I'm installing an LED as a function output on a GP40-2. I ordered a TSU-1000 soundtraxx decoder and have everything wired up. When I press F6 to turn the LED on it doesn't work. The function on the sound decoder is rated at 14 volts and 100mA. I hooked up a volt meter to check and I have 14 volts at the function output. I tested the LED and at 14 volts it lights up. It is a 12 volt LED with a built in resistor at 20mA. When I test the circuit with everything hooked up correctly and polarity correct the voltage of the output drops to 2 volts. Any advice would be appreciated very much.
Mike
Let's start from the beginning. You say "everything wired up", do you have one of the leads to the green wire and the other lead to the blue?
What are you using for a command station?
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probbaly have the LED backwards. Blue or the common pad is the +, not -. The function lead or pad is the -.
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rrinker probbaly have the LED backwards. Blue or the common pad is the +, not -. The function lead or pad is the -.
That was my first thought, but why does the output voltage drop to 2 volts then? If the LED were backwards, there should be no current flow, and the output should remain at 14 volts.
I suspect the LED-resistor combination. It may be drawing too much current for the decoder. It works on a 14-volt power supply, becasue there's more power available. Can you measure the current flow with the power supply and with the decoder for us and give us that info?
This is when I really like having a bunch of short clip leads.
It takes an iron man to play with a toy iron horse.
20ma shouldn't be too much, but then, see also why I don;t like those "12V" LEDs. Ordinary LED and 1K resistor. SImple and it works for DCC function outputs.
I wonder if that 20ma is "rated" or "measured." I think the OP is doing everything right, but he may have a bad LED-resistor combination. I also prefer the simplicity of a separate LED and a 1K resistor.
I hope he measures and posts the draw. Those 12V LEDs should be designed to work with 12 -14Vdigital circuits. I question the 20mA for the resistor and LED(although it may be stated)???
It would also be nice to know what resistor value it has?
Richard
If nothing else seems to help, you could maybe double check the CVs to be sure the decoder is set so that F6 is set to do what you want it to. Tsunamis have a lot of options and can be pretty complicated. I know I wasn't able to get my Tsunamis to do exactly what I wanted until I got Decoder Pro.
Thanks for your help. I'm getting a 26mA draw. I think I'm just going to get a regular LED ad 1k resistor and try that. I have a feeling its the built in resistor of the LED thats giving me problems.
I tired the function with a 2.6 volt 28mA LED and 1K resistor. When i tired the function the LED works, but it seems dull. When I turned off the function, the LED was even duller but still lit. Could it be a CV value in the decoder I have to change?
To give numbers when the function is on I have
2.4 volts at function leads
1.6 volts at LED leads
1.126mA at LED leads
1.3192mA at function leads
When function is off I have
1.6 volts at LED lead with .529mA and the function leads are 1.8 volts and .649mA
Your use of the 12 Volt LED has possibly damaged the decoder's output. Try to wire it to a different colored wire, which will then use a different function number, and see if it works okay.
Yes, I'm afraid Cacole is right. Examine the plastic coating of the decoder carefully. You may see a small dark spot, the size of a pinhead which indicates a burned-out component on the decoder.
OK, I'm up for some learning. Obviously, some of you have installed more decoders than I have and several of you have indicated the problem could be the 12 volt light. How is this, if the tsunami manual says "12-16 volt lamps can be directly wired to the function outputs"?
I use Evan Designs LED lights that are rated for 7-19 volts and draw 20 milliamps and have no problems. I have only used them as forward and reverse lights and not in the Function 5 or Function 6.
I'm not looking to start an argument, but I would ike some knowledge now if I ever run into this problem as I have a loco I plan to install ditch lights.
Which ones are you using? The Universal ones, or the ones they list as "solid LEDs for battery"? The Universal ones are probably a problem - they have a rectifier and other circuitry in there, which is completely unecessary for using as the lights on a decoder. Withotu an actual schematic of what they put under that shrink tubing, I can;t say for sure if this would actually cuase a problem or just not work - but I suspect it is at least the source of the "LED never turns off" problem.
If you want ot use an LED and not bother with resistors, the ones they sell for battery power should work, they are listed as good for 6-12V, so they migh be pushign the LED a bit at full decoder voltage. Again they don;t specify the value of resistor used in there, but 6-12 volts is actually a large range of current through the LED. And again why it is much better just to get plain LEDs and add your own resistor.
I see the universal 'chip' LEDs say 7-19 volts - thsoe are the ones that contain a rectifier, not needed. Their closest option are the ones that say 9-12 volts, if looking for the really tiny ones liek that to use for citch lights. Even so, there's just not enough information given. All of their LEDs keep saying they draw 20ma. At which voltage? 20ma at 9V, would be 31ma at 12V. Or 20ma at 12V would be 13ma at 9V. If they really are wiring them so that the LED runs at 20ma, that's the amximum for most white LEDs, and over it for most of the small surface mount LEDs. And if that's an average, or at the lower voltage, runnign them near the maximum voltage is goign to be too much current for the LED to handle. Generally bad design practice to run the device at a maximum rating. As an example, the oft-repeated suggestion of a 1K resistor for a white LED connected to a decoder results in just under 10ma for most white LEDs. THey are still PLENTY bright, and run at less than half the maximum rating.
You always have constant voltage with DCC, so the design has to be different than for an LED to be used on a DC loco where hte voltage varies from 0-12 volts.
ANd looking at some of their other products, the lack of technical info is frustrating. That 4 to one power splitter they have - this would be GREAT for powering multiple UP5 panels - IF I knew what size those coax plugs are. If they are the 2.1mm size Digitrax uses - perfect. If not, it's useless for that purpose.
Ask for an education, and you get one! Now, not to hijack the thread, but....
Randy, I am using the Universal Solid LEDs http://www.modeltrainsoftware.com/bl-212.html. With all of the reading and attempted learing about decoders and lighting, the often repeated advice was to install a resistor for an LED. So, when I finally started installing decoders and LEDs, I thought I would just buy one light unit that had all that. They say the rectifier, capacitor and resistor are all built in.
Yes, they don't give very much electrical specifics, but I installed them and they worked. So I thought I was on the right track. So, you say I don't need that rectifier? I can cut it out and reduce some of the 10 inches of wiring in a 5 inch space?
Currently I am using the 3mm light for front and back, I was planning on using the 1.8mm for the ditch
Thanks
Well, I suspect the resistor is in that lump too, so you'd need to add a resistor back if you cut that out.
SO you can save these fancy ones with all the extra wire (didn;t htink about that, either - you need to find space for all that unecessary junk as well) fo thngs like building lights, and just get some ordinary white LEDs. And a few packs of 1K resistors. None of my install pictures shows it very well, but I cut off the LED lead to about 1/4", and the resistor lead likewise, then solder the together. Hardly takes any space. If you plan to install more than basic lights (all I ever need for my 50's era equipment), Ulrich has a really handy little board to hold the resistors.
http://www.ulrichmodels.biz/servlet/the-597/LED-Lighting-Resistor-Board/Detail
You can get this all ready to go with 1K resistors, it supports up to 6 functions, and has individual pads for each LED's connecion to the blue function wire - so you don;thave to try and splice 5 or 6 wires into the blue.
Ulrich also has plain LEDs, in sunny white (for more modern locos) and golden whire) for older locos) as well as 1K 1/8 watt resistors.
First of all, you are talking about a hardwired Tsunami, and not a board replacement one, right? The reason I ask is I believe some of the board replacement ones are pre-configured for 1.5 volt bulbs and some are pre-configured for LED's, so I want to make sure that isn't the case here.
traintown To give numbers when the function is on I have 2.4 volts at function leads 1.6 volts at LED leads 1.126mA at LED leads 1.3192mA at function leads When function is off I have 1.6 volts at LED lead with .529mA and the function leads are 1.8 volts and .649mA
There are two things in the above post that lead me to believe that you are not measuring the current draw correctly. First of all, the current is constant throughout a series circuit, so you should not be getting different values at different locations. Second, you do not measure the current across two leads, you break the circuit at a single location and place the meter in the circuit in series with the rest of the circuit.