# Is it important that power supplies for LED strips have limited current?

I got some strip style LEDs [ link for the curious ], and would like to know if anyone can forsee complications hooking it up to a [very] high-amperage power source, namely a computer power supply. The computer power supply is supposed to maintain the stated 12V with good accuracy.

I'm planning to go ahead and try it, once it arrives, unless someone is reasonably sure I'll short circuit it.

## migrated from diy.stackexchange.comJul 17 '11 at 17:21

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• Most LED strips have built in resistors and thus are fairly tolerant of voltage variations. – Thomas O Jul 17 '11 at 22:13

Sometimes a misunderstanding about current/power pops up: it's not because a power supply can deliver say 10A that it also will do so. It's the load which determines how much current will flow. In this example any current the load wants is OK, as long as it's less than 10A. 1mA: OK. 100mA: OK. 1A: OK, 100A: not OK, because more than what the power supply can deliver. It will deliver the maximum (10A), and the load has to see what it can do with it. Since it asks for more the voltage will probably drop, and the device will not function properly anymore.

So stay below the maximum your supply can deliver and you'll be fine.

edit: Q & A

Q the question is how much does the LED strip act like a resistor, no?
A More or less, but not quite. LEDs don't act as normal resistors; they will always force a fixed voltage drop over them. If your LEDs are 1.4V then 5 of them in series will cause a 7V drop. If you have a 12V supply then the remaining 5V will be over a resistor you always place in series with the LEDs. That resistor is required because it limits the current, and you use Ohm's Law to determine its value. Suppose the LEDs need 20mA. That's the current through the LEDs and therefore also through the resistor, and the voltage drop over the resistor is 5V. Then, according to Ohm's Law $R = \frac{V}{I} = \frac{5V}{20mA} = 250\Omega$. That's how you can decide yourself how much current will flow by choosing the right resistor value.

• right, the question is how much does the LED strip act like a resistor, no? – gatoatigrado Jul 17 '11 at 22:46
• @gatoatigrado - I edited my answer to include this question. – stevenvh Jul 18 '11 at 4:48

It will be OK- as long as the total AMP combined from all the LED you use does not go over the rated AMP of the power supply...so in turn more amps means you can hoop up more LED's! yaaa! just dont go over the rated voltage of the LED. 12volt = 12volt. Have fun

So if your strip is a 10watt strip for example you calcualte it like this

10watts / 12 volts = 0.84Amps!

so in theory using a 450Watt power supply at 12Volt you have 37.5Amps MAX! But a computer power supply has several phases so that is split into 5volt/12volt per phase - and the phase max amps is always written on the PSU.

You also need to make sure that the LEDs input range is 12volt. They can vary form 3,5,9,12Volts respectively and need to be wired in series if lower that, or hooked up to a resistor; other wise it will glow, turn red.. and stop working. It will not short out- but the LED might get very hot and even smoke a bit if you over voltage it.

You can also use the 5volt line if your LED's are of lower voltage inputs.

A Computer power supply is one of the best to use as like you mentioned-- it has a very very stable 12/5volt supply. Which is important in electronics like hard drives/motherboards/ram etc.

Have fun

Watts/meter x length (m) = watts required. If you cut it shorter, it will only pull what it needs. you won't run into a problem making shorter strips, but you could run into trouble making longer strips and drawing too much current.