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I can find 12v warm white LED strips on Ebay, but I am running conventional, so need 3 - 6 volt LED strips which will light using my 1033 PW transformer when I crack it on.  Aren't the 12v strips for DCS or TMCC  where there is contant voltage on the track?   Or perhaps I need to use single LED's that light up at a low voltage ??  I already know how to build the circuit using a bridge rectifier, capacitor, and resistor.   Any advice appreciated.                                

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I have used gunrunnerjohn's constant current driver with a CL2 on the roll strips that break off in sections of 3 leds. I just tested a caboose with only 3 and it lights at 6.6 volts ac track voltage. Fluke true rms meter.

Anyway, it's all about your driver circuit. the leds raw will light at 2.3 - 3.4 depending on the color. It's the driver circuitry converting the AC and controlling the voltage or current that uses the rest.

The 20110 LED Regulator was really designed with command operation and constant voltage in mind.  I like the module Stan shows for conventional operation.  Had I known then what I know now, I might have attempted to do a fancier module with the capability of operating over a wide range of voltages.  I think that ship has sailed at this point.  It would probably be a larger module than the one I came up with, but of course it would also be more capable.

I just finished my sixth car with John's module. Took about 20 minutes. I just take bulbs out and tie in to pickup wires in case the next owner wants  to use bulbs. Tucked the module in the vestibule with rubber cement. I added a two pin connector so the roof can be disconnected.  To John. IMG_1260IMG_1257IMG_1256IMG_1255


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This topic has rekindled my desire to convert some of my passenger cars to LED lighting. 

I found the following modules on Amazon for $12.98.

]WGCD 10pcs Mini 360 DC to DC Buck Converter Step Down Module 4.75V-23V to 1V-17V       

  • The input voltage: 4.75 V - 23 V
  • The output voltage: 1.0 V - 17 V
  • The output current: 3 A (Max)
  • Conversion efficiency: 96% (maximum)
  • Switching frequency: 340 KHZ


I realize I need to add a rectifier and capacitor for AC current input.  Does anyone know a reason not to use these units?

Last edited by GregM

Those modules only handle 23V DC maximum, rectified 18V track power will usually exceed that, something to keep in mind.  I use similar modules that have a 28VDC maximum in a little P/S module I created.  You'll need at least a rectifier and a filter cap, and for DCS compatibility, the 22uh choke.  Here's The board I used and my module perched on top that  adds the choke, bridge, and filter caps.  Note the hole in the upper PCB to allow for voltage adjustment.

This is the schematic for the module.  I have a jumper option to use full-wave or half-wave rectification.  That's useful as most TMCC stuff has a common AC and DC ground.  If I use this in a TMCC environment where I want the DC to have a common ground, I use the half-wave feature.  If I don't mind the DC requiring total isolation, I use the more efficient full-wave feature.

John H posted:

I have a good reason right here. $18 gets you two modules and the only thing to add is a light strip. That was my point in my post. I think it's a pretty good deal.

 In Greg's defense, he's talking about ten of the modules for that price. Of course, you do have to add the other components to make a complete solution.


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Last edited by gunrunnerjohn

GRJ, thank you for the information you provided above.  It has been a long time since l did electronic "stuff."  A couple questions if you don't mind, what is the reason for "common ground" setting with LED lights?  Also would adding a resistor between the unregulated DC and the module be sufficient to prevent voltage overload?


The reason for my option was as I stated, sometimes I need a common AC and DC ground.  Other times, such as my passenger car lighting module, I don't have that requirement and I use a bridge rectifier.

The resistor is probably not going to do the trick.  You can buy the proper 28V rated module for the same price on eBay, that's the way I'd go. 

You could use some back to back 5V Zener diodes to drop the voltage a bit for each module.  A kludge, but it works.  You still need the other components, rectifier and capacitor, also the choke if you use DCS.

If you're going to get into soldering components together, you can probable roll your own easier than using the modules.  For low currents for LED lighting, constant current is the way to go.  You can tune the brightness by varying the resistor value.  This is basically how my lighting modules work.

Constant Current LED Passenger Car Lights


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Last edited by gunrunnerjohn

I go with 35V capacitors, they've always been sufficient.  The voltages on 18 volts end up being in the 26 volt range on the capacitor.  25V capacitors would probably fail pretty quickly with that voltage.  The circuit above is good for around 50ma without any heatsink, if you're driving 12V lighting strips with an 18V AC power supply, that results in .8 watts power dissipation in the LM317.  It'll get around 70C or so, but within it's operating ratings.  If you want more current, add a heatsink to the TO220 regulator package.

If you haven't yet placed your DigiKey order consider a 40 cent trimpot to adjust brightness.

In place of a fixed-value R1 in GRJ's diagram above you could use, say, a 27 ohm resistor in series with a 200 ohm trimpot to give an adjustable R1 range of 27 to 227 Ohms.  This would give a current range of about 5 mA to 45 mA.  This adjustment method is discussed/documented in one of GRJ's previous posts.

I realize you're not doing eBay but for anyone contemplating a roll-your-own you can get 200 ohm trimpots on eBay for about 10 cents each shipped.

200 ohm trimpots for 10 cents each


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Last edited by stan2004

Hi all - I did this conversion to my Polar Express but something seems amiss (don't want to hijack the thread): I don't have constant brightness (it still varies with power applied), and now there are tiny sparks/crackling where the wheels meet the rails when it rolls.  There's a very small hum too, changing pitch depending on power applied and whether or not the light strip is attached to the Buck (no strip = no hum).

I used these components:  Buck Converter,  Light string (3528)Bridge Rectifier, 220uf capacitor.  Piece of cake to solder up.  I removed both bulb sockets in there and ran the incoming power wires to one "~" of the bridge and the incoming black wires to the other "~".   "+" and "-" out to the Buck.  The power wires have a stripe on them (at least one does) and initially attached to the red wires of both sockets, opposite for the black wires.

The light string for the car lights up so I know the AC-DC conversion is happening.  Could something be improperly grounded or crossed (I don't see how, but...)?  Are my components wrong?  What should I check?

Thanks much

I believe I have the PCB matching the schematic, PCB layout passed all of KiCad's checks.  I just don't know if I left enough room around the components (using through hole for now) to be able to actually populate the board.  I think so, but we will see in a couple weeks or so.  I reworked the PCB a couple of times to get its dimensions under 1 inch by 2 inches.


1" x 2"?  Why was it so big?  That seems pretty large for those few components!  I would guess you have plenty of clearance for the parts with that much real-estate!  My Super-Chuffer is only 1" x .9", it has a ton of components.

Maybe we can help you get the size down, it also makes the boards a lot cheaper.


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Greg did say he's using a through-hole component design...a wise first step.  The components in his version would be about 50 cents per board in small quantities on eBay.  So even if the extra square inch increases board cost, in DIY quantities it might be a wash if eBay from Asia is an option.  Then there's the assembly and handling hassles of surface-mount parts which require the dexterity and eyesight of a teenager.  


Edited to clarify board dimensions.

This is the very first PCB I have ever had produced for me.  I only ordered three boards this go around for prototyping.  I hope I get better as I go along but for this time I was content when I got the board under two inches long, first layout was about 2.25 inches long.  Decreasing the board length did bring the cost down from my first attempt.  I really don't intend to produce that many boards in the long run, but if eventually these boards help others that would be nice.


P.S.  I never had the eyesight of a teenager when I was a teenager, let alone now.



Last edited by GregM

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