Surefire U2 Finally Reamed For 18650's

I finally reamed out my new Surefire U2 successfully (New Version) to use the new 18650's by LG 2600Mah. Tested on level 6 for runtime of 115 minutes with all 6 levels of brightness settings. Still bright for over 2 hours with only 5 levels of brightness.

I originally tried AW's 17670's with the same test, and the runtime was 50 minutes with all 6 levels of brightness settings.
This was totally worth modifying for myself, but I did take a chance of messing up a perfectly good U2.
Everything is working perfectly with great runtime!!!!!!!!!

Congratulations on your success, and your courage!

I've been in a week long wrestling match with my new "sleeved" U2. I can't seem to find a solvent that will break the plastic sleeve loose. I thought MEK was my best shot, but no luck so far.

I ordered some 17670's from AW as a compromise, but now that I see your runtime figures, I know I'll always want the 18650.

Enjoy your modded U2. I really think it is a great light!

Bill

There are some posts on how to remove the plastic sleeve...You are lucky to have a plastic sleeve. Mine is all aluminum that I had to ream out to fit the 18650's.

Good Luck on your modification...I know someone will PM you to tell you how to remove the plastic sleeve....Isn't that right CPF'ers

cd-card-biz said:

Congratulations on your success, and your courage!

I've been in a week long wrestling match with my new "sleeved" U2. I can't seem to find a solvent that will break the plastic sleeve loose. I thought MEK was my best shot, but no luck so far.

I ordered some 17670's from AW as a compromise, but now that I see your runtime figures, I know I'll always want the 18650.

Enjoy your modded U2. I really think it is a great light!

Bill

Click to expand...

I've reamed out 4 C/M series two cell Surefires, two three cell surefires, two Pelican M6's, all with a Dremel tool. Yes, that's right, did them all without a lathe. Went through a lot of bits though But it was all worth it since it cut my dependency on CR123's quite a bit.

C-C-B, did you try the freezer trick yet? My insert came right out after I put the battery tube in the freezer for 10 or 15 minutes. I just put my pinkie in the hole and pulled it out.

How smooth is the finish using a dremel? That sounds like alot work and patience!!!

CM said:

I've reamed out 4 C/M series two cell Surefires, two three cell surefires, two Pelican M6's, all with a Dremel tool. Yes, that's right, did them all without a lathe. Went through a lot of bits though But it was all worth it since it cut my dependency on CR123's quite a bit.

Click to expand...

With the use of the LG unprotected cell, how would you know when it's fully depleted? I'd like to use the same cell in my light, but have no experience handling lithium-ion whatsoever.

FlashKat said:

How smooth is the finish using a dremel? That sounds like alot work and patience!!!

Click to expand...

It comes out pretty rough but not too bad. Yes, it's a very lengthy process. Takes me well over an hour. Unfortunately, my dremel motor is toast now I guess reaming out that many tubes and all the heat/wear and tear takes its toll. Oh well, I need a newer model dremel anyways

BayMoe said:

With the use of the LG unprotected cell, how would you know when it's fully depleted? I'd like to use the same cell in my light, but have no experience handling lithium-ion whatsoever.

Click to expand...

I keep track of runtime in my head. Also, the cells get topped off after each use. This works for my pattern of usage, it may not work for everyone. If I know I'm going to need the light for an extended period where I may over discharge a Li-Ion, I switch to primaries. I have cells that are over four years old and they are still going strong, though I think it's time to retire them.

BayMoe said:

With the use of the LG unprotected cell, how would you know when it's fully depleted? I'd like to use the same cell in my light, but have no experience handling lithium-ion whatsoever.

Click to expand...

When there is no longer a level 6, i.e. when going from 5 to 6 produces no increase in brightness, its time to recharge that cell. Even if you keep using it for a while after that point, it won't over-discharge the cell.

LouRoy said:

C-C-B, did you try the freezer trick yet? My insert came right out after I put the battery tube in the freezer for 10 or 15 minutes. I just put my pinkie in the hole and pulled it out.

Click to expand...

Thanks LouRoy! I have read many threads about removing the plastic insert, but nothing about the freezer trick. It worked! Didn't quite get it out with my pinky, more like a flat blade screwdriver and light hammer tap. The insert is still intact so I can slip it back in for primary cells.

Grabbed a Pila 600P from my GL4 to test it and it works great! Seems just as bright as 123a's to me. Thanks so much for the tip.

BTW - Battery Junction (MattK on CPF) is having a sale on protected 18650 / 2200mAh for $6.19 ea. Purchased from Matt before and highly recommend. Ordering some now. www.batteryjunction.com if anyone is interested.

Bill

Would it be safe to run the light when the light switches over to level 4? Just curious. I'm going to get myself a 18650 cell for my U2!

Flashkat,

How did you ream it and what was the final inner diameter? Thanks for sharing.

Mbirds

wasBlinded said:

When there is no longer a level 6, i.e. when going from 5 to 6 produces no increase in brightness, its time to recharge that cell. Even if you keep using it for a while after that point, it won't over-discharge the cell.

Click to expand...

BayMoe said:

Would it be safe to run the light when the light switches over to level 4? Just curious. I'm going to get myself a 18650 cell for my U2!

Click to expand...

I've run my U2 with an 18650 li-ion cell all the way down to the point where it will only light up the lowest level. You can turn the selector ring back and forth from end to end, and the level never changes. It doesn't seem to do any harm to the cell. I've pulled them out and measured them with the voltmeter, and they have sufficient voltage left that I am not concerned about overdischarge. I can't remember the exact voltage, but I'm sure it's over 3.0. The circuit in the U2 seems like it must have been designed with li-ion chemistry in mind, based on the voltage cutoff.

Keep in mind that it is probably not wise to store a li-ion in a discharged state. The longer they sit around empty, the more life they lose. I think it's best to charge them up to 60~80% for long term storage. I typically just top them up all the way if I know I won't be using it for a while.

Here's another interesting bit I've noticed. When my U2 has depleted primary cells, it seems to strobe when you set it to a level that it can't maintain. When it has a depleted li-ion cell, it just steps down to the next lower level without strobing. Go figure.

The 18650 cell rocks. It's definitely the way to go if you own a U2.

I purchase a 18.5mm reamer from Mcmaster-Carr, and used a mill to ream it out since I don't have access to a lathe. I have a machinist background, so don't attempt this unless you have someone do it for you.

mbirds said:

Flashkat,

How did you ream it and what was the final inner diameter? Thanks for sharing.

Mbirds

Click to expand...

No, I know someone with a lathe and would like to figure out exactly what ID I should tell him so unprotected 18650's will fit. I thought I read 18.2mm somewhere else... Thanks.

PS, do you have any concerns about the strength after removing that much material?

18.2mm will be a little too tight of a fit...most batteries will measure around 18.2mm to 18.4mm. Even at 18.5mm the batteries are snug fit. I don't have any doubts about the strength, since the thinest part of the wall will be approximately 1mm thick on a round diameter made of 6061 T6 aircraft aluminum. I also tried stressing the weakest part with no problems.

You could probably break it off if you put 2 pipe wrenches on it and twist it hard enough :lolsign: :lolsign: :lolsign:

P.S. I just reamed out my 2nd Surefire U2 to 18.5mm...I have that much confidence in the strength and modification!!!!! I use to work as a machinist/mechanic which I did learn about the different metals and strength of most metals out there.

mbirds said:

No, I know someone with a lathe and would like to figure out exactly what ID I should tell him so unprotected 18650's will fit. I thought I read 18.2mm somewhere else... Thanks.

PS, do you have any concerns about the strength after removing that much material?

Click to expand...

Excellent! I think I will ask my friend to ream mine out to 18.5.

One last question: at 18.5mm can you still shake out the 2600mah cell, or do you have to remove both bezel and tailcap and push it out? Thanks again for the info.

I didn't ream the U2 since all of mine are of the old manufacture. I did ream an L4 about a month ago, similarly to what CM did... with a small drill, honing bits and rotating brush for the final (mirror) finish.

The internal chemical coating is no longer present, after such reaming.

I understand that the "Chemchote" is a passivation layer obtained with a chromium salt, but I'm still trying to understand how to do it pratically, since I have found no documentation either on line or on paper.

Regards

Anthony

FlashKat said:

I finally reamed out my new Surefire U2 successfully (New Version) to use the new 18650's by LG 2600Mah. Tested on level 6 for runtime of 115 minutes with all 6 levels of brightness settings. Still bright for over 2 hours with only 5 levels of brightness.

I originally tried AW's 17670's with the same test, and the runtime was 50 minutes with all 6 levels of brightness settings.
This was totally worth modifying for myself, but I did take a chance of messing up a perfectly good U2.
Everything is working perfectly with great runtime!!!!!!!!!

Click to expand...

Excellent :bow:

Will

You can shake it out just by removing the tailcap or bezel, or it will slowly slide out on its own.

Good Luck with your modification...I know you will like it alot!!!!!!

mbirds said:

Excellent! I think I will ask my friend to ream mine out to 18.5.

One last question: at 18.5mm can you still shake out the 2600mah cell, or do you have to remove both bezel and tailcap and push it out? Thanks again for the info.

Click to expand...