Surefire U2

Can it run on 2xRCR123, or do you have to use Primaries? I know it will run on 18560, but want to know all options.

Also, can the emitter just be swapped out?


Thank you

Tim

I'm pretty sure it can run fine on two RCR's without harm, but don't take my word for it.

The 18650 will only fit in older bodies if you remove the battery sleeve. The 17670 will fit in any of them. Leef make an 18650 tube for the U2.

The emitter can be swapped, but it's not plug and play. It take someone who knows what they are doing.

I'm pretty sure the U2 will let out the magic smoke if you try to use a pair of R123 cells in it. Each li-ion cell might be as much as 4.2 volts fully charged. Together, a pair of them makes 8.4 volts.

The circuit in the U2 is almost entirely boost. The Luxeon V wants to see somewhere around 6 volts, maybe a little more. A pair of CR123A primary cells will put out just a bit under 6 volts under load. A single 18650 cell is going to be 3.6~4.2 volts. Both of these are less than the direct drive voltage of the Luxeon, and work fine with the U2 circuit.

People have run a Luxeon V direct drive on three CR123A cells (about 9 volts, no-load) but they're relying on the primary cells to sag a boatload. They're also overdriving the Lux V a fair amount.

I'd seem to recall that best case for a pair of R123 cells in the U2 will be a stinking bright, overdriven, short lived flashlight. I'm pretty sure you lose all the levels - everything becomes the brightest level. Worst case is the driver circuit fries instantly, and you have no flashlight at all.

I wouldn't do it.

Here's a couple references about the L4 (which also has a Lux V and runs off two CR123A) and the U2 concerning the use of R123 cells.

don't use 2x R123 li-ion or you will fry KL4 head...

Yeah, 2 X RCR123a is a no-no. Instant hunk of useless metal.

For your U2, don't use normal 4.2v RCR123 cells - you will overdrive the LED and controller circuit.

I'd have to put up a big red flag and say NO GO to using 2x R123s in a U2.

I don't know about you, but I spent $279 for my U2. It costs me about $40 to fill the tank in my Honda for a week or two's driving. $40 buys a years worth of CR123's for my U2 and other SureFires, my hobby. Just look at it as a nominal expenditure for your pass time and don't practice false economy. I don't take risks with my beloved SF's.

I agree with Spence. I bought a pack of 72 primaries from Surefire in July.
I am not about to trust re-chargables in a light that costed $280.00.
Especially if they f--k up the 6 level brightness function.
Since I also EDC a Fenix P1D-CE that only uses one battery, that one is used much more than the U2.
As it is I will have a hard time going through 72 batteries in a year.
So I do not find primaries to be too expensive.
Besides, the last thing I want is another freakin charger.:sick2:

Thank you everyone for the responses, GREATLY appreciated. It sounds like the best scenerio is 2xCR123, but 1x18650 would be safe as well. I have yet to see the of the "magic smoke", nor do I care to.


Tim

I personally just bought a Leef body (excellent machining job) and 5 18650's with the low voltage alert I can run my cheap AW unprotected cells in it. In a pinch I can use CR123's as well.

You can use RCR123's but you need to make sure they are the 3.0V versions. The only "problem" with them is that they are fairly low capacity and only last about half as long as primaries. Most are around 750-850 mAh, where most primary CR123's are 1300-1600 mAh. I use the 3.0V RCR123 and like 'em for the most part.

Roger

i havent put primaries in my U2 yet
but i have only used Pila 168s (17670) and AW 18650 batteries in it (i have an older sleeved U2)
my U2 is my "go to" light for everything, and if im out at night it gets clipped to a pocket as a backup to my EDC.
i wouldnt try to us R123s in it, - especially at the price it cost

just run 17670s in it - theyre not much more than the R123s to purchase and easy to find (lighthound, Cpfmp etc),, work just as well as primarys (ok so they might run 10 mins less, and turn off suddenly *) but 10 cycles on them and they have paid for themselves - my one of my pilas lasted 2 1/2 years, the second one is still going at nearly 4


* - due to the protection circuit on my Lions the light steps down to L5 for about 10 mins, then L4, for 3 or 4 mins, then straight down to 1 where it runs for another 10 or so mins before the protection circuit kicks in
i havent completley drained the 18650 in it yet, but that is the way it behaved with the Pila 168s

How much difference (lower) performance is obvious with the U2 when running it with a 17670? Do all brightness levels function, as well?
Thanks and happy New Year to you guys!
Spence
:wave:

Spence said:

How much difference (lower) performance is obvious with the U2 when running it with a 17670? Do all brightness levels function, as well?
Thanks and happy New Year to you guys!
Spence
:wave:

Click to expand...

mine functioned perfectly on 17670, still works well on the 18650 i got a few months back
the light was designed to run on rechargeables from the beginning (early ones had a sleeve to stop 123 cells rattling, but allow 18650s to be used by removing the sleeve)
from memory it is also safe with non protected cells, it has a overdischarge protection built in - but i could be wrong

That's correct Unprotected cells are perfectly safe in a U2, it gives visual warning around 3 volts that batteries must be replaced. For $6 a cell for 18650's I got 5.