trainrails
New Member
I would like to install a LED headlight in a Athearn DC diesel to eliminate the bulb. I have all DC engines. I don't plan on changing to DCC. I bought some pre wired 12 volt LEDS & I'm not sure how to wire them in.
1st thing to check is the *actual* VDC coming out of your power supply. Most say 12VDC but that can vary. Reason for this is cuz there is a dropping resistor that could be included with the LED's to set a specific LED current. There could room to play, but to be on the safe side ...I would like to install a LED headlight in a Athearn DC diesel to eliminate the bulb. I have all DC engines. I don't plan on changing to DCC. I bought some pre wired 12 volt LEDS & I'm not sure how to wire them in.
I thought that every HO DC Engine is wired all the same so that they all run in the same direction at the same time. So if this is true shouldn't plus & minus be the same wire in all the engines? Also how do I tell which wire is plus or minus in the engine? I appreciate any help.1st thing to check is the *actual* VDC coming out of your power supply. Most say 12VDC but that can vary. Reason for this is cuz there is a dropping resistor that could be included with the LED's to set a specific LED current. There could room to play, but to be on the safe side ...
2nd - don't assume that the voltage going into the incandescent lamp is plus ( + ) on top, and minus ( - ) on the other side. Measure it so that you know the polarity of the connection.
3rd - how are those LED's marked. Is there a plus or anything? Hook one up to the the power pack track voltage while off. Now turn up the power to the rails slowly until the LED just lights. If it does not light at half power, crank down and switch the LED leads and do again. Ok, so you know which end of the LED is plus.
After figuring the above, now you can hook up the LED's. The front LED in a forward direction; supply plus to LED plus, the rear LED the opposite; supply plus to LED negative. This will allow the front LED to be on going forward, the rear led on going reverse.
The above should work unless there are electronics involved between the track and the LED's ( incandescent ). This would be a new game. IE. what is in that electronic package? More to play with!
Later
If the LED isn't pre-wired, the longer leg is the positive.3rd - how are those LED's marked. Is there a plus or anything? Hook one up to the the power pack track voltage while off. Now turn up the power to the rails slowly until the LED just lights. If it does not light at half power, crank down and switch the LED leads and do again. Ok, so you know which end of the LED is plus.
I just thought that I could buy 12 Volt pre wired LED & wire it in the bulb holder.Well, according to theory every engine is wired the same. Ya, your guess is as good as mine. Just to get your ducks in a row and make every setup the same when swapping incandescent/Leds.
The power pack should have a reversing switch - might be marked Forward/Reverse or Normal/Reverse or the like. IF the manufacture has done its job proper, with the switch set to Forward or Normal, the voltage at Track Plus will be positive in respect to Track minus. If those marks are actually imprinted there and you can read them. If not, you can figure out and mark the correct polarities on the power transformer with a laundry marker or the like. That should give you a standard starting position.
The individual engines also in theory should be wired the same. Ya, another guess again. This one is also easy to handle. You can clip your volt meter to the targeted light you wish to change with the red lead at the top, black lead to track minus, then turn up the power until you can see a voltage reading. If no voltage reading AND the engine moves, the Volt Meter is connected to the same source, move one clip. If all is like we are assuming, then the red lead is connected to positive, black to negative and you know what the polarity is. If the red lead goes negative, crank power down and physically reverse the engine on the track. You then know if you go through a bunch of them and all of a sudden you have to swap ends on the engine, somebody messed with the wire - or - the manufacture did something different. Also note if that happens it means that specific engine will not run the same direction of the others. More electrical playing is in order. It used to be with the engine running in the forward direction, looking down at the top of the engine the left rail is positive.
Oh, just a little note: Those older incandescents *usually* are TBase style bulb
View attachment 187014
Think of that solder blob on the bottom as positive.
later
You can, just make sure a resistor is fitted.I just thought that I could buy 12 Volt pre wired LED & wire it in the bulb holder.
You are correct. NMRA S-9 II A states, "Positive potential applied to the right hand rail shall produce forward motion."I thought that every HO DC Engine is wired all the same so that they all run in the same direction at the same time. So if this is true shouldn't plus & minus be the same wire in all the engines? Also how do I tell which wire is plus or minus in the engine? I appreciate any help.
Probably, true. Usually, if the vendor gives a voltage rating in the description they have built in a resistor. Don't make it hard for the sake of making it hard. Put the loco on the track. Use alligator clips from the current lamp frame to the LED. Apply power in the forward direction. If it lights your good to go, if it doesn't reverse the leads.I just thought that I could buy 12 Volt pre wired LED & wire it in the bulb holder.
Found that out on a used Athearn that I was given about 25 years ago! Took me a while before I figured out what the issue was. Ran great after that. It was given to me because, "it ran backwards"!However, in an Athearn yellow box or blue box unit, if one disassembles the thing and accidentally moves the front truck to back (and vice versa), it will reverse polarity to the motor (and the light socket).
You don't say whether you locomotive has a forward headlight and a reverse light. If so, when you get the polarity correct for the engine going forward, the rear light should be dark. When you throw the reversing switch to make the engine run in reverse, the headlight should go dark and the rear light come on. To get this effect, you will need to figure the polarities opposite
Yes I would like the headlight to be directional. Sorry for all the questions. I never did anything with LEDS.You are correct. NMRA S-9 II A states, "Positive potential applied to the right hand rail shall produce forward motion."
However, in an Athearn yellow box or blue box unit, if one disassembles the thing and accidentally moves the front truck to back (and vice versa), it will reverse polarity to the motor (and the light socket).
Are you wanting directional lighting, such that the headlight goes out in reverse?
If you bought some pre-wired, 12 volt LED's, I'm guessing that they already have built-in resistors. Mainly because all LEDs operate at about 2.2 maximum volts, if memory serves. Much more voltage than that (around 2-1/2 to 3 volts, give or take) and the LED will burn out. That's the job of the resistor, to limit the amount of voltage going to the LED.I would like to install a LED headlight in a Athearn DC diesel to eliminate the bulb. I have all DC engines. I don't plan on changing to DCC. I bought some pre wired 12 volt LEDS & I'm not sure how to wire them in.
A 3V LED only needs milliamps to work, that's why you have to have a resistor, and precisely why you use one on a locomotive, I'm not sure how a 12V LED would work, but I would assume exactly like an incandescent bulb which, if correct, defeats the point of switching from incandescent to LED, a 3V LED will give full brightness as long as it has power, even at low speeds.Just putting in an LED with resistor for 12V won’t give the desired results. It won’t be bright until 12V but then you’ll be going full speed.