Robotics battery and power management covers how a robot stores, delivers, and controls electrical energy. Students need this cheat sheet because motors, sensors, controllers, and radios all depend on stable power. Good power planning helps prevent brownouts, damaged parts, short runtime, and unsafe battery use.
It also helps teams choose the right battery, wiring, switch, fuse, and voltage regulator for a robot.
Key Facts
- Electrical power is found with P = V x I, where P is power in watts, V is voltage in volts, and I is current in amps.
- Energy is found with E = P x t, where E is energy in watt-hours if power is in watts and time is in hours.
- Battery energy can be estimated with Wh = V x Ah, where V is nominal battery voltage and Ah is amp-hour capacity.
- Runtime can be estimated with time = capacity / current, using hours = Ah / A or minutes = 60 x Ah / A.
- Battery capacity conversion is Ah = mAh / 1000, so a 2200 mAh battery equals 2.2 Ah.
- C-rate current limit is Imax = C-rate x Ah, so a 20C, 2 Ah battery can safely supply about 40 A if the rating is reliable.
- For components in parallel, the supply voltage is the same across each branch, but total current is Itotal = I1 + I2 + I3 + ... .
- A voltage regulator must be rated for the input voltage, output voltage, and load current, with extra margin for heat and motor surges.
Vocabulary
- Voltage
- Voltage is the electric potential difference that pushes current through a circuit, measured in volts.
- Current
- Current is the rate of electric charge flow through a circuit, measured in amps.
- Power
- Power is the rate at which electrical energy is used or delivered, measured in watts.
- Capacity
- Battery capacity is the amount of charge a battery can deliver, often measured in amp-hours or milliamp-hours.
- C-rate
- C-rate describes how quickly a battery can safely charge or discharge compared with its capacity.
- Brownout
- A brownout is a temporary voltage drop that can reset controllers or make motors and sensors behave unpredictably.
Common Mistakes to Avoid
- Using mAh as if it were amps is wrong because mAh measures stored charge, not instant current flow. Convert capacity with Ah = mAh / 1000 before estimating runtime or C-rate current.
- Ignoring motor stall current is wrong because motors can draw much more current when starting, pushing, or jammed. Choose batteries, wires, switches, and fuses that can handle peak current safely.
- Connecting a component directly to the battery without checking voltage is wrong because many sensors and controllers need regulated 5 V or 3.3 V. Too much voltage can permanently damage electronics.
- Assuming a higher capacity battery always fixes power problems is wrong because capacity mainly affects runtime. Voltage sag, C-rate, wire resistance, and regulator limits can still cause brownouts.
- Running lithium batteries below their safe minimum voltage is wrong because overdischarge can damage the cells and create a safety risk. Use a low-voltage alarm, battery management system, or controller cutoff.
Practice Questions
- 1 A robot uses a 12 V battery and draws 4 A while driving. What power is the robot using?
- 2 A 7.4 V battery has a capacity of 2200 mAh. Estimate its energy in watt-hours.
- 3 A robot draws an average current of 3 A from a 2.4 Ah battery. Estimate the runtime in minutes.
- 4 A robot controller resets whenever the drive motors start moving. Explain two power management causes that could create this problem.