Question from a lighting novice on the TOS lighting kit

[rkoenn]

I am lighting my first model and using the PL lighting kit for the 1/350 TOS Enterprise. The kit obviously makes things relatively simple but I have either fried 2 LEDs or they were bad OOB. So what I was wondering is after checking the output on the bus boards all of them appear to be running at the transformer voltage of 12+ V. I do not see any resistors in any of the LED individual light strings so was wondering what type of replacement LED do I need to repair this problem. One is a small LED for the impulse engines and the other is the main body flashing standalone LED. Any help with this would be greatly appreciated. I suppose I could call my son who is an electrical engineer but presume the experts here will probably know the answer to my question right off. Thanks in advance. I'm stuck doing some of the subassemblies because of this.

[rkoenn]

I have ascertained one final bit of information though. The flashing LED in the main hull is actually on a separate output, which supplies the flashing capability, and is outputting 5V instead of the 12V+ that the other outputs are at. I know most LEDs operate at 5V so I can replace that one with a standard LED. But I am still trying to figure out what replacement LEDs I need to light the impulse engines, there are two at the rear of the saucer.

[rkoenn]

For anyone who is interested I believe this is the story. A standard LED, as most know, typically runs on very low voltage, 2-5V. But LEDs are available that have built in resistors for 12V applications. They aren't quite as easy to find but they are out there. I bought a low voltage LED sans resistor at Radio Shack today and it worked for the flashing main hull light replacement. So i must have plugged that one into a 12V receptacle while testing things. I still don't understand the impulse engine lights as they plug into a 12V receptacle so it doesn't make sense that they fried. I am going to try to pick up a couple of 12V LEDs for the impulse lights locally if I can. I learned somewhat more from this than just how to do my first lighting job!

[TREKKRIFFIC]

I made a quick refernce chart for my own use but you may find it useful too:

LED Resistor Values

Input Voltage Resistor (ohms)
Circuit Type Parallel Series
# of LEDS 1 2 3 4

6V 150 1 X X
9V 330 150 1 X
12V 470 330 150 1


So for two impulse engine LEDs running in series (LEDs connected together positive leg to negative leg) off 12V you would need a 330 ohm resistor. If you were to run them in parallel (each LED connected separately to power) each LED would need it's own 470 ohm resistor. The resistor goes on the short leg of the LED but you probably already know this.[/img]

[RossW]

I don't think it matters which leg the resistor is soldered to - it should work the same if on the long (+ve) or short (-ve) leg of the LED.

For the PL lighting kit, I think the light tape runs at 12V but the other lights run off the zener diode voltage splitter. Each white connector has a different purpose so it's imperative you connect the right light to the right connector.

[TREKKRIFFIC]

I don't think it matters which leg the resistor is soldered to - it should work the same if on the long (+ve) or short (-ve) leg of the LED.

You know, I've heard that, yet, my own experience has been when I've tried it with the resistor on the positive leg the LED doesn't light.

[Trek 1701]

Nice chart, Trekkeriffic. That's the one thing that initially stopped me when I started lighting up kits. Your chart makes it look so much easier.

Time for me to experiment. I'd rather not want to spend $100+ on a lighting kit.

[Ant]

It absolutely does not matter which side of the LED you put the resistor. If the LED is not lighting then there's something else wrong.

(+ve)-----WW---|>|-----(-ve)

is electrically eqivalent to

(+ve)-----|>|---WW-----(-ve)

(sorry about the ASCII art!)