HOW TO--COACH LIGHTING.

[Ironduke]

Irondukes' comments about LED's not turning on if below 15.4 volts ( for 7 of in series) - well I run LED's that are nominal 2.2 volts at about 1.5v & they work OK - current is down a bit as I use a higher value resistor - makes them last longer; it also protects them if the mains power spikes a bit & increases the LED voltage. The amount of light from the LED is still suitable for normal use.

Hi Sol,

this is a list of LED forward voltages:

White and warm white: 3.2 to 3.8 volts
Blue (up to 480nm or so): 3.2 to 3.8 volts
Green and aqua (up to 530nm): 3.0 to 3.8 volts
Green and yellow-green (up to 570nm or so): 2 to 2.4 volts
Red, amber and yellow (up to 660nm or so): 1.8 to 2.4 volts
Infrared: 1.4 to 2 volts
UV: 3.2 to 4 volts
(source: www.ledsales.com.au )

Although admittedly my contention is based on theory. a LED has a voltage drop the same as a diode and until you reach that voltage no current will flow. Where did you get the 1.5V?

[sol]

Rob. as an example, a LED with a forward voltage of 2v & 20mA working from 12v needs a 560 ohm resistor but I have used upto 3000 ohms for blue LED & they still light OK even though the voltage across the LED is lower than the 2v. On my normal red/green LED's with a 10v source, I use 820 ohms & have measured the voltage & it varies from 1.5 to about 1.8v. I even spoke to Richard Johnson of DCCconcepts when I tested & used his Masterswitch units in that he supplied LEDs & 560 ohm resistors & he did agree that ,that is the minimum & they could be higher & would increase them to either 820 or 1K in future packaging.
The nominal value gives optimum light but we do not need that to be able to use them so by increasing the resistance thus lowering the voltgae gives a small bit of protection.

Regards
Ron

[sol]

I have done some further testing using a LED nominal voltage of 2.1 with 30mA.

My supply of 10.98v - using a 820 ohm resistor gives 11 mA & 1.9v across the LED & with a resistor of 2000 ohms, a current of 4.6mA & voltage of 1.7v & in both cases, the LED is lit enough for normal useage.

regards

[waz]

Hi Chaps !!!!!!

Just dropped in to say hello and glad some of you liked the article and that it may have been some use to you.
Sorry I haven't been here for some while but I had forgotten all about it.
There have been some interesting discussions amongst some of you which gives me the satifaction of knowing that at least it stimulated your thoughts and ideas.
I can't get into voltages and the number of which type of bulbs will work because I know little about these mystical things and the sorcery involved. That's why I took my own approach of keep it simple.
I can say that the last two coaches I did do have two G of W. bulbs in and work a treat.
If you have an idea for whatever type of bulb or bulbs to fit might I suggest that you try whatever. If it works, okay, if not, back to the drawing board and try again ( suck it and see).
Anyway, thanks for reading the article and I hope it was of use to some of you.
BTW. My lights still shine clear and bright without any problems.

My Very Best Regards to You All

BILL.

[RAF]

Hi, I was thinking about the possiblilty of using a grain of wheat bulb in the cab of a diesel loco using the method as described in the first post...

Would there be any problem in taking the power from the existing pickups of the locomotive by splitting the wire to the motor, or would this draw power from the motor???

[sishades]

You can do the above. I use LEDs in my locos as they do not give off any heat.

[pete12345]

The motor and bulb would just be in parallel. The result is that the loco will draw slightly more current from the controller. If you used an LED the cab light would only be on in one direction unless you used a bipolar LED.

[RAF]

The motor and bulb would just be in parallel. The result is that the loco will draw slightly more current from the controller. If you used an LED the cab light would only be on in one direction unless you used a bipolar LED.

well I was going to be clever in that I was going to have one LED wired one way in the front, and another wired the other way for the back, so that when you reversed the polarity and the train changed direction, the other cab would light.

I decided this was a waste of time though at the moment since I have no resisters to bring the current down, so when the 16V current goes through the LED it will just pop. And since thisi loco tends to only go in one direction I figured a grain of rice bulb would do the job well enough just in the front cab. What I'm thinking of using is gluing a very small choc to the inside of the roof and screwing the bulb into the choc, that way it will be away from any plastic and will be insulated. Also I have drilled two tiny holes where the lights of the loco where so the light shines through there too, but also provides a little ventilation.
Thanks for the help.