18650 Downsides

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ja10

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I have been searching all over the place trying to decide if I should make the move to the 18650 battery for my U2. I know this has been discussed at great length (I've read everything I could find about it), and people rave about the runtime, how great it is, and how glad they are that they have an older U2 that accepts the 18650 battery.

However, while 99% of what I read is positive, I did read a few comments last night that went something like, "Be sure you don't mess with the spring too much, or BOOM!". Someone else talked about how they have had the 18650 running for a while now, and they don't think it is damaging the light at all.

Would anyone mind explaining what I am risking by trying the 18650? I popped my U2 in the freezer last night and slid the liner right out, so I'm ready to get the battery. I just don't want to get too greedy about runtime and ruin my new light!

Thanks in advance.
 
There is no downside from my point of view. The light performs well and you have less risk of "vent with flame" problems associated with multi-cell lithium primaries. I would rather recharge than buy disposable batteries. The only worries I have read about are getting the battery tube liner out & the fact that the new U2's won't accept the 18650. I would not have purchased a U2 if I had to use primaries.
 
I agree that there is no real downside. I've not had to do anything to my springs to run LG or Sony 18650s either.
 
This is probably a stupid question, but the 18650's I'm looking at are 3.7 volt. Does the circuitry in the U2 reduce that to 3.0 okay?
 
I don't know much about batteries, but I believe if it's the U2 you're worried about, then you should relax and enjoy the light. I've read numerous threads here that the U2 has protected circutry (or something like it) that would not drain 18650s below a certain dangerous level, even with unprotected cells?

If anything, I have read that with 18650s, the U2 WILL loose some lumens at the initial use, something like 95 lumens (with primaries) versus 90 lumens (18650). But for twice the runtime, it's definitely a good trade.
 
The 18650's have a nominal capacity of 3.7 volts, and fully charged 4.2volts. The U2 will boost the current to the spec voltage of the lux V emiter, which may be 6-7 volts or so. You should get full regulation out of the 18650 battery, and you will get longer runtimes with the highest capacity ones. Look for the LG18650 2400mAh LiIon's for the longest runtimes.

Bill
 
daveman said:
Will U2's peak lumen suffer with 18650s?
Click to expand...

The peak lumens suffer a bit. Usually about 5-10%, so your light will be putting out about 90-95 instead of 100 lumens. I do think the 18650s can maintain that level quite a bit longer than the cr123s so they will even out.

The drop in output is barely visible, but can be measured on a light meter. For me the longer runtimes and free use outweighs the any downside of using 18650s.

Sverre
 
The DSD/Pila charger doesn't overcharge. The U2 doesn't overdischarge. The spring issue is a non-issue -- obviously you don't want to pull the spring out so much that it breaks a battery. That goes for any light.

The only problem I can think of is that the DSD is very bare bones and the power adaptor is shoddy and can blow an internal fuse when used on the european power system.
 
ja10 said:
This is probably a stupid question, but the 18650's I'm looking at are 3.7 volt. Does the circuitry in the U2 reduce that to 3.0 okay?
Click to expand...

The two CR123a's that typically feed the U2 give it 6 volts, while a single 18650 replaces both of those CR123a's and gives a peak of 4.2 volts.

U2 18650 runtimes http://www.candlepowerforums.com/vb/showthread.php?t=128188
 
daveman said:
Will U2's peak lumen suffer with 18650s?
Click to expand...
Quickbeam's site has a table showing the compatibility of Pila rechargeables with various lights. He says that the output of the U2 is the same as it is with primaries. He used the Pila version of the 17670 cell, the 600S. Of course the runtime will increase with a 18650. He tested an L4 with both primaries and a Pila 17670, and the output was identical. I would assume, as careful as Quickbeam is, that he also tested the U2, so any difference in output should be very small. I'm very happy with my U2 and the 18650's and 600S/600P batts that I now use exclusively.
 
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faucon, can you expand on quickbeam´s site? I own a brand new stock U2 with no plastic sleeve on it and I´ve been told I cannot use 18650 on it and looking for alternatives. much appreciated.
 
LED61 said:
faucon, can you expand on quickbeam´s site? I own a brand new stock U2 with no plastic sleeve on it and I´ve been told I cannot use 18650 on it and looking for alternatives. much appreciated.
Click to expand...
Hi LED61, unfortunately you're right from what I understand. Surefire narrowed the inner diameter of the U2 in its latest incarnation. I have a 'first generation' U2 that accepts 18650s. However, before I got my 18650s I was running my U2 on 17670s or Pila 600S cells. Runtime is less, but still very satisfactory in my experience. So you still have a viable rechargeable solution. Some brave CPFers have also bored out their new U2 to widen the inner diameter --- I think to 18.5mm --- to allow the use of 18650s. Personally I would hesitate to do this since the 17670 cells work perfectly well, but there are a couple of threads on doing this. You might check out Quickbeam's site (www.flashlightreviews.com) and look up his table on 'Pila compatibility'. Your choices would be Pila 600S cells or their equivalent, 17670s. Besides the Pila cells I use the AW protected 17670s, available from Lighthound among others. Good luck!
 
Thanks for all of the replies! This has helped put my mind at ease.

One last question - if cost didn't make a difference, would it be better to go with protected batteries? Or is the only risk with unprotected batteries over-discharge, with the U2 won't allow?
 
Bullzeyebill said:
You should get full regulation out of the 18650 battery, and you will get longer runtimes with the highest capacity ones. Look for the LG18650 2400mAh LiIon's for the longest runtimes.

Bill
Click to expand...

I just got some LG 2600mah 18650's, which are now the highest capacity 3.7 volt cells, for my U2. They work great in it, and as far as the protected and unprotected part goes, right now the 2600's are only available in the unprotected version and I only use them in the U2, which will not let them get discharged too far.

I am no expert about Li-ion batteries, so I would not try using them in other lights without further research. Some incandescent lights will not work on protected cells because the current draw will kick in the protection circuit in the cell. But then you have to make sure you don't discharge them too far or you will ruin the battery.
 
If everything goes according to plan, the special protection pcb on those batteries won't be used in the U2->DSD loop process. Only if something freakish happened to the U2 or DSD circuitry would that protection come into play. And planning for that would be super mega overengineering. This is a flashlight, not an aircraft carrier :)

If you want to be super crazy extra safe, unplug the DSD when you're not using it, only charge the cell when you're around (ie from when you get home to when you go to bed, or I'd charge it overnight), and take it out of the U2 when a power level or two starts to drop out. But these precautions realistically won't be necessary -- we've never heard of a DSD exploding an 18650, or a U2 overdraining one.

Also yeah, we talk a lot about 18650 because it is the holy grail, but the 17670 is perfectly viable as well. Look at it from the perspective of having a stronger U2 body, rather than having a smaller battery ;)

PS: li-ion cell lifetime is realistically defined by its age from being manufactured. So don't buy more than one cell unless you specifically require redundant power source. Whether you buy 1 cell or 10, all of them will be weak in 5 years, whether you use them or not. So get one cell and cherish it, charging it during the day or when you sleep. :)
 
ja10 said:
One last question - if cost didn't make a difference, would it be better to go with protected batteries? Or is the only risk with unprotected batteries over-discharge, with the U2 won't allow?
Click to expand...

I would go with protected ones. They have more advantages, so they are protected against short cuts in the light and in the charger and also against overcharging (in the case the charger go fail).

Best regards

____
Tom
 
Thanks everyone - I'm definitely getting the 18650 now. I just hadn't heard anyone talk about why not to get the battery, so it made me a little nervous. I'm placing my order now!
 
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