LED "failure"

I had a breadboard setup using a bunch of LEDs. I am in the process of moving these to a permanent installation. At least one of the LED will not light. It worked fine on the breadboard. I've tried swapping leads; swapping polarity and a few other things. Nothing. Could I have shorted the LED out or ruined it in some other manner. Maximum voltage appears to be less than 8 volts.

Thanks.

...don

There are a few ways to destroy leds:
- put too much current trough them for too long. In the datasheet you'll find a parameter If, the forward current that a led can endure and at wich the light is measured. You can use higher currents but then you'll have to make the mean current low by pulsing the current on-off.
- too high a reverse voltage is also deadly. Normal diodes can stand voltages of 20V and more without problems, but leds can not. The reverse voltage can be as low as 5V and more is destructive. (unless you add a very large resistance but then it will not give light when correctly polarised) Very important if you put a led on AC.
- a static electrricity discharge can also destroy a led. This is harder to control in hobby use.
- with high power leds you can destroy them if you do not cool them well enough. But I don't think that's the type of led you used, these leds come with a ceramic or metal base and put out about 1W.

I guess you reversed it with too much voltage.

Its very easy to protect from reverse.
I always put in line with the resistor and the Led a small diode
1N4841 or similar, this protects against AC and inverted DC.
Resistors are easy to calculate, you take your maximum
input voltage (ex. 12Volt) and the voltage of the Led (ex. 2Volt)
You calculate necessary drop down voltage : 12V -2Volt = 8Volt.
If your Led stand maximum (ex. 20mA or 0.020A)
your MINIMUM resistor value should be : 8Volt / 0.020A = 400 Ohm
so 470 Ohm is an approach.

But in general this will be for most application too bright, so
you will easy land with a 560 to 1000 Ohm for your application.

This Led will survive you !
Just a hammer can change history

Jim, when did I get a holy picture for my points ?

I'm using Miniatronics #12-050-18. It says use a 3v power source...but then it goes on to say attach the 470 ohm included limiting resistors and you can go up to 15 volt DC when wired in series. I don't think I've ever gone over 11 volts, but I __THINK__:woohoo: I have two burnouts that were on one side of a turnout. The other two did not burnout, yet all four are in the same wiring loop.

It does seem that its possible that too much voltage came from somewhere - but I'm not sure where. As an aside could a good lightning storm get to them even though nothing was turned on?

...don

Its better not to connect Led's in serial,
because they always have some different characteristics
and so the Led with the highest internal resistivity
will catch the highest voltage at the startup.
Better to put in parallel with one common + or - depending
from your application. As example decoders sucks to the
ground (-) so that you must put anodes (+) together.
But also in serial small little protection diode is necessary.
With decoders not, they are integrated by principle.

Thunderstorm ? It can catch your dog or your cat, not your Led.

zbarr474 wrote:

I had a breadboard setup using a bunch of LEDs. I am in the process of moving these to a permanent installation. At least one of the LED will not light. It worked fine on the breadboard. I've tried swapping leads; swapping polarity and a few other things. Nothing. Could I have shorted the LED out or ruined it in some other manner. Maximum voltage appears to be less than 8 volts.

Thanks.

...don

Most LED's are current limited and a ballast resistor is required to control the current based on voltage you are using. Without the resistor voltages as low a 3vdc can blow the device. Most LEDs that you can get in the Hobby Shops come with a ballast resistor for 12v. Knowing this it is possible to figure out what the correct value is for 10V for Z use if you want a bit brighter light but the resistor for 12v will still ensure you don't blow it with voltages below 12vdc.

regards
Garth

but I __THINK__ I have two burnouts that were on one side of a turnout.

You do not perhaps have those led in series or parallel with the coil/motor of the turnout? Can you draw a schematic of your setup (the problem area) and indicate wich led blows? Just on paper and a scan is fine.

OK, Problem resolved

If you put it in connection together with a coil,
the coil can generate easy about 500 ! Volt when
you cut down..................R.I.P.
minute of silence please.....

So in DC together with the inline diode (1N4841) you must
put another 1N4841 REVERSE to the DC Voltage and
PARALLEL to your coil.

If you fire with AC you will have no other solution
than to put rectifier bridge between your AC source and
the turnout coil. If not, it will never work !
And always you must put the diode reverse and parallel !

You just invented the electric chair for LED's

Cleantex wrote:

OK, Problem resolved

If you put it in connection together with a coil,
the coil can generate easy about 500 ! Volt when
you cut down..................R.I.P.
minute of silence please.....

Even with protective diodes, placing LEDs into any AC and/or switch-coil firing circuit is asking for trouble. Besides, the LEDs will not remain lit once the route is set and current is removed. (You're not leaving the coils energized all the time, are you?)

Rule of thumb: indicators--especially LEDs--should never be wired into the same circuits as switch machine coils or track power (where motors can generate harmful noise). LEDs should have their own dedicated power supply, and each LED its own resistor or current regulator.

If you want panel indicators for your turnouts, you should use auxilliary relays (Marklin makes them, I believe, as well as others), which have coils just like turnouts, and separate contacts to power panel indicators and/or route track power to frogs and rails. They are wired in parallel with the switch machines so that they act in concert with the turnout.

Guys - You are blowing this out of proportion. You are using a surveyor's GPS to measure the length of a row of corn [ a SHORT row ]

The LED is in series with a 470 ohm resister. The two are supplied as a unit from Miniatronics. Power is coming from an MTL power supply with the post set at 11 volts max so it can be used for Z. Since I am DCC all I use it for is the LED power, and have had the output set to about 8 volts DC. There is no connection between DC and DCC. The ATLAS Snap switches flip to power a green OR a red LED. 8 volts Power in through an on/off ATLAS switch to one end of the LED then in series to a resister then back to the Power Supply.

This is why I don't understand why I have a couple of failures.\
...don

zbarr474 wrote:

Guys - You are blowing this out of proportion. You are using a surveyor's GPS to measure the length of a row of corn [ a SHORT row ]

Sorry for the overblown reactions, but in the absence of a scematic or a clearer circuit decription (as you have now supplied), we could only speculate...!

You do have a mystery here, that's for sure. I can only perhaps guess that a spike is somehow being induced in the circuit somewhere, and without a protective diode, the LED may have bit it. The only other viable alternative is that the LEDs were out of spec and were going to fail anyway.

No, we are not making blow job in a corn field ..

It's just simple electronic, you must do the same with relay's
in any electronic circuit (anti-parallel diode) to not blow up
the end transistor. You do it, or you leave it and suffer.
I take sometimes a simple Led as indicator for 220Volt AC and it
is working if the protection exist.

Sorry on the photos. I don't upload enough here, plus my computer does things ITS way. The wiring diagram is simple. The ATLAS 200 is merely a switch setup that allows AC to control the coils, and DC to come off a second set of connections. The LED I'm having trouble with is merely getting about 9 volts from an MTL controller. The voltage goes through one of two LED depending on the switch setting. The switch coils themselves get about 9 volts AC that is coming from a Capacitance Discharge setup. The two voltages AC & DC NEVER see each other.

...don

I looked at your drawing, and from what I see there I don't see anything wrong with what you did. The only way I can see that something could happen is if it happens inside the power supply. (because the AC output and DC output interact in some way)

You do have adequate series resistors? Something like 1kOhm the size like in the photo's of Zbarr is fine. If that is OK, then I would try to fed the leds from a different power supply. Because of the Atlas switches this can be done without a problem.