RailPro > RailPro Specific Help & Discussion
Speaker Wiring
Stephen K:
So I failed to mention, for clarity, the front light is LED but the rear light is incandescent. Don't know, it's Just the way the loco came. The LM wiring diagram Alan posted is for LED and there is another similar diagram for non-LED. Basically the only difference between these 2 diagrams is the insertion of the resistors on the LED lights.
So I wired the rear incandescent light to the yellow lead with no resistor. Wired the front LED to the white lead with resistor. Connected both to the blue lead.
Alan:
--- Quote from: G8B4Life on March 26, 2020, 10:45:47 AM ---
--- Quote from: nodcc4me on March 26, 2020, 09:53:13 AM ---If you place the resistor in the blue wire I believe you can get away with just one.
--- End quote ---
I would strongly advise against that. While it's possible to do because the resistor can indeed go on either the positive (blue wire) or the function ground wires (white, yellow, green or violet) if you put only one resistor on the blue wire instead of a resistor on each of the ground wires you would have to make sure you only used one output at a time; ever. Failure to do that would quickly result in the destruction of the resistor and the LED's being powered at the time, and possibly damage the LM too.
Alan could explain the "how and why" behind the destruction better if he'd like, I forget all the proper calculations to show it.
- Tim
--- End quote ---
Death and destruction is not quite right. A resistor in the blue wire will limit the total current that can flow irrespective of the number of outputs active at any given time. Each LED would get dimmer (non-uniformly) as more outputs are made active and their respective LEDs light.
Think of it this way: Imagine each LED as simply a zero resistance wire. The resistor determines how much current will flow in the wire. Adding more wires in parallel to the first wire doesn't make the electrical path any less resistive hence no increase in current flow. Just less current flowing through each individual wire.
Ultimately you are still correct, single resistor in the blue wire is a bad bad idea.
G8B4Life:
Not to take this too far off topic...
Hmm, ok it seems like there is something wrong in my electronics theory there, which wouldn't be a surprise at that time morning (3am); or at all :-[ . It looks like my reasoning that in parallel each LED would try to draw ~10ma (~14v - LED drop (3.5v) / 1000 = ~10mA) is false. If it were true and each did draw that amount then the 1000 ohm resistor would be trying to dissipate nearly 4 watts, way to much for a 1/4 watt resistor hence the frying, however a circuit simulation supports what you said Alan. I'll post the simulator later (appears to be a handy web based tool); I'm going to bed now, it's almost 04:30 and I'm making a lot of spelling mistakes as I type!
- Tim
Alan:
--- Quote from: G8B4Life on March 26, 2020, 12:20:46 PM ---Not to take this too far off topic...
Hmm, ok it seems like there is something wrong in my electronics theory there, which wouldn't be a surprise at that time morning (3am); or at all :-[ . It looks like my reasoning that in parallel each LED would try to draw ~10ma (~14v - LED drop (3.5v) / 1000 = ~10mA) is false. If it were true and each did draw that amount then the 1000 ohm resistor would be trying to dissipate nearly 4 watts, way to much for a 1/4 watt resistor hence the frying, however a circuit simulation supports what you said Alan. I'll post the simulator later (appears to be a handy web based tool); I'm going to bed now, it's almost 04:30 and I'm making a lot of spelling mistakes as I type!
- Tim
--- End quote ---
Tim, I love that you reason through the problem.
However, it appears one of your fundamental assumptions is flawed. No component "draws current" even though that is the common lingo. There is no suction, vacuum, or otherwise negative pulling force. Rather, components "flow" what is available to them.
How's this for an analogy... a bucket full of water has a 1" hole in the bottom that drains into another bucket below. Does adding more buckets below for the water to drain into increase the rate of water leaving the upper bucket?
As the resistor (hole in top bucket) is setting the total flow, adding components (buckets below) simply divides that flow across each of the components. The total current (volume of water) doesn't change. Each lower bucket simply gets a percentage of the available water. Hence why LEDs get dimmer as you add more of them when flow control (resistor/hole) is on the supply line (blue wire/top bucket).
Alan:
--- Quote from: Stephen K on March 26, 2020, 11:06:54 AM ---So I wired the rear incandescent light to the yellow lead with no resistor. Wired the front LED to the white lead with resistor. Connected both to the blue lead.
--- End quote ---
That should work.
HC button assignments?
Bulb and LED known to be good?
Solder / plug connections known to be good?
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