Testing a Cree XHP50.2 J4 3A led

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Lexel
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for a customer I made once a MCPCB with driver circuitry on it
I used 2 0.47 Ohms in parallel for an XPL-Hi that pretty muh nailed the current to 3A tops from two high drain 18650 in parallel

Surprizingly the resistors stayed very very cool, I could have probably gone with lower than 2 0.75W ones
the main criteria limiting them is heat and they are usually rated on x mm² of PCB to dissipate the rated power

in general driving those LEDs close to their physical limits in parallel is not a good idea

JasonWW
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Lexel wrote:
for a customer I made once a MCPCB with driver circuitry on it
I used 2 0.47 Ohms in parallel for an XPL-Hi that pretty muh nailed the current to 3A tops from two high drain 18650 in parallel

Surprizingly the resistors stayed very very cool, I could have probably gone with lower than 2 0.75W ones
the main criteria limiting them is heat and they are usually rated on x mm² of PCB to dissipate the rated power

in general driving those LEDs close to their physical limits in parallel is not a good idea


Oh yeah, I forgot that mounting the resistors to the mcpcb helps dissipate heat much better than if they were mounted on a driver. Duh.

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sarge12
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JasonWW wrote:
stormrider88 wrote:
The basic data I cannot figure out is the manufacturer’s stuff (XHP50 > 6V 3A – 12V1.5A) I must be dumb, but I cannot figure out that Amp/V business… Facepalm

I can help with that last part.

The xhp50 and xhp70 are available in both 6 volt and 12 volt versions. Each emitter has 4 tiny dies which are 3V each.

So the 12 volt version have all 4 dies wired in series.

The 6 volt versions have the dies wired 2 in parallel and those 2 in series.

So 3 amps at 6 volts equals 18 watts.

1.5 amp at 12 volts also equals 18 watts.

Same power levels.

_Ohms law states volts X amps = watts
_
Make sense?

Actually Ohms law says amps times resistance equals voltage…It is watts law that says volts times amps equals watts. I know it is nit picky, but a guy named Georg Ohm came up with Ohms law, and Watts law is named after James Watt, an inventor. Though similar, it is 2 separate laws.

JasonWW
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sarge12 wrote:

Actually Ohms law says amps times resistance equals voltage…It is watts law that says volts times amps equals watts. I know it is nit picky, but a guy named Georg Ohm came up with Ohms law, and Watts law is named after James Watt, an inventor. Though similar, it is 2 separate laws.

Fixed. Thumbs Up

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