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Discussion Starter · #1 ·
I have been converting my engines over to LED headlights. In order to stop the light from flickering when running over switches etc. I have discovered that it is possible to add a capacitor to the circuit. What I need to know is what capacitor should be used and how would it be wired. I've seen CLU's for sale on Ebay for around $10 + shipping but I already have the LED's (3 to 3.2 volt) and the resistors (820 ohm) and just need the capacitors.

Ray
 

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You can add pretty much any size capacitor, it all depends on how large a drop-out you are protecting against. I hope you have diodes in those locomotive's lighting circuits as well to protect the LED's against reverse voltage! Also, electrolytic capacitors don't like to see reverse polarity.

Start with something like a 220uf at 10 volts across the LED and see how that works.
 

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Discussion Starter · #3 ·
You can add pretty much any size capacitor, it all depends on how large a drop-out you are protecting against. I hope you have diodes in those locomotive's lighting circuits as well to protect the LED's against reverse voltage! Also, electrolytic capacitors don't like to see reverse polarity.

Start with something like a 220uf at 10 volts across the LED and see how that works.
This is a direct current track voltage circuit. I thought that you could wire the capacitors positive side to the positive track voltage, negative side to the limiting resistor, the limiting resistor to the anode of the LED, and the LED cathode to ground.

At present I am wiring the limiting resistor to the positive terminal, to the LED, and on to the ground. The light only works when the train is moving forward because of the diode (LED).

The LED itself should protect the circuit from reverse voltage since it is a diode and will only allow the current to travel in one direction.

Ray
 

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Well, to reverse the train, you reverse the track polarity, no? That also reverses the polarity on the LED and capacitor.

No, the LED is NOT protected from excess reverse voltage! The normal maximum reverse voltage for LED's is in the 5-7 volt range, I'm sure the track voltage exceeds that at times. Also, the electrolytic capacitor doesn't like reverse voltage at all, and it'll turn into a firecracker! For this scheme to work, you really need a diode in series with the LED and capacitor.
 

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A true and safe working constant lighting circuit takes track voltage and runs it to a rectifier / regulator / buffer circuit (which has the capacitor in it) then to a control circuit for direction control. This not only keeps the LED constantly lit, but it buffers out any fluctuations in the track voltage or polarity. And like GRJ states you must put a diode in the circuit to stop reverse current if you’re going to directly hook an LED to track voltage.
 

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Here is what I used to make constant lighting in my HO passenger cars. I made this from parts available at RadioShack. I can look up part numbers if you like. You can see the bridge rectifier (round black) and the blue capacitor. All soldering was done on the underside of the circuit board. This takes DCC power from the wheels and provides DC current to the capacitor and the lights in the passenger cars. This greatly reduces light flickering and light remains on no matter what direction the train is traveling.

Here is a wiring diagram so you can see how it works.

The red wires go to the track voltage from the wheels and the black and white wires signify positive and negative current for the LED's. This was used on DCC track but it will also work on DC track to keep the polarity constant for the lights.
Hope this helps.
=Art
Here is a link to the bridge rectifier
Here is a link to the capaciter
 

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You can do it without the bridge just need 1 diode (2 would be better) a must for the cap to not be back feed reverse voltage.
 

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Yes, Ssean and Gunrunner are correct but the nice thing about the contraption I made is that it works equally well with DC and DCC plus the bridge only costs $1.39. You never know if a DCC upgrade is in your future wink wink.
-Art
 

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Another option is the Rapido Easy Peasy lighting kits. They are battery powered constant lighting with a magic wand that turns the lights on or off. A nice option if your soldering skills are not so hot.
Here is a link
-Art
 

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Discussion Starter · #12 ·
Here is what I used to make constant lighting in my HO passenger cars. I made this from parts available at RadioShack. I can look up part numbers if you like. You can see the bridge rectifier (round black) and the blue capacitor. All soldering was done on the underside of the circuit board. This takes DCC power from the wheels and provides DC current to the capacitor and the lights in the passenger cars. This greatly reduces light flickering and light remains on no matter what direction the train is traveling.
(Snip)
The red wires go to the track voltage from the wheels and the black and white wires signify positive and negative current for the LED's. This was used on DCC track but it will also work on DC track to keep the polarity constant for the lights.
Hope this helps.
=Art
Here is a link to the bridge rectifier
Here is a link to the capaciter
Looks simple enough, but I see two resisters on the board. Do you have any pics of the back of the board?

Radio Shack sells their parts on Ebay. All you have to do is cut and paste the description in the search bar. On top of that the shipping is free.

Ray
 

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No I don't have a pic of the back of the board but the wiring diagram is accurate. Yes there are 2 resistors in this example. The reason for this is that my first try the LED's were a bit too bright so I added a second one. you must use a resistor to run LED's or they will burn out. I really can't remember the size resistors but I use trial and error to get them to where I like the brightness. I made my own track power pickups on my concor passenger cars by wrapping an uninsulated wire around the axles and switched to metal wheels. It worked out pretty good.
-Art
 

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Discussion Starter · #14 ·
No I don't have a pic of the back of the board but the wiring diagram is accurate. Yes there are 2 resistors in this example. The reason for this is that my first try the LED's were a bit too bright so I added a second one. you must use a resistor to run LED's or they will burn out. I really can't remember the size resistors but I use trial and error to get them to where I like the brightness. I made my own track power pickups on my concor passenger cars by wrapping an uninsulated wire around the axles and switched to metal wheels. It worked out pretty good.
-Art
OK, I understand. My resistors should be OK since I bought them as a package deal with the LED's . I ordered the parts from Radio Shack thru Ebay yesterday (Free Shipping) to give it a try. It looks like it will be exactly what I was looking for.

Ray
 

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Discussion Starter · #16 · (Edited)

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Discussion Starter · #17 ·
Constant Lighting Unit Edit Post

Here is what I used to make constant lighting in my HO passenger cars. I made this from parts available at RadioShack. I can look up part numbers if you like. You can see the bridge rectifier (round black) and the blue capacitor. All soldering was done on the underside of the circuit board. This takes DCC power from the wheels and provides DC current to the capacitor and the lights in the passenger cars. This greatly reduces light flickering and light remains on no matter what direction the train is traveling.

Here is a wiring diagram so you can see how it works.

The red wires go to the track voltage from the wheels and the black and white wires signify positive and negative current for the LED's. This was used on DCC track but it will also work on DC track to keep the polarity constant for the lights.
Hope this helps.
=Art
Here is a link to the bridge rectifier
Here is a link to the capaciter
I got the parts in yesterday and hooked them up this morning to bench test the circuit.

Everything went great... It was simple and easy to put together, and worked just as advertised. The light cones on at full brightness with minimal current being applied, Changing direction has no effect on the light, and when you turn the power off it slowly dims.

This is what I was looking for, now to install it in my engines.

Ray
 

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Hi, I use an IC (integrated circuit) for my constant brightness loco headlight. It never blinks, it is one way only, and uses only a 10 ohm resistor with simple hookup. It turns on at about 3 volts and keeps the same brightness. safe up to about 20 volts. See CONSTANT BRIGHTNESS SUPER BRIGHT LED LOCO HEADLIGHT WITH THIS SIMPLE KIT
on ebay.
 
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