I use Brian's method all the time when driving LEDs or electromagnets.
The current limit feature on most power supplies is often overlooked,
but very useful.
K
On 7/29/20 10:05 AM, Brian via TriEmbed wrote:
Some tips and educated guesses:
This would be a great job for an adjustable benchtop power supply.
Set the current limit to something relatively small, say, 100 mA, and
start bringing up the voltage until the current limit is hit. Many
high-power LEDs like to run at 750 mA, so 100 mA won't be nearly
enough power dissipation to worry about overheating them just in the
process of finding out the voltage and polarity. You should find a
point where current starts increasing rapidly with small increases in
voltage, and that'll get you in the ballpark. Then you can set your
current limit to 750 mA and turn the voltage all the way up; whatever
voltage ends up across the LED at 750 mA is the rated voltage. As
others have said, do NOT run these at full power for more than an
instant without proper heat sinking.
Note that LEDs, being diodes, won't conduct at all until the potential
across them exceeds the junction voltage, and that these modules are
often individual chips wired in series. If you see 9 chips in there,
my guess is that the operational voltage is probably somewhere around
12 V (1.something volts for each junction, which is very reasonable).
If you wanted to take a 12-V power supply and just quickly tap the
leads one way and then the other, you probably wouldn't toast the
module (but you do have more than one, right? ;-) ). You could still
put a few hundred ohms in series as ballast if you wanted to be careful.
Finally, the "tray" that the silicon sits in is always the cathode,
but it looks like you might not be able to see through the cover. It
might be a reasonable guess to assume the chassis is the cathode (one
lead would be clearly isolated from the rest of the chassis, while the
other is not).
I take it there are no identifying markings on the device at all? No
numbers, codes, anything?
HTH,
-B
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