A Capacitor . . .

A capacitor is an electronic device that can hold a charge.  In the old days before the current super duper capacitor discharge electronic ignitions we used have a "condenser."   A condenser is a capacitor and is used to collapse the electrical field in the coil to generate a spark for ignition.  The principle is still the same but things are self contained and decidedly more reliable and long lasting because there are no moving parts like points to deal with.

Capacitors are basically a storage device.  This is why they can hold a charge.  And they come in many sizes and types.  Electrolytic capacitors are usually large in the ability to hold a charge.  Film capacitors are not large in size or volume and are usually quite small in the charge they can hold.

Capacitors can also be used as filters and tend to remove noise on the lines inside electronic circuits.  That is why a typical circuit board has a lot of little capacitors place here and there to soak the interference.

But because they can hold a charge, they can be used to smooth out drops in voltage.  These are generally known as filter capacitors and have large values in Farads.  A Farad is a rather large amount of capacitance, ergo the little ones are measure in microfarads, millionths of a farad.  So when one sees a 80 Farad capacitor, that is a big sucker and if charged up to a high enough voltage can actually kill you.  

In my radio control we have been having what we call brown outs.  That is when the battery temporarily drops below a specific voltage and shuts down the solid state receiver.  That voltage can be around 3.2 volts, all it takes is a quick dip measure in microseconds and the transistor goes dead and the receiver quits.  This is where the capacitor comes in, one can put one in the power circuit parallel with battery and when the battery starts to sink for any reason, the capacitor starts to discharge to hold the voltage.  Magic but functional.  And the capacitor can last as long as a second to keep that voltage up.  When the battery recovers, the system demand goes down, the voltage goes back up and the capacitor recharges.  It takes care of that sinking spell.

Of course if the battery demand is prolonged then there is not recovery, the battery goes down, then the capacitor and of course the airplane goes down too, it usually crashes.  But that is a different circumstance we can not protect for very well.  Fortunately, it is a rare occurrence.

I just ordered up some 3300 microfarad capacitors.  They are rated at 6.3 volts, pretty near the battery voltage.  I am sure it will last for a whopping half a second at the most.  But that is plenty for me.  All I have to do is put a plug on the end of the capacitor in the right polarity and plug it into the receiver and I am protected.