Resistor LEDs

It's surprising how much can be machined off an LED to make them smaller to fit in headlamp casings! 5mm will easily machine down to 2.5mm diameter and 2.5-3mm long.

Regards, Greg.P.

Is there a way to do this if you don't own a "machine"?

Use a file. It's easier if you can put the LED in a drill chuck but even this isn't necessary.

Although I've only taken the lip and top millimeter or so off a 3mm LED to fit it in in an O-gauge semaphore signal lamp casting.

Hmmm, you might chuck the LED in the Black and Decker and use a fine file very lightly - expect to destroy a few LEDs before you get what you want! (they're not that expensive) Find a friend who has a lathe. Buy a lathe. A basic Sherline will cost you about as much as a couple of (expensive) plastic locos and probably will give you an equal amount of pleasure. I'll bet you buy lots of useful accessories over the years :-)

Regards, Greg.P.

We kinda get off on a tangent - I would still like to know if anyone has ever used a resistor LED?

Yes I have. I had some surplus micro red LEDs which had a built-in resistor to make them work directly from a 5V power supply. They were perfect size for a RailRoad crossing flaser lights in N scale.

Since I was using them with 12V I still had to add a series resistor. I just calculated the value taking into consideration that those were now 5V LEDs not

1.7V LEDs. They works just fine.

So, I didn't actually buy them with intention of using them without a resistor - I bought them because they were cheap and very small.

:-)

Peteski

The ones at LC-LED's site are rated at 12v, and I'm wondering if you'd still need a resistor when running on DCC???

That is a tricky question. It depends on the value of the resistor within the LED. In other words, did they designed the LED to run at its full rated current at 12V or at a lower current. And of course this type of info is not given with the LED.

So, you would have to take some measurmants. Using a real 12V DC power supply (DCC is not a real DC), hook up an Ammeter in series with the LED and hook all of this to the 12V power supply. If the current indicated is

20mA then the LED is running at full current (most LEDs have 20mA operating current). In that case, you should add a resistor to it to run it from DCC. If it is less than 20mA, then there is some "room to play" and you can run it straight from DCC. that is because if you hook it up to voltage greater than 12V the current going through it will increase, but not enough to be out of spec.

All the above instructions show how anal I can be.

There isn't that much difference between 12V and 15V (or whatever your DCC voltage is). Also, there is some voltage drop caused by all the diodes and transistors within the decoder itself so the Function outputs dont have the full DCC voltage present.

Lets say that at 12V the LED is running 20mA. I calculated that at

15V the LED would be running 26mA (most likely safely, as the maximum current is usually around 30mA).

So, go ahead and hook them up directly to DCC or be as anal as I am and hook up a resistor. But then, why not just use plain LED with a resistor in the first place ... :-)

Peteski