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.

Quarter watt resistors heat dissipation at a quarter watt and an eighth of a watt of power seen in thermal by electronzap and electronzapdotcom
Quarter watt resistors heat dissipation at a quarter watt and an eighth of a watt of power seen in thermal

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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.

Equal series resistors split up supply voltage evenly scheatic diagram by electronzap electronzapdotcom
Equal series resistors split up supply voltage evenly scheatic diagram by electronzap electronzapdotcom

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.

Flir thermal images of 20mA through resistor and LED at different voltages for quick videos 4

Diagrams of common values:

 

1K and 100 ohm resistor current and wattage examples diagram by electronzap electronzapdotcom
1K and 100 ohm resistor current and wattage examples diagram by electronzap electronzapdotcom

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.


Higher voltage than you need wastes energy demonstration circuit basic electronics by electronzap

220 and 470 ohm resistor current and wattage examples diagram by electronzap electronzapdotcom
220 and 470 ohm resistor current and wattage examples diagram by electronzap electronzapdotcom
  • 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.

Switch controlled LED protected by resistor circuit schematic diagram with current and power calculations by electronzap
Switch controlled LED protected by resistor circuit schematic diagram with current and power calculations by electronzap

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:

Series or parallel resistors being used to simulate a single higher wattage resistor schematic diagram by electronzap
Series or parallel resistors being used to simulate a single higher wattage resistor schematic diagram by electronzap

How to substitute a higher wattage electronics resistor with lower value series or higher parallel

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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.

Circuits covered more quickly series:

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