Blown LED lighting

[lone ranger]

Here is a bachmann 2-6-6-2 logging mallet fitted with an ESU loksound XL chip. Unfortunately a previous owner had set the cv's for the LED's to full track voltage and blown all the lights.

I must admit its a bit of a so and so to get apart, all I have to do now is get some LED's to replace the headlight, backup light, cab light and two square one's for the fire box.

Thing is will it all go back together in time for the Essex winter meet on the 09/03/2013 ?? Gon'ner have to keep my fingers crossed on that one

 

[ntpntpntp]

Oh dear - did previous owner not wire the lights through the existing harness board and the plug-n-play socket then? That would have protected the lights.

Must admit I'm not a fan of using a decoder's voltage control settings: I always make sure any lighting that does go direct to a decoder has a suitable limiting resistor and assume full voltage will be supplied. That way it doesn't matter what decoder you use and doesn't rely on someone remembering to set the lighting voltage when fitting a replacement decoder in the future.

Good luck with getting it all back together. I haven't had mine apart to that degree!

 

[lone ranger]

Oh dear - did previous owner not wire the lights through the existing harness board and the plug-n-play socket then? That would have protected the lights.

Must admit I'm not a fan of using a decoder's voltage control settings: I always make sure any lighting that does go direct to a decoder has a suitable limiting resistor and assume full voltage will be supplied. That way it doesn't matter what decoder you use and doesn't rely on someone remembering to set the lighting voltage when fitting a replacement decoder in the future.

Good luck with getting it all back together. I haven't had mine apart to that degree!

Funny enough they were wired through the existing pcb board but they still blew &:

 

[Nodrog1826]

Agreed Ross.

Have flagged as suspicious it to the mods, checking the posters profile looks like someone who joined today,
posting an advert for their business. Was going to report it as spam, may as well do it now.....

 

[beavercreek]

Hi Jerry
When I am sorting out a problem with lighting either caused by someone else or me, I now tend to use 5-22v LEDs with bridge rectifiers built in to the wiring

 

[lone ranger]

Type LEDS in SEARCH which will help you understand these devices.
There is a long discussion on these on GSC,
No doubt more will be added from your query.

Hi ROSS,

Well, I did as you suggested, and I quickly learned two things:
- The search engine is not as user friendly as it could be in that it doesn't point directly at the results. For LEDs it returned 268 items but these are not 268 posts that mention LEDs; they are 268 threads that may mention LEDs anywhere within them. It is necessary to read each and every post within each thread to be sure you have stumbled upon each real mention of LED. Not too efficient when you're looking for theory. Sort of like reading enough dictionary words to assemble the Preamble to the US Constitution.
- Automatically disregard any search response that refers to a daily Coffee Break thread. The only hard information is the amount of ice outside.

Still, I did find some entries that began to hint that they might approach my area of concern. So I am going to follow your suggestion further when I have time to track down all the web sites that they referred to. Thank you for pointing me toward them.

Hi this site might help you. http://led.linear1.org/led.wiz The page this leads to will calculate for an array of LED's you will also see a link for a single LED, and at the top of the page there is a hyper link to LED BASIC's

Hope this is of help
PS this link was given to me by Bigjack

 

[beavercreek]

The other option is to use LEDs with resistors or even bridge rectifiers ( for any polarity AC etc) built in or already in the wiring. I do this when I feel lazy and can't be bothered to make my own. I get them inI bulk from Evans Designs in the states.any size or colour
That way no blown LEDs no matter what voltage (up to 24v ) or what polarity. Ideal if changing from DC TO DCC

 

[generalboy80]

Another option, which can have many advantages over the traditional volt drop/current limit resistor method is to use a current limiting transistor.

The important thing with LED's is that they are current driven, and while they require a minimum voltage (~3V for many white LED's) to give off light, the ammount of light is dependant on how much current is being passed through them. The voltage they can tolerate can be quite high, provided the current is contained to whatever is safe for them (typically ~20ma for white's although it is sometimes better to go lower because they can be too bright to look at). Exceeding the manufacturers safe current specification will shorten the life of the LED drastically, and providing no limit to the current will kill them very quickly, since the one real failing of the LED is its lack of ability to regulate itself.

I have used a CL2 IC from Supertex, which will limit the current to a constant 20ma and it works well. I run 22V PWM DC track power and the LED's run nicely with no voltage dropper other than a polarity protection diode to avoid blowing the anti-flicker capacitors I add. It will run drive several LED's in series, with the only caveat being that the supplied voltage must be modestly greater to the minimum supply voltage needed to get them to light (ie, 3 LED's needs ~10V or higher). A single LED needs a minimum of 5V to get lit when connected. At 22V supply voltage, the CL2 gets finger warm, but not enough to risk anything nearby and it can pass up to 90V according to the datasheet. It really is simple to use, as it's a TO-92 transistor package, but with only two pins to solder. My only gripe with it is that they're hard to get hold of outside of the USA, but they really do simplify matters greatly.