Dynamo charging battery cell

[Arbiter]

Electricity is one of the (few) areas of which my knowledge is somewhat lacking.

So please, bear with me on this one.

Is it possible to use a small dynamo, maybe even one of hand-driven size, to charge a battery cell?

How many watt would you be able to produce, what kind of battery would you be able to charge with such a dynamo? Can you also calculate, for example, the amount of revolutions of a circular dynamo, based on its circumference, necessary to charge a certain battery?

Would really appreciate some mybb education on this topic!

 

[BCO]

An Olympic level cyclist generates about 300W IIRC. So put a dynamo on an excercise bike and he would be able to charge a battery at a rate of around 300W/hr. That's about as fast as humanly possible to manually charge a battery.

 

[psichron]

Yes, it is most definitely possible. With the right circuitry you'd be able to charge any kind of battery. You can try to use rpm to calculate the output, but there's a lot of factors that would make it difficult like whether there's a gear ratio involved or not, the number of coils inside the dynamo, etc. If you can get a rating for a standard dynamo and work from that it would be easier.

The best estimate you could make would be to try and figure out what kind of power you're putting in to the system and then multiplying it by 0.8, which would mean the dinamo/charging system is 80% efficient which I think is a good bet.

You can get fairly cheap (R100-R200) 2Watt solar panels on ebay, so as long as you can manage more than that it would be worth it.

A standard cellphone/ipod battery charger is about 1.3Watt, a laptop charger is anything from 40 to 90Watt.

Edit: You might wonder, if it's so feasible, why don't we see things like this. The answer is simple: electricity is cheap, dynamos are not