Current budget
Total robot current against the 120 A main breaker, and the battery voltage it leaves.
Inputs
Supply current, e.g. your supply current limit.
roboRIO, radio, controllers and LEDs. Add the compressor’s draw if it runs at the same time.
A healthy battery is about 11–15 mΩ; wiring and the breaker add a few more.
Result
Total current
245- Battery voltage under load
- 7.7
- Share of main breaker
- 204.2%
- Power drawn
- 1,886
Check this: Above the main breaker’s 120 A rating: a sustained draw like this will trip it, sooner the further over you are.
How it’s calculated
Formula
With your numbers (converted to SI units)
What it means
Everything on the robot shares one battery. The more current flows, the more the battery’s internal resistance drags its voltage down. When it falls to the roboRIO’s brownout voltage (6.75 V by default on a roboRIO 2, a fixed 6.3 V on a roboRIO 1), the roboRIO disables motor outputs, which usually happens mid-push or mid-climb. The main breaker is thermal: it tolerates short bursts well over 120 A, and the further and longer it is overloaded, the sooner it trips.
Assumptions
- Steady-state draw; motor current spikes at start-up are higher.
- Brownout at 6.75 V, the roboRIO 2 default (configurable). A roboRIO 1 holds on until 6.3 V.
Learn the concepts behind this on resources.simbotics.org · All formulas