Electrical schoolwork...

[Kurt Deschler]

If there is more than one bulb to replace, you would be better off placing
the multiple LEDS in series and using a single resistor for the remaining
voltage drop.  That would both the power dissipated by the resistor, save
you space, and draw less current. My theory is that the next generation of
plug and play LED-based light bulbs will use a configuration like this.

As an example, 4 20mA 2.5 V LEDS in series:
(13-2.5*4) = 3V
3/.02 = 150 ohms
3*.02 = .02 W

	-Kurt

> Message: 2
> Date: Tue, 10 Feb 2004 03:01:32 -0500
> From: "Louis-Alain RICHARD" <laraa at sympatico.ca>
> Subject: RE : Electrical schoolwork...
> To: <antar at comcast.net>, "'Huw Powell'" <audi at humanspeakers.com>
> Cc: 'Quattro List' <quattro at audifans.com>
> Message-ID: <000201c3efac$18bda140$680bfea9 at LARAA>
> Content-Type: text/plain;	charset="US-ASCII"
>
> Wonderful ! (LOL)
> Thanks guys!
>
> I knew a question like this one would raise interest...
>
> So, after all this, here is what I can add:
>
> Like Ameer said, the 150 000 ohm figure is probably not useful since it
> depends on the DMM voltage. I did not knew this, now I (and all of us) do.
> This figure comes from a batch of green 3V LED I have here.
>
> After all these posts, I went to the basement and made some measures.
> However, I don't have any useful source for 12V in the house so let's play
> with 3V.
>
> 2 new AA batteries (2.8V total)
> various ohm resistances
> 3 green LEDs.
>
> 1 LED connected to 2xAA: very bright green, 2.7 Volt across the leads, not
> able to measure any current with my DMM (when series-wired).
>
> 3 LEDs in parallel connected to 2xAA: 2.48 Volt across, still bright green,
> still no current figures.
>
> 1xLED and 1x 500 ohm in series: dim LED, 1 volt across the resistance, 1.8
> volt across the LED.
>
> Does this confirm Ti and Ameer numbers? I guess so.
>
> But then I have a problem (like Huw said): my initial thought was that a
> small LED and a small resistance would be easy to insert IN the switches at
> the burned-bulb place (I already opened all the switches last year to check
> if it was feasible to replace only the bulbs: negative...). But now if I
> have to package a big 1W resistor IN the switch, it might me very
> challenging.
>
> Hum...
>
> The other solution would be to insert only the LEDs and find a way to place
> a single resistor elsewhere and carry an additional 3V wire to the different
> LEDs... A good way to ruin perfectly good switches and wiring...
>
> Or maybe if I can find some 12V LEDs, all this discussion would be a huge
> WOB...
>
> Yeah, thinking of it, this would be the ideal solution.
>
> Is such a LED exists? A long life, wide temp range 12V red LED?
>
> Answer tomorrow, after my visit to my NFNKLEPS (not friendly, not
> knowledgeable local electronic parts store)!
>
> Louis-Alain
> 1983 urQuattro
> 85-D-900463