LED's

Is there a web site that show how to wire LED's into a DC powered locomotive along with what other parts that are needed?

 

I don't know of a web site specifically for installing LEDs but take a look at www.richmondcontrols.com. Jim Hinds is the expert IMHO for lighting in model railroading.

Basically, an LED is a current activated device and therefore, needs a certain amount of current to operate. Generally, this is around 20ma, but someone, I'm sure will say something different. Anyway, to install an LED, you must know the voltage that will be applied. This can either come from the documentation of the decoder, or from measurement. Then, a guy named Georg Ohm developed a rule, henceforth known as Ohm's law, that allowed one to find the current in a circuit if the voltage and resistance is known. By transposition, you can find the resistance you need in our LED circuit if you know the voltage and the current you want.

Using my 20ma of current, if your decoder is putting out 12 volts, you would use the transposed formula R(resistance) = V(voltage) divided by I(current). Therefore, you would need a resistance of 600 ohms. 620 ohms is a standard value and would work just fine. The resistor is in series with the LED, so that the current must pass through both the resistor and the LED from the voltage source(decoder).

If you have any other questions or a specific problem/situation, email either Jim or me directly.

 

The one website I had bookmarked and has a name that sounds like it would help was not much help at all beyond getting the resistor value

For a DC loco (rather than DCC) in addition to the resistor you will need a diode or four to get the electricity going the right way. Depends what the light is for. The number of diodes may also affect the resistor value.

The advantage of places like Trainboard is you can get a custom answer (well, usually ) but you need to be a bit more specific about what you want to achieve - eg. is the light to be directional or 'always on'? Headlight/marker lights? Do you already have the LED or know which one you will use? (in which case knowing the data for it will be useful - the 20mA Skip mentions is a rule-of-thumb and can vary a lot.)

 

I'm looking at using the LED's as Headlites and also directional.

Jim

 

This is a diagram of a simple circuit.



I've shown the two directional options and also the non-directional using a bridge rectifier (which is 4 diodes in a small plastic case). This just turns the power round the 'right way' for the LED, regardless of the loco direction.

I haven't shown resistor values. LEDs usually need about 1.5V/20mA, but some 'white' LEDs need about 3V and 30mA or more, so the resistor values will need to reflect this (3V/20mA would need about 450 Ohms). This is why I asked if you had any data.

Working out which way round the forward/reverse directions are is probably best by trial and error.

There are more complex solutions to give more constant brightness, but there are various disadvantages to them.

[ 09. July 2004, 20:23: Message edited by: Mike Sheridan ]

 

Is there a LED that you would recommend that might be purchased from maybe Radio Shack?

Thank You

Jim

 

Jim, there is a place on ebay I have had excellant results from.They come out of Hong Kong but only take a week to arrive and shipping is free !!!They also take paypal and their prices are dirt cheap ..I yse their super brite 10,00mcd 5mm and 8000mcb white Leds,they run around 14.00 for 50,you can also buy in quanity of 10 to 10,000 up. The amber and utraviolet are cool also,plus they throw in free resistors.Check out cwithk ,store name on ebay ..

 

I've modified my post above with a better diagram and changed the text to suit.

I don't have any LED recommendations I'm afraid, but I'm sure I've seen discussions on TB about them. Try doing a search for LED or White LED. Failing that I would ask that question in the Inspection Pit, as it will be seen by more people there.

I got some 'white' LEDs for locos about a year ago. They were ordinary ones from an electronic store and looked a touch blue (common problem) when tested, but were OK. However, once I had fitted one in an engine, where it was working through a plastic light guide, it looked very blue; I think the plastic must have been absorbing some of the red end of the color. So I ripped it out and went back to a filament lamp. Next time I will pay the extra and get 'proper' white LEDs .

Hah! While writing this Tom has come up with some goods

 

Some have said that an orange Sharpie applied to a plain, white LED will take that blue edge off of the white lighe.

 

I searched for cwithk on Ebay but it can't find it. Would you have there web address by chance?

Thank You

Jim

 

"view seller's outher auctions"

TRY THIS LINK

and if you buy a lot of like 100, I'll buy a few off ya

 

If you don't use the diode/s and just use the resistor with a 3V LED in a DC system will anything happen to the LED when you reverse direction?

The engine only has one headlight.