Salvaging LED's and how to spec them

[bmwbykrydr]

Hey everyone, first post here. I'm using the LED display board out of a demolished automatic car wash as a source of salvageable LED's. You know, the display panel that tells you to pull forward, stop, waxing, washing? It's got two arrays of LED's, one above the other, each of them with 7 LED's high and 48 LED's wide, 672 total, each LED is about 1/2" apart and each is a red output. I have no idea what the specs are for the LED's, but I can tell you that each column of 7 LED's has a single resistor, Red Red Black Gold, 96 of them total. I can't see any info on the board that refers to a voltage and I tossed the control board a long time ago before I had the idea to salvage the LED's.

Is there a way that I can reverse engineer these LED's to figure out their specs so I can correctly design my circuit to use them. I bread boarded a series of 7 of these LED's with one 68 ohm resistor and that resistor gets really hot in a few seconds with a 12V source. I figure I must have the resistor wrong, but I need to figure out the right resistance for these LED's.

Any thoughts?

Don
Lincoln, Nebraska

[justDIY]

hi Don, welcome to the boards.

assuming we're talking ordinary round or rectangular 3, 5, 8 or 10mm leds, the specs are pretty universal.

Each led that is yellow or red is going to need 1.8 to 2 volts, at 10 to 20mA.  Each led that is green, blue or white is going to need 2.8-3.3 volts, and 10-20mA.  The exception is, if you have yellow-green or high-efficiency green leds, they need to be treated like red leds.  If you light up a green led with 3v and it turns orange, toss it in the trash and use 2v for the rest like that.

Using these numbers and the site's led calculator, you can figure out what resistors and power you'll need to light up different amounts of leds.

[bmwbykrydr]

Awesome, thank you. These are 5mm reds, by the way.

I called the OEM of the panel and they told me exactly what brand and model of LED they are. Then it was just a quick Google search and I had the datasheet.

Don