MJLED x 3 AAA NiMh?

Darkstar

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I believe tnat the MJLED is rated for a max nominal voltage of 3.6. Would I be able to safely drive one in my Rayovac headlamp?

Thanks
 

davidefromitaly

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if you use only one led i think it is a bit overdrived because the voltage don't drop (usually a ni-mh fresh of charger is around 1,35v)

is best to use 3-4 leds so the voltage drop further and they are less overdrived
 

WildRice

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FWIR the MJLED voltage is between 3.1 and 3.4v allowing it to be happy with alky or LI's, 3.6v will more than likely toast it. You would most likely need a dropping resistor to limit current to 100-120mA. Somebody chime in on the current specs as I am only guessing.
Jeff
 

Bimmerboy

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The MJLED unresistored on a 14500 is pretty risky. More than one person is running that combo with success although I'm not sure how... I tried it and fried it in under 10 seconds. The battery hadn't seen a charger in weeks, but it made no difference to that poor LED though.
The 14500, if I have this correct, is 4.1 - 4.2V (fresh off charger, no load), dropping to 3.6V under load. The Vf of the MJ, though opinion seems to vary on this, is roughly in the 3 - 3.6 range, so you're a little outside the safe territory. If you get a runaway LED, the 14500 is happy to provide the current needed to produce smoke.
So, can anyone recommend what ohm/watt resistor is good to limit a 14500 to about 100 ma, or even around 110 - 120 for a little overdrive?
I'm also wondering if just adding a Kroll introduces enough resistance to bring current down to a semi-safe range.

Davidefromitaly - just to understand, why does driving more than one LED from 3 X NiMH drop voltage? Is it because the larger load from three LED's causes the batteries to sag a little?
 

IsaacHayes

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I would safely say that 3-4 5mm leds won't cause NiMH to drop in voltage at all.

Heck, even 3x LuxIII driven at 1 amp won't cause NiMH to have much voltage sag!!!
 

Bimmerboy

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True. 4 of them would only take around 400ma (if I understand it correctly). CBP1650's would laugh.
Upon re-reading, was david saying that using more LED's would cause the "fresh off the charger" voltage to go down quicker?
 
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