Has anyone ever killed a SF U2 while running off a single li-ion cell?

...or am I the first one? I ask because my favorite light, a SF U2 modded with neutral MC-E, released the magic smoke yesterday, within seconds after putting in a freshly charged 18650 cell. Some components on the board literally burned out to a crisp.

The light had seen some serious use and already had many hours of runtime on it, but most of it was on primaries. I switched to 18650 cells fairly recently... so I'm thinking that an increased current draw from a lower voltage source might have stressed the boost circuitry too much, but still, the light had like 4 or 5 complete cycles on 18650s without any problems.

On a related note, I don't suppose anyone here has an spare U2 sandwich just laying around? Heh, thought so.

It should not have happened.

Peak Voltage of a MC-E is 4.2V (dropping to ~3.7V)... and peak voltage of 2 CR123As is ~6.4V (dropping to ~ 4.4V).

stressed the boost circuit? I haven't heard of anything like that.

Unless you put the cell in backwards, it shouldn't have happened.

First of all, this is a LuxV version of the U2. Unlike the newer SSC version, it uses a boost circuit. The MC-E was wired 2P2S, so its Vf was arond 6.5V, which is close to that of the LuxV that it replaced.

Anyway, with a current stabilized driver, lower supply voltage = higher draw current. I believe the light drew something like 2.2A on max from a single 18650 vs. 1.4A or so from 2 CR123A cells or something in the same ballpark.

Also, boost drivers typically operate at maximum efficiency when suply voltage is closer to output voltage. As supply voltage drops, efficiency decreases. Lower efficiency = more heat dissipated by the driver.

Been running mine for years on 18650s and no issues. One of mine has a neutral MC-E, but that one only has a couple of cycles since the mod (Milky).

Seems strange, let us know if you find the cause.

Sverre

Same here. I have a modded MC-E U2 and it only uses an AW 18650 IMR cell. It's been fine for over 20 charging cycles.

Might want to update the thread title to state this is a modded U2, not stock.

I've been running a U2 with MC-E for a year or more on single AW18650. Nil probs.

I have a Lux V U2 that tales 18650 that i would love to have modded to an MC-E. Suggestions on a modder to do it?

oldways said:

I have a Lux V U2 that tales 18650 that i would love to have modded to an MC-E. Suggestions on a modder to do it?

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Milkyspit. He did mine and it is perfect:thumbsup: Might take a while since he is kind of busy though.

Sverre

Are you using a flat top 18650, or one with a nipple? Brand of 18650? Using flat top, a make ship nipple would need to be used, and sometimes a small magnet is used, which can move around.

Bill

Thanks. I run AW 18650 nipple top. Works great.

oldways said:

Thanks. I run AW 18650 nipple top. Works great.

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I was speaking to OP.

Bill