Date:         Mon, 5 Jul 2010 12:03:02 +0200
Reply-To:     Jaap Nauta <jaap.bus@IAE.NL>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Jaap Nauta <jaap.bus@IAE.NL>
Subject:      Re: Switch to LED lighting??
Comments: cc: gneiss9@GMAIL.COM
In-Reply-To:  <AF4ACA2C-8A07-4B30-B248-267111B58276@gmail.com>
Content-Type: text/plain; charset=iso-8859-1

Most aftermarket CC's use the following mechanism to check safe operation:

The CC will sense the voltage at both sides of the brakeswitch. With the
brakes not applied, one side should read 12-14 volts, the other 0 volts
(using a small current). This way the CC knows it is correctly hooked up
to the brake switch.
If this precondition is not met, CC will not work.

In normal operation CC will switch off when both wires read (around) 12-14
volts.

Now to the LED problem: powerLED's are not very good in pulling the
voltage across them to zero at small currents (high internal resistance).
For example a Luxeon LED has internal resistance of multiple kilo-ohms at
small currents and around 5 ohms at normal operation.

Solution? add indeed a resistor parallel to the LED. Would start with a
few hundred ohms, 1 watt resistor, that should do the job.

Became a bit technical, hope still understandable :-)

Jaap
'87 Caravelle 1.6D

> Subject: Re: Switch to LED lighting
>
> "Guessing LED 'fools' the Cruise Control that brakes have not been
> applied yet."
>
> and,
>
> "If a particular cruise control setup detects the current in the
> stop-light line to tell that the brakes have been applied, the lesser
> current drawn by equivalent LEDs might not trigger the cruise control to
> drop out when the brakes are applied."
>
> That wouldn't explain the fact that whoever had originally ran into this
> Cruise Control problem, not getting the vehicle (with brakes not
> applied) to set the speed.
>
> So that brings us back to the original question as to How can LED
> lights screw up the CC from working?  At first I was thinking a
> frequency given off from the lights to the CC unit but that seems
> silly.  I am still baffled as to how the cruise control works or
> doesn't work.  My seems tempermental on the best of
> days!  ...Anyways, I doubt that there was actually a connection to the
> CC problem and installing LED bulbs in your tail-lights/signal-
> lights!?!
>
>
> Trevor Reynolds
> Airdrie, AB, Canada,
> '91 GL 2Wheel drive, AT, Westy "SEN".
> http://westfalia-91restore.blogspot.com/