Gravity powered lamp

Gravity powered lamp

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Das Bruce
Posts: 3544
Joined: 23 Nov 2005, 06:16

Gravity powered lamp

Post by Das Bruce »

Indigogo page

This seems like a cool idea, but my math doesn't work out.

The bag is filled with about ten kilograms of dirt and lifted a metre, so:

E = mgh = 10*10*1 = 100J

Conservative estimate for power consumption of an LED light of five Watts gives only twenty seconds of life.

Do they have some super efficient LEDs?
Is my math pants on head retarded?
Are they telling porkies?
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knorke
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Joined: 22 Feb 2006, 01:02

Re: Gravity powered lamp

Post by knorke »

math seems right (for 100% efficiency) but the used LED is probally much smaller.
So you get a light as bright as the capslock LED on your keyboard, and it hangs 2 meters above ground.

But even if it was brighter:
The purpose of the lamp is to provide people in third world
fail. imo for such use stuff must be easy to repair and repurpose.

To make it less fail:
-Not make everything from molded plastic, impossible to repair.
See 30s and 60s in video, (all these small plastic crap), too many different parts and stupid shapes.

-There is a dozen different types of screws. Use same screws everywhere, if possible in a way they can be losend/tightend with improvised tools or hands.

-make the case shaped in a usefull way that you can attach to other things (holes for screws etc) instead of fancy shape like that other robot from Wall-E.

-make the eletric stuff in a way that not everything is soldered to some tiny board

-make the axis for belt outside of case

-make belt in a way that it can run contiously, atm it has this stupid
buckle that prevents that. Then you could it attach to whatever else energy source you might have (horse, bike, water, wind, hand crank)

-make it so it works with simple piece of string instead of fancy belt.

-make it so that from 3 broken ones you can make a new one with no tools

tl;dr
omg apple made a lamp
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Licho
Zero-K Developer
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Joined: 19 May 2006, 19:13

Re: Gravity powered lamp

Post by Licho »

Run a bicycle for 10 mins, mine shows at moderate load i spend 700 000J in those 10mins..

Much better than using hands and back to charge gravity light.

People in africa often have access to old bicycles and old 12V car batteries and use those to charge phones. I think it would be better to give them sets - for example dynamo to charge battery using bicycle or simple solar pannels + voltage converters, led lights etc.
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Prominence
Posts: 97
Joined: 24 Jun 2008, 07:21

Re: Gravity powered lamp

Post by Prominence »

From the video, I see chain like string for rotating the gear. So, when they pull up, it will send kinetic energy to the DC motor. The name made it sound like it is only powered by the gravity, but it will also be powered on its way up like it is shown in the video.

The energy transferred on its way down can be approximated with the potential energy, but then its way back up is different story since kinectic energy equation involves velocity which we don't know. Also I see some gears, and as you might know large to small gear results in higher output velocity. And there is additional possible power generated from motor that keeps on spinning after pull from the string until the friction and the gravity stops it.

Relavent Equations:
force = m*a
U = m*a*h
U would be measured in Joule which is also equals to W*s
Watt = Volt * Current(Amp)
Watt = Joules / Second

Typical 5mm RGB LED power consumption 3Volt * 0.02Amp = 0.06 Watt
And this is an instance watt. So, I guess integrate it to find watt consumption at certain time interval.

So the total energy transferred would be kinetic energy for pulling the string and weight up plus potential energy for way back down. Problem is we don't know the velocity that goes into kinetic energy equation.

It's been long time since I last dealt with physics and electrical, and my mind goes blank after this. Maybe they hyped it 2 to 3 times the duration.
dizekat
Posts: 438
Joined: 07 Dec 2007, 12:10

Re: Gravity powered lamp

Post by dizekat »

Obvious fail - the energy stored in the weight is indeed too little to provide light of any use for any time.

One rechargeable AA battery at 2400 mAh and 1.2 volts stores 2.4*3600*1.2 = 10368 Joules, approximately equivalent to 1 metric ton lifted to height of 1 meter. It can also last a lot longer than this plastic.

I should get in on this "for third world" stuff. E.g. a souped up version of this contraption I've built a while back: http://www.youtube.com/watch?v=kW7J6gh4eY0 with a few coils and magnets for generator, can be built using minimal tools. I've also made a battery (a supercapacitor actually) from activated carbon and salt water; it had shit energy density but sure as hell beats lifting sand.
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jK
Spring Developer
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Joined: 28 Jun 2007, 07:30

Re: Gravity powered lamp

Post by jK »

Why not use a water system?
E.g. Let the sun evaporate ~2-10L water and let it condensate it 2m above the boiler and then use the gained high for energy production?

Sterling engine is possible too, if you put it into the wall and use the heat difference between the room and outside. Should be easy enough to make a `compact solution` with integrated light and usb power for mobile phones.
dizekat
Posts: 438
Joined: 07 Dec 2007, 12:10

Re: Gravity powered lamp

Post by dizekat »

jK wrote:Why not use a water system?
E.g. Let the sun evaporate ~2-10L water and let it condensate it 2m above the boiler and then use the gained high for energy production?
Too inefficient... to evaporate 1L of water, takes 2.2 megajoules, and flowing down from height of 2 meters, it produces energy of about 20 joules, for efficiency of under 0.001% .
Sterling engine is possible too, if you put it into the wall and use the heat difference between the room and outside. Should be easy enough to make a `compact solution` with integrated light and usb power for mobile phones.
I'd rather run it on solar heat, or burning some plant matter.
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jK
Spring Developer
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Re: Gravity powered lamp

Post by jK »

dizekat wrote:Too inefficient... to evaporate 1L of water, takes 2.2 megajoules, and flowing down from height of 2 meters, it produces energy of about 20 joules, for efficiency of under 0.001% .
Target isn't efficiency, it's minimal costs and simplicity.
I'd rather run it on solar heat, or burning some plant matter.
The purpose of this gravity lamp was to replace exhaustible raw materials: oil, coal & plants. Yes plants are exhaustible in many areas of this planet (savannas & `grass deserts`).
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Das Bruce
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Joined: 23 Nov 2005, 06:16

Re: Gravity powered lamp

Post by Das Bruce »

I've been thinking about building a solar generator but I'm not sure on how to turn hot water into electrical energy.
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Prominence
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Joined: 24 Jun 2008, 07:21

Re: Gravity powered lamp

Post by Prominence »

Let's not ever forget energy can not be created or destroyed due to mainly friction.
That means, the energy must come from some mass.

I was confused by how stirling engine works. The heat source expands the gas and push the pistons away from the heat source. And on the otherside of the piston is cooled to create low pressure. This certainly pushes the piston in one dirction away from the heat source, but confusion happens on its way back to the heat source. The engine being closed system with no point of that heated gas escaping, I don't see how that piston move back and forth unless the piston is not sealed.

I also see from the many examples of this device, the wheel is overbalanced wheel to have it's motion assisted by the gravity. For now, I remain skeptical of stirling engines.
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Prominence
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Joined: 24 Jun 2008, 07:21

Re: Gravity powered lamp

Post by Prominence »

Das Bruce wrote:I've been thinking about building a solar generator but I'm not sure on how to turn hot water into electrical energy.
Turning hot water into steam for expansion would be best bet. I think it be costly though since solar power does not give great amount of output.

http://www.youtube.com/watch?v=uJGpbvvJA2I
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maackey
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Joined: 02 Jul 2008, 07:11

Re: Gravity powered lamp

Post by maackey »

you are skeptical of sterling engines?!?

http://www.youtube.com/watch?v=Rd7nLOEsqj8 -- a good explanation (sixty symbols)
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Funkencool
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Joined: 02 Dec 2011, 22:31

Re: Gravity powered lamp

Post by Funkencool »

Prominence wrote:I don't see how that piston move back and forth unless the piston is not sealed.
They aren't.
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Prominence
Posts: 97
Joined: 24 Jun 2008, 07:21

Re: Gravity powered lamp

Post by Prominence »

maackey wrote:you are skeptical of sterling engines?!?

http://www.youtube.com/watch?v=Rd7nLOEsqj8 -- a good explanation (sixty symbols)
That video was better than the most. I am still confused about the displacement piston and its fucntion. Seems like the power piston is being assisted on its way down by the overbalanced wheel and displacement serving as an insulator I am guessing.

This thing is not very practical, since it requires large heatsink to dissipate the heat faster. And video also mention lower power output on same sized engine when comparing it to combustion engines which is expected since large heatsink requirement.
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