Hi all,
As someone who likes to think about backups, I’m curious about the use of a hand-crank or foot-crank generator for charging flashlight batteries. However, I’m sure it’s a very labor intensive way to charge a battery and I’m not sure it’s worth the effort.
Has anyone ever tested one? Can they even generate the current needed to charge an 18650 reasonably?
Just curious.
The ones that I have seen are garbage.
You hit the nail on the head with your own post.
Assuming you’ve some sunshine, solar will allow you to charge cells while doing other jobs.
Micro wind generation has always interested me, but I don’t live anywhere windy enough.
Edit to add: comments mostly based on hand crank chargers, pedals would be slightly more practical.
I found this super expensive model but looks like it would actually work. Down side would be cranking to get 20-30W for half an hour to charge up a single 18650.
Also found a pretty good discussion on eevblog about this subject.
I do wonder if a home-built pedal generator based around an old exercise bike might work… but it would have to be a method of absolutely last resort, last thing you want in a survival situation is to be burning more calories/tiring yourself out.
I’ve no idea of the output, but how about a hub generator on a bicycle, then if you need to go anywhere, you can charge cells on the way!
My god this sounds like hell.
If you crank it too fast youll overcharge the batteries or fry the charger and if you crank too slow youll be cranking that thing all day or it won’t charge at all. So you’ve gotta find out the ideal RPM and then you need to maintain a fairly constant RPM for at least a full hour if you’re fast charging.
That’s if you even can fast charge, because in the quick Google search I just did the model I found required you to crank it at 2000RPM to get 20W, which means to fast charge 1 21700 using a 4A charging current or two 18650s at 2A you’d need to spin this hand crank an inhuman 2000 full revolutions a minute, or 33 times a second at a constant rate for a full hour without stopping. No thanks lol. I’m sure more efficient models exist but just seeing that one is a big nope for me
I found some on Amazon that looked questionable. These looked much better: K-TOR Electric Power Generator Products
However, they seem a bit pricey. The foot crank one looks way more reasonable, but its expensive.
Yeah, I looked at the crank generators with curiosity, but it was a very skeptical curiosity. I agree that a small solar panel is a much more practical solution to the issue at had. Since I do a fair bit of camping, a small solar panel might be a good thing to have around anyways.
We used a very portable bicycle-type charger in the Army to charge our big radio batteries.
+1 for solar panels. The good ones (>=100W, monocrystaline from reputable manufacturers) work even when it’s cloudy, albeit supplying less power (but less is always better than nothing), but still certainly more than enough to recharge flashlight batteries.
Get more batteries or other ways to charge them. In an emergency situation you don’t want to use your own body to power something. The conversion to electric energy is extremely inefficient and supplying you with food is more difficult than having a spare battery.
I agree. I remember those crank bike lights that were powered by the spinning tire. They only produced like 5 lumens and once you stopped the light turned off.
I don’t think the footcrank device looks at all reasonable. What it probably should have for smooth pedalling is a flywheel, though that would make it far less portable/stowable. Not sure whether the price is worth it, first I would like to see a real world test.
They are good for use in a nuclear bomb shelter for exercise and because you would be stuck indoors without solar, but for normal prepper situations there are better ways for today.
Now we’ve all decided they’re impractical, who’s going to build a BLF human powered generator “because they can”?
Hook it up to a capacitor and drive a couple of XHP70s or something 
If I had time/funds/space, I’d go with a rowing machine with a permenant magnet generator. The DIY wind guys have been building generators for years, there’s plenty of guides.