The Pittsburgh Garden Railway Society sets up layouts at a number of community events and train shows each year. We have an assortment of buildings that sit along the track and I like to see lighting inside of them as it adds to the realism of the display. Options for powering the lighting for these buildings include running wires to each building from some central location or operating from batteries. I am not a big fan of either of these methods of getting power to the buildings. Since each building is quite close to the track and the track has power most if not all of the time, I decided to experiment with pickups that would feed power from the track to LEDs that would light the buildings.

Details on how the track pickup & circuitry are on my web page here:

http://trainelectronics.com/Articles/TrackPickupLEDs/

dave

Pretty cool Dave!

So this needs about what, 4 volts on the rails to light up?

Have you thought of also adding a nice large storage cap, inrush resistor/mov and an “anti-drainback” diode in the structure to keep the lights going when there is no track power?

What is the cost to print the housing? I guess it’s pennies if you have your own machine.

Regards, Greg

Greg -if you use a single LED or a group of LEDs in parallel they will light up a bit above their forward voltage as the bridge rectifier drops the voltage around 1.4 volts. If you wire LEDs in series (my preferred method with this type of circuit) you need to have sufficient voltage to equal all forward voltages added together - since we run about 12 volts on the track at a normal speed we can easily light 3 LEDs in series to full brightness.

Any caps (super caps, perhaps) would go in the buildings as I wanted to keep the track unit small enough to fit between a pair of ties. The only issue with super caps is the need for voltage regulation as they like to do bad things when fed more than their rated voltage!

Each unit weighs 8 grams - I pay about $32 for a kilogram of plastic — that comes to about $0.25 each - not likely to break the bank!

dave

My voltage estimate was based on having the CL2 in the circuit, although I have not measured the voltage drop across one…

Yes, in the building, that is why I said: "in the structure "… I did mean structure as house or building

This might be a nice product to offer by the way, or at least the track connector piece.

Regards, Greg

All those years I spent with Midwest RAILS: http://www.midwestrails.org We just hid transformers under the table and ran AC power cords under the layout. A whole bunch of 6ft heavy extension cords daisy chained together.

I’ve spent a few weeks helping “Sully” get his railroad ready for our “Tour.” The tour was yesterday. He runs 21v DC to the track and has a revolution in each loco. Since the track so handily distributes DC around the layout, I just connected to the split jaw rail clamps using a bridge and regulator wherever I wanted power. The bridge just so I didn’t have to worry about polarity.

Yep, DCC on my layout provides a constant 24v power source.

constant track power has a number of advantages

Greg

My LED power supply takes track current (either AC or DC) reduces it to a constant amperage and feeds it to any number of LEDs’ If you’ve got a neighborhood, one such power supply can be tied to the track (I just attach the power supply to nearby Hillman clamps), and run a bunch of LEDs in parallel (my preference).

Almost no draw on your power supply, and power available anywhere on your layout!

P.S. Dave B gave me good advice on using LED drivers. He can help you too!

How about making a few of those bars? I’d bet our club would buy about a dozen …

Dick - Let me do a bit more work on the design and some testing - once that is done I would be happy to print you some

I’ll drop you an email when I have that done.

thanks!

dave

Dick, if you were referencing me about using LED drivers or getting help, I think I may already have equal experience to Dave.

The first LED I used at work was at Hewlett Packard in 1976.

The first LEDs I used in a personal application was a digital clock made only from flip flops and decade counters in TTL, in 1974.

Of course I learned about them in college earlier than that.

I don’t remember how long I have been using the CL2 LED current supply, but I was using it when I heard about it on the forums.

I’m not shy nor arrogant about getting help, and asking questions, but I do understand this stuff.

Greg

p.s. running LEDs in parallel is not really the most efficient in most cases, in general you have way more voltage than current with most supplies. The distribution of current will also be uneven, probably not important in your case, but could lead to a lot of variation in intensity.

Gents - the other advantage of putting the LEDs in series with the current limiting IC is that each LED gets 20 mA so long as the voltage exceeds the sum of the forward voltages, which it does in my applications.

dave

As I indicated in my last sentence…

What’s the advantage of installing the LEDs in series vs. parallel using the CL2?

For instance, I’ve got my buildings wired for lights, using solar landscape light solar panels as a power source. My depots could have upwards of 6 LEDs just in that building alone, and in some cases, I’m running multiple buildings off of one feed. In my case, I’m powering them with solar landscape lights (approx 2.5v), so by default everything has to be parallel.

Could I not just use the output of one of these track clips to feed the power to the buildings with the LEDs in parallel? (All the LEDs in these installations are identical.)

Later,

K

Kevin - The short answer is that, for your solar application, there is no advantage putting your LEDs in series. They would not even work - to put them in series the voltage that is available has to be at least equal to the sum of the forward voltages - since you are supplying only 2.5 volts keep them in parallel!

As far as pulling track power using one of the track clips you would need to limit current using a resistor or the CL2N3. If your LEDs are in parallel they would SHARE the 20 mA supplied to the circuit by the IC making them dimmer than if you have LEDs in series where each would get 20 mA. Hope that makes sense!

For more info and a more in-depth explanation see:

http://www.trainelectronics.com/LED_Articles_2007/LED_104/index.htm

dave

“What’s the advantage of installing the LEDs in series vs. parallel using the CL2?”

As I stated before, normally you have a lot more voltage than current “available”.

With 12 volts, putting say 3 in series uses 20 milliamperes.

putting 3 leds in parallel would use 60 milliamperes.

Now, since you specifically asked using the CL2, if you put 3 in parallel with the CL2, then you are “wasting” the voltage in a way, and also splitting the 20 ma between 3 leds, which might not give you the brightness you wanted. Also, the variation in the LEDs could result in uneven brightness.

To summarize you can run 3 LEDs in series for 20 ma total, or 3 in parallel for 60 ma total.

Of course, you can come right back and say 6.66 milliamperes per LED worked fine. Maybe so. If you have a lot of leds, then you could use the CL2 in a creative manner to again use less power.

Basically the CL2 “wastes” all the voltage from the supply down to the LED array… the more voltage the LED array uses, the less is “wasted”

So, for a typical example, like lighting a train car, this can make a difference for an entire consist of lighted cars, the total amps drawn will be less.

In your case Kevin, having such a low voltage is not typical or even possibly feasible, and is not, of course a typical example.

Greg

Thanks, Dave. The solution in my case would be to keep the buildings wired in parallel as they are now. If I were to use a 12 volt supply instead of my solar arrays, then should one 20mA CL2 prove inadequate in providing enough current to illuminate the LEDs in the buildings at the desired brightness, I can simply add one or two additional CL2s in parallel to increase the available current.

Later,

K

Actually each CL2 should be used for a string (series) set of LEDs, LEDs like to run at 20 milliamps, and that’s what the CL2 provides. If you have a CL2 run LEDs in parallel, 2 parallel legs, with the same number of LEDS in each leg, would be supplied with around 10 milliampes of current. I am not sure they would even light up at that amount. 3 legs and each leg would be supplied with around 6.6 milliamps of current and they surely wouldn’t even light up at that level. In fact, one leg may light up dimly because one leg may not even get enough power to forward bias the diodes.

David, you should experiment with some LEDs, you would be surprised that many LEDs, while MOST are rated at 20 ma, they will have almost the same brightness at 10ma.

Also, wile experimenting, measure the voltage required… even though red leds are normally rated at about 2.7 volts, often they will illuminate at a much lower voltage.

I was “living” on datasheets for a while until a friend showed me a number of examples where LEDs worked at voltage and current levels much lower than the datasheet.

I have a loco with a small headlight that is really bright at 6 ma… could not believe it.

Regards, Greg

Greg, ok. I haven’t played around with LEDs beyond the “numbers”.