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-   -   Determining forward voltage of LED's (http://www.plantedtank.net/forums/10-lighting/245130-determining-forward-voltage-leds.html)

 NWA-Planted 02-14-2013 01:55 PM

Determining forward voltage of LED's

Is there a way to determine forward current on unknown leds?

I ask because i ended up scrapping my custom led build just to much money... So i picked up a beamswork 36" fixture which features 24 x 3 Watt leds.

I see a potential for upgrading the stock fixture to, as it uses no active cooling so chances are the leds are not running full strength which to me implies potential for new drivers which means you could probably make the fixture dimmable

However i would need to find the correct current so i don't burn them out

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 HD Blazingwolf 02-14-2013 02:21 PM

im no led guru, but led's seem to be either
voltage limited
or amperage limited to control intensity
the key is finding which one

of course u can also find the circuit board. look up the resistor to figure out some voltage, ohm, wattage math and figure out what ur led's are using

if its a 3w led though, i wouldn't drive it much harder without adding heat dissipation or the wont last very long

 NWA-Planted 02-14-2013 02:24 PM

Re: Determining forward voltage of LED's

Oh yes some fan cooling would be added.

I found some 3 Watt leds that have a 750ma constant and 1000ma peak. So i figure those would be close to the same, guess one thing i could do to start would be to measure the stock forward current to see what they are running... Hmmm

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 Hoppy 02-14-2013 08:48 PM

The forward voltage drop is a nearly constant value for any given LED, and it varies with LED models. But, the current is widely variable, and it is by varying the current alone that we adjust the amount of light emitted by the LED. One advantage of Cree LEDs is the great data packages that are provided for all of their LEDs. The cheap ones we can buy on Ebay, for example, don't come with that data. And, LED light fixtures don't come with any data at all, except, for some, the PAR vs distance.

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