# What is the best way to power an LED strip?

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How it Works »New Instructable »I am looking into purchasing some LED strips for a project, but I don't know how to power the LED strip. For example: This LED Strip needs 24 VDC, but what would be the best way to supply this? Would I use an outlet? Are there batteries for this type of thing?

Thanks for your help.

Thanks for your help.

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active| newest | oldestThree 9 volt transistor batteries wired in series (the positive leg of one battery tied to the negative lead of the next) will work and will allow a couple of hours of operation. Only one very simple modification is required for this to work.

Three series 9 volt batteries equal 27 volts. (9*3=27) So to limit the current to 80 milliamps required by the strip you have chosen we need to use up the extra voltage so to speak. Three volts is the difference between 24 volts @ .08 amps that the strip needs to operate and the 27 volts the three batteries can supply.

To do this a little basic Ohms Law will give us the answers we need.

First the strip requires 24 volts @ .08 amps (80 milliamps same thing) we have 27 volts so 27 - 24 = 3 Volts. We can then determine what the resistance we need to keep the extra voltage from harming our strip. Using the formula E=I * R (E = Volts, I = Current in amps, R = Resistance) and rearranging the formula to solve for R (resistance ) R = E / I (3 / .08 = 37.5).

We have determined that we need a 37.5 ohm resistor in series with the circuit. Resistors come in standard sizes unless we pay extra for precision so a ~40 ohm resistor will work fine.

Second the resistor in a series circuit will need to dissipate the same current as the board does so we need to make sure that the heat generated by that current does not burn up the resistor. Power in watts can be determined by the formula P = I * E (P in watts = I in amps * E in volts)

So using the 3 volts and the current in the circuit .08 amps the result is:

.08 * 3 = .24 watts Again resistors come in standard wattages so select a resistor that is a quarter watt or larger. .5 Watt resistors are a good size to work with so I suggest you use a Carbon Composition 39 Ohm 1/2 watt with a tolerance of 10%.

Here is one source www.tubedepot.com/r-30bj500.html they cost about 25 cents. Radio Shack probably has a resistor that will work as well and many electronic hobby stores are good sources.

Good luck with your project.

I drew a circuit to help out a little see the attached.

Instyle LED Drivers

1,choose LED Power Supply 110-220V AC to 24V DC

2,choose Waterproof LED Power Supply AC 110V/220V to DC 24V

and you can buy good Flexible LED Strip from www.ledstripworld.co.uk.

BTW, how many amp the transformer you need to be depends on the power consumptions of the strips, so first calculate the power consumption, and then determine the LED transformer model.

if anyone can ansswer I would be grateful.

Cheers

or you could always just buy a 24v transformer like this

http://www.usledsupply.com/shop/24v-power-supply.html

i use these all the time for projects with leds usually in the 12Vdc side with a http://www.newark.com/optek/ovq12s30w7/30-led-light-strip/dp/19P2486?in_merch=Popular%20Products&in_merch=Popular%20Products&MER=PPSO_N_C_EverywhereElse_None

Otherwise, if you DIY your leds strips you need a current limit somewhere - be it a resistor, or current limited supply.

As others say you just need 24 volts. A wall wart, or switch mode power supply would work. There are lots, but 24v is rather uncommon. You'd probably only run 24v if you are running a LOT of them, since each only ends up drawing 80ma (about 2 watts each).

If you plan on running a significant number of them, and want a cheap power supply - consider strands that are 12 volt - as the supplies will be far more common, and you can DIY one out of a computer power supply (instructions here on ibles)

You could use this as a single power supply, and run anything else with a regulator to step down the voltage.