Hacker News Reader

Comment by mcpackieh | Hacker News Reader

> USB hand crank

Are any of those actually effective for charging a phone? I used to have a hand cranked radio, but radios built for this only need a minuscule amount of power. Does anybody have real experience using one of these to charge a phone? How long does it take?

View on HN

I have an emergency radio / USB-C battery combo thing with like 5000mah and the math on the hand crank says I'd have to crank it continuously for like 48 hours to charge it. It's completely useless. I'd die from exertion just trying to charge it if I was stranded.

You don't need to crank the whole 5000mAh, you just need to crank enough for your phone to get a phone call or two out, and that's assuming the battery wasn't already charged prior.

I mean, sure, the person you replied to wouldn’t but if this was your primary method of charging your device, as the original comment suggested, then you would need to crank the whole 5000mAh. Multiple times, since I assume you’ll want your phone charged more than twice.

If a phone call or two was enough to end homelessness then it would have ended a long time ago.

5000mAh battery at 3.7V nominal has roughly 18-20Wh of juice. Your crank would only be putting out 400mW of power if it truly took 48 hours to charge.

Internet seems to think most hand cranks can output somewhere between 5-15W, which would mean you'd only take 1.3-4 hours to fully charge said pack. Plenty of juice in an emergency situation, and certainly plenty for a phone call or something. Maybe that's a big giant crank thing though, and the tiny plastic crap ones only put out the wattage you're talking about though.

It's a tiny plastic crap one :)

iPhones charge at 20watts. Doing that sustained by hand is probably fairly tiring but would be trivial wattage for say biking. From my experience the hand crank radio's would be pretty futile for charging a phone. There are some charging specific devices out there that can generate decent power.

https://www.amazon.ca/Powerhouse-Watt-Hand-Crank-Generator-Q...

There was a video a few years ago in which a professional cyclist is connected to a generator (bike included) and their continuous power output was around 100 W which they could maintain for a few hours. But it would be unreasonable to expect this amount of exertion from an untrained person.

Edit: weeeelll. I'm either thinking of a different one or completely messed up the numbers and duration: https://youtu.be/S4O5voOCqAQ

Yeah, pro cyclists can put out 400W for an hour. The 20W it takes to charge a phone is less effort than walking, it's honestly the bare minimum a grandma puts into a bike to get it to roll down the road.

Assuming my exercise bike wattage is accurate I think most decently fit people could average 100 watts for an hour with a bit of sweating but not like, full on panting. 20 watts is low enough that it's awkward to generate that little power in terms of speed/resistance.

After 6 months of training I went from 150W/h to 200W/h. For most bikes, 100W is like riding 18-20km/h.

Reply on news.ycombinator.com