How do kinetic watches work exactly?
More importantly, precisely how much energy can such a mechanism produce 
Basically it’s an unbalanced mass on a pivot within the watch.
Ballpark back-of-the-envelope calculation: If we assume the mass is 10 grams, and you are swinging your arm once a second for 8 hours with a height difference of 10 cm, and the mechanism is 100% efficient at storing the energy, that comes to a whopping 280 joules of energy. Your mileage may vary.
I seem to remember some talk a while back about a piezoelectric fabric that could be used to make clothing that would generate enough electricity to run wearable computers and the like - anyone remember this or did I dream it?
Assuming that swansont’s 280 J figure is correct, then to put it into perspective it’s enough to power:
- a 2000 W oven for 0.14 seconds
- a 100 W light bulb for 2.8 seconds
- a 15 W refigerator bulb for 18.7 seconds.
It’s also enough to run a mechanical watch for a few days.
It crops up from time to time.
A piezo suit ain’t gonna power your laptop. It’ll power your calculator, maybe even your palm pilot. But so will a battery that’ll cost a few bucks and last for months. Guess which option people will take.
Swansont, I appreciate your reply, and the link/info was interesting. But I was wondering about kinetic watches, which differ from the self winding “automatic” watches that use a spring - which is what your link leads to. My understanding so far is that kinetic watches use a weight that somehow transfers energy to a capacitor, but there is no spring. They can keep a charge for up to 6 months…
Does anyone know the mechanism behind kinetic watches, and more importantly just how much energy they produce? enough to run a pda? a cellphone? only a watch?
jamesb@seductive.com
It’s the same principle. When you move your arm you move an unbalanced weight in the watch. In the case of an electronic kinetic watch, the unbalanced weight is connected to a generator instead of a spring.
According to astro’s link, Seiko watches work in the same way except that the energy is not stored in a spring, but converted to an electric charge and stored in a “Seiko kinetic energy unit”. I am guessing that is a capacitor. The rest of the watch is then a regular quartz watch with step motors and the like. I am guessing that the claim the capacitor can hold a charge for 6 months is in a case where it is not being discharged.
I would like to draw your attention to the fact that “kinetic” refers to motion, which makes Swansont’s link correct because it describes the same method of generating power. As to how much power it produces, it would be the same as would be generated by a watch with a spring, except probably less because of the conversion of energy types.