why vehicles use 12v electric systems? Why a seemingly strange arbitrary figure like 12? Why not 10?
In: 0
Why would 10 be any less arbitrary than 12?
Car batteries (traditionally) are lead-acid chemistry.
A single cell of a lead-acid battery has a nominal voltage of about 2.2 Volts but work sufficiently down to around 1.8 Volts. So, they average out to around 2.0 Volts.
A single car battery has multiple cells in it (meaning that it’s a battery pack rather than a single battery, technically speaking). Six cells, to be exact.
6 X 2 = 12
Also, early cars were only 6 Volts (3 cells). But as cars got more and more complex, the voltage needed to be increased to accommodate the changes.
So, going from 6 Volts to 12 Volts meant that two 6 Volt batteries could be wired together to give the 12V instead of 10, which wouldn’t require entirely new battery components to be produced.
In the end though, 12 Volt just worked and the carmakers adopted it as a standard across the industry. It is somewhat arbitrary, based just on “we need to pick something, so how about this?”, but there’s quite a bit of logic behind it as well.
Basically you need a fairly large voltage to get the car started (rather than use a crank handle) initially this was 6 volt but increased to12 to cope with engines with a high compression ratio which need more power to get them going.
Lead acid cells have a nominal voltage of 2.1V but will often be considered as 2V. The result is battery voltage will be a multiple of 2.
The early cars had battery voltage of 6V ie 3 cells. 5V would not be possible, it is not a multiple of 2, the closes alternatives are 4V and 8V It was enough to start the engine of that era and power lamps etc. When cars got engines with higher compression ratios the starter engine needs to work harder. If you increase the voltage you do not need as high current and thick wires so the battery voltage was increased in 1950.
If you have 6V batteries and what to increase the voltage the simplest way is to initially have two 6-volt batteries. Then you can connect any part design for 6V in the middle and new stuff including started motor on the edges for a 12V system. Over time when everything runs on 12 V you can use a single 12V battery.
Trucks today often have 24V because you need to start larger engines. They are often two 12V batteries. One advantage is the weight, a single 24V battery would be twice the size and weight so quite impractical to handle.
So 10 V would not be possible if the system was created by using two identical lower voltage lead-acid batteries.
Lead acid cells have a 2V output.
To make a 10V battery would take 5 cells, and 12V six cells in series. If you arrange the cells linearly then a 10V battery would generally be shorter. If you want to make a rectangular arrangement of cells then you’d prefer 12V since you can create a rectangle using 6 equal sized cells, but you cannot do so with 10V and its 5 cells.
Earlier batteries used 6V (3 cells). When they wanted more power it was fairly easy to just wire two 6V batteries in series and get 12V. Telecom used 48V (which is a multiple of 12, but not 10).
Vehicles use 12v electric systems for a few reasons. First, 12 volts is strong enough to power most electronic systems in a car (like headlights, windshield wipers, and so on) without taking up too much power from the vehicle’s battery. Second, 12 volts is also the perfect voltage of electricity to jump start a car in case of an emergency.
My first car was a 1989 Ford Escort. I had an old battery that had finally given out and I needed to buy a new one, but instead of just buying a new one, I decided to give the old one a jump start. I was able to buy a very low voltage jump lead (only 12 volts) and with that, I was able to give my car enough of a boost to get it started and back on the road.
So, 12 volts is the perfect number of volts you need to give a dead battery a jump start and also to power most electronic systems in a car without taking up too much power from the vehicle’s battery.
Latest Answers