Several weeks ago I posted some info on my installation of an Intellipower
converter with Charge Wizard replacing the Univolt in my '76 Tradewind.
As many of you may know, the Univolt has an additional wire which connects
to the main fuse panel to activate the "power on" light on the central
control panel when shore power (120 Volts) is connected to the trailer.
Other, non Airstream, converters do not include this "power on lead", hence
the "Power on light" does not go on when the converter is operating.
My son and I studied the wiring diagrams etc. and did some "industrial
archeology" to determine how the indicator lamp actually worked. From this,
we implemented a rather elegant solution (which causes the Power On light to
function properly - come on whenever external 120 volt power is connected to
the trailer). I am happy to share our solution with other Airstreamers who
may wish to use it on their trailers. As it turned out, the Univolt actuated
the power on light in a rather counter intuitive manner.
First some background:
The "power on light" on the central control panel is intended to show that
120 volt shore power is connected to the trailer and the converter.
Since the control panel is wired for 12 Volt components, the indicator
light needs a 12 volt source, actuated by a live 120 volt feed. The design
of the control panel is such that the 12 volts is supplied to the control
panel by a common feed. Thus, there actually is 12 volts at the "Power On"
indicator lamp as long as the 12 volt battery is connected, whether or not
shore power is connected. HOWEVER, the GROUND (or return) from the indicator
light is NOT connected to ground UNLESS the Univolt lead connects it to
ground - which happens when the Univolt is energized by the 120 Volt power
hookup.
Hence the Filippi solution is to connect the ground lead of the indicator
lamp to ground when 120 volts is supplied to the trailer, via a 120 volt AC
relay as follows:
The power converter (in my case an Intellipower with Charge Wizard) is
plugged in to the trailer's 120 volt duplex receptacle under the galley
sink. [On my '76 Tradewind, the converter is mounted on a shelf behind the
stove, adjacent to the sink.] I fashioned a small electronic box with a 120
volt power cord (which plugs into the other receptacle in the duplex outlet)
and is connected to a Radio Shack 120 volt relay. A wire from the main fuse
panel (which would have run to the Univolt power on lead) is connected to
one of the closed when energized terminals of the relay. A second wire is
connected to the other side of the "closed" relay circuit and connected to
ground. I used is a plug in type relay, so I mounted a relay socket to my
"Control Box". This small electronic box is fastened to the shelf behind
the stove and is accessible from the sliding panel on the side of the
cabinet on the lounge end of the cabinet. If I don't want the bright power
on light to glow while hooked up to shore power, I can simply unplug the
relay.
Thus, when 120 volt shore power is available to the converter (and my
control box) the 120 volt relay activates and completes the circuit on the
power on lamp, and, voila, the lamp lights!
I have some photos of the installation which I will be happy to e-mail to
anyone who is interested, or post for the archives if you think this would
be desirable.
Sincerely,
Oliver Filippi