Date: Tue, 19 Mar 2002 18:49:13 -0800
Reply-To: Joel Cort <joel_cort@YAHOO.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Joel Cort <joel_cort@YAHOO.COM>
Subject: Re: High beam blue (light bulb) - Solution!
In-Reply-To: <005301c1ceeb$20efafe0$0200a8c0@ralph>
Content-Type: text/plain; charset=us-ascii
Whoa what a dissertation on LEDs' Thanks Mr. Pants!
Seriously though I don't think that Leo ever got a straigth answer on
what to do about his burned out HighBeam indicator. The same thing
happen on my van, I went to the dealer for this "dealer only item"
and they wanted someting like $8.00. I raised hell and said this is
a friggin light bulb and the A-hole kept telling me it is an LED and
thus the cost! Of course they would have to order it.
Luckily VW uses the same parts on a lot of vehicle. I went to a junk
yard and poked around looking for a Vanagon... no luck but I did spot
some Jettas and Rabbits. I selected the best one and tore into what
was left of the dash. I grabbed the little light bulb, with the blue
cap and all the other colored LEDs as well ... did I mention the
clock for a spare.... and all the instrument illuminating lights. I
felt guilty so I had to purchase something. I clipped a dome light
out of the rabbit and purchased that for $3.00. Not too bad for a
couple hours work digging around. The dome light has a time delay so
the light dims after a few seconds of closing the doors - great.
So Don't go to the frigging dealer for this. Go to a pick-a-part junk
yard and help yourself. The bulbs and LEDs come out very easily once
you have the dash unit appart. Likewise on you system it will not be
too hard to replace the burnt out "led"
Cheers,
Joel
89 Syncro Westy
Rockchester NY
--- "Mr. Pants" <mrpants@MINDSPRING.COM> wrote:
> The first blue LED's weren't available to the public until about
> 1991-1992
> and even then they were quite dim by even that days standards. It
> wasn't
> until late 1995/1996 that ones were developed that would have been
> bright
> enough to use in an automotive environment.
>
> While I'm still coming up to speed on the vanagon, I can
> (hopefully) give
> anyone the knowledge they'll need to replace a incandescent lamp
> with an
> LED.
>
> First and foremost, unlike a lamp, which is pretty much a
> resistor/inductor
> that gives off light, the D in LED is diode, a semiconductor switch
> which
> conducts in only one direction. It has a anode (positive) and a
> cathode
> (negative). Place a battery correctly across it and once the
> voltage reaches
> a certain point (which is different for different materials used to
> make
> them) it turns for all practical purposes into a short (which just
> so
> happens to give off light) This is why you need a dropping
> resistor, to make
> sure that current doesn't surge through the led once it's biased
> on. Normal
> red, green and yellow LED's usually take about 1.7 volts to turn
> them on.
> New material LED's often take more then 3 volts to turn them on
> (Blue,
> White)
>
> Ok here comes the math. For a car, I'm assuming a normal 12v
> system, and
> I've picked a random blue LED from Radio Shack, Cat.#: 900-7170.
> The VF
> (forward voltage drop across the diode) is listed as 3.7 Volts @
> 20ma (.02
> amps)
>
> Mr. Ohm taught us that Voltage = Current times Resistance or V = I
> * R
>
> In our circuit, we'll drop 3.7 volts across the LED, leaving 12 v -
> 3.7 v =
> 8.3 volts left that we have to handle via the resistor (so the LED
> doesn't
> blow it's top)
>
> Also, since this is a series circuit, we know that current is equal
> at all
> points (trust me on this one) so that the resistor will also have
> 20ma
> running across it. Since we have the voltage and the current, we
> can figure
> out the resistance we need.
>
> Once again V = I * R, so we also know that resistance equals
> voltage divided
> by current R = V/I so we get
>
> 8.3 volts /.02 amps = 415 Ohms.
>
> Now you're not going to find a 415 Ohm resistor at Radio Shack, but
> that's
> ok because long ago people took such things into account and
> created the
> standard value of resistors we have now. The most common type, the
> E12
> series, is set up so that at worst the worst you'll ever be off
> from a given
> value is 10%. I happen to know that 470 Ohms is in that series, and
> will do
> just fine (in fact since the charging system in a car can get over
> 14 volts,
> it gives us some added safety as well)
>
> The last thing we need to figure out is the power rating of the
> resistor we
> need. This is measured in watts, and in a DC circuit the formula is
> Watts
> equals Volts times Amps or W = V * A
>
> The voltage across the resistor is 8.3 Volts and the current is .02
> amps or
> 8.3 *.02 = Watts
> From this we get 0.166 Watts or 166mW. The most common resistors
> usually
> come in 1/4 (250mW) or 1/2 (500mW) ratings. While the 1/4 would be
> ok, I
> usually like to factor in an extra level of safety (in this case I
> seem to
> remember Radio Shack charges the same price for both styles) so I'd
> go with
> the 1/2 watt.
>
> I hope the above makes sense. If it didn't or was way too long
> winded,
> please forgive me in advance. If anyone needs help with a
> conversion, email
> me direct and I'll help you with anything I didn't explain well
> enough.
>
> Cheers,
> Tom Corbitt
> 84 GL owner (yet unnamed)
>
> ----- Original Message -----
> From: "John McLean" <jaymac@INTERNETCDS.COM>
> To: <vanagon@GERRY.VANAGON.COM>
> Sent: Sunday, March 17, 2002 5:48 PM
> Subject: Re: High beam blue LED
>
>
> > > It isn't actually an LED. They didn't make blue LEDs in those
> days.
> > >
> >
> > I'll have to admit I would'nt know the difference between
> incandescent and
> LED. However
> > everyone (including my Bentley - copyright 1991) refers to these
> indicater
> bulbs as LED's.
> >
> > After reading the responses that corrected my error I went back
> to the
> Bentley to have a
> > look again. In the picture displayed they show what I assume is
> a real
> LED (page 90.19) and
> > a point is made of the polarity of the bulb. I did not notice
> this on
> the bulb that I used
> > in my own repair. The bulb I used only had two thin wires that
> were
> exactly alike. It
> > would appear that what I installed was in fact an incandescent.
> >
> > John McLean 87 Vanagon GL
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