Ever had one of those days where a cat was
chewing up your circuit board? Or maybe you have an old amplifier where
the capacitors seem to be leaking this yucky poisonous goo? If you have ever been in that situation you might
be able to fix the circuit board by replacing the capacitors. Let’s run through an example where I replace
this capacitor from a circuit board. First up some theory. What is a capacitor? A capacitor is an energy storage device that
can be used to smooth out voltages. Every capacitor will have two important ratings:
capacitance and voltage. Capacitance is a way of saying how much energy
the capacitor can hold at a given voltage. Capacitances usually expressed in microfarads (uF). Ninety nine percent of the time when you are
replacing a capacitor, you want to use the same capacitance rating or very close to it. The capacitor over here is 470uF.
If I want to replace it I should ideally use another 470uF capacitor. The other important number is the voltage rating.
The voltage rating is the maximum voltage that the capacitor can handle before it explodes.
Now I want to say that again, the voltage written on the side of the capacitor means that this is the
maximum voltage that the capacitor should ever be exposed to. It does not mean necessarily that the capacitor
is at that voltage. For example this is a 16 volt capacitor. This does not mean that it is charged to 16
volts like a battery. It means that if charge it up to 5 volts
it will be fine. If I charge it to 10 volts it will be fine. If I charge it to 16 volts it will just
about handle it. And if I charge it to 25 volts it will explode. Going back to our example capacitor I can see that
it is rated at 16 volts. If I want to replace it I should use a 16V or higher rated capacitor. Now it turns out that the only 470uF capacitors
that I have in my parts box are rated 25 volts. And that’s totally fine.
If the original circuit only required a 16V capacitor, if I use a 25V capacitor
that just means I get a bigger safety margin. Next let’s talk about polarity. The negative side of an electrolytic capacitor
will always have these little negative symbols. All you have to do is make sure that you match
up the polarity with the original capacitor. If you get the polarity backwards, this is what
happens. So now that I have the correct polarity i’m going to
replace capacitor and solder it in. Finally I want to give you a little safety
warning. If you ever seen any of these big capacitors with high voltage ratings like 200
volts, you should be careful to not touch them if they are charged. Remember a 200V rated capacitor could very
well have 200V on it, and that would kill you. Alright have fun replacing capacitors!