Electronics > Beginners
Free Energy Hand Crank Generators -- 2.4A/5V Possible?
dmills:
--- Quote from: Psi on September 23, 2019, 01:55:36 am ---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. :-DD
--- End quote ---
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:
--- Quote from: dmills on September 23, 2019, 02:11:16 am ---
--- Quote from: Psi on September 23, 2019, 01:55:36 am ---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. :-DD
--- End quote ---
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?
--- End quote ---
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:
--- Quote from: james_s on September 23, 2019, 03:15:50 am ---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.
--- End quote ---
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.
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