A friend of mine came over and asked me if I can put LED's in his train, he has one of those huge aristocraft engines. He specifically wants the LED's to maintain brightness, regardless of the supply to the track from his regulator. I am wondering if anyone has experience in this, since I barely have experience in 8X8 grids LOL. He wants head lights, on to go forward, and reverse lights when he is going backwards. This seems easy enough to me, just anode/cathode backwards for reverse. But what about continuous brightness? How does one regulate that ?
Thanks in advance to all suggestions.
Hi, what scale and guage is the train,also what is the voltage from the track that powers the train.
Have you googled " model train led lighting " you will be surprised at the number of solutions there are out there.
Tom... 
sensai:
He specifically wants the LED's to maintain brightness, regardless of the supply to the track from his regulator.
If he's using analog control a dedicated on board battery will be needed (is there enough room for them and some charging circuit?)
If he's using digital you're set to take the juice from the tracks.
That's your first job to figure out.
You need to know what voltage is being supplied, if it's a constant voltage it's sinply a case of using a resistor...
Tricky part will be reversing, if it's minus voltage, then it's as simple as flipping the led with a resistor.
Hi, I took my own advice and googled aristocraft trains, I hope the one that we are discussing is the G scale or GARDEN Railway size, which will help in getting lights going.
My cousin has G scale, he is still controlling by analog current in the tracks, but you can get DCC systems for them.
Constant rail volts will help, but if not, yes a recharge battery would work, and there should be, hopefully, few space constraints.
Tom....
Maybe a constant current source like the NSIC2020BT3G, that will limit the current through the LED to 20mA regardless of the voltage (within reason).
Rob
Irrespective of scale, it's down to how the loco is powered.
If it's electrically powered via an Analogue system (not DCC) then the voltage will vary through the track, and will = 0 if the loco is stopped. If the loco is reversed this is achieved by reversing the polarity of the track voltage. So the lights will be full on at full power (ie full speed) and completely off when stopped. The way around this would be to have a separate power supply for the lights, but include a monitor for polarity to switch colours according to direction.
It it's electrically powered through a DCC system the loco will have a decoder chip, you just need to program Function 0 (Lights) and off you go. The track for DCC has a constant voltage irrespective of loco speed - so lights will have constant brightness even if loco is stopped (unless the bit of track its on is isolated of course!). There's lots of info on the web, such as http://www.dccconcepts.com/index_files/DCCdemystifying.htm and many others.
The difference between analogue and DCC is that with analogue you control the track, with DCC you control the loco - if you haven't come across this before you need to let it sink in!
If it's steam powered then an on-board power supply and probably a remote (e.g.wireless) switch will be needed (I would think, assuming the track is unpowered) for the lights.
We need more electrical information, is it analog control, digital...? What power source is available inside the train?
In very simple cases you can use a resistor to get the voltage to the right level (more or less) but normally you'll use special "constant current" ICs for the job.
Lighting up a LED correctly isn't as easy as it seems.
fungus:
Lighting up a LED correctly isn't as easy as it seems.
it is.
cjdelphi:
fungus:
Lighting up a LED correctly isn't as easy as it seems.it is.
So why are there hundreds of special ICs to do it?
You can also ask on the forums at mylargescale.com - lots of guys that know trains and electronics there.
The big question is he battery or track powered?
whoa lots of replies, thanks people. Ok the train is powered by the track, so as he kicks up the power to the track from his ac/dc converter, power to track varies. It is 12 volt power supply. I was thinking of rechargeable battery power to LED's and recharged from the track, but now I see the replies, it seems to me it might be the way to go. He is supposed to get me all the specifics in the next day or two.
Thank you very much for the help and suggestions, as well as the questions, which I need to ask to get the proper information.
fungus:
cjdelphi:
fungus:
Lighting up a LED correctly isn't as easy as it seems.it is.
So why are there hundreds of special ICs to do it?
If you used a 1k resistor it would be safe to use on any voltage that one can touch with your own hands...
So why require more? Simples - to regulate the brightness... lighting one up is childs play
This any use? LED circuit - Wikipedia.
Plus I've set up a chart for the LED's I have in stock, I've attached it in case its useful. No prizes I'm afraid for spotting the "deliberate" mistakes!
OptoElecronicsResistors.pdf (320 KB)
Thanks for the links, I am still waiting for my friend to contact me, could be a while since he got shifted to night shift. I will update when i get the information from him.
Thanks again.