What is that clicking noise when you try to start a car with a dead battery?
In: 12
A regular gasoline powered car has an electric starter to start the engine turning. The battery powers the starter for a few seconds until the spark plugs firing begins to take effect.
The starter is an electric motor with two main parts. The motor itself which of course spins to turn a gear, which turns a gear on the engine, and a solenoid to engage that gear with the engine.
But this starter gear isn’t always engaged. Normal engine speeds would spin the starter so fast it would be destroyed.
So, the gear slides into place only at the beginning of cranking the engine when you’re holding the key in the start position. Basically the way gears are changed in a manual transmission. Instead of making you pull a lever to shift the starter gear into position there is a solenoid on the side of the starter which moves it.
A solenoid is an electromagnet that attracts a piece of metal when you feed electricity to the magnet. Give it 12 volts and the starter gear is slammed into place just before the starter motor starts turning.
Normally that sound is drowned out by the sound of the starter motor and then in a second by the engine running. When you release the key from the start position the solenoid loses power and a spring pulls the gear back to disengage it from the engine.
When the battery is almost dead there’s not enough power to spin the starter and that click you hear is the solenoid pushing the starter gear into place. Clack! But no starter spinning or engine running noise so you can hear the gear shift position forward and then the spring pull it back when you release they key.
If you keep trying to crank it what little energy is still in the battery is wasted and each successive clack is quieter as the battery gets weaker. Eventually it won’t even click anymore.
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