[Vwdiesel] Gross underestimation of 'typical' voltage of LED

[jon]

Not to toot my own horn, but I'm an engineer. I'm on vacation next week 
(in our Diesel Westy, of course), so as all good engineers do on vacation, 
I'll come up with a design for a comparator-based (op-amp) monitoring 
circuit. In fact, the Westy water tank level circuit is pretty much that 
(hmmmm, wonder would if that display could serve dual purpose?). Seems 
like the Westy water tank circuit is based on an LM339, or 324, IIRC.

One could probably even use a PIC chip (or BASIC stamp, which is a PIC 
that is pre-programmed with a BASIC interpreter). It has A to D 
capabilities, but I don't know how good it would be in millivolt 
resolution. Havta think about that as well. Of course, a PIC chip (and 
especially a 'stamp) would be an expensive fuse to replace. But, I can 
think of ways to protect it...like a zener and a fuse. Or, a zener AS a 
fuse (yes, I have seen cheap commercial products do that). Those flame out 
quite nicely, and spectacularly. Or, even a "solid state" fuse. Those work 
nice.

But, not as much "fun" as having an electrolytic capacitor blow up in my 
face, with shrapnel embedded in my lip. As we all know, and 40 Volt 
electrolytic cap doesn't like 70 Volts AC. ;-(

But, I like simple stuff, so I'll probably just stick with the Ammeter. 
But, I'll publish the circuit for other folks to fuss around with.

J


On Tue, 21 Dec 2004, Mike & Coreen Smith wrote:

> Hmmmmmmmm, now I have you thinking.
> ;-)
> 
> I won't bet against you now, but would like to see it working to be "sure".
> 
> Mike
> 
> 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: Tuesday, December 21, 2004 7:52 PM
> Subject: [Vwdiesel] Gross underestimation of 'typical' voltage of LED
> 
> 
> Ha Ha  Houdini says "you think I can't escape this one" :o)
> 
> Just about to bet against myself when...
> 
> Chuck out the unballasted and/ or convert to 12V ballasted. then run from a
> switched supply through the 4 LED's then down to each glow plug. ...
> Ah but I hear you say  "but the LEDs will re route through the other
> glowplugs"
> 
> Not if you incorporate high current 'blocking' diodes in the glow plug
> supply lines...
> Whats the voltage drop across one of those? 0.6V?  It's a lot but may help
> preserve the plugs :o)
> 
> Mike and Coreen says...
> I bet it does not work Mark....... :-(
> 
> If the wire was .001Ohms, and you have 10 amps coursing through it, you'll
> have a voltage drop of
> only 10mV across the LED. (hardly enough to light an LED)
> 
> If wire was .01 Ohms.........100mV drop..........still way off.
> 
> If wire was .1 Ohms .........1V.........uh-uh, still no, (and your wire
> would now be so crappy it would be dissapating heat like a glowplug and
> getting warm. LOL!!!
> 
> 1 Ohm.........oh-oh! Now we have an external glowplug.  Engine bay nice and
> toasty., hee hee
> 
> The thought is there but IMHO still needs work.
> 
> Back to hall sensors, op amps and the like, methinks.
> 
> Mike
> 
> 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: Tuesday, December 21, 2004 6:33 PM
> Subject: [Vwdiesel] Re: Miser's method elaborated :o) Proof of the
> pudding...
> 
> 
> 
>   ----- Original Message -----
>   From: Mark Shepherd
>   To: vwdiesel at vwfans.com
>   Sent: Tuesday, December 21, 2004 9:55 PM
>   Subject: Miser's method elaborated :o) Pt 3 Ahh...
> 
>   Tomorrow I'll rig up an unballasted LED to check if it works Place yer
> bets folks (I accept Paypal :o)
>   Actually this morning I put a spare rear window heater switch into one of
> the blanks and wired it in series with the Glow plug relay so that it can be
> turned off earlier or allow recycling whilst engine running if lumpy :o)
> 
> 
> 
>   +___________________________i====> G/P
>                 |                                |
>                 |_______i<i_____|
>                             LED
> 
>   The lack of Visual on this site makes it very tempting to drag everyone
> off to Yahoo :o(
> 
>   Miser
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