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Sat Sep 30 16:06:38 EDT 2006

the battery wiring harness. There is battery charging and engine
starting. Thirdly, the current required to service the car's electricals
also shares this harness. These currents flow through 2.0 feet of
16 mm sq. wire from the alternator to the starter (0.00066 ohms),
then through 5.5 feet of 25 mm sq. wire from the starter to the big
splice (0.0012 ohms) and finally through 8.3 feet of 35 mm sq. wire
from the big splice to the battery terminal (0.0012 ohms). There are
additional resistances contributed by the various crimped and bolted
terminal joints. In my opinion, adding 0.0005 ohm per crimp is more
than fair. Most such joints likely have greater resistance. Using these
numbers, we have total resistances of:
     battery to starter > 0.0044 ohms
     alternator to battery > 0.0056 ohms

A run of 2 AWG from battery to starter would have a resistance
of about 0.003 ohms if 0.001 ohms was allowed for termination
losses. The improvement would mainly come from the elimination
of the dreaded splice.

So, during starting, we could expect a voltage drop of 0.44 volts,
battery to starter, per 100A of starter current. Meanwhile, keep in
mind that there are also the following ground connections and wires
in this current path. These are (1) battery terminal to battery ground
strap connection, (2) the battery ground strap itself, (3) the ground
strap to chassis connection, (4) the chassis itself, (5) the chassis to
engine grounding strap connection, (6) the engine grounding strap
itself, (7) the grounding strap to engine connection, (8) the engine
block itself, and, ta ... da ... (9) the engine block to alternator case
connection or block to starter. This helps put the importance of
Excellent ground circuit connections into perspective since, if we
attributed as much as 0.00025 ohms to each of these elements,
we would have to add as much as an additional 0.0023 ohms to
the various circuits (The ground path resistance is probably greater
than this.)

Then the circuit from the battery to the fuse panel consists of
two 6 mm sq. wires (combined, they are about 10% shy of a single
AWG #6) which are also close to 15 feet long. This branch has a
resistance of about 0.0066 ohms in the wire with approximately
an additional 0.001 to 0.002 ohms or so in connection resistances.
So we have roughly
     battery to fuse panel > 0.008 ohms (for a grand  total of)
     alternator to fuse panel > 0.014 ohm

So, for example, if the car's total electrical consumption is 50A, we
can expect a total voltage drop of about 0.7 volts from the alternator
to the fuse panel if the battery is not being charged or discharged.
(The drop will be greater if the ground circuit is considered also.)
I wish I had access to a milliohm meter to verify some of these

> Modern vehicle wires are puny, barely capable of carrying the load the
> device they feed is "supposed" to draw.  Works great when new, not so
> great after a few years.  The old stuff was crazy, 12 ga all over the
> place.  Must have been on sale.

Motivated by the desire to load my trunk with some hefty audio amps,
I changed out my starter-to-battery run wiring to a continuous hunk of
1/0 AWG cable. The reduction of wire resistance and the elimination of the
splice crimps should help significantly. From the battery terminal, I'll
a run of 4 AWG via a 100A fuse providing juice to the amplifier rack in
the trunk.

But will the 110A alternator handle it? Or will the external voltage
help? Or an Ultranator? To be continued ...

Anyway, I'll be putting some of these hard core wiring materials in the
Marketplace soon so stay tuned there if this sort of thing appeals to you.

DeWitt Harrison
'88 5kcstq

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