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led powering question Answered

I am building a garduino since planting season is coming near and this would be a great to start me seedlings off in. right now I have 3 banks of three red leds rated at 1.8v and in one of he instructible they said 7v was sufficient but i am connecting a 9v and can only power 2 leds and also I would like to go with an ac-dc converter but everyone i found has at least 800+ mA can someone point me toward a good power supply at the end I am looking at about 25 red and 8 blue LEDs

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__DELETED__

7 years ago

The amp rating on ac-dc converters is just the maximum they can put out. Whatever you hook up to them will only draw what it needs.

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andy70707__DELETED__

Reply 7 years ago

This. Also, remember how LEDs react in series and parallel. In series, you need to add the voltage together, so for 33 LEDs, as you said, in series, would require nearly 60v (1.8v does seem a little low for an LED, most are rated at 2.1-3.3v, and I usually use 3v). However, in parallel, you can run them all off the voltage as 1 of them (in this case 1.8v). As you can't usually buy AC-DC convertors below about 5v, I would get a 12v power supply, and run them at 2v each, so you would have 6 in series, and then sets of 6 in parallel. And as H4ZZ498 said, the current rating is the max, it will only draw what it needs. LEDs are typically 25mA, giving a total of 825ma, which is actually just above the limit for your power supply.