Date:         Sun, 20 Jun 2010 11:20:53 -0700
Reply-To:     "Mike \"Rocket J Squirrel\"" <camping.elliott@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "Mike \"Rocket J Squirrel\"" <camping.elliott@GMAIL.COM>
Subject:      Fresh water tank level meter
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

As I've previously posted here, sometime after moving from SoCal to
Central Oregon, the freshwater tank LED panel stopped being useful: it
only showed the red light, regardless of water level.

There were two issues that needed fixing, and here's the scoop for the
archives, I'll pop a short article onto the wiki later today.

Depending on which year/model Westy you have, you will have one of two
types of water level sensors: a mechanical type which uses a float, reed
switches, and magnets; or it could be a straight electrical type which
uses electrodes and the conductivity of water to sense the water level.

I don't know anything about the first type, which looks to be a Rube
Goldberg arrangement if I know my Rube Goldberg. Mellow Yellow uses the
second setup.

The conductivity type can be identified by opening the inspection hole
in the top of the tank and peering down: if you see four studs
protruding into the water at different levels on the forward side of the
tank, you have the conductivity type. The studs are the electrodes. I
have no idea what the float type sensor looks like.

Symptom 1: No matter how full the tank was, the red light was always on.
Cause: the push-on connector with two green wires had been pulled off
the spade on the uppermost electrode on the outside of the tank. This
due to some extra electronics I had installed into that compartment and
the weight of one of the new wires had tugged the wires off the
electrode. Fix: Push the connector back on.

Symptom 2: After fixing that, I found that the yellow lamp never lit. As
the tank filled, the lamps went from "none" (empty tank), to "red"
(almost empty), and stayed red until the water level reached the
uppermost electrode when the green lamp (darn near full) light comes on.
Cause: I did some poking around with a voltmeter and found that the
panel was receiving output from all the electrodes but it appeared that
when the electrode that should be giving the yellow indication was
underwater, the resultant voltage was not low enough to switch the lamp
circuit to yellow. The water here is apparently not conductive enough.
Fix: there are a couple ways to go about this. One would be to change
the trigger voltages on the panel circuitry by dorking around with
different resistor values, David Beierl has worked up how to do that;
the second was the one I used: screwing a stainless steel washer and nut
onto the protruding stud of that contact in the tank. This increased the
surface area of the electrode decreasing the resistance to current flow
through the water. BTW, I chose the mechanical, rather than electronic,
solution mainly because I'd rather not do rework on the old circuit
board, and because the nut-and-washer approach is more easily
field-serviceable if adjustments are needed to accommodate for
differences in water conductivity.

It is suggested that an assortment of washers of various sizes be part
of every Westy owner's kit of parts so allow fine-tuning of the system's
sensitivity when traveling to locales where the conductivity of the
local water deviates significantly from the stuff back home.

[Editor's note: Make believe it's Friday when reading the last paragraph.]

  --
Mike "Rocket J Squirrel" Elliott
84 Westfalia: Mellow Yellow ("The Electrical Banana")
74 Westrailia: (Ladybug Trailer company, San Juan Capistrano, Calif.)
Bend, OR
KG6RCR