So why 12V and not 18V? What’s with the different levels for cordless tools 12/18/24.
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The oldest auto batteries used zinc-carbon which run at 1.5v. Cars thus used 6v to power electrical components. As cars started to pull more power this was upped to 12v. Modern passenger cars simply haven’t needed more voltage so 12 remains as the standard.
With basic chemistry, it is pretty simple to create a 1.5V battery. So you will see many batteries operate on integer multiples of this.
AA/AAA batteries are 1.5V. 1.5*6 = 9V batteries (those big square ones). 1.5*8 = 12V (car batteries and other larger batteries).
12V is just a good medium between “useful” and “low enough power to not have the potential to kill”. It’s also nice to have a low voltage, as you can keep wires (and therefore cost and weight) smaller.
Someone decided to go with 12v back in the early days and it just became the standard. To a certain extent it was the highest voltage you could get out of an early battery without needing more than one person to lift it. (Lead-acid batteries are heavy, and the more voltage they put out the heavier they need to be). Once a few manufacturers had settled on 12v that was the size the battery makers produced, so every other car manufacturer just went along with it. So light bulb manufacturers built lamps that worked at that voltage, etc.
For power tools using 12/18/24 . Most are powered by a battery pack that itself contains standard cells taped together. These batteries originally each output around 1.5v, so it was easy to combine them in multiples of 2×1.5 or 3v. Modern Lithium cells put out 3.7v so you sometimes see the packs listed as 18v when they actually put out 5×3.7 or 18.5v – as long as the pack is mated with equipment designed to actually use the voltage it’s putting out, there isn’t a problem – but it is one reason why power tool batteries so often use proprietary interfaces.
Modern EV’s are actually slowly ditching the 12v battery and moving to a more powerful 30v low voltage system – or at least several manufacturers have announced they will do this, I’m unsure if any are actually in production.
It’s a convenient voltage for all the components. It’s a good voltage that works with the battery, headlights, startup motor, radio, etc etc.
The spark plugs have to have voltage stepped up anyway, so voltage doesn’t really matter for those.
Voltages that are too low would waste energy to the resistance of wires in the car, and voltages too high would have to be stepped down. As to why 12 instead of 18, it probably doesn’t make too much of a difference, so… Standards.
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