Industries & Professions

Skill Builder: Understanding Capacitors

I wrote my book Easy Electronics to help beginners familiarize themselves with electronics easier, faster, and more cheaply than ever before. A dozen hands-on experiments show you the basics, and each takes half an hour or less. You don’t need any tools at all.

Some capacitors have colored cans.
Others don’t. The color is not important.

You will need:

  • AA batteries (3) with holder
  • Alligator Jumper Wires (3)
  • 470µF capacitor
  • 100µF capacitor
  • 1 kΩ resistor
  • 5mm LED through hole
  • SPDT slide switch.

EXPERIMENT:

The type of capacitor shown here is called an electrolyte. The storage capacity, known as capacity, is 470 µF – but I’ll explain that in a moment. 50V is the maximum voltage, but a voltage rating of 10V or higher is fine for this experiment.

The short lead is the negative side, which is also marked with a minus sign. This is because this capacitor is polar – never connect an electrolytic capacitor to a power supply the wrong way round.

You can create this circuit in two steps. This part only charges the capacitor with current when the slide switch moves up to the left.
Some of the voltage from the battery is transferred to the capacitor, although you can’t see any signs of it just yet.

Add the 1K resistor and LED with the negative side of the LED sharing the negative leg of the capacitor.

Now move the switch to the bottom right. The capacitor discharges through the LED.

Move the switch to the top left and wait 5 seconds for the capacitor to charge. Now you can discharge it again and light the LED again!

If this diagram seems complicated to you,
Try sketching a copy of this, replacing the alligator wires with simple lines to connect the components.

HOW DOES IT WORK?

Inside the capacitor you are using are two metal plates called the plates. They are separated by a paste called an electrolyte, which is why this capacitor is called an electrolyte.

When electrons flow into one plate, they try to create an equal, opposite charge on the other. You can imagine that the plates have positive and negative charges that attract each other.

TIMED COORDINATION

The 1K resistor was needed because you charged the capacitor with 4.5V from the battery pack and the LED can only handle about 1.8V. The resistor prevents the LED from being damaged.

The resistor also controls how quickly the capacitor discharges. Replace a 10K resistor (brown, black, orange) and the LED will be darker than before and it will take a lot longer to fade out.

There is still something to try here. Again use the 1K resistor. Remove the 470µF capacitor and replace a 100µF capacitor. Flick the switch back and forth and the LED will now light up very briefly.

Electricity moves quickly, but a capacitor and resistor can make things happen slowly.

CERAMICS

Capacitors like the one shown above
are less than 1/2 “wide. They are dipped in a ceramic compound.

Most ceramic capacitors have no polarity.

Many ceramic capacitors have a code printed on them instead of their actual capacitance.

Some ceramic capacitors are in the shape of circular discs.

In simple circuits of the type you built, you can usually substitute a ceramic for an electrolyte if you wish. Note that ceramic may be more expensive at values ​​around 10µF and higher.

UNITS

Capacitance is measured in farads, abbreviated to the letter F. However, a 1F capacitor is very large. In hobby electronics we mainly use capacitors with microfarads, abbreviated µF. The µ symbol is the Greek letter mu, but µF is often printed as uF.

There are 1,000,000 microfarads in 1 farad, 1,000 nanofarads (nF) in 1 microfarad, and 1,000 picofarads (pF) in 1 nanofarad

SCHEME

There are two symbols for capacitors.

On the left is a polarized capacitor like an electrolyte.

On the right there is an unpolarized capacitor like a ceramic.

Some people use the symbol to the right everywhere in a schematic and let you decide if you want to use an electrolytic capacitor and if so how to handle it.

YOU MAY THINK:
A capacitor may be similar to a battery. After all, both store electricity.

However, a battery uses chemical reactions, and even a rechargeable battery wears out after a limited number of charge and discharge cycles.

A capacitor does not use chemical reactions and can still work after a few years.

In this schematic showing the circuit just built, the double switch has completed a circuit with the battery so that the battery charges the capacitor.

In this scheme, the double throw switch is in its other position, completing a circuit from one plate of the capacitor through the resistor and the LED back to the other plate.

This article is from the book Make: Easy Electronics, which is available at MakerShed and other booksellers. A complete kit of all the components used in the book can be found here.

[Feature Photo by Michael Dziedzic on Unsplash ]

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