Lux measurement of U2 - UPDATED w/ MEASUREMENTS!! (Again!)

dizzy said:

Where did you get the 2400mAh 18650 from? I have only seen the 2200mAh 18650's from AW and Lighthound.:help:

PS: Nice graph, by the way.

PSS: Your member join number is only 5 behind me. Wow, thats close.

Click to expand...

Batteryjunction has LG 18650s at 2400mAh for $8.50. These are not protected, so unless you know your way around Li-ions they might not be a good idea. LG makes very good batteries so these should be among the very best on the marked.

The U2 wont kill unprotected batteries so a DSD charger and some knowledge will make this a very nice solution for your U2. I use Sanyo 2400mAh, but I haven't seen these for sale anywhere.

oh, yeah, i hope this light can handle being submerged for a LONG PERIOD OF TIME. I will be taking mine camping, and we plan on going fishing while walking in the creek, down the creek at night .

also, just spotted this.... nice tailcap.:

http://forum.flashlight-fan.com/gazouimg/P1010385.JPG

-David

I hate it when the editor eats my post.

Oh well. Sorry, no writeup this time. Here's my runtime plots for some 18650 cells.

I'm surprised by that rapid step down just after the start. Makes me think your LuxV is not making good thermal contact with the heat sink. Neither of my two U2s show that severe an initial drop with the 18650 cells. I suppose it could have something to do with the cell itself, though it shouldn't. The maximum the U2 will draw from a cell while in regulation is about 1.5 amps, and that shouldn't be overtaxing a 2000 mAh Li-ion cell.

In my original message, I started to explain where I got these cells. They're all scavenged from dead laptop packs. The Panasonics are probably three or four years old, and have lived a hot and difficult life. I think they're only rated for 1400 mAh or so anyway. The Sonys are a little better. I'm sure I'd be much better off just buying a new cell for ten bucks, but these are free.

I was also a bit surprised by the sudden drop in the first ten minutes. After I got tired of testing the Panasonic and thought about the results, I decided to try a different cell. The Sonys drop too, but not nearly as fast or as far. Until I can get something better in there, I'm going to blame the cell. The light does get warm on a fresh cell at the start of the run, so I know there must be some kind of thermal path in there.

I've also used these Panasonic cells in a Mag 2C with 20 watt lamps. Curiously enough, they show similar performance. That is to say, they start out nice, bright, and white. Within five minutes or so, they dim down a bit and go a little yellow. If you turn off the light and let it rest for a while, it comes back up again.

i plan on somehow getting a u2 onto my head... in other words, i want to use it to illuminate in front of me, but i cant hold it with my hands... is there any way to attach it to a cap or anything like that?

-David

cheapo said:

i plan on somehow getting a u2 onto my head... in other words, i want to use it to illuminate in front of me, but i cant hold it with my hands... is there any way to attach it to a cap or anything like that?

-David

Click to expand...

I've used mine as a headlamp using a slightly modified headlamp-strap, but it is a bit on the heavy side for wearing on ones head. I made the strap for use with HDS and other single cell lights which aren't that heavy.

I think it is way to heavy to fasten on a cap. Might be OK on a helmet with Two-Fish Lockblocks to afix it....

Good luck and enjoy

wasBlinded said:

I'm surprised by that rapid step down just after the start. Makes me think your LuxV is not making good thermal contact with the heat sink...

Click to expand...

As I noted earlier, all my 18650 cells are gutted from "dead" laptop packs. I've got some orange Panasonic CGR18650HG cells, green Sony US18650GR type G5 cells, and now some red cells of unknown origin. All these cells are heavily used, from a laptop environment where they spent most of their life getting cooked by a Pentium processor. I don't expect much out of them, except for them to cost me nothing.

You can learn a lot from reading the RC forums. Those guys seem to know their rechargeable lithium cell technology. I believe the orange Panasonics once had a rated capacity of 1800 mAh. The Sony G5 should have been good for 2150 mAh. I don't know what these reds are, but they kick the snot out of my oranges and greens.

I think my U2 has perfectly fine thermal transfer. I'm going to blame any performance issues on the old, beat-up cells I'm using. The RC guys seems to say that li-ion can sag badly under load, especially if your cells are near the end of their life. I believe that's what is happing on my earlier charts. If I truly was seeing a thermal issue, I would expect that all my cells would settle out around the same lux reading. This is not the case. The oldest cells I have settle out around 1500 lux. The Sonys look like they may end up somewhere in the 1600s. The reds will hold almost 2000 lux for nearly an hour before they start to give up.

Here's my latest chart:


Extra credit question:
Can anyone identify an 18650 li-ion cell in a red wrapper? The only text seems to be IL4FJI3 and 0026975. These came out of a Dell C640 laptop pack. The pack had a rating of 4460 mAh at 14.4 volts.

Hi guys!

Well, the dealer I bought my U2 through was kind enough to send me a new one, and I'm sending the old one back to him to deal with Surefire... SO we'll see what happens with this one!

I also just bought a new Meterman LM631 light meter, so I am ready to get this thing tested!

Results to come when both the new U2 and the light meter are in my hands!

John

Wow John, sounds like you have a great dealer there. I hope your new U2 is more to your liking.

Can't wait to see the new results with the new Meterman. Thanks for the heads-up.

I'm really looking forward to doing more tests, oddly enough..

I'm even thinking about offering runtime testing services to people, if they provide the light and the batteries (obviously they'd get everything sent back)... what are people's thoughts on that?. I don't think I'd want to charge for it, as people already would be paying shipping, which adds up after a while.

-John

Ty;

The red ones are Sanyo cells.

I have some brand new 2400 mah Sanyo cells that perform quite well in my U2 Cree lights.

Larry Cobb