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Date: 08/08/19 10:39
Correct Resistors
Author: SD608708

I plan to use two(2) 1.5 V bulbs wired to one output and a common for a headlight, which resistor should I use?

Paul B
Canton, GA



Date: 08/08/19 11:10
Re: Correct Resistors
Author: PHall

Need a few more things to answer the question.
Are the bulbs wired in series or parallel? What's the voltage this is operating on? i.e. 12 volts, 14 volts...



Date: 08/08/19 11:47
Re: Correct Resistors
Author: ESPEE5318

and MA of bulbs



Date: 08/08/19 16:18
Re: Correct Resistors
Author: ChrisCampi

PHall Wrote:
-------------------------------------------------------
> Need a few more things to answer the question.
> Are the bulbs wired in series or parallel? What's
> the voltage this is operating on? i.e. 12 volts,
> 14 volts...

And wired to what? Is this DC or DCC? I DCC, what decoder are you using? If an Athearn unit your most likely already set up for 1.5v lighting.



Date: 08/08/19 18:39
Re: Correct Resistors
Author: funnelfan

Unfortunately 1.5v microbulbs can be hard to figure out. You need to know the input voltage and the current draw of the bulbs. The resistors generally fall into a range between 400~800 ohms. I bought a small potentiometer (adjustable resistor) that had a range of 0~1000 ohms. I set it to 1000 ohms and hook it up in line with a bulb and attach to the power source. By very slowly turning down the ohms until the bulb is at the correct brightness, then measuring the resistance of the potentiometer, I get the value I desire and round it up to the closest matching resistor.
You can calculate the resistor need to get the desired voltage drop using Ohm's Law;  Voltage / Current = Resistance. So 12.5v drop / 0.015amps = 833 ohms. But the actual results can vary from the calculations.

Ted Curphey
Cheney, WA



Edited 1 time(s). Last edit at 08/08/19 18:41 by funnelfan.



Date: 08/09/19 15:56
Re: Correct Resistors
Author: SD608708

The bulbs are wired in series if that helps figure out the correct resistor.

Paul B
Canton, GA



Date: 08/12/19 15:19
Re: Correct Resistors
Author: SPED

Paul,

I now use a Soundtraxx 810159 JST-21PNEM Adapter with a TCS (1032)VR1.5 for 1.5 volt lamps. You never worry about resistors again.

Ed



Date: 08/12/19 17:32
Re: Correct Resistors
Author: SD608708

Thanks Ed.

Paul B
Canton, GA



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