LED's / RESISTORS

[Truck]

Hi Guys,

I was wondering about using 1/6 watt 1k ohm resistors for led's. I know pretty much everyone is using 1/4 or 1/2 watt resistors.  So my question is would it matter much to use a 1/6 watt resistor? 

I beleive there is not that much wattage being used. But some of you guys know more about this than I do, so thats why I am asking.  Thanks in advance,

                                                                        Truck. 

[locoi1sa]

Truck.

 One of the reasons I use LEDs for the lighting is the heat build up. A 1/6 watt resistor will get quite hot. The larger the resistor the more heat it will absorb.

       Pete

[rrinker]

 You have to figure the actual power, in watts. I^2 * R will give the wattage the resistor will need to dissipate.

 For a white LED on typical DCC track voltage, a 1K resistor results in just under 10ma through the LED. So .010 x .010 x 1000 = .1 watt.. 1/8 watt is .125 so you could go to even a 1/8 watt resistor and not melt it. 1/6 watt resistors aren;t as common, but since that's .167W, that's also OK. The general difference is size. 1/4 watt is very commn and they aren;t that big, so unless you are absolutely cramped for space, the 1/4 size is fine. The 1/8 watt isn;t that much smaller and if you are using  3mm LED the LED will still be bigger than even the 1/4 watt resistor.

                            --Randy

[Truck]

Thanks , Randy & Pete

 I was curious besause I saw an auction for the 1/6 watters on ebay, I think it was like around $4 for a hundred of them.  I was impressed at how small they were.

I model N & HO scale and add as many light functions as I can. You can imagine at one resister per led if you start adding ditch lights front and rear plus mars light that would be 5 resistors in an N scale that takes up some space. 

But heat disipation is also a factor. I may get some surface mount resistors and see how I fair with them.

What do ya think?

                                              Truck.

[locoi1sa]

Truck.

 I have absolutely no experience with surface mount resistors. I can tell you I had put 2 decoders and headlights, front and rear ditch lights, roof beacon, and number board lights in an old SD45 for a friend. I used a TCS T6 and FL4. The ditch lights and num boards were SM LEDs but everything else was 3 mm sunny whites and one amber for the beacon. The SM LEDs already had the magnet wire soldered on. I used copper foil tape for the blue wire buss bars stuck to styrene strips. The function wires have 1/4 watt 1K resistors.  I will never do it again.

     Pete

[BroadwayLion]

I use 1/4 watt resistors because that is what my distributor sells on the cheap. I can buy 1000 for $10.00. 1/8 watt resistors would cost $35.00 and do not come in the size I want.