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.
How to install LED headlight in a Athearn DC diesel to eliminate the bulb
- Thread starter trainrails
- Start date
ctclibby
Well-Known Member
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
trainrails
New Member
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.
Smudge617
Well-Known Member
If the LED isn't pre-wired, the longer leg is the positive.
ctclibby
Well-Known Member
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
Think of that solder blob on the bottom as positive.
later
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
Think of that solder blob on the bottom as positive.
later
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Smudge617
Well-Known Member
The loco is wired the same way, when you switch your controller to reverse all you are doing is reversing the polarity to the rail so you need to work out which rail is the positive when your controller is in Forwards as @ctclibby has described above and wire the LED into whichever pickup is on the positive side, then wire the rear LED the opposite way round to the front LED.
trainrails
New Member
I just thought that I could buy 12 Volt pre wired LED & wire it in the bulb holder.
trailrider
Well-Known Member
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 for both.
Dub
Lionel 3 Rail
The next step is using a multimeter to measure the polarity of the engine connections, the track and transformer output. From there it can get more complicated.
Also, some prewired LEDs can be a universal connection regardless of AC or DC and work within a voltage range,
Just using an LED and a resistor may not be enough to have it last. The voltage varies and causes spikes which could burn it out.
That is where the fun begins.
Also, some prewired LEDs can be a universal connection regardless of AC or DC and work within a voltage range,
Just using an LED and a resistor may not be enough to have it last. The voltage varies and causes spikes which could burn it out.
That is where the fun begins.
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Smudge617
Well-Known Member
You can, just make sure a resistor is fitted.
Can I suggest that either you paint the LED (LEDs produce little heat) or use some sort of shroud, like shrinkwrap, over it to focus the light forwards, otherwise the entire nose and cab will light up.
Iron Horseman
Well-Known Member
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?
Iron Horseman
Well-Known Member
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 will caveat that by saying if the vendor has NOT built in the resistor this method will blow the diode.
santafewillie
Same Ol' Buzzard
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"!
dennis461
Well-Known Member
For Athearn, forward running is POSITIVE on right rail, NEGATIVE on left rail.
And light bulb center pin is POSITIVE, outer shell is NEGATIVE.
So, using a LED and 800+ ohm resistor alone will have the light on when running forward, off running backward, if you connect red wire to positive, and black wire to negative.
(I use LEDs that come with a resistor mainly and red/black wires.).
Red is POSITIVE in my picture. Green is NEGATIVE.
And light bulb center pin is POSITIVE, outer shell is NEGATIVE.
So, using a LED and 800+ ohm resistor alone will have the light on when running forward, off running backward, if you connect red wire to positive, and black wire to negative.
(I use LEDs that come with a resistor mainly and red/black wires.).
Red is POSITIVE in my picture. Green is NEGATIVE.
trailrider
Well-Known Member
Now, if you want the light on the top of the cab to light when the engine is running in reverse, just hook the LED opposite. The light on the front end will be off and the light on the cab will light.
trainrails
New Member
Yes I would like the headlight to be directional. Sorry for all the questions. I never did anything with LEDS.
Mixed Freight
Well-Known Member
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.
An LED only lights with the current going one direction. It doesn't light if the current is reversed. Very desirable for directional lighting. Also means you can't hook it up wrong (as far as hurting the LED). It either lights, or it doesn't, depending on the polarity of the current. Your forward/reverse switch on your transformer controls the polarity to the rails, of course.
Take an LED and hook one wire to one polarity on your loco frame, and hook the other wire up to the other polarity. If the LED lights up in the forward direction of your loco, you're good to go. If not, simply reverse the LED wires, then it should light up in the forward direction.
Once you get a forward light hooked up, take another LED and repeat the procedure for a rear light. That should get you wired up.
kjd
Go make something!
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.
There is a way to use some diodes to drop 3V so LEDs work at low speeds. I don’t know how right now but to figure it out I’d start by looking at a factory board that has LEDs attached. Kato for example.
There is a way to use some diodes to drop 3V so LEDs work at low speeds. I don’t know how right now but to figure it out I’d start by looking at a factory board that has LEDs attached. Kato for example.
Smudge617
Well-Known Member
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.
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