If you have the motivation to make us some nice open boost drivers I wouldn’t want to discourage you. I’d much rather be wrong about it being more work than most want to do for free.
Buck is the best in practice in a flashlight due to lower current input and lower current output when lots of watts power is needed as output, resistance does not become enemy number one in this case, neither the cells need massive current capability, in theory people get all super extremely scared of "series issues", yet the whole flashlight industry runs on 4S 18650 or 3S 18650 flashlight and I have not heard or read any issues whatsoever.
It appears to me to cut it more than in half. 18350s, like 14500s don’t have half the capacity of 18650s as one might hope. I see numbers like 800 mAh, not 3.4 / 2 = 1,700.
We were talking about running two in series, so it’s necessary to compare Watt-hours, not Amp-hours. They would be at different loads too, and then there’s the question of driver efficiency. We can compute the capacity, but have to guess a bit about the load and driver efficiency. My estimate is that two 18350s in series to run a 6V emitter probably have a little more than half the runtime of one 18650 and a boost driver, assuming the highest capacity batteries for both and on the order of 2A (12W) to the emitter.
I prefer single cell lights for size and ease of use, I’m also a lumen junkie. Let me explain my view on ease of use, I can take any cell of the right size and put it in a light. No grouping cells by manufacturer or age or its use history like in multi cell lights. A group of drivers for the newer higher voltage Cree leds would be very welcomed in my book. Single 18650/26650 with XHP35, XPH50, and MT-G2 are the lights I’m wanting. Fenix PD40 gets a lot of use from me. The SC600 Mk III 18650 XHP35 is already ordered. I have almost no electrical engineering skills so I buy what’s out there. If our forum engineers or hobbyist designed a driver that meets these needs I’ll be in hog heaven. These are the levels of modification I can “safely” do. Being a P60 diehard fan I’d also love to see XHP-35, XPH-50 and MT-G2 single cell dropins.
I guess I don’t see the point of boosting 4.2v all the way up for an XHP35… Just use an XP-L
Yes, for the watt hours to be the same the two would have to have half the charge capacity each.
which emitter indeed. Let the mob decide?
So specs are out on the SC600-III. It falls a bit short of what I’d hoped for - 1300 lumens on high for the cool white version, and only 1126 for the neutral. Neutral takes a bigger hit here than it did in the XM-L2 model.
On the other hand, runtime is improved at every output level. That doesn’t mean much at the highest level, as Zebralights are thermally regulated and would run longer if they get throttled for producing too much heat, but at the lower levels, it’s significant. 24 minutes more at 360lm. 3 hours more at 70lm. ZL’s spreadsheet claims a slight CRI bump for both cool and neutral tints and the cool is now a more daylight-like 5700K as opposed to the old 6300K.
Is this all worth the effort? Well… maybe. Certainly, if you’re buying a $95 single-cell flashlight, I think Zebralight does more to justify its price than many, perhaps any similarly-priced products. If you’re building a light and you have the choice between a $5 driver and $5 emitter or a $20 driver and $10 emitter, the relative impact of those costs is more significant.
Worth it or not, once I have a couple other things completed, I think I’ll try my hand at building a boost driver. I’ve never really done any electrical engineering, so I probably won’t come up with the best driver ever, but I bet I can come up with something that works.
Go for it! I’m looking forward to seeing what you can come up with!