Building Systems That Work
Power Budgets & Batteries
13 minStudent plan
Add up what your circuit actually draws, size the battery from it, and find out how long the thing will really run.
After this lesson you can
- Add up the worst-case current draw of a system
- Work out runtime from capacity
- Say where the power is actually going
Adding up the draw
A power budget is a list: every component, what it draws, and whether it draws it all the time.
An Arduino Uno idles around 45 mA. An LED at full brightness is about 20 mA. A small servo can pull 500 mA while moving and almost nothing while still. A GPS module might average 30 mA.
Sum the ones that run continuously, then decide honestly how to treat the intermittent ones. Two numbers are worth having: the average draw, which sets battery life, and the peak draw, which sets what the supply must be capable of delivering without its voltage collapsing.
Designing to the average and ignoring the peak is why a project works on a bench supply and resets constantly on batteries.
In the full lesson
- Adding up the draw
- Capacity and runtime
- Where the power actually goes
This lesson comes with the Student plan. The first module of Engineering Foundations is free.