Re: [Phys-l] cars and physics

[Bill Nettles <bnettles@uu.edu>]

Here's the response I got from my 70-year-old mechanic friend re: switch to 12V. This guy rebuilds anything from 1929 pickup trucks with wooden frames to installing a 5.0L V8 in a Miata. He's been around a while, and even works on airplane radial engines every now and then.

" Forget the coil.  Coil is only a step up transformer that uses an interruption in the primary circuit to collapse the electro-magnetic flux & cause the spark - you knew that!
At twice the voltage you use half the amperage for the same current.  Ergo, wires one half the size gauges size (approx.) and therefore wiring is much cheaper to make.  
If you save $20.00 per vehicle times what? 2-3 million vehicles then-!!  Primary Reason!! (excuse pun))
 
There has been much experimentation on 42 volt DC elec. systems but the problem seems to be arcing when switches or relays open to stop current flow.  Eats up contact points.
 
The hybrid cars you've read about go up to 500V DC and I don't know about the control circuits.  They do have water cooled rectifiers to get voltage down for accessory (A/C, P/S, heater, lights) useage.  Yes, you have to have A/C, P/S even if the engine is not running.   Pete, Sr.  PS: Could expound more, but not enough time! Pete, Sr."

via Bill Nettles

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of brian whatcott
Sent: Tuesday, February 22, 2011 12:10 PM
To: phys-l@carnot.physics.buffalo.edu
Subject: Re: [Phys-l] cars and physics

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.
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