# Adding LED lights to rolling stock



## sachsr1 (Mar 3, 2016)

I've been looking at adding lights to some rolling stock, and I've had good luck with the copper tubes over metal wheel sets. I was looking at adding a capacitor to reduce flicker. I know this has been talked about before, but bear with me. Rather then build a little circuit what would be wrong with using one of these?

https://www.ebay.com/itm/AC-DC-Conv...var=552502857259&_trksid=p2057872.m2749.l2649

The only thing I see that's missing is a current limiting resistor before the capacitor.


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## gregc (Apr 25, 2015)

i just tried adding some lights to 3 passenger cars on DCC.

i bought some white LEDs. added a pair of kadee #5 spring pickups to one of the trucks. Soldered a pair of LEDs in series with a 1k resistor. connected them to each side of the pickups using 30g wire thru a hole drilled thru the floor of the car.

since the pickups were held in place with a #90 screw, i just attached the wires to the pickup under the screw.

yes there was flicker. adding wires between the cars fixed that (need to neated it up). could have added pickup to both trucks on each car.

no reverse diode (or i could have connected the LEDs in parallel with opposite polarity). no capacitor (or battery). just tried out the simplest approach first before assuming more complicated approaches.

i think the 1k resistor is too small, the LEDs seem too bright.


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## Lemonhawk (Sep 24, 2013)

Not sure why they claim 12v output as the output voltage of that circuit is totally dependent upon the input voltage. There are a couple of things to try, but first are you DC or DCC? DCC is a nice because it can be rectified and with that circuit would produce a constant voltage that you could use to light the LED's with an appropriate resistor. Dimming with a resistor may not actually get you dim enough as LED's are really current devices and will just shut off eventually as you try to dim them. Dimming the LED's with Pulse Width Modulation gives you much better dimming control but really complicates the circuit. If you're DC then you need a little buck/Boost power supply like this https://www.banggood.com/DC-DC-Boos...-p-1087346.html?rmmds=search&cur_warehouse=CN.


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## Lehigh74 (Sep 25, 2015)

I’m not too good with electronics, but I can say without hesitation that it won’t work…because there are none in stock.

Seriously, I’m not too good with electronics, so I just ordered some of these. They cost 10 times as much, but I know for sure they will work.
http://hennings-trains.shoplightspeed.com/jw-a-20110-led-lighting-regulator-2-pcs.html


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## Lemonhawk (Sep 24, 2013)

The board's that lehigh74 talks about are a great solution for DCC and support GunRunnerJohn, I believe.


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## DonR (Oct 18, 2012)

The 1.10 unit in your attachment appears to be
what you want. 

I would, however, install power pickup in both
trucks, and use LED strip lights. They can
be attached to the car ceiling for even distribution.
No resistor needed, the 3 LED sections have a 12V
DC input which the available unit produces. It's
also less expensive that buying the caps and
diodes.

This post assumes you are running DCC on
your tracks. 


Don


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## sachsr1 (Mar 3, 2016)

I'm running DCC. The ones I linked are from an something that I've already ordered. They seem to be the same basic circuit I've been seeing for DCC led lighting. 

How about these?

https://www.ebay.com/itm/3W-LED-Dri...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

Here's a link to some that are in stock.
https://www.ebay.com/itm/AC-DC-Conv...hash=item4b0e8692e2:m:mMxX9iZZTPj4rviGqiiOYmw


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## Lemonhawk (Sep 24, 2013)

The constant current Power Supply may be just what it says and adding a resistor in series will not dim the LED, something that lehigh74's mentioned board does accomplish.


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## Tom_C (Jan 8, 2016)

I use a cheap bridge rectifier, a capacitor and a section from an LED strip like this:

https://www.amazon.com/Flexible-Non...TF8&qid=1519587760&sr=8-5&keywords=led+strips

It's pretty bright though, but that can be toned down.


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## gregc (Apr 25, 2015)

if you're going to charge up a cap, do you really need a full-wave bridge? wouldn't charging the cap through a single diode (and resistor) be sufficient?


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## Lehigh74 (Sep 25, 2015)

That looks to be cool white, Tom. I also ordered a few LED strips, but I got them in warm white (one is 2700K and one is 3100K).


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## Tom_C (Jan 8, 2016)

gregc said:


> if you're going to charge up a cap, do you really need a full-wave bridge? wouldn't charging the cap through a single diode (and resistor) be sufficient?


Yeah, if you knew which way the power was coming in.


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## Tom_C (Jan 8, 2016)

Lehigh74 said:


> That looks to be cool white, Tom. I also ordered a few LED strips, but I got them in warm white (one is 2700K and one is 3100K).


I'm not sure which ones I actually bought, I just found that link fast and posted it, but thanks for that information... maybe I bought the wrong type.

ADDED: Actually, I bought warm... these are the ones I bought: https://www.ebay.com/itm/Led-Strip-...200147&hash=item28499df593:g:UsEAAOSwj99aM3T3

And here are some relatively cheap bridge rects: https://www.ebay.com/itm/25pcs-DF06...~EAAOxyNo9SsJZo:sc:USPSFirstClass!20110!US!-1


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## sachsr1 (Mar 3, 2016)

Lemonhawk said:


> The constant current Power Supply may be just what it says and adding a resistor in series will not dim the LED, something that lehigh74's mentioned board does accomplish.


Wouldn't a larger value resistor dim the LED? The voltage coming out a DCC decoder is constant, and the bulb gets dimmer if you put in a bigger resistor.


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## sachsr1 (Mar 3, 2016)

And here are some relatively cheap bridge rects: https://www.ebay.com/itm/25pcs-DF06...~EAAOxyNo9SsJZo:sc:USPSFirstClass!20110!US!-1[/QUOTE]

I have a few of those laying around, and was looking to order more when I found these all ready to go. For about .60 more each I think it would be worth it, if they’ll work.


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## Tom_C (Jan 8, 2016)

sachsr1 said:


> I have a few of those laying around, and was looking to order more when I found these all ready to go. For about .60 more each I think it would be worth it, if they’ll work.


Do you mean these? https://www.ebay.com/itm/322366247650?rmvSB=true

Yeah, looks like they will work. I wouldn't use the other one you posted that looks to be limited to 12v input.


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## sachsr1 (Mar 3, 2016)

I’m not 100% but I think the ones I got were good up to 16v AC. We’ll see if they plume white smoke


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## Lemonhawk (Sep 24, 2013)

A decoders output is a voltage source, not a constant current source. A constant current source (a lot of LED drivers are constant current sources) will keep the current the same, so as you put resistors in series with the LED it up's the voltage to keep the constant current and if the current thru the LED remains the same, so does the brightness. A constant voltage source would allow you to put resistors in series with the LED and result in lower current going thru the LED and it would dim. With a constant current source you can put a resistor in parallel with the LED and get it to dim, and that is what I believe GRJ uses in his little LED driver, a constant current driver with the resistor in parallel.


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## Bwells (Mar 30, 2014)

Lemonhawk said:


> A decoders output is a voltage source, not a constant current source. A constant current source (a lot of LED drivers are constant current sources) will keep the current the same, so as you put resistors in series with the LED it up's the voltage to keep the constant current and if the current thru the LED remains the same, so does the brightness. A constant voltage source would allow you to put resistors in series with the LED and result in lower current going thru the LED and it would dim. With a constant current source you can put a resistor in parallel with the LED and get it to dim, and that is what I believe GRJ uses in his little LED driver, a constant current driver with the resistor in parallel.


Do you mean in "series"? It still seems like you would need a voltage regulator such as a 7809 or 7810.


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## gregc (Apr 25, 2015)

Tom_C said:


> Yeah, if you knew which way the power was coming in.


isn't this DCC?



sachsr1 said:


> Wouldn't a larger value resistor dim the LED?


yes, the current limiting resistor with a constant voltage source such as the one you mentioned (below)



sachsr1 said:


> Rather then build a little circuit what would be wrong with using one of these?
> 
> https://www.ebay.com/itm/AC-DC-Conv...var=552502857259&_trksid=p2057872.m2749.l2649
> 
> The only thing I see that's missing is a current limiting resistor before the capacitor.


so now you need a resistor in series with the capacitor board to minimize in-rush current when you power up the track and a current limiting resistor in series with the LEDs, just like the on in series with the LED on the capacitor board



sachsr1 said:


> The voltage coming out a DCC decoder is constant, and the bulb gets dimmer if you put in a bigger resistor.


but some decoders (TSC T1) have the ability to dim the LEDs (they drive the output with PWM).


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## Tom_C (Jan 8, 2016)

gregc said:


> isn't this DCC?


I thought someone mentioned using it on DC also, but maybe I didn't read it correctly. In any case, having a full bridge would let you run it on any track, but if building it to only run on your own DCC track and never intend to sell/trade then it should be fine with a single diode.


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## sachsr1 (Mar 3, 2016)

> so now you need a resistor in series with the capacitor board to minimize in-rush current when you power up the track and a current limiting resistor in series with the LEDs, just like the on in series with the LED on the capacitor board


Something small like 100ohm 1/4watt?


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## sachsr1 (Mar 3, 2016)

So at $1 each these will actually be a better fit?
https://www.ebay.com/itm/3W-LED-Dri...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

It's hard to tell from the photos in the description if there's in-rush limiting resistor on this circuit.

Nevermind!!!!
These would be better since they can take more that 12v AC 
https://www.ebay.com/itm/High-Power...ly-DC12-24V-/201705815956?hash=item2ef69a7f94


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## gregc (Apr 25, 2015)

sachsr1 said:


> Something small like 100ohm 1/4watt?


think about this. If DCC is ~15V, then the initial current will be 150 ma. if you have 5 of these on your layout, there's an initial surge of 0.75 A that quickly diminishes. is this enough to trip any protection.

i just have a PowerCab and a 2nd cab. I don't believe it can supply even 1A w/o shutting down. But I use a lamp to limit current and prevent shutdown. A lamp is another way of dealing with in-rush current.


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## mikek (Dec 29, 2013)

Since the polarity reverses on my DC track, I have to use a bridge rectifier, a resistor for led protection, and the biggest cap I can fit into the car. A big cap will carry the light over breaks in current from track irregularities, and maybe I don't need so many pickups. Led strips are great, mine have resistors built in. Easy to mount, nice spread on the illumination.


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## Waddy (Dec 18, 2014)

All my passenger cars are LED.

I use a full bridge rectifier with a choke on both the positive and negative inputs. A capacitor and 1k ohm resistor with LED light strips. 

Power to the track is an 18v brick. The output to the LED's (1K ohm resistor) is 8.75 v. The LED's are bright but not too bright.

I also mount a small single pole on/off switch under the car so I can turn off the LED's when I want.

(One one set of cars I also mounted a small dimmer switch but realized I didn't really need it.)

I like building my own set-up so that I can easily change out components for whatever reason. 

BTW; I really like 24 gauge stranded SILICON coated wire for these installs. And work in general. The wire is extremely limp and easy to work with. I can strip the coating with a thumbnail for soldering. It is also more wear resistant than plastic and takes heat to 600 degrees. So it (silicone wire coating) doesn't melt even if you solder right up to it.


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