Lightbringer, won’t the current limiting resistor burn off a ton of energy like that?
The higher electrical efficiency of using LiFePO4 cells will be entirely offset by their lower energy density, if runtime is what you are after. They have about 1/3 the energy density of good Li ion cells.
As others have said using multiple LEDs will be more efficient. I think a quality buck driver will be more efficient than a linear driver in this case. For example the XHP70.2 produces 418 lumens at .3A and 5.35V. If we say
the battery voltage is 8V then the efficiency is only about 67% with a linear driver, while a quality buck driver can be greater than 90% efficient.
But as lightbringer explained as the battery voltage drops the linear driver efficiency increases, so overall the efficiency difference between linear and buck won’t be that high.
I know it doesn’t answer your question directly but here’s my answer. I was in USMC infantry for years multiple deployments. I know weight counts trust me getting shot at in mountains with 100+ lbs on your back is not fun. But in all reality. You already probably have a small 18650 light that has a low mode that will run 15-20 hours check the specs and do a runtime test yourself. If you can get close to 17-20 hours per battery you’d only need the light and a 4 pack case of batteries. I’d choose 3400/3500 variety.one 100 gram flashlight and 250 grams in batteries. Is under a pound and won’t make much difference in your load in all seriousness.
But I don’t know your physical conditioning or what not. But I know what it’s like to hike in your own food and water for a week or so and ammunition, body armor with 110+ degree temps. Under a pound for your lightening needs is great and easily doable with what you have now. Even you carried our or two more batteries would still be under or around a pound. But my thinking if you can get close to 20 hours. A couple hours before the sun comes up you have light coming in you can start to see inbetween night and morning like 5 am it’s dark but not nighttime dark. So even if a battery lasted 17 18 hours it would still work 2 days per battery. One in the flashlight w 4 case or 2 2cases with ncr GA or ncr and your covered. Even a extra battery for peace of mind is under a pound still. 10 days would be covered. Just my 2 cents on it alot of lights have a low mode around 100ish lumens. Your original plan was to carry your device and 4 18650s anyway. Same weight as a flashlight and 4 batteries.
Yeah, Li-Ion seems to be the most advanced (highest energy density) for sure.
The potential efficiency of a buck driver would have to be weighed against the impact of needing a second cell - more weight. Could use smaller cells like 2x18350,but Wh/gram is lower than 18650 cells.
But now maybe I see where Lithium Primary cr123a might work - at low currents (0.3A) the xhp70.2 Vf is 5.35v per TA’s test, so with 2xcr123a the battery voltage and Vf would be very closely matched. Is that thinking correct?
Speed4goal, I’m drunk on the UltraLight backpacking kool-aid - I used to brag about how much my pack weighs, now I “brag” about how little it weighs (“brag” in quotes because it’s not that light compared to many.) (and I understand that in the military you don’t get a lot of choice to carry a lighter pack)
My current base weight is about 11.5lbs, and I’m attempting to get closer to actual “ultralight” at 10lbs, so 1lb is a lot. I’m in good shape and could lug around a 50lb pack, but the UL mindset and reduced pack weight allows me to cover more ground when hiking, and more importantly I ENJOY the hike, rather than suffer through it as a necessary evil to get to the campsite.
My lighterpack:
https://lighterpack.com/r/3kkgbi
No.
You can take big capacity from primary cells if youll discharge them much below 3v. So for 2 cells and single xhp70 you need boost driver.
Ah, OK.
It should be quite small. Need to test first how much current without any resistor, then try small values if you want to limit current further.
Oh ok I got you, I was thinking it was around the same weight as your first prototype device. Nothing wrong with going ultralight everyone has their thing. I’ll probably always be stuck in the mindset to bring more supplies then needed just incase. Probably around 25 30lbs
But hey it gives you a reason to build and play with a new toy and show everyone look what I built.
Well, with Energizer Ultimate Lithium AA primaries, you could use 2x and not need a boost driver. These have about the same mAh capacity as a good Li-Ion 18650 and even 2x will weigh less than 1x Li-Ion 18650. You will not have the ability to recharge them, and they are pricey for single use. At the low current draw, voltage will be better matched than Li-Ion. Use multiple LED’s in parallel to increase the efficiency. Putting them in parallel keeps the Vf the same (or actually lowers it due to lower current draw per LED). “Here’s HKJ’s review/test”:Test of Energizer Ultimate Lithium AA of the Energizer Ultimate Lithium AA Primary.