"Decoding" an existing DCC installation in an LGB 23450

Greg Elmassian

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I agree, it is operator error.

But me taking that attitude to a friend who just destroyed something won't make him happy!

So, for me, for inexperienced people, and even some experienced ones, the "safer route" is the way I advise.

On this specific issue, I gotten in so many arguments with a newbie who is really intent on not adding a resistor....

But, for the people who have blown their LEDs, there is normally contrition, and a more careful attitude in the future.

All I can do is give my "best" and "bulletproof" advice... and withstand the guys saying "I have been running LEDs without resistors since there were dinosaurs".... for every guy that lucked out there are 10 guys with blown up LEDs.

Greg
 

JimmyB

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The easiest approach is to buy the LEDs with the resistors already installed in the wiring like I use.
Most of the LEDs (with resistors) I have seen are for 12 volts, and as I like to use duel colour (White/Red), I haven't seen any of these. As a rule of thumb, I use a 1kohm resistor, and this will light with 9 volts, and is good for 24 volts, I understand LEDs are current and not voltage dependant, but this is easier understood as voltage.
 

PhilP

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Most of the LEDs (with resistors) I have seen are for 12 volts, and as I like to use duel colour (White/Red), I haven't seen any of these. As a rule of thumb, I use a 1kohm resistor, and this will light with 9 volts, and is good for 24 volts, I understand LEDs are current and not voltage dependant, but this is easier understood as voltage.
True..
You can get caught-out, if you have a low voltage switched source, and are trying to use (say) two bi-colour LEDs at each end..
Red and white LEDs have different Vf (forward voltages) and you can have one colour not light, as the voltage across the LEDs is dragged down..

Google 'ledcalc' for a comprehensive calculator..
LEDs is series, or parallel, and any number.

PhilP
 

JimmyB

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True..
You can get caught-out, if you have a low voltage switched source, and are trying to use (say) two bi-colour LEDs at each end..
Red and white LEDs have different Vf (forward voltages) and you can have one colour not light, as the voltage across the LEDs is dragged down..

Google 'ledcalc' for a comprehensive calculator..
LEDs is series, or parallel, and any number.

PhilP
Phil, normally around 12 volts (3S Li-Ion) battery, but good for 4S, and my 18 VDC power pack. The red LEDs are slightly less bright, but I am content, nothing blows (darn that does it ;)), each ti their own if they understand the limitations.
 

PhilP

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1k is a good 'safe' value (for the voltages we go up to) and you can always go down, a little, if you want to get more light out of them.

If you 'under-run' the LEDs, they will normally last longer..

PhilP
 

LGB333

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Most of the LEDs (with resistors) I have seen are for 12 volts, and as I like to use duel colour (White/Red), I haven't seen any of these. As a rule of thumb, I use a 1kohm resistor, and this will light with 9 volts, and is good for 24 volts, I understand LEDs are current and not voltage dependant, but this is easier understood as voltage.
I use full track power output through the decoder for the 12v. LEDs with resistors I use and they work fine.
 

Greg Elmassian

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At the voltages I use (24v) the current would be excessive, over 20 ma... but they are more rugged than they were 10 years ago.

I try to use efficient LEDs and find they are full brightness around 10 ma... so I use resistors calculated for that, and the forward voltage drop of the LED.
 

FatherMcD

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At the voltages I use (24v) the current would be excessive, over 20 ma... but they are more rugged than they were 10 years ago.

I try to use efficient LEDs and find they are full brightness around 10 ma... so I use resistors calculated for that, and the forward voltage drop of the LED.
Greg, this question is posted as a reply to you as I got the information I used from your website. I bought some of the Supertex CL2 current regulators. I hooked up a flashing red and flashing orange LED in parallel and connected them to the CL2. (I took a chance with the parallel connection.) They are providing a great firebox flicker. Is anyone else using current regulators? I don't recall the price being excessive and it sure saved struggling with resistor calculations. Am I missing something that makes resistors superior to current regulators for LEDs?
 

Greg Elmassian

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the current regulators are great, maybe they are making them in 10 ma now. I have about 100 on hand of the large cases and of the smd ones (for Z scale). I also have a stock of resistors, so often I will use resistors for my own stuff since I run 24 volts and will set the current the way I want. For people that have all kinds of voltages, the CL2 is the way to go, even if 20 ma is more that is necessary.
 

JimmyB

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Greg, this question is posted as a reply to you as I got the information I used from your website. I bought some of the Supertex CL2 current regulators. I hooked up a flashing red and flashing orange LED in parallel and connected them to the CL2. (I took a chance with the parallel connection.) They are providing a great firebox flicker. Is anyone else using current regulators? I don't recall the price being excessive and it sure saved struggling with resistor calculations. Am I missing something that makes resistors superior to current regulators for LEDs?
So never having heard of CL2 (but then why should I have) and working out it did not mean Chlorine, I had a read on a number of articles, and have a number of points:
  • Why have 3 legs when only 2 are required.
  • If this is directional then it will not work with bi-colour (2 -leg) LEDs.
  • Some TD sheets inform that a resistor is still required.
Though to be honest most of the information was on Texas Instrument items as the Supertex items do not seem to be available in the UK.
 

PhilP

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Greg Elmassian

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PhilP, only 2 leads used.... 3rd is not connected.

Explanation here, along with link to data sheet:

Never seen a circuit where it NEEDS a resistor added, these run up to 90 volts input. I'd love a link to see what that is about.

Greg