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Powering LED array with 12V AC/DC converter? Answered

Hi! Long time lurker here! I have a project in mind that involves the construction of an array of 121 LEDs in an 11x11 configuration. I want to power the LEDs off a 12V AC/DC adapter, but I'm a little unsure about how current works in this case. The adapter is a regulated 12V 1A adapter. The LED array, however, needs only 820 mA. I know the maximum DC current is 30 mA so if the full amp is spread across the 41 parallel series it should be passing ~24 mA through the LEDs. Will this cause any major problems? Is there a way to limit the current to the suggest 20mA? Furthermore, if anyone has any good ideas as to how to mount 121 LEDs in a square grid of inch spacing, I'm all ears. I considered using pegboard, but I can't seem to find any, and veroboard large enough is also proving difficult to source. I don't really have the resources necessary to make my own PCB. Maybe I could drill some pegboard of my own and attach some thin conductive strips for the 12V and 0V rails. Thanks for any help! I've taken a practical electronics course at university and done some soldering (just op-amps and the like), but this is the first real electronics project I've taken on, so any help is greatly appreciated.


I'm assuming you are using individual LEDs, and not LEDs that are already arranged. You made a reference to a number of strings, but I didn't know if that part was carved in stone.

Each LED will need about 2 volts across it, maybe a little more or less, depending on the color. This will limit the number of LEDs that can be put in series in a string. If the voltage drops across the LEDs exceed 12 volts, they will not light, or the will be dim.

If you put say, 4 LEDs in a series string, you would need a total of about 30 strings, (plus one odd string with only 1 LED) which will then be placed in parallel. Each string should have a resistor in series with the LEDs, to set the current. You can set the current in each to whatever you want based on the following.

Resistance = (12Volts -Number of LEDs in each string * Voltage drop across each LED) / Desired Current

So, to use 4 LEDs per string and each has a voltage drop of 2 volts, and you want it to carry a current of 20 mA, the resistor used in each string should be : (12 volts - 4*2volts)/20mA= 200 ohms.

If you used this arrangement, you would have 30 strings, each with 20mA flowing in it, for a total of 600mA, which should work fine with your supply.

Any luck with this LED array?

I'd drill your own board if you want then 1" apart. Be sure to post an I'ble eh? L

sinking such a small amount of current is easy (if it is actually necessary).

Ohm's Law.

And here is a Calculator that may help you along.