# Wattage – Electrical Power unit

Power is the amount of work being done. The unit used for power is called the watt. Some forms of power in electronics include an LED lighting up, motors spinning, and when things heats up as current is forced through them.

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• Watt: A unit of power – Rate of energy transfer
• P = VI – Power (P) in watts (W) equals the voltage in volts (V) times the current (I) in Amps (A)
• 1W = 1 joule per second = 1V times 1A

Heat is just wasted power unless your goal is to heat something. Heat is also what damages electric components. Therefore, it is important that you keep the power consumption of all components below half of their maximum wattage rating.

Keep in mind that you may only get a maximum and/or recommended current rating for some components instead of a wattage rating.

Series components split up the voltage across them and therefore also split up the power dissipation.

## Diagrams of common values:

Most resistors are rated for a maximum of 1/4W (0.25W), and should ideally be kept below 1/8W (0.125W) to ensure a long life.

This diagram shows the current and wattage for a 100Ω and a 1,000Ω resistor with different voltages across them. The highest voltage next to each of them is close to the maximum voltage you would want to put across them.

• 3.3V  across  100Ω  –  3.3V/100Ω = 0.033A (33mA)  through the resistor |  0.033A x 3.3V = 0.1089W heat generation.
• 5V  across  220Ω  |  5V/220Ω = 0.0227A (23mA) through the resistor |  0.023A x 5V = 0.115W heat generation
• 9V  across  1KΩ  |  9V/1000Ω = 0.009A (9mA)  through the resistor|  0.009A x 9V = 0.081W heat generation.

### Resistors with the added protection of an LED voltage drop.

Below are resistor values and supply voltages that are slightly higher than the desired 1/8W (0.125W) of a 1/4W (0.25W) resistor alone. But, by adding  a series LED, there is enough of the voltage dropped to make it safe for the resistor.

Forward biased LEDs typically have a forward voltage of about 2-3 volts; which is dropped from series components.

Commonly available values being given. Numbers are rounded off. Higher value resistors are even safer to use.

• 9V:         2V LED drop = 7V across resistor  –  470Ω/7V = 0.0149A (15mA) through resistor and LED – 0.015A x 7V = 0.105W heat generated by resistor.
• 12V:       2V LED drop = 10V  across resistor –  10V/1000Ω = 0.01A (10mA)  through resistor and LED – 0.01A x 10V = 0.1W heat generated by resistor.

#### Bonus video and diagram:

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##### Related topics:

Other basic electronics topics that you should know before moving on to more advanced topics.

555 timer is an integrated circuit (IC). Being an IC, it has complex circuitry combined in a single package with external pins/terminals to connect to other circuitry. You can easily make all kinds of fun circuits with just a 555 timer and the components covered above, so I think it’s a good component to learn next.

Transistors will probably be the most challenging components to learn. Understanding them will help you understand all of electronics much better, and help you the most in being creative while designing your own circuits.

Other topics:

These pages are still being compiled.