Why don't cars have AC electric outlets?

[Crafter_Man]

*Originally posted by Musicat *
**If a higher DC voltage for car electronics is so good, why stop at 42 volts? Why not 52? 62? Or, <gulp>, 120?

What made 42 the magic number? Wasn’t the boost from 6 to 12 some decades ago made for the same reason? Why did they only go from 6 to 12? **

Not sure, but it probably has to do with two things:

Safety. I believe 40 V (or around there) is the “critical” voltage level when it comes to human safety, i.e. a voltage below 40 V is generally considered “safe.” Generally.

Battery manufacturability. The higher the (battery) voltage, the more difficult the battery is to manufacture.

[Musicat]

*Originally posted by Crafter_Man *
I believe 40 V (or around there) is the “critical” voltage level when it comes to human safety, i.e. a voltage below 40 V is generally considered “safe.” Generally.

T’ain’t the voltage, m’friend, tis the current. Stand near a Van DeGraf generator and 100,000 volts will pass thru your body without harm. Very low amperage.

What’s high voltage?

[Briny_Deep]

Great info here, thanks. I didn’t know a couple of cars now had 'em.

I see Doreen is managing a monitor and a PS2 with no problems. What happens if you push the envelope and do have your George Foreman Grill, your hairdryer, your laser printer and your Hello Kitty ricemaker all going at once? Do you blow a fuse, cream your alternator, drain the battery, eject the warp core, or what?

[Crafter_Man]

*Originally posted by Musicat *
**T’ain’t the voltage, m’friend, tis the current. Stand near a Van DeGraf generator and 100,000 volts will pass thru your body without harm. Very low amperage.

What’s high voltage? **

Sorry to resurrect this one.

Um, no, sorry, you’re incorrect. And we’ve discussed this countless times before.

If it were really just due to “current,” then a car battery would fry you when you placed your hands across the terminals. After all, a car battery can put out 500 amps, can’t it?

A Van DeGraf generator won’t fry you because you really don’t have 100,000 volts making low-resistance contact with your body.

Suffice to say, if you want to get zapped all you need is enough voltage across you body so that over 10 mA flows through your body. There is no “magic” voltage level this occurs at, since it depends on your body resistance. But direct skin contact over 48V is considered “risky territory.”

[Tuckerfan]

*Originally posted by masonite *
**Great info here, thanks. I didn’t know a couple of cars now had 'em.

I see Doreen is managing a monitor and a PS2 with no problems. What happens if you push the envelope and do have your George Foreman Grill, your hairdryer, your laser printer and your Hello Kitty ricemaker all going at once? Do you blow a fuse, cream your alternator, drain the battery, eject the warp core, or what? **

You’d blow a fuse. Depending upon how the car’s wired up, you might blow a couple.

[Rick]

*Originally posted by Musicat *
**If a higher DC voltage for car electronics is so good, why stop at 42 volts? Why not 52? 62? Or, <gulp>, 120?

What made 42 the magic number? Wasn’t the boost from 6 to 12 some decades ago made for the same reason? Why did they only go from 6 to 12?

You don’t know how long I’ve been waiting to ask these questions! **

An electrical cell full charged puts out 2.12V. To recharge it you have to overcome internal resistance of 0.2V So to fully recharge a 12V (6 cell battery) requires 6 * 2.32 = 13.92V rounded off in converstaion to 14V.
An 18 cell battery (36V) would have a charging current of 41.76V call it 42 for short.
I was told by one of the engineers for our company that the reson for 42 was that in Europe; voltages above 48 require special training and certification. The car makers did not want to have to retrain/certify all of the technicians.

[ftg]

Umm, being grounded and then touching a Van DeGraf generator is very dangerous.

The demos you see of people touching them require that they stand on insulating plastic platforms and are ordered to be very careful not to touch anything else. In particular, they are not to step off the platform during the demo. (A major concern when they feel little sparks and might panic.) Also, the demos I have seen ask the “victim” to put their feet together hard to avoid inadvertent shocks leaping between the feet.

[Crafter_Man]

*Originally posted by ftg *
**Umm, being grounded and then touching a Van DeGraf generator is very dangerous.

The demos you see of people touching them require that they stand on insulating plastic platforms and are ordered to be very careful not to touch anything else. In particular, they are not to step off the platform during the demo. (A major concern when they feel little sparks and might panic.) Also, the demos I have seen ask the “victim” to put their feet together hard to avoid inadvertent shocks leaping between the feet. **

Are you sure about that?

The tabletop VandeGraaff Generators I’m familiar with do not appear to be dangerous. After all, it’s just a belt and a few combs! And I believe the reason you’re asked to stand on an insulator is to maximize the effect.

Here’s more info on it:

http://www.amasci.com/emotor/safe.html

BTW: The author of that page is a frequent poster here. Perhaps he can chime in.

[scotth]

Crafter_Man is quite correct.

The reason for standing on the insulating platform is to allow the charge to build up in you. It is quite save to be grounded and hang on to a VandeGraaff Generator. That would just hide all the interesting effects.