Alternator problem & ?

[Huw Powell]

> I have just read your response to Dennis about grounds. A couple of
> questions.
> 1.  I grind or wire brush down to the bare metal when I am redoing a
> ground wire.  What is the best method of sealing this connection?

It depends in part on where it is.

Inside the passenger compartment, "not much" will suffice just fine, I
think.  I am a *big* fan of dielectric grease to help keep corrosion to
a minimum, ie between the connected parts.  you could wipe it off after
and hit it with a dab of paint and probably not worry again.

Areas exposed to more or less environmental stress are tougher.  I like
to try to use existing studs, etc., so I am not just 'scraping paint off
the body' to get contact.  Again, dielctric grease, and I've played with
battery corrosion prevention spray paint here and there.

A nice way to get a decent ground is to bolt your wires up with a
stainless bolt into an existing threaded hole, if you can find one.

> 2.  What do you mean by , "...zero is getting lifted a couple of
> volts."  The answer is probably basic electronics which I lack, but I
> would like to get some understanding of this.

There is some resistance to any part of a circuit.  In this case, the
"return" wiring to ground for the circuits has enough resistance that
when a very low resistance device (heater fan, cig lighter) is placed in
series with it, it forms a voltage divider according to Ohm's laws, for
which I will make a simple example now.  Say the 12 volt source wiring
is good, and has negligible resistance, and the high current device is a
5 ohm load.  if the ground path exhibits 1 ohm of resistance, the 12
volts will be divided over this network, showing 10 volts across the
device and 2 volts across the ground wiring.  So now, the point at which
the device is attached to the ground wiring is at 2 volts above ground,
which will affect any low current devices whose circuits share that
ground.

The affect is just the same if the resistance is in the 12 volts feed
side, but people are less likely to look for a voltage aberration on the
ground side (the example above still measures 12v at the device, if the
extra resistance is in the 12 volt side, it would measure 10 volts at
the hot side).

I hope that helps a tiny bit...

--
Huw Powell

http://www.humanspeakers.com/

http://www.humanthoughts.org/