This is normal.
The diode is like a one-way-valve for the power. It is supposed to
allow current flow from the main batteries and charging systems to
the generator battery so that the generator battery stays charged,
but not allow current flow from the generator battery to the house
batteries so that the house battery useage can't discharge the
generator battery. A series circuit-breaker protects the wiring and
diode from damage in high-current situations like cranking the genset
with a dead genset battery.
I don't remember what year this started, I believe '83 on the PT
and '87 on the FC? Prior to this system the FCs used a "battery
isolator" located just rearward of the house batteries (started
around '82). This isolator wiring changed in '83 or '84 also, but by
now most of the isolators have failed.
A retrofit has been around for more than a decade to add a diode and
circuit-breaker in series between the house batteries and genset
batteries on the FC, usually located at the Aux. Start relay under
the entrance steps.
If this diode fails, and they do, it usually fails open. If you can
light a 12v bulb with the disconnected genset positive lead, it is
likely good as is the circuit-breaker. It is more difficult to check
for a short, but you could disconnect the house batteries and all
charging systems and see if the house positive lead will still light
a 12v lamp (like a brakelight bulb).
As likely as a failure of the diode is a weak connection somewhere
which will show 12v on the battery cable, might light a light, but
not enough current would pass to keep the battery properly charged.
You could try something with a larger 12v draw such as a spotlight or
12v compressor to test the diode circuit for a weak connections (or
visually).
- Jeff Miller
in Holland, MI
--- In
WanderlodgeForum@yahoogroups.com, Curt Sprenger
wrote:
>
> Jeff,
>
> On our '87 PT38 the gen. positive battery cable is still hot when
> disconnect from the gen. battery. Would this this be a bad diode?
Thanks!
>
> Curt Sprenger 1987 PT38, Anaheim Hills, Calif.
>
>
> Jeff Miller wrote:
>
> > The generator battery is charged via a stud-mount diode in the
> > charger compartment, not through this solenoid.
> >
> > - Jeff Miller
> > in Holland, MI
> >
> > --- In WanderlodgeForum@yahoogroups.com
> > , "mrkane1952"
<mrkane@>
> > wrote:
> > >
> > > My local NAPA stocked a replacement relay which is externally
the
> > > same, NAPA-Echlin ECH ST84. The solenoid is marked "50-12V"
> > > and "6AC." This resembles the markings on my original which are
> > > only partially legible. Price ~$38.
> > >
> > > I'm replacing it as I, too, am having generator battery charging
> > > woes.
> > >
> > > M.R.Kane
> > > '85 PT40
> >
> >
>