Niles Project ~ Resistification

Because LED's are diodes and don't behave like a resistor, a current limiting resistor is needed to prevent the current from exceeding the operating limits of the LED's.

Determining the size of resistor to use was simple enough. John McWhirter and I soldered the 4 LED's together in series. Then we attached a best guess resistor in series with them. Then we gave the circuit "the juice". 15 volts DC. We then carefully considered the results. If the lights were too bright for what I wanted, we would then replace the resistor with a" stronger" one. If the lights were too dim, then we replaced the resistor with a "lighter" one.

Actually, it was easier than I'm letting on because John has built a box with an array of resistors in it. A rotary switch switches from one resistor to another. So all we had to do really was connect our LED assembly to it and with a simple flip of the switch, find the the setting that gave me the illumination I was looking for.

Eventually we determined that a 1000 Ohm resistor (brown, black, red, gold bands) provided the right amount of juice to the 4 LED's to achieve reasonable illumination for the interior compartments of the trolley.

For the one headlight, we determined that a 15000 Ohm resistor works best (brown, green, orange, gold bands).

My next objective was to determine the most unobtrusive location to mount the resistors. I can't mount the resistors on the circuit board because they would interfere with the ability of the circuit boards to slip between the bulkheads and the ceiling. It would also be nice if the resistors weren't someplace visible through the windows. So this is where I got clever...

I need a jumper from the blue wire (lighting positive common) bus on the bottom of the circuit board to the LED leads on top of the circuit board. So why not have the resistor fill that bill? The leads to the resistors were bent so that one lead solders on top and the other lead solders on the bottom with the resistor itself on the front edge of the circuit board. Works for me. Yes sir! Works for me just fine!

Dandy

Niles Project ~ Interior Lighting Wiring Schematic

This is going to take a little planing.

Things are getting a little complicated:

• The decoder can't light 8 interior LEDs because of milliamp limitations. So the LEDs are going to be split between two functions of the decoder. Four LEDs on the purple wire, and four LEDs on the green wire.
• The LEDs have to be oriented correctly. Unlike incandescent bulbs, LEDs have a positive and negative side to them.
• The LEDs require resistors.
  
• The blue wire of the decoder is the common positive lead to all the interior lights and to both headlights.
• In attempt to keep things neat and tidy and serviceable, circuit board is being used as a mount for the interior lights, a bus for the headlights, and as a soldering pad for the decoder wires.

So after a lot of trail and error, I drew this schematic to help make things crystal clear:

Okay, so here is where we left off...

This shows the top and bottom of one of the two circuit boards (as it sits in the car). On the top, the copper cladding has been cut vertically to electrically isolate the LEDs so that they can be wired in series. On the bottom, the copper cladding has been cut horizontally. The top strip will be the bus for the blue wire, the bottom strip will be the bus for either the white or yellow headlights wire. The vertical cut provides a soldering pad for either the purple or green wire.

So that's the plan man. Time to put the plan into action. Yes sir! Put this plan to action!

Dandy

Birney Project ~ Installing the Decoder

"You've got too many damn lights in that thing!" George Huckaby.

I may have blown out all my lights, but the Southern California Traction Club has blown out entire decoders trying to get these things to work properly in trolleys running under live overhead! As a grateful benefactor of the trials and tribulations that the SCTC went through, I drew the following schematic based on the findings of the club (clicky to make biggy) :

This schematic illustrates how the TCS M1 decoder is to be wired in my model of SDERy Birney #301. The model has 10 (yes 10!) incandescent light bulbs in it, five of which would be lit at any one time (If I had to do it again, I would rather use LEDs in conjunction with fiber optics). The schematic also includes the necessary resistor that was so agonizingly missed the first time. I have the choice of having one 1 watt 100 ohm resistor* on the white wire and another on the yellow wire. Or one big 2 watt 100 ohm resistor* on the blue wire. Considering how big the resistors are (they are bigger than the decoder!) and how hot they get (and they get hot!), I decided to go with the one big resistor. BUT! That means not all the lights can be lit at the same time! Or else "poof"! Out go the lights yet again! That's a disaster waiting to happen, I'm going to have to be damn careful. Yes sir, Damn careful.
* Note: The value of the resistors were determined by some of the club members using wizardry and gadgetry that I'm not familiar with.
Bonus! Check out the March 2010 issue of Model Railroader for a resistor selector device on page 26.

First, the decoder is mounted to a piece of 3M 4011 Double-sided Mounting Tape, which in turn is mounted to the ceiling of the model.

Then comes the surgery. Two wires from 10 bulbs = 20 wires, plus 7 from the decoder, plus two from the motor, and two from the connector. Let's see, that's... 31 wires that all have to make specific connections with each other and the resistor, all in an itty bitty living space!

In this photo, we're looking through the cutout in the floor to the cutout in the subroof. I'm trying to keep the decoder (which also gets hot) as far away from the hot resistor as possible. So the decoder(right) is mounted to the roof through the subroof cutout. On the left side of the cutout I mounted a weight (simply for better running). The resistor (left) is glued half on the subroof and half on the weight. Hopefully this will help dissipate all that heat. There is officially no more room for anything else in this model!

Everything tucked up into the ceiling pretty nicely, preserving the seethroughableness of the car, even at this low angle. Good enough for me. Next stop will be the programing track to program the decoder. Then I'll officially take my place among the ranks of DCC-ers. Yes sir! I'm getting with the program!

Dandy

Birney Project ~ Boom! Boom! Out go the lights!

Dammit! My worst fear has come to pass. I blew out all the light bulbs. F!

Deciding to take the plunge into the world of DCC, I managed to blow out all 10 light bulbs. I thought it was going to be a simple matter of replacing the Utah Pacific Constant Lighting Unit with a decoder. But no. Apparently a resistor is needed between the bulbs and decoder. The total rating of the bulbs have to be under 100 millowatts and how bright the lights shine depends on the resistor. The size resistor needed can be determined from the website of the manufacturer of the decoder, but not on the instructions that come with the decoder. I didn't know that so... pffft! Blown bulbs.

This disaster blew the wind out of my sails. I focused on other aspects of life for a while. Then, after a sufficient time of pouting, I'm back. Birney has been disassembled, blown bulbs ripped out, and new bulbs installed.

Sorry about the lack of posts for a while, but I'm back on track now. Yes sir! Back on track!

Dandy