Yeah, the final measurements for output are what really matters, everything else is really just working back from that!
Remember that a good high capacity IMR 26650 even under load would be well over the forward voltage of the XM-L LEDs (maybe 3.9v under load fully charged with the XM-L vf of around 3.3v @2.3-2.5 amps) with the full calculation you get:
6.6 x 3.9 = 25.74
/100 x 90 (assume 90% efficient circuit) = 23.166
/3 (3 XM-Ls) = 7.722
/3.3 (each 3.3v vf) = 2.34 amps to each emitter.
According to the spreadsheet that means nearly 900 lumens for each U2, which would make almost the claimed amount at the emitter(s ).
hehe.... Redforest UK's calculations are deep....i understand part of it only at first glance.
Anyway Xtar S1 is 475Hz PWM for my copy (see if production copies are different), that's not too bad and very usable. Just received my 5 x XM-L Trustfire TR-J12, it's 124Hz. Now that's bad!
It's not DD aka Direct Drive. I think Selfbuilt chose the wrong word. If you apply his definition of DD, then each and every Ultrafire, Trustfire, Uniquefire is DD.
I measured only 6 amps plus at the tail. It should be approx 15A (good cells) at the tail if it were to be DD. heh.... Also with Direct Drive, it would never be able to do > 30 mins run, let alone 76 mins till the knee drops.
Selfbuilt has provided lots of data in CPF, hence i don't feel like it's nice to mess up his review thread just due to a bit of "semantics".
It certainly is not boosted as the current falls as it's discharged, because the 3 cells are in parallel. TM11 managed to pull it off though. Not the same experience as those with cells in series like TK70, TR-J12, Uniquefire 3900 and the likes.
You might wanna check out his graphs. 400 -> 300 in 60 mins. Drop of 25%. Can you see a difference between 75% and 100%, yes you can....try a thrower light that has 40k lux and 30k lux at a distant target. But in real life usage without A/B, no way.
It is not regulated in a straight line, definitely. So it is not 100% perfect, that i'd agree. In fact many 2 x 18650 lights like Fandyfire STL-V6 has a flatter line regulation. A lot of 1 x 18650 lights like even the Jetbeam RRT-2 XM-L cannot maintain a flat line regulation till the end like the multi-cell lights. All 1 x 18650 light sucks? I just want to put some perspective into things. Maybe i may seem to be defending the light because I got a "review copy", but allow me to present my case.
This so-called lack of regulation is the least of my worries. Though the nearly 500Hz PWM is unobtrusive and very usable, it is still mildly visible and i guess to the purist flashaholics that is "not nearly enough" because Olight/Fenix/Jetbeam/Nitecore can do it anyway (which is true). The PWM needs to be pushed up to at least 1kHz....heck while they are at it just push it up to 5kHz (and be done with it) if they can't drive it by varying the current like the Sunwaymans. :D
This is the difference in throw output at a distant object, the difference is ~ 33.3%.
As long as we are talking about higher draw lights like in the 2.5A range (corresponding lumens in the > 600L range), it proves to be very difficult to do with single cell. Take for example, a Lumintop TD15X. Check out the 1 x 18650 curve. (this is Selfbuilt's work)
usd175 is delivered i guess, direct from XTAR. I am not supposed to say, but of course it's easy to guess that i paid a slightly lower price (and taking a caculated risk as well as being an early adopter or rather tester!). I don't even have lanyard or O-rings!
The other dealers have not really got stock yet, i have asked.
2100 why can you not say how much you paid for it?
Many reviewer get there lights for Free and they state this, some just say evaluation copy or review copy.
I'm a straight talker as most of you lot know. I said the Dry was ugly. I have no problems when people review lights that they get for free, I will always take the reviews with a pinch of salt.
What I do not like is when people are not clear whether they got it free or not.
I thought the SR92 battery pack contained 6x 18650 cells, this only uses 3 so it's hardly a fair comparison. I do agree however that the lack of regulation is not ideal and is a deal breaker for me, along with the PWM. Not that I need any more lights at the moment or in fact ever.. (I'm sure this won't stop me in the future though!)
A little known fact is that PWM actually uses current, (not only as it involves bursting the LED at a higher current and so doesn't take advantage of higher efficiency at lower current inputs) but each switch from on/off of the LED uses a tiny amount of electricity, this means that lower freq PWM is actually higher efficiency then high frequency, and is why zebralight originally used it in L2 mode of the H51 etc as it was more efficient to use low freq PWM than current control as the current to the LED would have been below optimal efficiency level. I'm not sure if this consideration comes into question when manufacturers are deciding what frequency to set PWM but it's an interesting fact.
I for one think it's one hell of a light. I even told Rick that last week on the phone. But I also can now say they won't be selling very many to US buyers for $175 shipped to the US. For that kind of money, I can buy a brand new Fenix TK70 for $164 shipped to my door.
I brought in 1 x 18650 sincel-cell lights for comparison because those are just single-cell lights, ie 3.7-4.2V discharge range. This Xtar S1 is a 4.2V light, just that it is like 9AH in capacity with 3 cells in parallel. But then there are also 3 LEDs and 3 individual drivers. This is more of a technical/engineering topic rather than a semantics "how many cells the light's got".... My understanding is that it is not easy to boost a light of this nature to maintain a pretty flat output all the way till the cell is near 100% discharged (driver input voltage is below emitter's Vf). A cell could be at 3.0V under load and you still want to get 700 lumens from it. I am not a driver expert, maybe those into electronics can chime in.
Don't worry how2/xed8888/chicago X....i am not mad or anything, and anyway it's natural to suspect that i got a free light. The light was sent to me on promise that i don't reveal what i paid because that'd affect the on-sale price....but i certainly did not pay a budget light price. Still comfortably above 100 bucks. LOL!
Remember, i got the light and and shared measurements before I could see any reports at BLF and CPF (except the folks at shoudian), ie i dived in 100% blind. And such things are definitely not for fun and laughter, if you know what i mean. I have actually asked like 5 vendors for availability.
I am not sure if i understand the word direct drive correctly. With DD that it means the light is directly driven by the cell right? It could be direct hardwire, it could go through a driver's electronics but basically in DD mode the driver does not limit nothing. This is my understanding.
But if there is a resistor in there or a driver which limits the current, then it is not direct drive though it could be unregulated (seperate matter). This is because in the CPF reviews, the direct drive is mentioned multiple times. Maybe it's coz i have been doing playing with too many DRY 3 x XM-L, now that's DD. heh... (ok so the latest driver is still 90% PWM in Turbo). Perhaps i am wrong and the correct info is something that i can learn too.
Here (it's the same as place as the XTAR 18700 group buy) :
Look bros...it is funny that the word objectivity should even be mentioned. I thought real-world scenarios sharing is good. LOL!
Ok...I presented all the beamshots + measurements and that is objective data. But I need to be "subjective" as well because in the real world that is important too. It's the same in the Hifi/Photography/car mods arena. Specs and measurements tell you that part of the story only. As a professional photographer of many years (Chicago X too), we only know that too well. Same goes for car mods, which X dabbles in as well as for income. LOL! I am not saying that it's not important, numbers is the lifeline of engineers.
What is the diff of 20% out? It's 20%...nothing more to that. If you want throw, you'd need heck lots more. If you have lights that surpass 0.5-1 mil cd you probably can appreciate this more....else it'd always be in that XR-E/XM-L 50-60mm head diameter kind of performance and range and say that hey this XM-L thrower throws very well. I'm just trying to bring this sense of "scale" into the big picture....
PS. I have experience (in events) in which we've got several billions of candlepower comfortably from nearly 50 advertising search lights each of > 5kW (it was a mix), and it threw 10km, but barely only. Of course they were trying to light up the clouds (the wispy ones, cirrus). That's real world sharing for you.... and that's the truth of searchlights in the real world. LED Search & Rescue lights often advertise that they can do 700m, 1km. :)
I just want to put some perspective into things. Maybe i may seem to be defending the light because I got a "review copy", but allow me to present my case.
