Lee,
It sounds like you have it handled.
FYI
Miniatronics has 1.5mm and 3mm LED's. If the 3mm is a bit big you can machine the diffuser down a bit to make it fit your application.
Thanks guysI was not able to find LEDs the right size so I bought a 12V, 60 ma bulb and put a 100 ohm resister in line. The new bulbs is slightly larger than 2.4 mm which is not ideal but works. I may put a larger resister in because the light is a little too bright. I have come to the conclusion that this Bachmann Thomas is not very good (piece of junk). The gears that make the eyes move create a lot of drag. I don't think my little buddy will know or care. He's only 2 years old and really loves Thomas trains The other posts indicated that they won't run very well even if converted to DCC. I'm hooking it up with some cars and a diesel "B" unit on the tail end. It looks good and he won't care. And again thanks for the help everyone.
Lee
Definitely don't use the 90ma bulbs - direct to track power the current draw is OK but they are likely too high to connect to a decoder function output. And 90ma bulbs in direct contact with a plastic shell (if they press right in to the headlight hole) will melt the plastic when running at full power.
People may wonder why their old plastic locos didn't melt using big high power 12 volt bulbs under DC - simple: they weren't running on a constant 12 volts, most of the time you probably ran the loco at 1/2 to 3/4 speed, 6-9 volts, so they didn;t get nearly as hot as they do when running at full voltage all the time as happens with DCC.
The smallest 'regular' LEDs are typically 3mm, 0.6mm biger - they will probably fit. You can cut the leads very short and solder flexible wire, like decoder wire, to them and use shrink tube to insualte as mentioned above. In fact, if it's 2 LEDs and you are connecting directly to DCC track power, they two LEDs can be connected to each other back to back which eliminates the need for a standard diode for protection. Each LED will protect the other from excessive reverse voltage.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
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yankee flyerLEDs have the bare posts and could present a problem.
A little bit of heat shrink on the bare LED leads will solve that problem. Solder thin wire leads to the LED, noting polarity for later. Insulate the solder joints and bare leads with heat shrink. No problems.
HiThe reason I wanted to use the tiny 2.4 mm bulbs is because they are the right size and have two thin wires that can run back to a connection point. LEDs have the bare posts and could present a problem. The bulbs that I have now are 90ma so I'll see about getting a lower current bulb.thanks
You need to know the current rating of the bulb to pick a resistor. 1.5 volt bulbs come in all types, from 15ma and 30ma types (these are the kinds you want, they dont get hot) to 90ma (not so good). But with the larger resistor required for the lower current bulbs, the resistor itself gets hot and needs to be a pretty big one.
LEDs are far better. Pick a variety of white LED (golden white, sunny white, etc), add a 1K resistor. If it's connected directly to the DCC track power you should put a standard diode across the LED int he opposite direction to protect the LED from reverse voltage.
Trying to run a Thomas train on my DCC layout. I disconnected the gearing to the wheels so that I can push the Thomas with one of my other locos from the back of it's train. I would like to put lights on the Thomas. I have the wheel pickups to take power from the track. For a 1.5 V 2.4 mm light bulb, what resister value should I use? I've seen different values suggested of 100 ohms and 1K ohms. I have already burned out one bulb.
Thanks for any help