Re: Resistors

Marcus Ammann

Hi Steve

Knowing the voltage applied to an Incandescent Lamp is critical for the
lamp's brilliance. A small variation in voltage with a 1.5 Volt lamp can
lead to a large variation in the Incandescent lamp's brilliance.

Conventional Multimeters cannot accurately measure DCC voltages and the
decoder's internal electronics (Diodes etc) further drop the voltage, so
using the DCC track voltage when determining the "voltage dropping" resistor
value, is not suitable.

The voltage inside the decoder DC applied to the Lamps, Motor etc, is DC.

Measure this DC Voltage using your Multimeter on "DC Volts" with the
Multimeter "Plus" connected to Function Common and the Multimeter "Minus"
connected to a Function Output. Don't forget to select the Output
(Function), ON.

See the Topic "If you still want to use Incandescent Lamps." in the article
below, to determine the resistor value etc, at:


-----Original Message-----
From: WiringForDCC@... [mailto:WiringForDCC@...] On
Behalf Of wirefordcc
Sent: Monday, 21 January 2013 3:27 AM
To: WiringForDCC@...
Subject: [WiringForDCC] Re: Resistors


If you are using a typical volt meter, then the readings you get when you
try to measure DCC track voltage will be high. That is why you measure
16.9V. This is because the typical voltmeter is calibrated to read
sinusoidal AC like that comes out of the wall.

DCC is square-wave AC. If you want to measure it accurately, you can build
a simple circuit that you can use with your voltmeter. Visit my website for
the circuit:

Or you can buy DCC volt/ampmeter. It's about $54 from places like Traintek:

Or you can assume you have a typical voltage on your track of about 14.5V.
Using the equation on my website at:

I compute that you need 867 ohms. 867 is not a standard value. Radio Shack
sells 1,000 ohm, 1/4 watt resistors that you can use. p/n 271-1321. 910
ohm is a standard value and is closer to 867. It is Radio Shack p/n
55049170. You can put two 1.8K resistors in parallel to get 900, Radio
Shack p/n 55049411.

If you track voltage is a little less that 14.5, you can use a 820 ohm, 1/4
W resistor, Radio Shack p/n 55049392.

Wiring For DCC

--- In WiringForDCC@..., "Steve" wrote:

I have a NCE system and took a measurement and at the track its 16.9 volts
AC. The transformer says 15v but its 16.9v. I am installing a TSU 1000 from
soundtraxx in my K-27's and K-28's and a TSU750 in my PSC Geese. What
resister do I need for the 1.5v 15ma light bulbs? Thanks in advance, Steve


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