Resistors and LEDs for 2-8-4

[uncbob]

Need info on the resistors values for the front headlight and tender rear light for the Bachmann 2-8-4

Also the LED types used

[richg]

Does the loco have LED's now?

LED Resistor Values

Measured with 12.2 VDC supply using 20 ma max current LED's. Values will vary some depending on actual DC supply value. Most LED's for our use are 20ma.

Resistor      Current
1000 ohm    9.0ma

750 ohm     12.45ma

680 ohm     13.12ma

510 ohm     16.25ma

1/8 or 1/4 watt just fine.

Many use the 1K. If you want the LED brighter, go with the lower value. Dimmer, or maybe more yellow, the higher value.

Rich

[uncbob]

Thanks

[uncbob]

What about the bulbs/LEDs ? or whatever are used for the headlight and tender light
I need to know what to order 

AS I had posted on a previous thread I burned them out when I hard wired a sound decoder because I didn't use resistors so they have to be replaced

[richg]

What about the bulbs/LEDs ? or whatever are used for the headlight and tender light
I need to know what to order 

AS I had posted on a previous thread I burned them out when I hard wired a sound decoder because I didn't use resistors so they have to be replaced

There is a variety of LED's available.
For bulbs, many use Miniatromice 1.2mm diameter, 1.5 volt bulbs with a resistor. I use them with a 470 ohm resistor.
Bubls that operate at 12 o 14 volts get o hot and can melt the plastic shell. Has hapened to some who were not aware.
The below fellow has a good site on DCC and lights.

http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm

After you read the page, go to his Home page, The Main North HOME.  There is a ton of very good DCC info.

The Main North HOME

Miniatronics site.

http://www.miniatronics.com/Merchant2/merchant.mvc

LED's

http://www.moreleds.com/railroad.htm
http://www.nmra.org.au/Hints/SMDs/Using%20SMD%20LEDs.html
http://hackaday.com/2010/12/13/diy-clamp-helps-with-surface-mount-soldering/
http://www.richmondcontrols.com/
http://www.youtube.com/watch?v=5ZyueLerawc

Store all LInks as you or someone else will need them
Pass them on when you see the same question.

Rich

[Jim Banner]

I suspect Bachmann, like many manufacturers, uses whatever LED's are available the day they order them.  For most applications, 3 mm warm white LED's are the choice.  No other specifications necessary.  And from Rich's numbers, that is probably what he was using too.  I could give you part numbers but chances are you would go to a lot of trouble finding exactly those parts while turning down many other suitable parts during your search.  I could do the same for the resistors but again all you really need to know is their resistance and power rating.  The full part number would also specify tolerance, temperature coefficient, maximum temperature, material, mean time between failure and a few other things.  But really, for our application, who cares.  These details might matter in some applications but not outs.

Most of the LED's I use in headlights and tender lights are taken from strings of warm white LED Christmas lights bought cheap after Christmas.  These LED's cost about 15 cents apiece and replace both 3 mm and 1/8" LED's and bulbs.  For resistors, I use 1000 ohm 1/4 watt ones costing about $3 per hundred at my friendly local electronics wholesaler.  If the light is a bit bright, I add another 1000 ohm resistor in series.  If it is a bit dim, I add another 1000 ohm resistor in parallel with the first.  If I need finer tuning, I use a pot and then pick the closest resistor value from the ten thousand or so resistors I keep on hand but I very rarely resort to this.

Whatever LED's you use, be careful not to overheat them while soldering.  My favorite trick is to hold one LED lead in a hemostat placed right next to the case of the LED.  The hemostat not only conducts the heat away but also hold the LED still while I solder a wire to it.  A small piece of shrink tubing finishes off the joint nicely.  Repeat for the second lead.

Jim