little problem... need some help

[master_train]

I have a question for you and hope ou can help me here:
Im using DCC in my layout. now i know that the decoder light outputs is 12-16 volts and i have f7 genesis loc and his bulbs is 1.5 volts.
what can i do to solve this volts problem?

[grumpybob]

Who's decoder? Not sure whether it is digitrax or not, but you don't have to change the bulb. If it isn't, then:
first, as i did, change the bulb to a 12 volt bulb. or put in a resistor, and unfortunately i am not home to give you the value in line with the light wire.

[master_train]

Hey grumpybob, I dont want to change the bulbs, because thats special microbulbs and i cant find them in 12 volts.
so, if anyone know, or, have experience with that problem- i'll appreciate your advice.

[B_Kosanda]

Use 1/8 watt resistors in line with the bulb. I think mine are about 400 Ohms. Start with a higher value first to make sure you don't pop the bulb, say 1000 Ohms. Work your way down to the value that provides 1.5 volts across the bulb. If you don't have a voltmeter, this is a good excuse to buy one at Radio Shack. If not, just eyeball it.

Bill

[NHGuy]

It depends on what the track voltage is and what the current (milliamp) of the bulb is. My track voltage is 14.5 vac with a NCE Power Pro. I use 1/4 watt 820 ohm resistors with 1.5 v lamps at 15ma. If they are 30ma bulbs then you can go to a 1/2 watt/ 300 ohm resistor. If 40ma then you can go to a 1 watt/300ma resistor. The outputs of the head light outputs are rated at 40ma-100ma depending on the decoder model. So there is plenty of room to put any lamp(s) up to 100ma on that output.

LED's on the other hand require more resistance to work properly in which case you can use a 1/4 watt/1K resistor in line with the output. I put them on the output side to the anode of the LED. Those are the white and yellow wires. The blue wire being common.

Depending on the decoder they will recommend what works for thier decoders. So always follow the manufacturers specifications.

Generally, these are the ones that work fine for most decoders.

Bill S.

[OlsmilinEd]

It depends on what the track voltage is and what the current (milliamp) of the bulb is. My track voltage is 14.5 vac with a NCE Power Pro.
Bill S.

How did you measure that voltage? A volt meter will not give you an accurate reading. DCC puts a square wave on the rails and a volt meter is designed to give you the RMS voltage reading on a sine wave. I doubt the difference is enough to blow the bulbs in the example we're discussing here, but in some applications using a volt meter on a square wave can get you some way off base readings. Using a calibrate scope would be more accurate in a critical application.

Cheers

[rrinker]

The function outputs are rectified DC, so you can accurately measure the voltage being supplied to the functions. Blue is positive, any function lead is the negative.

With a 1.5v bulb, you don't have a huge amount of room for error - and you definitely need to know the current draw to determine resistor value and size. LEDs have a bit more leeway in safe current levels, and if you shoot for a middle level current limit - say the LED can safely handle 25ma, calculate for 10ma - the voltage across the track you get using the AC reading of a voltmeter is close enough - or you can use the manufacturer's spec for track voltage. Or better yet, if you are using white, sunny white, or golden white LEDs - the resistor is a 1k 1/4 watt, for anywhere from 12-20 volts on the track.

--Randy