Re: [Phys-l] cars and physics

[brian whatcott <betwys1@sbcglobal.net>]

On 2/22/2011 10:22 AM, Edmiston, Mike wrote:
> /snip/ the change from 6 volts to 12 volts occurred in about 1953.  Cars in 1953 had very little of the "electrical stuff" that is the norm today.  Aside from the stuff under the hood and the lights, you had an AM radio, a heater fan, and a cigarette lighter.  Perhaps the starter was the primary impetus for the change.  The higher compression engines, especially with eight cylinders and approaching 500 cubic inches, would be much harder to turn over than a lower compression six cylinder.  Aside from higher performance engines, there wasn't much else changing in 1953 that I am aware of.  It seems a 6-volt to 12-volt change in 1953 would have to be related to the engine.  If not the ignition, then the starter.
>
> Michael D. Edmiston, PhD.

I see the merit of Mike's position.  I fancy there was a desire for brighter headlamps too. The AM radio was likely driven by a an electromechanical inverter
vibrator arrangement, which was rather greedy.

There were three ignition design cases (at least) of interest at the time.

1) Leave ignition on with a stationary engine.
There was no reactance to cap the current limited only by the coil series resistance.  It could grow very hot.     A motivation to increase coil R naturally.
2)  The L/R at the smallest dwell time at high speed on an eight cylinder engine
tapered the spark voltage.    A motivation to reduce coil R naturally.
3) A coldest day start using maximal power transfer to the starter....and least current to the coil.       A motivation to switch the effective coil resistance
when starting - hence the starter activated ballast.

Brian W