Vanagon EuroVan
Previous (more recent) messageNext (less recent) messagePrevious (more recent) in topicNext (less recent) in topicPrevious (more recent) by same authorNext (less recent) by same authorPrevious page (February 2009, week 3)Back to main VANAGON pageJoin or leave VANAGON (or change settings)ReplyPost a new messageSearchProportional fontNon-proportional font
Date:         Sat, 21 Feb 2009 20:51:50 -0500
Reply-To:     David Beierl <dbeierl@ATTGLOBAL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@ATTGLOBAL.NET>
Subject:      Re: Where does this relay go?
Comments: To: Jim Felder <jim.felder@gmail.com>
In-Reply-To:  <4d1b79350902211713u1a5098f0o2953a5271f06e1e0@mail.gmail.co m>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 08:13 PM 2/21/2009, Jim Felder wrote: >the coolant light blinked slowly at first, but as the engine heated >and the temp needle rose, the blinking became more and more of a >constant red light until, at needle center, it was on full time. When >I reached my destination, I turned it off and restarted and it was >fine ever since.

Fascinating. I've never heard of like behavior. What year is this beast?

>I don't know what's in the control module, but I doubt that it is >really a relay...

It's not. It's a rather fancy circuit that sends a very high-impedance (weak, if you will) square wave out on the active level sender terminal. If that square wave is tied to any constant level between ground and +12 through a resistance of about 180K or less it will be quenched, and the gauge driver remains inactive and floats with the temp sender output. However if the square wave continues for several seconds without being quenched, the gauge driver goes active and pulls the sender line down to a level corresponding to an overheat condition (not all the way to ground, which would burn up the gauge). That triggers the flashing light in the gauge, which flashes for several seconds whenever it's triggered (and it's this behavior that gets out of hand inside the gauge and leads to constant flashing for no cause).

At this point the old (large) and new (small) controllers part company. The old one applies a steady overheat signal until the square wave can reestablish itself, which drives the needle into the hot zone. The new one applies an intermittent signal which keeps triggering the blinker without greatly affecting the gauge reading. The new one also latches on, so the blinking will continue until key-off regardless of what the level sender sees.

I had a lot of enjoyment tracing out and analyzing the interior circuit of the old-type controller. It was cleverly done. I haven't seen inside the newer one, but I suspect they put things into a single no-doubt-proprietary chip that were wired out on the old one, since the new one is half the size and does more.

-- David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/ '89 Whitestar "Scamp"


Back to: Top of message | Previous page | Main VANAGON page

Please note - During the past 17 years of operation, several gigabytes of Vanagon mail messages have been archived. Searching the entire collection will take up to five minutes to complete. Please be patient!


Return to the archives @ gerry.vanagon.com


The vanagon mailing list archives are copyright (c) 1994-2011, and may not be reproduced without the express written permission of the list administrators. Posting messages to this mailing list grants a license to the mailing list administrators to reproduce the message in a compilation, either printed or electronic. All compilations will be not-for-profit, with any excess proceeds going to the Vanagon mailing list.

Any profits from list compilations go exclusively towards the management and operation of the Vanagon mailing list and vanagon mailing list web site.