Oops, I sent 8.4v through a 6 volt max driver - now what ?

My error, I documented this driver as accepting 3 - 9v and connected a single Q5 and two fully charged 18650's in serial.

http://e-lectronics.net/driver-board-950ma-njg15-modes-p-435.html

I noticed that after about 30 seconds the emitter went from very white to very blue light, and the copper slug it was mounted to heated up much faster than normal (this is just a test emitter.) Out of curiosity I checked the amperage between the batteries and driver, and again between the driver and LED and was surprised to see 2.5a both places.

So what happens in such a situation ? Do the chips on the driver fry and allow unrestricted amperage to pass ? Once an LED turns blue as it did, is it typically done for good ?

I'm asking not out of real concern for the components, but more as a learning exercise.

thanks

dieselsmoke said:

So what happens in such a situation ? Do the chips on the driver fry and allow unrestricted amperage to pass ? Once an LED turns blue as it did, is it typically done for good ?

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Not sure about driver failure modes, but as for the LED:

If it was still lighting up, it's still a functioning LED. Too much current will blow out the bond wires, killing it completely; anything below that is just overheating. Now heat can/does degrade the phosphor and/or diode, but the immediate blue shift is caused by a temporary degradation -- the phosphor just doesn't work as well when it gets hot. When it cools back down, the LED should probably be usable, with just some accelerated aging (so potentially some tint shift/brightness loss) from the heat.

Obviously, the quicker you shut it down after it turned blue, the less damage, and if you let it cool down before you hook up the ammeter, you may have gotten away with completely unnoticeable damage. Does the LED look ok now when driven properly?

(For the driver, IIRC absolute max rating on the AMC7135s is 7V -- dunno whether they'd fry or just temporarily malfunction at 8.4V...)

Benson said:

Obviously, the quicker you shut it down after it turned blue, the less damage, and if you let it cool down before you hook up the ammeter, you may have gotten away with completely unnoticeable damage. Does the LED look ok now when driven properly?

Click to expand...

Thanks for the reply Benson.

It was a long time between the test when it turned blue and again when I checked amperage, so the LED was cooled and came back on as a normal white color, even with the 2.5a driving. From that I'll assume I got lucky and will continue to use the emitter as the ginuea pig.

Next test will be to properly connect a single 18650 to the driver and see if the driver is functional. I'll post a follow up.

Well, the board doesn't seem too happy. With a charged single 18650 source, I'm seeing a max draw of 180ma when tested either before or after the driver, and no ability to switch modes.

I think it's toast