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85 LEDs taking 20ma each individually wired with a resistor, what ma power supply is needed? Answered

For 85 LEDs each taking 20ma wired individually with a resistor off of a single 9v power supply I would need at least a 1700 ma power adapter correct??...I would probably go with a 2000ma one though just to be safe.?


85 * 20 = 1700. Yes. 1.7 amps. You shouldn't need to go much above that, but it generally won't do any harm if you do.

While orksecurity is right, the solution to wire each LED individually is just a waste of energy.

What kind of LEDs do you use? (The options you have depend on the forward voltage which is different for different LED colours)

Have a look here: http://led.linear1.org/led.wiz

E.g. with red LEDs (Uf=2.0V) you can go with only 440mA totally consumed current!

Yea I know its kinda a waste but with varying colors meaning varying voltage I just wanted to be safe and wired them each with their own aproprite resistor. Thanks though for confirming my question.


You want as many series leds as you can fit on your power supply. If you have 9v supply and 2v leds, you need 4 in series plus a resistor to burn off the last volt to make 9.

And if you find 85 red LED with 1.7 Vf then you can run on 340 ma

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