UltraFire WF-602A Question

Hi I just bought 10 Ultrafire 602a's , sold a few and gave a few away as gifts . Great little torch for the price! Well of course I kept one for myself " the brightest of the bunch ,almost twice as bright as the next closest of the 10 ". I can't get it to run on rechargable AA's , if they are hot off the charger they work,but if I let them sit for a while no go?! I know it's not a tall cap or Battery length problem, does it have something to do with the 1.2 volts of a rechargable as it works awesome on alcalines.( brighter than my best Q3, and real close to my L1T w/123a tube which is a scortcher.) The one I gave to my son which is about 1/2 as bright "2nd brightest of the bunch" runs fine on rechargables. I even switched bodies and tail caps with his and still a no go?! Guess thats the price I pay for keeping the best of the bunch for myself :thumbsdow. Any ideas? This thing is awesome bright , just wish I could use my rechargables. Thanks for any help

Poor circiut design on this lights...mine doesn't fire up, if the battery is below 1,15V.
Best used with a Energizer L91 1,5V Lithium AA.

You could have a high flux led (think u-bin or something luxeon) but the VF of the led is high. So it's bright, but requires lots of voltage, therefore putting more of a demand on the circuit, and with a low input voltage, it won't fire up.

They don't use luxeons but a clone btw. I still need to get around to putting a S bin H Vf luxeon1 in mine and see how it improves. Might do that tonight.

Something I forgot to mention is if I take a Battery hot off the charger it will run none stop for well over an hour,but if I run it for 5min shut it off for any amount of time it will not come back on. Or if I run it for a few minutes on a alk. battery then switch real quick to a rechargable it will work, but if I let it sit a while it's a no go?! Almost like it needs more juice to light a cold LED than a warm LED? Think it has something to do with the LED temp. If I run it on rechargables for 30 min shut it off turn it right back on no problem , shut it off for 2 min or more nothing.

It's a well known fact, the battery recovers volts, after a while, enough to fire the circuitry again.

I see a less extreme version of this behavior in my 2 x 602As. The circuit drains a lot more current than the Fenix 1xAA's, and it takes more battery voltage/current to start it up than to keep running it. Mine run about an hour to 50% off a measured 1800 maH nimh. After about 40 minutes it won't light up if turned off. It also runs noticeably warmer than the 1xAA Fenixes with the energy it's not turning into light.

It's an OK light for the price, but the same sized Fenixes have significantly more efficient circuits than this model Ultrafire. Other's have said that the 2AA Ultrafire 601A has a circuit which is closer to (but still less than) the Fenix L2P in efficiency.

get the utrafire 3.6V lithiums (AA size and charger) and stick one in there. you will be blown away.

Is it safe to use those in the light? Or is it overdriving the circuit and possibly goign to fail eventually?

Does the manufactor say it's ok?