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I've go this LED

what is the wattage and rated voltage of this LED?

Polarity is marked but no rating is written on its body. It's claimed to be 5 watts.

Has anybody worked with this? What's the voltage rating?

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    \$\begingroup\$ Read the data sheet if it has one. If it hasn't then use an ammeter and a voltmeter and gently raise the voltage on a power supply upwards (bit by bit from 0V) until volts x amps = 5 watts. If it burns before 5 watts is reached then it serves you right for buying LEDs without data sheets from crappy sources. If you have a data sheet then provide a link if you don't understand it. \$\endgroup\$ – Andy aka Nov 8 '15 at 14:36
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    \$\begingroup\$ Before you apply watts of power to it, mount it to a heatsink (5C/W or thereabouts or it WILL burn up quickly. \$\endgroup\$ – Brian Drummond Nov 8 '15 at 14:58
  • \$\begingroup\$ The seller should tell you. Otherwise google "5W led" and hope you find a visually similar one that happens to have the same electrical characteristics. It worked once before... but for 5W leds, there are lot more possibilities. Actually yours looks like a 3s3p one, which could narrow the search down a bit. \$\endgroup\$ – Fizz Nov 8 '15 at 15:04
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    \$\begingroup\$ looking by the arrangement inside the LED, looks like 3 groups of 3 LEDs in series, so I'd guess 5W/3 = ~1.7W, 3.6Vforward*3 = 10.8V, Power = V.i, ~1.7 = 10.8*i, i = ~150mA per group, so ~450mA total at 10.8V (10.8*0.45 = 4.86W) \$\endgroup\$ – Wesley Lee Nov 8 '15 at 15:52
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    \$\begingroup\$ You are asking the wrong question. An LED needs to be driven with a current source, not a voltage one. This will control the voltage to achieve a desired current through the LED. (When you use a resistor with a small LED you are approximating a current source) A starting point for figuring the current would be the wattage divided by the forward voltage measured in operation. You might read some data sheets for other similar parts, look at driving circuits, and experimentally put small currents through it with a current mode power supply or else a series resistor. \$\endgroup\$ – Chris Stratton Nov 8 '15 at 16:36
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Instead of asking, measure it. You already know not to exceed 5 W. Hook up the LED to a variable power supply, maybe with a 1 Ω power resistor in series. Measure the voltage and current as you slowly crank up the output of the supply, then you can see directly what the voltage and current is at 5 W.

Note that this is, of course, all in the LED's datasheet. Unless you are getting a really good deal and are willing to live with the consequences of not knowing the specs or that the part might be counterfeit, don't buy something without a datasheet.

Be careful about running this unit at more than a watt or two. It most likely is only specified for 5 W at a certain case temperature that can't be achieved without significant heat sinking. Forcing 5 W through it just sitting on the bench will likely destroy it. Of course, without a datasheet, you don't know how "embellished" the 5 W figure from the seller is. Nobody would buy surplus 3 W LEDs and resell them without the datasheet as 5 W LEDs. Nah, that never happens, no need to worry about it.

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The housing points to High Power LED, as statted on the question. The internal arrangement shows, more likely, three strings in parallel. From my experience, those chips are normally rated at 350m. Therefore, 3x350mA = 1.05A. The voltage will depend on the resistive part of the LED curve, but it should be no issue when you have a proper driver with constant current characteristics.

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