Date:         Tue, 29 May 2007 00:11:09 -0500
Reply-To:     Matt Roberds <mattroberds@COX.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Matt Roberds <mattroberds@COX.NET>
Subject:      Re: Fabricating a radiator fan on indicator light,
              with surprise ending!
Comments: cc: Kenneth Lewis <kdlewis@NORTHSTATE.NET>
In-Reply-To:  <20070527040810.UXTB8096.eastrmmtai106.cox.net@eastrmimpi03.cox.net>
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed

> From:    Kenneth Lewis <kdlewis@NORTHSTATE.NET>
> Date:    Sat, 26 May 2007 16:57:09 -0400
>
> As expected, the LED lit brightly when the fan was energized and
> mashing the button forced the fan on.

Looking at the 1990 wiring diagram that's available online, the
connections for the button would be:

One terminal of the pushbutton switch to relay terminal 30 (+12 V in)
Other terminal of the pushbutton switch to relay terminal 86 (coil +)

This energizes the relay coil whenever the button is pushed, regardless
of what the thermoswitch is doing.  It should even work when the key is
off.

For the LED:

One end of resistor to terminal 87 (+12 V out, switched)
Other end of resistor to one terminal of LED
Other terminal of LED to body ground (this one doesn't go back to the
relay - just needs to go to a handy ground)

The LED has to be connected the right way around and there are ways to
tell, but one simple way is to hook it up with the resistor and try it
(quickly) and if it doesn't work, swap the connections to the LED.

> The unexpected result was; as you started to drive, air flowing through
> the radiator made the fan's propeller rotate.  This caused the motor to
> act as a generator and produce voltage, in turn illuminating the LED to
> about half brightness.  Benefit? As long as the LED glows at any speed
> above 15mph you know the fan's bearings have not bound up! QED.

That is incredibly clever.  I like it.  (Next time, tell people you knew
all along that the windmilling fan would light up the LED.  They'll
really think you're a genius then.  :) )

Matt Roberds