What's the deal with 12v.

[VTEC_Inside]

I'm sure I knew this at some point, but what prompted the decision to use 12v in our cars?

I got wondering about it after reading that the new Accord v6 uses a 28v circuit for its active engine mounts.

[Eye of the Tiger]

12v is a good level for mechanical switches, as higher levels produce higher temp sparks that
burn out contacts more quickly.
Solid state systems often don't use 12v. Most ECUs run off 5v.

[shp4man]

I had a '54 Ford that was 6 volt positive ground. Just sayin'

[Soup DeVille]

I'm sure I knew this at some point, but what prompted the decision to use 12v in our cars?

I got wondering about it after reading that the new Accord v6 uses a 28v circuit for its active engine mounts.

Lead acid battery cells are 2 volts a piece, so you can get any combination of 2 volt increments you want. 6 was used for along time, but eventually shown to be less reliable than 12. 12 was easy when going from 6, you just used two batteries instead of one. 18 and 24 made the early lightbulb filaments too long and more easily broken.

[AutobahnSHO]

Some cars now are 12/24. I think the hybrids use something higher for the drive motors, but I'm too lazy to look it up..

Majority of military trucks are 24v.

[MX793]

Some cars now are 12/24. I think the hybrids use something higher for the drive motors, but I'm too lazy to look it up..

Majority of military trucks are 24v.

Pretty much all commercial trucks are 24V, though a number of subsystems (such as the lighting circuits) are 12V.

[VTEC_Inside]

Lead acid battery cells are 2 volts a piece, so you can get any combination of 2 volt increments you want. 6 was used for along time, but eventually shown to be less reliable than 12. 12 was easy when going from 6, you just used two batteries instead of one. 18 and 24 made the early lightbulb filaments too long and more easily broken.

I figured it was predominantly due to old school tech that's just dragged on.

The battery design seems like it would have been the driving force.

A mechanic buddy of mine showed me a hybrid power pack a while back. I believe it was 144v or something like that. It was just a massive bunch of C sized cells wired together.

[Madman]

American cars switched from 6v to 12v sometime in the mid-1950s.  (My old 1952 Chevy had 6v electrics)

Old VW Beetles continued using 6v long after everyone else switched to 12v.

[Soup DeVille]

I figured it was predominantly due to old school tech that's just dragged on.

The battery design seems like it would have been the driving force.

A mechanic buddy of mine showed me a hybrid power pack a while back. I believe it was 144v or something like that. It was just a massive bunch of C sized cells wired together.

I believe most cars still use plain old lead acid starting batteries, but yes, with modern cars increasingly using electrical power for everything from power steering to water pumps, the days of the 12 volt standard are probably limited.

[Soup DeVille]

American cars switched from 6v to 12v sometime in the mid-1950s.  (My old 1952 Chevy had 6v electrics)

Old VW Beetles continued using 6v long after everyone else switched to 12v.

I want to say they switched somewhere around '68 or so.

[FoMoJo]

I want to say they switched somewhere around '68 or so.

'55 mostly, if I recall.  Push starts were pretty common before then.  It was always wise to park facing downhill; especially in cold weather.

[giant_mtb]

I had a '54 Ford that was 6 volt positive ground. Just sayin'

What an amazing story.

[280Z Turbo]

I believe most cars still use plain old lead acid starting batteries, but yes, with modern cars increasingly using electrical power for everything from power steering to water pumps, the days of the 12 volt standard are probably limited.

It seems to me that if we used something like 48v systems on cars, we could make wiring harnesses thinner, thereby reducing weight.

[Soup DeVille]

It seems to me that if we used something like 48v systems on cars, we could make wiring harnesses thinner, thereby reducing weight.

Probably, but a lot of that has been solved by going to a can-bus type network system. The systems that really need some power to work generally have pretty short power leads.

There's also some argument to be made that the wires just have to be a certain thickness to be durable and resist corrosion.

Like I said, I think we'll eventually see a change in the standard- just dropping that 40 pound lead acid battery for a five pound lithium-ion or something would do wonders.

[sparkplug]

Probably, but a lot of that has been solved by going to a can-bus type network system. The systems that really need some power to work generally have pretty short power leads.

There's also some argument to be made that the wires just have to be a certain thickness to be durable and resist corrosion.

Like I said, I think we'll eventually see a change in the standard- just dropping that 40 pound lead acid battery for a five pound lithium-ion or something would do wonders.

lithium batteries..  well they might... you know...

Nuclear explosion Green Screen (HQ)

[SVT_Power]

I figured it was predominantly due to old school tech that's just dragged on.

The battery design seems like it would have been the driving force.

A mechanic buddy of mine showed me a hybrid power pack a while back. I believe it was 144v or something like that. It was just a massive bunch of C sized cells wired together.

That's gotta be a mild hybrid system. A chevy volt at full charge is almost 400V, and I want to say its capacity is around 16 kwh?

[12,000 RPM]

Probably, but a lot of that has been solved by going to a can-bus type network system. The systems that really need some power to work generally have pretty short power leads.

There's also some argument to be made that the wires just have to be a certain thickness to be durable and resist corrosion.

Like I said, I think we'll eventually see a change in the standard- just dropping that 40 pound lead acid battery for a five pound lithium-ion or something would do wonders.

Do batteries get smaller/lighter for a given amount of charge capacity as you increase their voltages? CCA requirements haven't changed.

[Byteme]

It seems to me that if we used something like 48v systems on cars, we could make wiring harnesses thinner, thereby reducing weight.

Not to mention cheaper, given the high price of copper.

[Byteme]

I had a '54 Ford that was 6 volt positive ground. Just sayin'

Jaguar E-types were positive ground until 1964. 

[MX793]

Do batteries get smaller/lighter for a given amount of charge capacity as you increase their voltages? CCA requirements haven't changed.

Generally, for any given battery type, as the voltage and capacity go up, so does the size/weight of the battery.  If you want to go lighter, you need to change to a more power-dense battery type (like going from Lead-Acid to Li-Ion).

[Madman]

Jaguar E-types were positive ground until 1964. 

Positive earth!  Get your terminology correct, man.  It's a Jag, after all! 

[Soup DeVille]

Do batteries get smaller/lighter for a given amount of charge capacity as you increase their voltages? CCA requirements haven't changed.

Slightly, but the real difference is that motors can be made smaller and lighter, because the same diameter of wire can carry more power.

[Morris Minor]

Positive earth!  Get your terminology correct, man.  It's a Jag, after all! 

Thank you. Thought I was going to have to jump on that myself.

My dad's Rover P5 was positive earth too - that would have been 1963 or 4.