Wireless Chargers: Magic Electricity
How does your phone charge without a wire? Induction. Understand the physics of magnetic fields and why we don't use it for robots (yet).
Wireless Chargers: Magic Electricity
You put your phone on the pad. It charges. No plugs, no clicks. It feels like sci-fi magic, but it’s actually 19th-century physics discovered by Michael Faraday and Nikola Tesla. It is Electromagnetic Induction.
Coils and Magnets
Inside the charging pad is a coil of copper wire. Inside the back of your phone is a smaller coil of copper wire. They are essentially a Transformer cut in half.
- The Transmitter (Pad): AC electricity flows through the coil. This creates a rapidly changing Magnetic Field.
- The Air Gap: The magnetic field expands and collapses invisible through the air (and your phone case).
- The Receiver (Phone): The magnetic field passes through the phone’s coil.
- Induction: The magnetic field pushes the electrons in your phone’s coil, forcing them to move. Moving electrons = Electricity.
The Efficiency Problem
If this is so cool, why don’t we power everything this way? Why do robots (and electric cars) still have plugs? Efficiency.
- Copper Wire Connection: ~99% efficient.
- Wireless Charging: ~70-80% efficient (at best).
Where does the missing 20% go? It turns into Heat. That’s why your phone gets hot on the wireless charger. The magnetic field leaks. Energy is lost crossing the air gap.
Robotics and Induction
In high-level robotics (FTC), we care about every single electron because our battery is small. If we wasted 20% of our power on wireless transfer, our robot would be slower, weaker, and the battery would die 30 seconds early. So we stick to reliable XT30 connectors (plugs).
However, industrial robots use this principle for Data.
- NFC (Near Field Communication): This is the tech in Apple Pay or Hotel Key Cards. It uses the exact same Induction physics to transfer bits instead of watts.
- RFID Tags: We use these to let robots know “I am at Checkpoint A” without needing complex cameras. Ideally, the robot drives over a tag, induces a current, and reads the ID code.
So whilst we still plug our robots in to charge (for now), the principles of invisible magnetic fields govern our motors, our sensors, and our radios.