# Re[2]: Re[2]: AC vs DC lamps

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In response to Kirby Smith's extracted comment:

>> difference depends on the impedance of the alternator-battery  connection.
An alternator generating 100A peak currents into a 0.05  ohm circuit could
generate 5 volts of peak ripple on top of the  battery voltage.  Its not the
ac component of the ripple but the 13.6V  for a charging battery plus 5
volts of interconnecting wire drop that  gets you!<<

Huw Powell <human@nh.ultranet.com> wrote on Tue, 28 Jan 97 14:13:30 -0500

>I think your assumptions are a little shaky there... let's come back into
real world numbers, if I assume my 90 amp alternator running full peg, I
just measured an eight foot bit of 10 GA wire, with two 16" 16 GA leads, on
my GenRad bridge and got .025 ohms.   Hmmm I'll run and get some 4 GA which
is what the two 8 GA wires on my car are equivalent to .... ok the closest I
could find lying around was an 8' piece of 6 GA.  Which without the 16"
leads measures .0055 ohms.  So that wire would yield a voltage drop of about
half a volt.  So 14 V at the alternator would yield 13.5 V at the battery.
And I suppose, of course, the return line would also cut the voltage even
more at the lights.  I dunno.  If I start popping bulbs like popcorn I'll

Clearly I had better clarify my post.  The values specified above were only
intended to be illustrative of the point that little wiring resistance is needed
to make the alternator voltage higher than that of the battery.  This was in
response to earlier unquoted posts about lighting connections and questions
about observed differences in burnout rates.  Relative to the above counter
example of Huw's, the wire terminations need to be considered as well as the
intrinsic resistance of the wire.  Of course, I'm sure all Quattro list members
have pristine battery connections, so any observed burnout rate differences are
anecdotal and of no statistical significance. <g>

***                 ...Kirby    (Kirby A. Smith)                 ***
***              ksmith1@mailgw.sanders.lockheed.com             ***
***              [=]   kirby.a.smith@lmco.com                    ***
***  Opinions expressed herein are entirely those of the author. ***

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