[R-390] Re: LED lamp replacement

[Bob Camp]

Hi

Assuming you really want to go this way here's the basic data:

Page 1333 in the online Digikey catalog (www.digikey.com) has a number 
of high intensity LED's. They come in several colors and in white.

The voltage drop on the colored ones is a little under or a little over 
2 volts depending on the color. The white ones have a voltage drop of 
3.6 volts.

If you run them off of the 25 volt AC supply you will have about  33 
volts DC to work with. If you drop about 1/3 of the supply across the 
series resistor then you get 22 volts on your string of LED's.

The resistor is sized to give you 20 to 30 ma through the LED's. Eleven 
volts and 25 ma would get you a 440 ohm resistor. 390 and 470 are the 
closest standard values. A one watt size should work ok. The value will 
take a little fiddling to get the voltage right. I would start at about 
390 and work down to about 180 ohms.

 From there on it's a matter of picking a color and  figuring out how 
many of them add up to 22 volts. If say 11 orange LED's does not make 
sense then the resistor size can change to match the new load.

A full wave bridge of 1N4148's to convert the AC to DC and maybe a 10 
uf 35 volt cap across the stack of LED's completes the project.

The resulting circuit looks like:

Four diodes in a bridge, AC ends to the 25 VAC filament line and to 
ground. DC ends to the resistor and diode / 10 uf cap combination. 
LED's all go in series with each other.

That may not be clear enough to follow along .... sorry about that.

	Enjoy!

		Bob Camp
		KB8TQ


On Jul 7, 2004, at 3:50 PM, Rbethman wrote:

> First - When you get a new car or truck with those LED taillights, 
> remember how WELL they get the attention of those behind you.  You'll 
> live LONGER.
>
> Second - I'd like to get circuit info on LEDs in lieu of the dial 
> lamps.  Whom can send it by mail?  Does someone have this on a web 
> site?
>
> I may even tackle the UV for the meters!
>
> Bob N0DGN
>
> Kenneth G. Gordon wrote: