[Vwdiesel] Miser's Glowplug guardian...

[Mark Shepherd]

Oops
Funny how bosses turn up when extra curricular exercises or
'foreigners' are being
 done in works time:o)

Maybe the circuit doesn't work; but I cant see why. Maybe my
description is poor.
 I'll try again verbally.

I have separated each glowplug supply with wire back to the
common supply point. Each line is isolated
from the other three by means of a power diode.
This is neccessary because of reverse current (after GP
relay has turned off) created by:

Imagine an LED ballasted to take 12 volts supplied from the
instrument powerline
(maybe incorporating an inline switch to isolate) The other
end of the LED is wired to the nut of a Glowplug.
Whilst the GP is being heated the voltage at the nut is more
or less 12V; so the LED has 12V on either terminal and so is
off.
When GP heating has finished the LED comes on because a
circuit is made from instrument power line
through LED to the GP nut and through the GP (1 ohm) to
earth. This is saying GP good.
However if GP burns out and fails open circuit; the LED will
go out ...
Except there will be a tendancy for the LED to make a
circuit back up the GP power line and down
one or all of the other three lines and GPs to earth.
 I'm hoping the blocking diodes will prevent this rerouting.
The bank of 4 LEDs should be on for as long as the GPs are
good , but not being heated.
If unwanted cycling takes place then LEDs will turn off
during the power period and then come back on.
The blocking diodes should help with longevity of the plugs
due to the lower voltage at plug.

The Miser


Mike wrote:

I still haven't constructed a "working" model with the LED
and blocking
diodes. (Ie: that works right)
The one I built (I think) was the same as your schematic but
did not work
like it was
supposed to.  Boss was breathing over my shoulder one
day......"What's this
contraption on your bench supposed to be Mike?"....Me: "Err,
nothing
Boss......(pushes it aside)"

LOL!


Mike, Coreen & Corey Smith
699 Rte 616 Keswick Ridge
NB
Canada
E6L 1T1
----- Original Message -----
From: "Mark Shepherd" <mark at shepher.fsnet.co.uk>
To: <vwdiesel at vwfans.com>
Sent: Thursday, December 30, 2004 7:04 PM
Subject: [Vwdiesel] Slowing death of Glowplugs


> I think this confirms what I said about the vulnerability
of
> the plugs. It also makes me want to set up the passive LED
> system and using the blocking diodes in each GP supply
would
> reduce the applied voltage and  power output of each plug.
> Being able to turn off the glow plugs as soon as engine
> starts also helps and this is now incorporated into my
> Quantum.
> Mark(The Miser)UK