# Current Draw for LED Projects

I am working on a project with LED strips that would consume 12V and 20A. The problem is that the household wall outlet limitation is 15A, and 20A current draw would potentially start a fire. I have been searching for tutorials of large current LED project, and none of them really addresses the current draw problem.

I found an adequate power supply. It is Meanwell RSP-320-12. http://www.mouser.com/ProductDetail/Mean-Well/RSP-320-12/?qs=Uzd%2Fwh%252bZzhBChmc2p7rgKQ%3D%3D.

How can I make it work with a 15A wall outlet limitation?

• When you say 15V in your last sentence, do you actually mean 15A? Commented Oct 3, 2017 at 16:11
• only if you used a linear power supply, which nobody uses for hi-power LEDs... Commented Oct 3, 2017 at 19:12

Drawing 20A on 12V means 240W which on 110V is 1A and a bit (a bit more once you consider efficiency of the conversion).

The spec sheet of the power supply you linked says that it will draw 2.7A max on a 115V input.

The power supply will convert the high voltage low amps into low voltage high amps.

The power outlet is either 110V AC or 230/240V AC. Ignoring modern Switch-mode power supplies, to convert the power outlet voltage down to 12V, you first need to step down the voltage (using a transformer) and then rectify the AC voltage to DC voltage.

Working backwards, to get 12V DC you need: `12 x square_root(2) = 16.97 V AC`.

A transformer can step down AC voltage. For example it can step down 110V AC down to 16.97 V AC.

The formula for an ideal transformer is:

``````V x i (primary side) = V x i (secondary side)
``````

And using this to find the current draw on the primary side:

``````110 x i (primary side) = 16.97 x 20 (secondary side)

i (primary side) = 16.97 x 20 / 110

i (primary side) = 3.08 A
``````

So if you have an outlet that provides 110 V AC then an ideal AC-DC converter would draw 3.08 A.

• 12Vp-p is 8.485Vrms, not 16.97Vrms. You need to divide, not multiply. Commented Oct 3, 2017 at 21:08
• @Majenko you are correct for a bridge rectifier circuit, however my calculations are correct for a full wave rectifier. sowter.co.uk/rectifier-transformer-calculation.php Commented Oct 4, 2017 at 0:33
• People still use those...? For that matter, people still use transformers...?! Commented Oct 4, 2017 at 8:14