Free Energy Hand Crank Generators -- 2.4A/5V Possible?

[Undweeber]

I've looked into hand-crank generators, and most that are sold seem to be complete trash, having plastic gears, horrible gear ratios (marathon spinning), cheapest DC motors.
They are usually only able to power old android phones at best and are most suitable for cellphones of the previous decade.

One hand crank that does stand out is the one that produces 120V ("pocket socket"), it appears to also be decent handheld size and not a child hand size, the issue is too much power conversion DC-AC-DC, or worse AC-DC-AC-DC, while it seems to be sufficient to power 1A requiring devices, I have not seen it being used with 2.4A bricks, and whether it can produce enough power, the manufacturer does not seem to list the wattage its capable of, so its probably bad.

Third option is Chinese handhelds designed "for military" that are super cheap on alibaba in bulk, but become 3X more expensive on aliexpress/amazon, $170 for 30W one, made of metal, but the specs while promixe 3A max, say that nominal is 1.5-2A, probably meaning that you have to spin it super fast, meaning gearing sucks (low torque).


Any suggestions? Is there a high torque gearing that provides nominal ~30W that would be capable of 2.4A 5V quick charging?

[soldar]

For how long do you think you can generate 50 W by hand cranking?  If you are seriously thinking of generating that order of magnitude I think you need to go with foot pedals and be fit. If you are not fit you soon will be.

[james_s]

I remember using stationary bicycles that measure your effort in Watts, seems like I found I can produce about 100W for a reasonable amount of time but that's a good steady workout. I think 30W with a hand crank would be a very brisk sprint. Unless you've got the upper body of He-Man you're not gonna be able to sustain that for more than a few seconds.

[Monkeh]

Since when is food free?

[IanB]

I haven't looked, but I guess there might be exercise bikes that use a generator as a load instead of friction or whatever they use normally. You could then logically charge your phone while you work out. Or at least charge an accumulator that later charges your phone. But electricity is so cheap there wouldn't be any real point. I would guess food is a much more expensive source of energy than the electric socket in your house.

[Gyro]

I remember RACAL used to make hand crank generators for emergency military radio use. They used to put out 24V at about 2A. The one design feature that really got me was the use of a shunt regulator for voltage regulation. Beyond rated voltage, they would become harder and harder to turn. Completely non-intuitive!

Macho types (remember this was the army) used to crank them until they either overheated, or they bent the handle shaft. 

Edit: The Clansman one...

[soldar]

I remember using stationary bicycles that measure your effort in Watts, seems like I found I can produce about 100W for a reasonable amount of time but that's a good steady workout. I think 30W with a hand crank would be a very brisk sprint. Unless you've got the upper body of He-Man you're not gonna be able to sustain that for more than a few seconds.

To produce 30 W output you'd probably be doing close to 50 W input. There is no way to do that in a handheld device.

Long time ago I saw in a boat a pedal crank which could be mounted on a bulkhead and worked while lying down on your back on the setee. Yes, about 100 watts was what someone in very good shape could output for some time while 50 Watts was much easier and could be done for much longer time.

I have also seen a hand actuated piston water pump. It was a wheel, about 50 cm diameter, mounted on a wall at arm's height so it could be turned by a man standing sideways to the wall. It elevated water maybe about 15 m and it produced a pitiful flow for all the work it required. I remember the man would very often turn around and switch arms because he could not maintain the effort for more than a few minutes.

I think we often do not realize how cheaply we can buy energy and how much energy it takes to do even the smallest things.

[james_s]

Since when is food free?

At least in the Western world, we typically eat much more food than is necessary to survive, so burning that excess energy is desirable and harvesting the energy is "free" compared to just throwing it away by conventional exercise or getting fat. I doubt anyone is going to buy extra food just so they can generate electricity.

[soldar]

Not only that, you can save the gym's fee.

[dmills]

The clansman machines were interesting because people frequently misunderstood them.

They had a status light that turned on at a certain (fairly low speed), and if you didn't know the trick of it you would at that point be thinking 'this ain't so hard', the trap was that that was the lamp test, to make the radio work you needed to speed up until the lamp went OUT!

As I recall the pedal variant was far more practical.

12W by hand for long enough to be useful? BIG ask!
I do question however the need to go down the fast charge route, 500mA charging looks far more practical...

[Undweeber]

the reason 500 is not practical is because most batteries today can accept 13W+ easily and there is no reason trading technology that you need to use for subpar technology that you have to use, a 15 minute workout would charge a phone for half a day (in low power mode), a 1 minute workout could charge a supercapacitor based flashlight.

30W is a lot I admit, but what about 13-15W that has got to be achievable, yes muscles can be conditioned to it also, hand switching isnt a crime either

[james_s]

Well nobody is saying it can't be done, only reasons why 50W hand crank generators may not exist as a commercial product. You may be able to make one yourself though, brushless motors are cheap and readily available in countless sizes and shapes. Gears, belts and other mechanical bits can be found surplus.

[amyk]

2.4A at 5V is only 12W, and sustaining 12W with the feet is not hard --- normal walking already takes >100W.

[Psi]

Hand crank generators can put out up to 400W but that is peak and no one can sustain that for more than a minute or so.
etc https://www.electricpedals.com/hand-crank-generator

A more typical max power for a person over a longer period is about 50W.


Hehe, this is interesting. An electric car, like a Nissan leaf uses about 155 watts per km.
So if you had 3 people in the car, all using one of those 50W hand cranks, you would have about enough power to run the car on average.    Or at least you'd have enough to maintain speed.
Someone should totally build that, it would be so cool.

[IanB]

normal walking already takes >100W

I think this is somewhat of an over-estimate. Walking is very efficient and humans can walk for a very long time (a whole day) without getting tired. This indicates the mechanical power output to sustain walking is quite low. Mechanical power outputs greater than 50 watts are usually associated with vigorous exercise where you will tend to break a sweat and unless very fit cannot be sustained for extended periods.

Mechanical output should not be confused with base metabolic load at rest, which is in the order of 80 to 100 watts. This is not mechanical output, it is merely internal energy consumption to sustain life.

[dmills]

An electric car, like a Nissan leaf uses about 155 watts per km.
So if you had 4 people in the car, all using one of those 50W hand cranks, you would have enough power to run the car on average. 

I think you have a units error there somewhere, watts is a unit of power, consumption per distance travelled is going to be in a unit of energy.

I would bet on 155Wh per km, which looks somewhat more reasonable... Now can your 4 people keep it up for an hour to move the car 1km?

[Psi]

An electric car, like a Nissan leaf uses about 155 watts per km.
So if you had 4 people in the car, all using one of those 50W hand cranks, you would have enough power to run the car on average. 

I think you have a units error there somewhere, watts is a unit of power, consumption per distance travelled is going to be in a unit of energy.

I would bet on 155Wh per km, which looks somewhat more reasonable... Now can your 4 people keep it up for an hour to move the car 1km?

oh true, i forgot that it only takes a minute or two to cover 1km
but takes 1 hour to get 150Wh from the hand cranks.

[james_s]

It would probably be easier and more efficient to have those four people get out and push the car along from the back. Otherwise you've got conversion losses going from mechanical to electrical and back again.

[Rick Law]

It would probably be easier and more efficient to have those four people get out and push the car along from the back. Otherwise you've got conversion losses going from mechanical to electrical and back again.

Let's refine that further.

The friction is at the tires where they meet the road.  For a typical car, you would probably be pushing horizontally well above ground level, probably pushing at the top of trunk lid.  So, the horizontal push force vector at trunk lid height translate to at where the tire meets the road as a forward horizontal force vector plus a downward vertical force vector.  That downward vertical force at the tires increases friction -- making your car harder to push.

Now, switch that to pulling the car at trunk lid height of the car, now you are in business.  the horizontal pull force vector at trunk lid height translate to at where the tire meets the road as a forward horizontal force vector plus an upward vertical force vector.  That upward vertical force at the tires reduce friction -- making your car easier to pull.

Now that we made it into a more efficient configuration, let's not stop there...  There is an animal call the "ox", they have huge pull strength.  But you do need to add the methane diverting tail pipe for your ox.

For better speed, we can probably explore something call a "horse"...

[Berni]

The problem with hand crank generators is not how inefficient they are, but the amount of effort needed to turn them.

To be able to provide a good amount of power you need it to be reasonably ergonomical so it needs a large handle to let you use as much of your arms motion range as possible (Your arm gets tired mostly acording to the force its making rather than the force*distance that is power). And even when you have that you are going to get tired after doing this for <10 minutes. Humans might be good at making lots of peak power for a short period but are not very good at making a large mount of continuous power unless you are an athlete in the right discipline. This is why we used oxes, horses, windmills, waterwheels ..etc as our source of power trough history and we still use some of them today except for the living ones being replaced by the internal combustion engine due its its convenience and lower operating cost, not to mention higher power output.

So a better solution is to have a solar panel that folds up into about the same size. Yes it produces much less instantaneous power, but it can run for many hours without any effort. Just set it up in an open area and done, or hang it on top of a backpack or similar.

Heck even a generator made from a tiny RC combustion engine could be made to run for hours and hours providing 100s of W if you bring half a liter of gasoline with you.

[Nominal Animal]

For better speed, we can probably explore something call a "horse"...

You're absolutely right!

In fact, I did some research on how to maintain those, and it turns out we could produce most of their fuel requirements locally, with relatively little effort!
Why hasn't anybody tried this before?

← He's just resting.

[soldar]

The Gossamer Albatross was the first human powered airplane to cross the channel. The National Geographic article published at the time reported in tests the "human machine" could maintain 220 W pedaling for two hours which was the expected duration of the flight. It ended up taking almost three hours.

[Nominal Animal]

It is also interesting to note that even at rest, an adult human produces 50 - 100 W of heat.
We aren't really that efficient as engines.. but nevertheless, given enough distance, a fit human can outrun every other land animal on Earth.
Looking at pedaling instead of hand cranking makes a lot of sense to me.

If only there was some kind of vehicle, that us humans could propel ourselves forwards using pedaling as a way to generate the propulsive energy!

[radiolistener]

it seems that the best free energy is solar panel 

[Gyro]

It is also interesting to note that even at rest, an adult human produces 50 - 100 W of heat.

I believe the brain accounts for about 25W. Ymmv of course. 

Intel have a looong was to go!