LM2S output

[Josephbw]

Does anyone know offhand what the voltage output is for the light controls from the loco module?
Thanks, Joe

[KPack]

Don't quote me on this but I think it's 12V.  I haven't measured with a multimeter so I can't confirm.  Should be fine to use with typical 12V bulbs, but needs resistors for LED's.  I use LED's only and use 1K ohm 1/4 watt resistors. 

-Kevin

[nodcc4me]

The PWR-75 puts out 12v to the track. Older DC locomotives use incandescent bulbs that use track voltage directly. I would think the LMs would have to output 12v to keep them at the prescribed brightness, but I have not taken an actual measurement.

[KPack]

Al - the PWR 75/56 supplies output 14.2 volts to the track, not 12.  That would be too high for bulbs I think, so I'm assuming that the modules step it down to 12 volts before it gets to the light outputs and motor.

-Kevin

[hirailer]

My LM2S light output measured 10.6V with the forward LED's on.

Mel

[G8B4Life]

The function output voltage is about half a volt less than track voltage, so at 14.5v (PWR-56, PWR-75 etc) track voltage the function output voltage is about 14.0v. At 12v track voltage the output would be about 11.5 volts.

Given Mel's example, 10.6v with the LED on, add about 3.5v that the LED drops the voltage by and that comes out to about 14v, which is the same as I measured the bares wires at.

Now an equally important question is whats the current rating for the function outputs?

- Tim

[William Brillinger]

Here is what Tim Ring has to say...

I asked: What is the output voltage and current capacity for the light functions on the LM2's ?

Tim's Reply: The voltage on the blue wire is basically track voltage and the outputs sink current (i.e. they do not output voltage).  This is the DCC specification for outputs.  The LM-2 can output 200mA on any one output and the total of all outputs simultaneously on can not exceed 200mA.  There is an inrush limit that will likely limit you to about 4 incandescent lights coming on at the same time.  If you attempt to draw too much power the outputs will turn off and display a output short message on the handheld.

[nodcc4me]

Al - the PWR 75/56 supplies output 14.2 volts to the track, not 12.  That would be too high for bulbs I think, so I'm assuming that the modules step it down to 12 volts before it gets to the light outputs and motor.

-Kevin

Kevin, as you stated, Ring publishes the rated output of the PWR-75 at 14.2v. I measured my track voltage at a feed and got 12v on my analog meter, which I have found to be pretty accurate. The buss and feeds are heavier than required. There were 15 locomotives on the rails but none running.

Have you taken an actual voltage measurement on the track? I am wondering why my measurement was so low.

[Josephbw]

Thanks a lot guys. I have a BLI loco that I had to remove their decoder and replace with a LM2S. Their front light board had a 151 ohm SMD resistor on it, and I had to know what the RP output was to determine if I could incorporate that or if I had to add to it or replace it. I wound up replacing the resistor with a 1K 1/6W resistor.

Apparently BLI has a different output for their lights, hence the different resistor. It's all back together now and all is well.

Thanks again,Joe

[llxlocomotives]

Did you measure the output from the power supply terminals and the wire where it connects to the track as well as on the track.  I would try it with out an engine running and also with an engine running.  No load and with load. 

In a similar test with a bench DC supply, when it shows 12 volts, the track shows 11.7 volts consistently. 

I am courious about the voltage to the motor at this condition as well.  In some recent tests with DCC modules the motor is indicating one to two volts loss(less).  Is the Railpro module the same, less or more?  Does the number of functions matter?  Especially sound in the same overall circuit. 

Larry
llxlocomotives.com