[A/S] '64 Globetrotter 19' electricals

["Christopher H. Dow" <dow@xxxxxxxxxx>]

Well, I'm glad I've owned a few British cars, as that seems to have been
a good training ground for the Airstream.  Not that the manufacturer did
anything wrong, but we have a term in the Land Rover communtity called
SPOT--Stupid Previous Owner Trick.  I think we have a few SPOTs in our
trailer.

First, a description of the electrics as described in the manual:  It
states that ours is a univolt trailer.  It further states that there are
two 12V systems, and one 110V system.  There is a 12VDC system for
lights, and a 12VAC system for the 'fridge and the pump.  

Next, a description of the behavior I found in the trailer:  When I'm
hooked up, most things are fine.  The water pump engages when I flip the
switch, the 12V lights in the trailer work, and all but one outlet (by
the sink) works.  However, the 'fridge does not work (electrically) when
I'm hooked up (and have flipped the switch to "electric").  When I
switch over to battery power, no electrics work at all.

Now, a description of what I find in the trailer:  
There is the usual "black box" with separate switches for moving the
lights and pumps from "City Power" to "Battery Power".  Removal and
inspection has shown this box to be some relays and ways to hook up
wires.  Further inspection showed a wire leaving this box (from the
lights side of the city/battery switch) and terminating in a wad of
electrical tape (it was not connected to anything).  There is a
transformer of some sort sitting on the floor of the rear compartment
(near the H2O heater) that I have yet to reach and inspect, but I
suspect it is a 120VDC to 12VDC transformer.  There is no box labeled
"Univolt" or "Newmark".  There was a very large inverter with the same
kind of clips found on battery chargers in the rear cabinet.  The 50A
(yes, 50A--not 30A like all the parks have!) plug for hooking up had had
a standard 3-prong adapter connected to it for some time (based on how
difficult they were to separate).  

I suspected there was a reason why there was no connection between the
black box and the battery, as the most recent PO seems to have been a
man of reason.  Hence, before I connected the unconnected wire to the
battery, I hooked up an inline fuse for it.  When I connected the wire
to the battery (while the switch still was set to "City Power", the fuse
(tube-type, like in English cars :-) fried quite brilliantly.

So, here are my hypotheses and conclusions from this data an my little
experiment:

1.)  The PO knew the 12VDC system was bad and used the stored inverter
to hook up when he was away from power.  By this I mean I think he
clipped the inverter onto the battery and plugged the hookup plug (with
its 3-prong adapter) into the transformer.  Further evidence to support
this conclusion is that he had mounted a 2-prong to 3-prong adapter on
the inverter.

2.)  The lights are somehow on 12VAC.  Lights don't care about DC vs.
AC, and most humans can't see the cycling.  I'll hook a DMM up to the
light sockets later today to determine this once and for all.

3.)  There is a dead short in the 12VDC system somewhere, and that's why
some PO disconnected the black box from the battery.  Hence the fried
fuse.

4.)  I have a lot of electrical work ahead of me!

I'm thinking about setting up a three-way charging system:  
*  Inverter/charger for having 110VAC while operating from the battery
and 
   charging the battery when I'm hooked up.
*  Solar charger for charing the battery when I'm not hooked up.
*  Wire from tow vehicle.

I have a pretty nifty charging system on the tow vehicle that will only
charge the trailer battery when it needs it and when the tow vehicle's
battery is in good shape, so I only need to get the first two systems. 
I would, however, like the switching between the three charging systems
to be automatic.

If anyone has any ideas or comments about this, please let me know.

Thanks,
C