There’s a chance Cree XM-L 3 will be better. Or XHP35.2. Or XHP35.2 HI. Or Nichia NV4B35AM.
Hard to tell. 
Good to keep those in mind as potential alternatives. Thank you a lot for the help.
Thanks everybody for your hulp. Before I bite the bullet I have only two remaining questions:
Has anybody info on the relative efficiency of the driver of C8+ ramping (regulated FET) versus C8+ 12 group/(statements, runtimes or tailcap measurements) [or FT03 Fet driver]?
Does anybody know if TIR lenses exist for these optics?
Many thanks!
That “ramping” driver from Convoy should rather be called a driver with two adjustable modes + 1 special mode, it’s very different from the ramping firmware from the M21C-U.
I find the timing to get into the mode adjustment a bit hard, but maybe there is something wrong in the switch from the host that I used, I can’t tell.
If you know which two output levels you need then the ramping driver is suitable, but I wouldn’t use it if you need to adjust it often in the field.
Some members like that driver, so maybe they had a better experience with it.
Thanks. I am specifically looking for info on the respective efficiencies: C8+ with regulated fet (the “ramping” firmware) versus C8+ with 7135s (the “12 groups” firmware).
(I am aware of the fitmware’s modes. I hope that the ramping is not too quick to find out —with some patience— and then select a specific efficient current level in the 1,5A mode 2 -if that mode is more efficient with 100-400 lm (and I’d just set mode 1 on very low) and once I know leave these levels in memory most of the time.)
The efficiency at the same current will be the same for both regulated FET drivers. The ‘ramping’ driver lacks thermal regulation, so don’t use the 100% mode for too long or you may damage the LED. The ramping is discrete and slow enough.
edit: check this post for more info
Yeah,that is one of the good links on the subject.
The C8+ with the eight 7135s (12 group firmware) is a different kind of driver, not a regulated fet driver I thought? But do you mean that the efficiency is extremely similar between these two drivers at specific currents?
I didn’t read the part about the 7135 driver (with PWM). The efficiency will be about the same at 2.8A, the regulated FET drivers will be more efficient at lower currents. In both cases excess voltage will be lost at the driver, but LEDs lose efficiency in lm/A, not just lm/W, as current increases, so 1A from running 2.8A at 35% PWM duty cycle will result in a bit less output than 1A from a constant current driver.
Many thanks for your help! Can I bother you with some last remaining questions?
I found with some additional reading this weekend that I misread your answers because I had a few misconceptions and hence wrong questions.
- Should I understand that 8*7135 based drivers use PWM at all current modes except 2.8A (instead of PMW only on modes below 0.35A & modes above 0.35A simply opening gates of additional 7135s) and that the 4-mode and 12-group firmware both use a slightly different but equally efficient version of the ‘ramping’ firmware’s regulated FET (instead of using the older 7135 based drivers) hence your post here. Is that right?
- Are there more efficient options that come stock in affordable flashlights (I only saw buck or boost in models with ca. half the throw, like like SP35 —so vs. C8+ their efficiency is ca. 115% in lm but 55% in cd, I’d guess)? Is the Sofirn C8G-SST40 driver less efficient than the C8+’s regulated FET?
If the C8+ SST40 lacks more efficient alternatives for my purpose, I think of deciding on the ‘ramping’ version but I have four final questions:
- Is the ramping not too quick so that one may with some patience select a specific current level?
- Are mode 1 & 2 equally efficient (I first read the UI flowchart of the driver as saying mode 1 ran on an 8A FET vs. mode 2 on a 1.5A FET module)?
- If the blinking modes run only on 100%, can it be used for hours without damaging internals (I might use blinking on more extended cycling trips)?
- Does it have low voltage protection (how does it operate)?
Many thanks for your advice and patience!
I only forgot this: in another interesting thread on this driver I read something worrysome:
What could he mean with “low modes once displayed and other times not” and is he talking about other regulated fet drivers, not the C8+’s?
Define ‘Affordable’, a $30 budget is different from a $200 budget. Also you need to decide which size is too big.
Normal 7135 drivers use PWM for all modes but 100%. There are drivers with multiple channel like 1+7 or 1+7+FET that archive a bit better efficiency doing that.
I don’t know whether the C8G uses a buck or a FET, the original C8G used a boost driver but they ran out of XHP35s (they seriously need a better supply chain). The SP35 has lower throw because the reflector/head is small. They can make a good buck driver but they often choose FET for higher maximum output and low price. For high throw they went all the way to CULPM1 with the SF47T (2 cells), that’s said, it’s not very different from a single cell Convoy with the CULPM1 8a driver.
A low current choice of LED will depend more on beam profile, efficiency doesn’t change too much.
SST40 or one of the Osram has about 2.9V foward voltage at a bit less than 1A for 300-400 lm, so 3.7V average from Li-Ion means 0.8V or 22% of the power wasted. A buck driver won’t be 100% efficient but it will help.
The situation is a bit different if you are running it at higher current. At 3A vF is about 3.3V, the regulated section will be 4.2 to 3.3, about 80% of the runtime, 3.75V average so 0.45V avg. loss, 0.1V in the other 20, so around 0.4V or 11.
To compare some high throw flashlights at high mode:
Convoy L21A CULPM1 680lm for around 110 minutes (Samsung 30T 3000mAh)
Convoy L21A XHP35HI 96min (it should be about 1000lm-1100lm, high mode has 55% of the output of turbo) vs SST40 6A driver 135min (700 lm for the M21B with same driver) (Littokala 4000mAh???), the XHP35 HI is brighter and has more throw.
Wowtac A4v2 XHP35HI 1050lm avg for a bit over 90min (5000mAh 26650)
Acebeam L18 (CSLPM1) 586lm for 106min (5100 mAh 21700 from Acebeam). The Convoy got the same runtime with a smaller battery. On the other hand Lumeniac got 390lm for 258min, so something doesn’t make sense with 1lumen review.
Manker UC22 III (CSLPM1) they claim 710lm for 144min (4800mAh) battery. The II version has a regulated output, so I would trust that runtime, I’m not sure if I would trust the output, but it looks reasonable compared with the Convoy. I found no technical review for it.
Sofirn SF47T (CULPM1) about 600lm for 251min (2 x Sofirn 5000mAh)
Lumen output are not exactly comparable because of different meter calibrations.
I believe calculation to get power efficiency of the driver is different.
If the calculation is inaccurate please correct me.
Damian linked to an example on how to calculate it in his post above:
Many thanks for your feedback all of you.
So far I thought my ideal flaslight would be with an SST40 with most efficient driver possible in the optics, size and budget of a C8+ or M21A (or at most the optics, size and budget of an FT03) WITH options for 10° TIR optics but that seems only possible for S2+ size torches?
I am looking now at your Osram options from a throw/watts perspective. So far I really liked the beam of the CULPM1 in Funtastics video you linked. Especially at 300lm: enough throw and light closeby but low enough closeby so as not to spoil night vision (which I find also more relaxing while riding).
Also (OSRAM CSLNM1.TG & CULNM1.TG 1mm², CSLPM1.TG & CULPM1.TG 2mm² - Flashlight Modding and DIY Parts - BudgetLightForum.com), the osrams are clearly less efficient than the SST40 in lm/w, but e.g. the CSLNM1 bests all those Agro linked to above in terms of lm/watt versus cd/mm2.
I’ll get back as soon as I can if I may. Many thanks meanwhile!
Led4power’s calculation in that link is actually incorrect. It is taking the average of the starting and ending efficiency, and that implies that the efficiency changes linearly with time which is not the case. Even if the cell’s discharge curve was linear, that doesn’t lead to efficiency increasing linearly because the expression for efficiency has the cell voltage in the denominator. A linearly increasing efficiency implies a discharge curve with a concave-up shape which is not what you see with Li ion cells and that is why the calculation is incorrect.
The correct way is to find the time-average voltage of the cell discharge, and divide the LED voltage by that average cell voltage. Which is what ggf31416 did.
You can sort of estimate the average voltage just looking at the discharge curve, or a more precise way is to use HKJ’s data. At the discharge rate of interest, divide the measured Wh by the measured Ah.
Thanks for the feedback! It makes sense that it does not change linearly over time! The rest I’m not sure I understand: I’d have thought that in this case, the led is driven at a constant current and hence the numerator (led Vf) is a constant. Now, if the denominator (cell voltage) halves/triples/etc… than the total value of the ratio doubles/triples/etc…, no? So that aspect aspect it is linear, only the discharge does not happen linear over time?
If by ‘time average’ you mean this: Temporal mean - Wikipedia ; than that seems like the best way to do it, but also a lot of sampling calculations, no? With battery discharge, does the result differ a lot from the “the supposed linear” result?
EDIT: The discharge curve of the Samsung 35E at 7A draw looks extremely linear though (except with drops at the start and end of the safe range wich are however also quite symetrical). So if I only use that battery, I would be quite accurate with LED4power’s simple method, or is it a lot less symetrical at lower current draws (I can’t find data on those lower draws)? Samsung 35E
Yes, cell discharge is sort of close to linear. But I’m saying even if the discharge is linear that calculation is wrong. A quick example of what I mean about the efficiency not being linear with discharge is: with a 3.0V LED and battery going from 4V to 3.8V the efficiency changes by 3.9 percentage points. The same change in voltage at the bottom of the discharge, going from 3.2V to 3V results in a larger change in efficiency, 6.25 percentage points. The end result is that calculation overestimates the efficiency by 3-5 percentage points.
OK, lets outsource the voltage curve integration to HKJ. Samsung 35E . IIRC 7135 loses at least 0.1V even when Vf is below battery voltage.
For Vf = 2.8V we don’t need to be concerned about what happens below that voltage because that’s already the cutoff. We need 1A but we can use the data for 2A to account for resistance outside the driver (that’s arbitrary). We got 11.838Wh/3.327Ah = 3.558V avg. under load, but it can be done without using that voltage, we have 3.327 * 2.8 = 9.315Wh out. 9.315 out / 11.838 in = 78.7% efficiency or 21.3% loss. 2.8V / 3.558V gets the same number. I know I’m neglecting significant figures.
For Vf = 2.9V, lets assume that we lose a constant value of 0.1V in the unregulated region, we have 3.2Ah above 3.0V and 0.127Ah below. The regulated region contains about 11.5Wh, 11.5/3.2 = 3.59V. So we lose (((3.59 - 2.9) / 3.59) * 3.2 + 0.1 * 0.127) / 3.327 = 18.8% loss (with many sources of errors).
For Vf = 3.3V I think the regulated region ends at 3.4V, have 2.35A, 8.5Wh above = 3.62V avg, 0.977Ah below, so (((3.62 - 3.3) / 3.62) * 2.35Ah + 0.1 * 0.977Ah) / 3.327 = 9.2%. I took the wrong data as the current is about 3A rather than 1-2A but that correcting that will only increase the efficiency.
The point is that linear drivers are quite efficient when the Vf is about 3.3V or higher, for example when running a SST40 at 4.5A, but they lose efficiency at low current where the Vf is lower (overall driver+led efficiency still increases).
That’s the first chart with many colors, 2 lines for each load as there are 2 samples.