Request for U2 runtime graph with Pila cell

[KevinL]

I'll second turbodog's assessment that it's brighter. (now if only lithium ions weren't such a PITA to charge)

Even though the U2 is using a constant current circuit, let's look at the following figures:

3.8V x 1.4A (U2 is also limited on the input side) = 5.23W of energy available.

Let's say the Luxeon Vf starts high - these figures are assumed but will serve to demonstrate why the light gets brighter. Say, 7.1V, 800mA. 5.68W required. Now, since the U2 is current limited, it doesn't have enough energy to drive the light at full power, so you'd get 7.1V, but only around 730mA.

If the Vf does continue to drop, let's say, to 6.9V, the current will go up another 30mA, enough to make a difference.

I was hoping that the U2 would be able to deliver a wide open level 6 even on 18650s - I'd love to think of it as the light with no compromises. In the meantime, using higher mAH cells, which hold their voltage better under load helps a lot. The Maha C777Plus2 is an education in cell capacity unto itself.

 

[cliff]

[ QUOTE ]
KevinL said:
I was hoping that the U2 would be able to deliver a wide open level 6

[/ QUOTE ]

Are you noticing this diminished level visually or by some type of meter? Maybe my eyes are getting dim with age, but I don't think I'll be able to bum myself out sufficiently over the Level 6 issue without better light measuring equipment than I now have. Level 6 is a big step up from Level 5 on my 2-day old U2 for a good long time on 168s, and I can't see much difference with primary cells.


Better dumb and happy I suppose, but if the Vf drops and it gets brighter I probably won't notice that either.

 

[KevinL]

I am measuring by eye as well and while I can't tell that much of a difference between rechargeables and primary cells, I can tell when the rechargeables drop out of regulation on level 6 after 20 minutes.

You're using the most important light meter of them all. If yours works, great - apart from the visual acuity issue, your U2 might have a lower forward voltage and thus be able to hold it for longer. If there is no difference visually, that's where it counts, regardless of what the instrumentation says. Sometimes I wish I couldn't tell the diff either then I'd be a happy camper with all my lights /ubbthreads/images/graemlins/grin.gif

 

[kj]

Here is my tentative result. I'm taking the level 2 runtime now and will take the level 1 (and may retry the level 6).

Level 5
Level 4
Level 3

 

[KevinL]

kj, YOU ARE THE BEST!!!! /ubbthreads/images/graemlins/bowdown.gif /ubbthreads/images/graemlins/clap.gif

Thank you so much, these are the charts we desperately needed to see. Not only does it portray U2 runtime accurately, it shows that on level 6, the difference is not that substantial, and that the problem may lie with my cells rather than with anything else.

You have no idea how far those graphs have gone to set my mind at ease about using 18650s.. I really think it's my cells that are the ones compromising and not the light - it would be wrong to blame the U2. Losing level 6 completely at 20 minutes indicates a cell that just can't take the heat. Running it through the Maha analyzer seems to confirm this - the cell discharges to only 1200mAH down from its nominal capacity of 1800mAH. The cell is probably junk, but luckily I have another 1600mAH/1800mAH cell to work with that seems to work a lot better.

I feel a lot better now. /ubbthreads/images/graemlins/thanks.gif

 

[turbodog]

[ QUOTE ]
KevinL said:
kj, YOU ARE THE BEST!!!! /ubbthreads/images/graemlins/bowdown.gif /ubbthreads/images/graemlins/clap.gif

Thank you so much, these are the charts we desperately needed to see. Not only does it portray U2 runtime accurately, it shows that on level 6, the difference is not that substantial, and that the problem may lie with my cells rather than with anything else.

You have no idea how far those graphs have gone to set my mind at ease about using 18650s.. I really think it's my cells that are the ones compromising and not the light - it would be wrong to blame the U2. Losing level 6 completely at 20 minutes indicates a cell that just can't take the heat. Running it through the Maha analyzer seems to confirm this - the cell discharges to only 1200mAH down from its nominal capacity of 1800mAH. The cell is probably junk, but luckily I have another 1600mAH/1800mAH cell to work with that seems to work a lot better.

I feel a lot better now. /ubbthreads/images/graemlins/thanks.gif

[/ QUOTE ]

I would for sure say your cell is junk. Both of my pila 168s cells will run level 6 to within 5 minutes of complete discharge (45-50 minutes or so).

 

[SilverFox]

Hello Kj,

Excellent work.

Looking at your graph, I went back to my U2 Battery Comparison graph and checked the data at 40+ minutes for the SureFire batteries and 50+ minutes for the Pila 168a. The voltage was just over 3.4 volts.

I may hazard a guess that level 6 dies when the voltage drops below 3.4 volts.

Tom

 

[PaulW]

KJ,

Good graphs. The comparison between the Level 6 graph and the Level 5 graph tells the whole story about whether the light is regulated on a Pila cell. Since I want to run my U2 with the Pila 168a (with a capacity of 1200 mAh) instead of the Pila 168s (with a capacity of 1800 mAh), the runtime will be a little longer. I think the curves would just shift to the right.

It appears that for Levels 1 through 5, the runtime graphs for the 168a would pretty much be equal to the ones for the SF 123A. For Level 6, the 168s voltage does indeed appear to be gradually dropping the light out of regulation. And so will the larger 168a. The Level 6 results are disappointing, but not as bad as I thought they might be.

I’m wondering now about how different the Level 6 graph would look for a U2 with a different Vf. My guess is that the droop in Lux becomes less as Vf decreases. Maybe someone has a more educated guess than mine.

Thanks for your excellent work KJ,

Paul

 

[Klaus]

I would guestimate that using a 2400ma 18650 the runtime would equal or even beat the SF123 one, and now there´s the 2550ma Sony ones jut around the corner too /ubbthreads/images/graemlins/grin.gif

Klaus

 

[turbodog]

Has anyone tried an 18650 BARE cell? Someone posted that the light appears to have protection built-in for that cell so that may very well be what surefire plans on supplying later on.

 

[Klaus]

The data supplied in this thread and elsewhere suggests the behaviour is sufficiently similar to the L4/L5 driver and therefor won´t deep-discharge a bare cell - no longer boosting below 3,5V is plenty for a bare Li-Ion in my book.

Klaus

 

[cy]

Thanks KJ, excellent work.

Klaus, where can I find the sony 2550 mah 18650?

pila 168A enroute, but would like higher capacity.

 

[KevinL]

[ QUOTE ]
turbodog said:
Has anyone tried an 18650 BARE cell? Someone posted that the light appears to have protection built-in for that cell so that may very well be what surefire plans on supplying later on.

[/ QUOTE ]

mmmmm? someone callin' my name? /ubbthreads/images/graemlins/tongue.gif

ALL my work with the U2 has been done on either primary cells (non-rechargeable 123s) or the 18650s. All unprotected. I know, cuz I stripped the 18650s from laptop packs. I've gone thru two packs so far and the Maha is working overtime.

I've confirmed that the light wlil not deep-discharge an unprotected cell, it will not even fire on 3.0V, not even on level 1. The 'danger' threshhold for lithium ions is 2.5V, so this should still be reasonably safe.

 

[KevinL]

[ QUOTE ]
turbodog said:
Has anyone tried an 18650 BARE cell? Someone posted that the light appears to have protection built-in for that cell so that may very well be what surefire plans on supplying later on.

[/ QUOTE ]

mmmmm? someone callin' my name? /ubbthreads/images/graemlins/tongue.gif

ALL my work with the U2 has been done on either primary cells (non-rechargeable 123s) or the 18650s.

I've confirmed that the light wlil not deep-discharge an unprotected cell, it will not even fire on 3.0V, not even on level 1. The 'danger' threshhold for lithium ions is 2.5V, so this should still be reasonably safe.

 

[K-T]

Lots of good infos here, thanks for the work on the graphs. /ubbthreads/images/graemlins/bowdown.gif /ubbthreads/images/graemlins/clap.gif /ubbthreads/images/graemlins/wink.gif

 

[Klaus]

[ QUOTE ]
cy said:
Klaus, where can I find the sony 2550 mah 18650?


[/ QUOTE ]

cy, only information I have is an article referenced on CPF a week or so ago

Sony 2550ma

Klaus

 

[JanCPF]

WOW KJ, thanks a lot! /ubbthreads/images/graemlins/happy14.gif /ubbthreads/images/graemlins/bowdown.gif Those graphs was exactly what I initially requested.

It doesn't really look all bad on level 6 all though it isn't in perfect regulation. Dang, I might be in the market for one of those U2s after all.

Jan (gotta turn in now /ubbthreads/images/graemlins/sleepy.gif)

 

[KEN TYE]

I am using 18650A bare cells . I can run well over an hour, I think I did a test when I first got the light and was getting hour and 20min on level 6 with no drop outs. when it was time for the cell to die it went very fast , this is why I keep 3 cells with me

 

[FlyUSArmy]

Wow this thread grew fast. When it 1st started, I had been carrying my U2 for a couple days using it intermittently, powered by a Pila 168S and knew it retained level 6.

The thread got me curious so last night I checked to see what my Pila U2 performance was.

The light ran at level 6 for about 45 minutes, after which level 5 was as high as it would go. It supported level 5 for about another 10 minutes. By 90 minutes runtime, it was down to level 1. At 2 hours, level one was noticeably dimmer but still going.

So it seems there is some 'your mileage may vary' factor. I am completely satisfied with my U2 on a Pila and plan to get a 168A for it for the higher capacity.

 

[cy]

got my pila 168a in, lights up level 6 with no problems.