Re: [Phys-l] cars and physics

[David Bowman <David_Bowman@georgetowncollege.edu>]

Regarding:

> I'm suspicious of this answer.  You might be able to save some
> money on wire, but you just doubled the number of cells in the
> battery.  In 1953, could you really save enough money on
> smaller-sized wire to compensate for the increased cost of the
> battery?  True, each cell in the 12-volt battery could be smaller
> than each cell in the 6-volt battery, but it's easier to make wire
> than it is to make batteries.  It seems to me the 12-volt battery
> would cost more than the 6-volt battery even if it didn't use much
> more material, and I don't think wire was very expensive back then.
> They were still making pennies from copper back then.
>
> I'm not saying there is no way this is the right answer, but I will
> remain suspicious until I see more data.
>
> Michael D. Edmiston, PhD.

I certainly don't know anything about the relative economics of wire and lead-acid battery production, so I can't comment on ME's suspicions.

However, another potential advantage of a 12V system over a similar power 6V system suggests itself.  I would expect the reliability of a 12 V system to be better than a 6V system for comparable quality terminal connections, and would expect the wiring terminal connections for comparable reliability between 12V & 6V would be cheaper to make for a 12 V system.  This is because all the connections in the 6V system would draw twice the current through them as the corresponding 12 V connections.  This would mean that the 6V system would be more vulnerable to ohmic losses in the terminal connections than the 12 V connections.  I would expect that a 12 V system could tolerate looser and more corroded connections before failure than the corresponding connections in a 6 V system.  This might make a significant difference in the harsh under-hood environment that such terminal connections typically find themselves in.  Prevention of premature failure in the 6 V system would require more rugged, corrosion resistant, and heavier duty connections than the 12 V system would need for comparable reliability.  The connections most vulnerable to corrosion and exposed to the highest currents are the battery terminal and starter connections.  So I would, therefore, expect that the 6 V system would need better (i.e. more expensive) maintenance of those connections than the 12 V system.

David Bowman