Just curious: Why isn't anyone recommending picking up an old used DC transformer used to run things like HO trains, etc.? I had always thought that's what I'd do to run some of the LEDs planned for our layout.
I know almost nothing about this topic, so all replies will be helpful for me.
Thanks.
Steven J. Serenska
That's not an awful idea, but not always ideal....
I like to play with cheap boards that normally operate at 2-3volts. One accidental bump to high voltage could burn out an unregulated circuit easy.
That's why wall warts tend to work out so well for some folks. They have a constant supply. Normally new ones are pretty clean in delivery too. I've seen a few "noisy" supplies, ac leaks in older small DC variable "power packs" too.
LEDs all use DC. IF there is AC coming into a device with LEDs, it needs to be converted.
Most LEDs I have worked with use 4.5 volts DC and very very little current. You need protect them for a current overload.
The simplest way to power an LED from an AC transformer in the 12 volt range is to wire a bridge rectifier across the output poles to convert to DC, and then install a 1000-1500 ohm resistor (maybe 1/2 watt) in series with the LED.
IF you still have a Radio Shack open inthe area, a bridge rectifier will run a couple of bucks and a package of resistors will run less than 2 bucks.
You can play with the resistors to adjust brightness. the bridge can be a small one with a 25-50 amp capacity.
25-50 amp?
6amp would likely be extreme overkill for just a flashing led strobe.
A small, old school transitor sized 3amp bridge rectifier is likely still way more than enough.
Smaller, cheaper than that, a few diodes placed properly, is the same thing as a bridge rectifier.
http://en.wikipedia.org/wiki/Diode_bridge
What Stan wants to do is smooth out the "ripples" that still remain, with proper capacitance.
I.e. a capacitor acts like a tiny quick release battery, to even out the power ripples when AC reverses towards 0 volts/negative volts, on each AC cycle(60 hertz). Polarity change, and voltages are constants in an active "pure DC".
