Rick's note may stimulate questions, so I'll try to short-stop them now:
Before Gene Fisher, with Dave Mumert's cooperation, determined that the
simple single diode APC should be a 100% fix for the Nichrome wire problem,
we used a more complex fix: The wiring diagram shows that wire to have a
resistance of 10.0+-10% Ohms. So, some of us CUT OUT the Nichrome wire and
replaced it with an equivalent fixed power resistor and copper wire. Or
even the resistor plus a diode. Or, as in Rick's case, a light bulb
drawing about 1.2 Amps. In my case, I used the diode+resistor and an
aluminum-cased power resistor; they're both still in place after 15 years
or so. Some folks, including Jim Bounds, apparently didn't see the "." in
"10.0" so install(ed) 100 Ohm resistors. That works, but causes another
minor problem: the alternator may well not begin to produce current until
the engine RPMs reach 1500+, where the residual magnetism in the
alternator's field is sufficient for initial excitation.
Another "fix", which I've done since converting from an isolator to a
combiner to separate my batteries, is to convert the alternator to "single
wire". That is, simply connect terminal 1 of the alternator to its output
stud. "Single wire" is obviously a misnomer since the #2 terminal, remote
sense, is still there, though now redundant without an isolator diode in
the circuit. This "fix" does impose a small parasitic current drain
through the new connection.
There's lots more history to this, but probably no longer of interest to
most folks.
Ken H.
> Based on my experience, the APC protects against most failures related to
> the nichrome wire, but not all. The wire is there to provide
> current-limited load on the alternator to excite the field winding and get
> the alternator going. But the wire itself is needed. You can cut it and
> replace it with a current-limiting resistor. See the linked diagram:
>
>
>
http://www.gmcmhphotos.com/photos/10-ohm-alternator-wire-77-2f78-models/p3731-apc-cable-circuit.html
>
> Earlier coaches didn’t have the diode at the top.
>
> I didn’t have a resistor when Ken H and I fixed my alternator at Bean
> Station a few years ago, so we used a light-bulb harness and light bulb,
> which is still lighting up a spot behind my glove box.
>
> Rick “who bought the resistor but still hasn’t installed it” Denney
>
> On Fri, Jun 22, 2018 at 9:40 PM Dave Stragand <
>
dave.stragand>
>
> > Hi All,
> >
> > First off, let me say I have already purchased my APC cable. (It was the
> > first thing I bought for the coach, actually).
> >
> > My question is, without the APC, what wires could burn up in the dash,
> and
> > where are they located? I’m trying to sort out the mystery of many
> > previous-owner-run wires and missing wires in the engine compartment
> (like
> > the missing wire at my combination valve, different wire to temperature
> > sender, etc) and wondered if that may have been one of the reasons. I
> > always prefer going back and fixing things right when I can.
> >
> > -Dave
> > 1978 Transmode near Pittsburgh
> >
> >
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> --
> Rick Denney
> 73 x-Glacier 230 "Jaws"
> Off-list email to rick at rickdenney dot com
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