Wondering about Dynamos being used to generate power

DAgent

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So, I was talking to a mechanic friend of mine who told me why electric cars don't need or use dynamos (except for some hybrids) and it got me wondering.

Looking around online for more details, did in fill in some gaps, but it left me thinking about what could be done if dynamos were developed further to be more efficient and added into basically any device that has some turning part/s.

Imagine you have a desk fan with a dynamo fitted that is charging up a battery that the fan itself could use when unplugged, or even use to power up your smart phone/tablet/laptop/etc.

Imagine exercise equipment where the gym goers are peddling away on exercise bikes, pounding on the treadmills or pumping out reps on the pec deck and these are also hooked up with dynamos juicing up some batteries somewhere, lighting up the gym and maybe the sound system too. Or not depending on their playlist...

I know there are some hand crank dynamos out there for camping and survival situations, but would this be feasible in any way, either with my examples or ways I've not thought of? Or would some other technology be needed instead to have this kind of effect?

And yeah, it is very much like the hamster in it's wheel powering up the starship Enterprise! :D
 

farntfar

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Whatever. You have to remember that energy is conserved in a system.
The old idea that a dynamo being turned by an electric motor could supply the electricity to turn the motor always falls down.
There is always some energy lost in conversion, usually as heat. So you don't get as much electric energy from the dynamo as you need to turn the motor fast enough to power the dynamo.
Yes, a dynamo connected to a turning system can be used to generate electricity, rather than just be lost. It's what happens in your car, where the turning of the engine also turns an alternator (similar to a dynamo), which keeps your battery charged, and the lights on etc. But it's not nearly enough energy as you need to make the car go, which comes from the chemical energy of igniting the petrol (or diesel etc).

Perpetual motors have been dreamed about for ever, in one form or another, but basically, it's what entropy and the 3 laws of dynamics are about. You will always lose some useful energy in any process.
 

Christine Wheelwright

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What @farntfar said. EVs and hybrids do regenerate during braking, but they use the main motor rather than a dedicated dynamo. I think someone did recently come up with gym equipment that would generate power. It is a bit of a gimmick though. Adds hugely to the complexity and cost of the equipment (and the carbon footprint involved in its manufacture). The average plump gym-user probably works out at about 100W on a stationary bike or treadmill.....so lets say 50W after electro-mechanical losses. Just not worth capturing that.
 

Foxbat

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There was a time when dynamos were used to power bicycle lights. It’s a good example because it was so hard to pedal because of the extra resistence the dynamo created. In effect, some energy from the leg muscles was lost due to the friction and resistence they needed to overcome and, therefore, not all energy was transferred to the dynamo. The same would apply to the fan example. Some of the energy would be lost during charging (mostly as heat).
 

Swank

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I once tried a pedal-powered smoothie maker. It was essentially a stationary bicycle drivetrain turning a blender in place of the motor. I'm a strong cyclist, and it was a horrendous amount of work. And a blender is a pretty light piece of electrical gear. So don't presume that the amount of horsepower/watts it takes to generate a useful amount of electricity can be had from a little pinwheel or some other minor motion.
 

hitmouse

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I used to have dynamo powered bike lights. They were great except:
They appreciably increased the effort of peddling.
They were never as bright as decent battery-powered bike lights, even going fast downhill.
The lights went out when you stopped at a junction

This was in the pre-LED era, but still.
 

Dave

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Imagine exercise equipment where the gym goers are peddling away on exercise bikes, pounding on the treadmills or pumping out reps on the pec deck and these are also hooked up with dynamos juicing up some batteries somewhere, lighting up the gym and maybe the sound system too. Or not depending on their playlist...
Edward G Robinson as Sol Roth in Soylent Green (1973), set in 2022 with dying oceans and year-round humidity, due to the greenhouse effect, resulting in pollution, poverty, overpopulation, euthanasia and depleted resources. He rides a bike to provide them with electricity.

However, regarding making devices more "efficient", as others have mentioned there is the First Law of Thermodynamics (Conservation of Energy) and you cannot have a "Perpetual Motion Machine", you can only change energy from one form into another. There will always be a loss of energy due to friction as heat, sound, light. You can reduce those but you can never totally eliminate friction (or air drag.)
 

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