LEDs

[dex]

Operate strictly with DC.. Anyone have info on the easiest circuit for wiring LEDs in  HO locomotives

[jward]

not entirely true. led's are diodes, thus they can also convert ac to dc.

for ideas on using them in locomotives, do w search for "constant intensity lighting" as most of those circuits can be modified for led's in place of bulbs.

[richg]

not entirely true. led's are diodes, thus they can also convert ac to dc.

for ideas on using them in locomotives, do w search for "constant intensity lighting" as most of those circuits can be modified for led's in place of bulbs.

Here is a link I have had. Notice 1.5 volt bulbs and LED's. Constant lighting goes back a long ways.
It does reduce the top operating speed of your loco. Which may not be a problem. The power pack might have to be turned up a little more than usual to get the loco to move as compared to one without the constant lighting.ys.

http://www.awrr.com/ConstantLighting.html

Rich

[richg]

not entirely true. led's are diodes, thus they can also convert ac to dc.

for ideas on using them in locomotives, do w search for "constant intensity lighting" as most of those circuits can be modified for led's in place of bulbs.

A bi color LED with show a third color. A green/red bi color LED will show yellow, might not be pure yellow though. Don't know if anyone has ever tried to use LED's as rectifiers. I never have as common rectifier are designed for that purpose and are cheap enough.
Also, using a LED with AC can ruin the LED because of the reverse voltage.
Most LEDs have low reverse breakdown voltage ratings, so they will also be damaged by an applied reverse voltage above this threshold. The cause of damage is over current resulting from the diode breakdown, not the voltage itself. LEDs driven directly from an AC supply of more than the reverse breakdown voltage may be protected by placing a diode (or another LED) in inverse parallel.
Some time go I posted a circuit to use and LED with AC as someone wanted to use LED's with DCC track voltage.
I believe it was Jim Banner who added a little more. A diode for reverse voltage protection.
.
Search the archives. You will find the circuit.

Some use the reverse diode protection with DC to operate the Tortoise switch machines and an LED. That is another complete discussion.

Rich

[jward]

i have used them in cases where i wanted both a rectifier and an indicator light. you'd only want to use them to rectify low current circuits.

note that the bi colour led's come in two varieties: 2 lead and 3 lead. the 3 lead leds are actually red and green led's in parallel, with the third lead a common connection. you get yellow when both led's are lit. the yellow colour is fairly easy to adjust with these, by using different values of resistor in series with one of the leads (not the common lead)....

the 2 lead bi colour led is a different beast altogether. it is actually red and green led's connected in reverse parallel. hook them up to dc one way and the red lights, reverse the polarity and the green lights. apply ac and both light, making yellow. these are useful for direction indicators on a dc layout. one place i used them was to indicate whether the polarity of a reverse loop was set for a train to enter. if the polarity is correct you'd get green, if it was set wrong you'd get a red. 

[Jim Banner]

The three lead double LED's are usually called bi-colour LED's while the two lead ones are sometimes called tri-colour LED's because the internal LED's are so close together that when both are illuminated, their colours add.  The colour can be varied somewhat by controlling the forward and reverse currents independently.  White LED's are also double LED's (blue plus yellow) but are connected in parallel so that both light at the same time.  The original "white" LED's were quite bluish because blue LED's are more efficient than yellow ones.  In pure white and warm white LED's, a yellow filter is added to block some of the blue light.  This filter is usually visible when you look into the end of the LED.

There are even LED's with FOUR leads.  They contain 3 LED's in one package, one red, one green and one blue.  Anyone dealing with colour photography or colour TV will immediately recognize these as the three primary colours.  Basically, these LED's can reproduce all colours by lighting the LED's at different levels.  They are mostly intended for display signs but could also have applications in model railroading.  These triple LED's are relatively expensive (a couple of bucks each) but not outrageously so.  One example example of a 5 mm version is Kingbright type WP154A4SUREQBFZGW, available from Digi-Key as their part number 754-1492-ND.  The data sheet is available in .pdf format at this link:
http://www.kingbrightusa.com/images/catalog/SPEC/WP154A4SUREQBFZGW.pdf.

Jim

[dex]

Thanks All.. your replies are appreciated and helpful.

Sorry I confused some of you.. I ment to say I operate strictly on D.C. and am not planning to go over to DCC