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A $5 Lamp Powered Solely by Gravity

enpundit.com

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Re: A $5 Lamp Powered Solely by Gravity

#71

Post by meatmanek »

mynameishere wrote: post #66
FrojoS wrote: post #61

Earlier quoted context omitted.

But those require a battery, which will only survive so many (hundred?) recharges, no?

I think they use capacitors. At any rate, almost anything would be better than "gravity power". Even a flywheel.

I'm not sure why you think flywheels would be a better energy store than a bag of rocks.

Flywheels have a lot of engineering hurdles that can't be met for $5: - they need to be well-lubricated, clear of dust (which I imagine to be a problem in some of the environments they're trying to sell to) - they need to be perfectly balanced, or the shifting center of gravity will vibrate the housing - sapping away precious energy. - they need to run at high, ever-decreasing speeds, which means generators that can extract a constant power level at different speeds

Re: A $5 Lamp Powered Solely by Gravity

#72

Post by libria »

ars wrote: post #26
tonyarkles wrote: post #5

Earlier quoted context omitted.

If you read some of the followups and tweak the math a little bit, it works out reasonably well. Instead of 20kg and 1m, 20lb and 2m, which comes out about the same (49.42mWh). If you have to lift it every half hour, that's 100mW for a half hour. That's more than enough power to get a useful amount of light out of an LED. For example, this LED uses 68mW https://www.sparkfun.com/products/531 and is marketed as "so bri…

It's hurts to look at it because it's focused into a very narrow beam. Very bright sure - in one tiny spot, and totally useless to illuminate a room. They even include a photo of the beam pattern - it's almost as focused as a laser. (You can tell on an LED by looking a the top - round tops are focused, flat ones spread out.)

It depends on the type of LED. Back when I was playing with them, Luxeons had a 180 degrees beam pattern while Crees were 70 degrees and neither had a built in lens like the cheap ones do (they used some kind of gel cover).

They really should consult some lighting experts or flashlight junkies to get the best bang for the buck.

Re: A $5 Lamp Powered Solely by Gravity

#73

Post by rorrr »

pdonis wrote: post #57
ars wrote: post #30

Earlier quoted context omitted.

Using the numbers above and the typical LED efficiency you get 5 lumen of light per half hour ASSUMING perfect mechanical efficiency. http://www.wolframalpha.com/input/?i=20+kilogram%E2%80%90for... A simple wax candle produces 11 lumen. And there is no way you will get anywhere near perfect efficiency. So at best, this will product maybe 1/3 of the light from a candle. If you directed that light into a small spot, it…

But you can adjust the ballast weight and the height; instead of 20 kg over 1 meter, how about 30 kg over 2 meters? That's a factor of 3 difference.

How many people can lift 30kg 2 meters up? How about doing it continuously?

You're also forgetting that it require human energy to power it, which requires food, which is usually more expensive than batteries or gasoline or kerosine.

Re: A $5 Lamp Powered Solely by Gravity

#74

Post by libria »

tarice wrote: post #7
dsl wrote: post #4

Not to nitpick, bit it's not powered by gravity, it is powered by people going over every 30 minutes and lifting a weight back up to its top position. EDIT: Apparently people don't understand that using gravity to generate energy is a thing, and the title "Powered Solely" suggested someone found a way to do that.

People couldn't lift the weight without consuming energy from food. Doesn't mean that it's powered by food. The machine converts gravitational potential energy to electromagnetic radiation. People generate the gravitational potential energy by lifting the weight using kinetic energy, which was likewise created by converting chemical energy. It's easier just to say "Gravity" because, without gravity, it wouldn't work…

When I think "powered solely by gravity" I think of something like a hydro electric plant which can generate more energy than is required to operate it.

At any rate, the phrase was written by Enpundit, not GravityLight. Their indiegogo page is less dramatic and more scientific about what powers their lamp:

http://www.indiegogo.com/projects/282006

Re: A $5 Lamp Powered Solely by Gravity

#75

Post by rtkwe »

kevinh wrote: post #34
bmelton wrote: post #15

Earlier quoted context omitted.

If you had an infinitely long rope and access to an infinitely deep chasm, then there's no reason it wouldn't be considered a perpetual motion machine.

With an infinitely long rope and an infinitely deep chasm there would not be substantial gravity pulling it downward to have perpetual motion.

No gravity would simply approach infinity as you descended the well. And since we're being pedantic that's not an issue.

Re: A $5 Lamp Powered Solely by Gravity

#76

Post by ColinWright »

nwh wrote: post #68
biot wrote: post #46

Earlier quoted context omitted.

I was a bit disappointed by the title. I was hoping for something akin to a sterling engine, which is powered solely by a heat differential. As long as the heat differential is present and barring any mechanical issues, the sterling engine will operate continuously without intervention.

They're incredibly efficient. There's one on my wireless router that happily spins away all day.

Technically, really technically, and very pedantically, I expect what you have is a hot air engine, because it's unlikely that it includes a proper regenerator, which is technically what differentiates a Stirling Engine.

However,

Yes, Stirling Engines can be wonderfully efficient, and they are a delight to watch in action. Lovely machines.

Re: A $5 Lamp Powered Solely by Gravity

#77

Post by ColinWright »

biot wrote: post #46
dsl wrote: post #4

Not to nitpick, bit it's not powered by gravity, it is powered by people going over every 30 minutes and lifting a weight back up to its top position. EDIT: Apparently people don't understand that using gravity to generate energy is a thing, and the title "Powered Solely" suggested someone found a way to do that.

I was a bit disappointed by the title. I was hoping for something akin to a sterling engine, which is powered solely by a heat differential. As long as the heat differential is present and barring any mechanical issues, the sterling engine will operate continuously without intervention.

If you bury a heatsink, and then have an air-flow heatsink, it's plausible that you could power a Stirling Engine with this kind of power output.

You wouldn't do it for $5 though. Efficient Stirling Engines with a reasonable amount of torque actually require significant engineering, and that comes at a cost. However, they wouldn't require significant maintenance, they would provide power all the time that could be stored (again, at a cost), and might be able to trickle power an entire village.

Re: A $5 Lamp Powered Solely by Gravity

#78

Post by vinnybhaskar »

nuclear_eclipse wrote: post #29
pyre wrote: post #8

Earlier quoted context omitted.

Gravity is the storage mechanism. When someone says something is battery-powered, do you start an argument about how that technically isn't correct?

Gravity isn't the storage mechanism; the ballast bag is. Gravity is the mechanism used to unleash the stored energy, the same way that the electro-chemical voltage difference between the two components of the battery is the mechanism that unleashes the stored energy in the battery. If anything, it's a ballast-bag-powered light.

I'd say you have the most accurate description of when they say "Gravity Powered". While lifting this thing, the energy gets stored and gravity is just a means by which the stored energy is released.
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