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Comment by nimos | Hacker News Reader

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...

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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.

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