I've decided to put signals on my N scale layout and have an NJ International single head, two light signal (red/green). I bought a Miniatronics 12V 1Amp PS to power them thinking they were 12V LEDs since my 4.5V PS didn't seem to make them work. But the 12V PS doesn't make them work either. However, if I connect them to my track (DCC - Zephyr), they work.
Questions:
1) What is the voltage and amperage for these LEDs, I can't seem to find any information on them?
2) Since my track is AC why does that work since I've seen other posts saying LEDs don't "like" AC since they're directional?
3) What do I need ot do to make them work?
Thank you,
Eric
I'm kinda likin this stuff
The simple reason they don't work is you probably have them hooked up backwards with the power supply. LEDs are polarity sensitive. They should have come with instructions which woudl indicate the power supply voltage required. I'm assuming they have resistors built in since they didn't fry when you hooked them to the track. LEDs don't like AC simply because they cannot stand a large voltage applied across them in the reverse ddirection. This is not something that will instantly damage the LED, but it will greatly shorten the life of it if kept up. Properly wired, an LED should last so long that our grandchildren will still be able to use the same one.
If the instructions mention that one lead is the anode or the cathode - the anode goes to the plus side of the power supply and the cathode to negative. I'm pretty sure the NJ signals are common anode, which means that the anodes of all teh LEDs are connected together as one wire, adn then there are two or three (depending if it's a 2 color or 3 color signal) additional wires which are the cathodes of each individual LED. Connect the common to the plus of your 12V power supply and connect each other wire in turn (through a resistor - which should be supplied) to the negative and each one should light.
ALWAYS make sure there is a resistor in the circuit. Even with a 4.5 volt power supply, running an LED with no resistor WILL destroy it. The resistor needed for 4.5 volts is less than the one needed for 12 volts, but it is still needed.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Randy, doh!
Of course! And thanks for the lengthy and informative reply. I did have the PS leads switched and that fixed it. I can see why the AC worked, the correct polarity would have been present every second phase and quick enough that the eye wouldn't detect any flickering.
There were no instructions or specs with the signals so I still don't know what the voltage or amperage of the LEDs is. But they did have resistors attached. I'll check their color bands at the next chance to help narrow down the other specs.
Most LED's are around 3.3v. A 1k resistor on 12v. DC is a good starting point. You may need to go smaller if they aren't bright enough. Be careful because they pop real EZ.
Most WHITE (and variation - like golden white, sunny white, etc) LEDs are 3.1-3.3V, and are so bright a 1K resistor is perfect for 12-14V. The most common color LEDs, red, green, yellow, are typically 1.9-2.1 volts. That same 1K resistor at 12-14V puts more current through them BUT they usually have higher current limits and aren't nearly as bright. Also, there is usually considerable variation in the light output between the different colors so it is common to see a different resistor value for each color in an attempt to 'even out' the brightness levels.