor has stalled and kill the power to that motor. Then that motor no longer drags down the power rail, and the digital electronics and all the other motors continue to operate normally. ("soft-start", "current-limiting", "torque-limiting", etc. are more sophisticated forms of this idea). (Those big capacitors, also absorb some of the energy that comes out of the motor when the PWM turns "off", and later put that energy back into the motor when the PWM turns "on"). The above capacitors protect other things from the motor's electrical interference. I suppose one could argue that step (2) above prevents a stalled motor from eventually, after many seconds, overheating and failing -- but that's not really its primary purpose.
