Car Battery Boosting by PHONE

Quick Overview

It is possible to jump-start a car with a dead battery using only a smartphone, as demonstrated by successfully starting a Toyota Matrix after charging the battery for 30 minutes using a custom boost converter circuit powered by the phone's 5V USB output, which provided 2,700 Joules of energy, significantly more than the 2,400 Joules required for one successful crank.

Key Points: The experiment successfully used a phone's 5V USB output to charge a dead car battery enough to start the engine after 30 minutes of charging. The car starter required approximately 2,400 Joules of energy per crank, calculated from the 12V battery capacity and 200A average crank current. The phone's charging circuit, running at a constant 0.3 Amps for 15 minutes (900 seconds), delivered 2,700 Joules of energy, which was sufficient for one successful crank (2700J > 2400J). The charging circuit employed a custom boost DC-to-DC switching converter design, which takes the 5V input and boosts it to charge the 12V car battery. The host performed multiple charging attempts, with one 30-minute charge resulting in the battery voltage rising from 9.49V (no load) to 10.75V (under load), which allowed the engine to crank twice before failing again. After a total charge time of 41 minutes and 2 seconds, the battery voltage reached 10.73V, and the phone's charging current dropped, suggesting the phone stopped supplying power. The final successful crank occurred after the host gave the battery an extended charge, indicating that while challenging, providing enough cumulative energy from a phone can revive a dead car battery.

Context: The video explores the feasibility of using a modern smartphone's battery to provide enough energy to jump-start a standard gasoline car with a dead 12V lead-acid battery. The host, Mehdi Sadaghdar of ElectroBOOM, designs and tests a custom boost converter circuit that steps up the phone's 5V USB output to a voltage high enough to push a small charging current into the 12V battery. This demonstration aims to quantify the energy stored in a typical smartphone battery relative to the high energy required to crank an engine.