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gravity light

 
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emordnilap



Joined: 05 Sep 2007
Posts: 13970
Location: Houǝsʇlʎ' ᴉʇ,s ɹǝɐllʎ uoʇ ʍoɹʇɥ ʇɥǝ ǝɟɟoɹʇ' pou,ʇ ǝʌǝu qoʇɥǝɹ˙

PostPosted: Tue Apr 01, 2014 2:29 pm    Post subject: gravity light Reply with quote

emordnilap wrote:
This variation on a wind-up torch doesn't make it into the 'greatest' category, but it's pretty good.

Quote:
It takes only 3 seconds to lift the weight which powers GravityLight, creating 30 minutes of light on its descent. For free.


Mike Peplar, if you're out there, you said you were going to get one as part of crowd-funding trials. Did you? They're supposed to be in production this year, 2014.

The only thing I dislike about it so far (I admit I haven't seen one except on deciwatt.org's video) is that it involves what looks like a lot of plastic or nylon.
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adam2
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Joined: 02 Jul 2007
Posts: 6208
Location: North Somerset

PostPosted: Tue Apr 01, 2014 3:32 pm    Post subject: Reply with quote

This has been discussed before, and I have my doubts about the viability of it.
Will undoubtedly work to an extent, but the energy stored by a reasonable weight at a reasonable height is very limited indeed, and the light output is therefore minimal.
The output is probably about one tenth of a watt. That little power is affordable from dry cells, at far lower capital cost.

4 alkaline D cells would cost about 4 and supply one tenth of a watt for about 1,000 hours, or between 6 months and a year of evening use.
I suspect that a lot of alkaline D cells could be purchased for the cost of the gravity light.
Whilst in theory the gravity light would eventually pay for itself as compared to the ongoing costs of battery replacement, this presumes that the gravity light lasts long enough to repay the purchase cost.

Other options include a very small PV system, a whole watt could be produced for several hours a night by a 5 watt PV module and a scrap car battery.
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emordnilap



Joined: 05 Sep 2007
Posts: 13970
Location: Houǝsʇlʎ' ᴉʇ,s ɹǝɐllʎ uoʇ ʍoɹʇɥ ʇɥǝ ǝɟɟoɹʇ' pou,ʇ ǝʌǝu qoʇɥǝɹ˙

PostPosted: Wed Oct 04, 2017 3:33 pm    Post subject: Reply with quote

Update: GravityLight 2 is not cheap.

Available from
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kenneal - lagger
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Joined: 20 Sep 2006
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Location: Newbury, Berkshire

PostPosted: Wed Oct 04, 2017 11:26 pm    Post subject: Reply with quote

0.085W power output for 20 minutes sums it up really. Thank goodness for LEDs.
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careful_eugene



Joined: 26 Jun 2006
Posts: 443
Location: Nottingham UK

PostPosted: Thu Oct 05, 2017 12:34 pm    Post subject: Reply with quote

Basically the same principle as a grandfather clock.
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clv101
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Joined: 24 Nov 2005
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PostPosted: Thu Oct 05, 2017 5:54 pm    Post subject: Reply with quote

Not a fan. That kind of budget could produce a better solar based solution.
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adam2
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PostPosted: Thu Oct 05, 2017 7:41 pm    Post subject: Reply with quote

Agree, solar or even disposable batteries would be a better bet.

Option 1, three alkaline D cells would produce 0.031 amp/31ma for about 600 hours, at a cost of about £3.
At several hours of use each night, the cells would need replacing about twice a year at a total cost of about £6 a year.
Ten years replacements would be about £60, a significant saving over the cost of the gravity light.

Option 2, A 6 volt, 5 cell nickel cadmium battery of 4AH as used for emergency lighting, and small PV module of about 5 watts. Total cost about £25. And would supply about TEN times as much power as the gravity lamp at lower cost.
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