Author Topic: Great Idea - Gravity Powered Light  (Read 14506 times)

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Offline Zero999

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Re: Great Idea - Gravity Powered Light
« Reply #25 on: August 01, 2015, 06:02:14 pm »
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The indigogo unit was $25.00

Wrong.

Really - I paid $50, and for that I got a unit PLUS some villager got one GRATIS. The $25 perk just sent one to a villager for nothing. i.e. zero cost to the person that counts. How many solar woznames and replacement batteries can you buy for nowt?

The whole point of this campaign wasn't to provide 1st world geeks with a crap toy but to apply modern technology to a 3rd world problem, and have the 1st-worlders pay for it. I reckon they got a result.

I don't doubt the neatness of the idea or the well meaning behind it, I just think there is already an existing superior solution in solar.
They would have been better off taking your $25 and giving the people some solar gear.
I agree. Solar is a much better solution.

The batteries should last a long time, especially if they're never completely discharged.
 

Offline ez24

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Re: Great Idea - Gravity Powered Light
« Reply #26 on: August 01, 2015, 07:19:53 pm »
Don't those wind up torches store vastly more energy? If so then what's the point of the gravity one apart from marketing buzz?

Good idea for a video.  If you ever had one, you would not ask this question.  It takes hours of hard winding to get minutes of light.  I trashed 3 of them.   When you see them in a store, they are running off a battery but once the battery dies it is a different animal.

If I remember it took about 2 minutes of hard winding to get 10 seconds of light.  Even in an emergency it gets to the point where you spend so much energy that it becomes impracticable.

This device (wind up light) would make a good debunker video and it has electronics inside it.  I think it is worse than the batterizer. 

It has been several years since I had them so maybe new ones are better, another reason for a video.  I would like to know how long it would take to recharge the batteries.  Two people working very hard might be able to charge them (I bet it would take them days).

The ones I had look like these (different name)

http://www.amazon.com/Mitaki-japan-2pc-Wind-up-Flashlight-Set/dp/B002XU7G6Q/ref=sr_1_5?ie=UTF8&qid=1438456291&sr=8-5&keywords=hand+crank+flashlight#Ask

If you look at the reviews most give the review before the battery dies.  The only good thing about it is you can use it to find another flashlight.



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Offline Mechanical Menace

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Re: Great Idea - Gravity Powered Light
« Reply #27 on: August 01, 2015, 07:30:36 pm »
It has been several years since I had them so maybe new ones are better, another reason for a video.  I would like to know how long it would take to recharge the batteries.  Two people working very hard might be able to charge them (I bet it would take them days).

I've had good ones and ones that work just as you describe. Even the good ones don't seem to like it if you crank them too fast though, they seem to charge better at a steady relatively low rpm.
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Offline rs20

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Re: Great Idea - Gravity Powered Light
« Reply #28 on: August 01, 2015, 11:03:51 pm »
Ever tried charging a wind-up torch? I have many of them, and once they run flat they are shelf fodder. This gravity light gets another half-hour of use just by lifting a bag off the floor - fast, simple, free. If a wind-up torch was like this I would have just the one and it would used all the time...

If you ever had one, you would not ask this question.  It takes hours of hard winding to get minutes of light.  I trashed 3 of them.   When you see them in a store, they are running off a battery but once the battery dies it is a different animal.

Have you considered that you might be comparing a cheap, badly implemented wind-up torch vs a well implemented gravity lamp? Don't knock the idea of a spring just because past implementations have been useless/cost-cut to death.

Also, wind-up torches that recharge the batteries are different to wind-up torches that store the energy in a spring. The latter is much more involved from a mechanical engineering standpoint (hint: such things are not on amazon for $11), but would be the fair gravity-for-spring comparison vs GravityLight. I think the wind-up torches you're thinking of have only one or two moving parts.
 

Offline PlainName

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Re: Great Idea - Gravity Powered Light
« Reply #29 on: August 02, 2015, 12:59:49 am »
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wind-up torches that store the energy in a spring

Fair cop - I was thinking wind-up battery rather than spring. I did have an expensive spring one at one time, but it went kaput and became bin fodder. I bought a wind-up spring-powered radio/light for a friend and that didn't last very long either. Gave up on them after that.
 

Offline matseng

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Re: Great Idea - Gravity Powered Light
« Reply #30 on: August 02, 2015, 02:25:57 am »
Enough with the "solar is better"...  Everyone doesn't live in a nice sunny place with clear skies all day long.

I spent 10 years in a northern location where I had about 4 hours of daylight during the winter months, and unless I have a bigass expensive solar panel there's no way I can charge a battery enough to light up the dark hours.

Also, nowadays I live in Malaysia, while there's no shortage of daylight since it is like 3 degrees north of the equator I have heavily overcast conditions basically all the time. A day where I see a predominantly blue sky is faaaaar apart.  So I'd get just a fraction of the energy you Arizona or Tennant Creek, AU guys would get....
 

Offline EEVblog

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Re: Great Idea - Gravity Powered Light
« Reply #31 on: August 02, 2015, 02:27:29 am »
Even better idea: store the energy in a spring that gets wound up...? No need to lift a weight to absurd heights for longer light, springs can store the energy much more densely.

That is how the wind up torches work. You input hundreds of watts of biomechanical energy for a minute to wind up and it stores it.
 

Offline EEVblog

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Re: Great Idea - Gravity Powered Light
« Reply #32 on: August 02, 2015, 02:29:49 am »
Ever tried charging a wind-up torch? I have many of them, and once they run flat they are shelf fodder.

No I haven't used one, but can you please explain why it's useless?
Surely a wind up torch can store more energy than 1m of gravity?
Sure it takes a bit longer to "charge", but so what if it lasts longer?
 

Offline ez24

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Re: Great Idea - Gravity Powered Light
« Reply #33 on: August 02, 2015, 04:46:09 am »
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You input hundreds of watts of biomechanical energy for a minute

I think you mean mW a minute, my guess is 1 mW per minute at full force

I think I read that a Tour de France rider could make 100 watts, and that is with legs, not fingers.

Actually now I think you were joking.     Hundreds of watts a minute  :-DD
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Offline vk6zgo

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Re: Great Idea - Gravity Powered Light
« Reply #34 on: August 02, 2015, 06:38:20 am »
Bicycle headlamps work fairly well,without that much extra effort by the rider.
And that's with incandescent lamps.

Hand operated "magneto torches" have been around for over 100 years.
They have a spring loaded "trigger" which when squeezed,rotates a permag generator.

Makes your hand sore after an hour or so,but if you don't need light you don't squeeze,which alleviates that.
My father had one years back which was made of metal & worked for years.
I bought a plastic one about 30 years ago,which also worked well till the plastic mechanism broke!!

A fairly large spring can store a lot of energy.

With the older rotary mowers you wound up a spring,which on the release turned a 1 or 2 cylinder engine against compression.
OK,it all comes out at once,but it doesn't have to.

Re :the falling weight.

Back in the day,the rotation of the lens of lightouses was driven by clockwork,using a weight which every few days was wound up to the top of the lighthouse.
As it fell slowly,it created enough power to turn the whole,quite heavy lens system.

All that is necessary is to put down a bore hole of similar depth to the lighthouse height,then use a similar mechanism to drive your "gravity powered light".
 

Offline rs20

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Re: Great Idea - Gravity Powered Light
« Reply #35 on: August 02, 2015, 06:58:35 am »
I spent 10 years in a northern location where I had about 4 hours of daylight during the winter months, and unless I have a bigass expensive solar panel there's no way I can charge a battery enough to light up the dark hours.

If your only only benchmark is powering an 80mW LED, you don't need a big solar panel at all, even in northern locations.
 

Offline PlainName

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Re: Great Idea - Gravity Powered Light
« Reply #36 on: August 02, 2015, 07:47:03 am »
Surely a wind up torch can store more energy than 1m of gravity?

Surely that depends on what mass you're lifting through 1m of gravity? And what spring is in the torch? Blimey, don't your video rants teach you anything?  :-DD

Quote
Sure it takes a bit longer to "charge", but so what if it lasts longer?

I was thinking battery torch when I wrote that, and they say you get about 10 minutes output for 1 or 2 minutes winding. I suggest you get a wind-up something and actually wind it for 2 minutes. It is a mere moment when you say and think it, a bloody age when you're having to actually do it. And then do it again not long after. And again...
 

Offline rollatorwieltje

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Re: Great Idea - Gravity Powered Light
« Reply #37 on: August 02, 2015, 10:55:52 am »
Quote
You input hundreds of watts of biomechanical energy for a minute

I think you mean mW a minute, my guess is 1 mW per minute at full force

I think I read that a Tour de France rider could make 100 watts, and that is with legs, not fingers.

Actually now I think you were joking.     Hundreds of watts a minute  :-DD
Riding a bicycle at roughly 20km/h takes between 70 and 100 watts, that shouldn't cause increased breathing for most people. Tour de France riders churn out well over 300 watts.

During WW2 squeeze lights were quite common, like the Philips Knijpkat. It used a 2.5V 100mA lightbulb. The light would only run for a few seconds per squeeze, so I guess about half a joule per squeeze? If your squeeze takes 100 milliseconds that's about 5 watt.
 

Offline EEVblog

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Re: Great Idea - Gravity Powered Light
« Reply #38 on: August 02, 2015, 11:38:28 am »
Quote
You input hundreds of watts of biomechanical energy for a minute
I think you mean mW a minute, my guess is 1 mW per minute at full force
I think I read that a Tour de France rider could make 100 watts, and that is with legs, not fingers.
Actually now I think you were joking.     Hundreds of watts a minute  :-DD

A cyclist can produce up to about 400W.
Ok my figure of a "few hundred" for hand cranking might be a bit optimistic, but it's not mW!, or W, it would be at least 10's of W capability there surely?
 

Offline george graves

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Re: Great Idea - Gravity Powered Light
« Reply #39 on: August 02, 2015, 11:55:06 am »
Being that there are millions of people that simply can't read, or cook, or do much at all at night - It's little things like that can help. Awesome stuff.  With that in mind - who cares about efficiency too, too much?  Or gravity vs a spring?

I wonder how efficient you could make a fiberglass-reinforced, styrofoam, peltier-cooled fridge with no moving parts
- and only opened it once/twice/three times a day?  Seeing that 3mm of foam will keep coffee hot for just about forever, how about 100mm of foam to keep things cool - and let a peltier to it's work with a similar set up - or solar.  Anyone have a link to people working on such a thing?
« Last Edit: August 02, 2015, 11:58:20 am by george graves »
 

Offline VK5RC

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Re: Great Idea - Gravity Powered Light
« Reply #40 on: August 02, 2015, 12:00:02 pm »
I would have thought arm power was pretty rotten 10W or so but a quick search found
"Arm power has a maximum output of slightly less than half that from the legs……"
http://myweb.wit.edu/ELDERF/Human_power_page.html
This implies you might get up to the 100W range esp with a good cranking position.
Whoah! Watch where that landed we might need it later.
 

Offline lewis

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Re: Great Idea - Gravity Powered Light
« Reply #41 on: August 02, 2015, 12:00:09 pm »
Good idea for a video.  If you ever had one, you would not ask this question.  It takes hours of hard winding to get minutes of light.  I trashed 3 of them.   When you see them in a store, they are running off a battery but once the battery dies it is a different animal.

If I remember it took about 2 minutes of hard winding to get 10 seconds of light.  Even in an emergency it gets to the point where you spend so much energy that it becomes impracticable.

I had one of those wind up radios once, I used to charge it using a power drill. That was really easy.
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Offline SeanB

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Re: Great Idea - Gravity Powered Light
« Reply #42 on: August 02, 2015, 12:06:11 pm »
Springs have a very well known failure mode of breaking, as to get any sort of useful energy storage you have to run it at a point where it will have a fatigue lifetime that is measurable. Just running it at low deflection it will be a very inefficient energy store, so you run it higher and live with it having a limited life. Might be millions of cycles, but it will fail sooner or later and it will be both expensive and heavy to get to that point.

Had a few of those cheap wind up torches, the best one was converted to use red LED's ( I had a few lying around, and white ones would have meant buying them, and at the time they were rather new and expensive) and the worst one went to having a joule thief built inside to drive a white LED and charge the internal NimH cell from USB, after the spring broke along with the plastic gear train.
 

Offline EEVblog

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Re: Great Idea - Gravity Powered Light
« Reply #43 on: August 02, 2015, 12:34:23 pm »
I would have thought arm power was pretty rotten 10W or so but a quick search found
"Arm power has a maximum output of slightly less than half that from the legs……"
http://myweb.wit.edu/ELDERF/Human_power_page.html
This implies you might get up to the 100W range esp with a good cranking position.

Thanks for the confirmation. Seems my gut feeling was correct.
I've produced circa 400W on a bike myself, and knowing how much relative biomechanical energy can be had by the arms/shoulder/torso combination, half of the legs seems about right. Would vary a large amount depending upon angle of application, and total muscles used etc. e.g The Karate kid "wax on wax off" lateral technique would probably be 1/5th the output of a good double hand side stance crank that engaged the shoulder and torso etc.
 

Online amyk

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Re: Great Idea - Gravity Powered Light
« Reply #44 on: August 02, 2015, 01:45:54 pm »
I would have thought arm power was pretty rotten 10W or so but a quick search found
"Arm power has a maximum output of slightly less than half that from the legs……"
http://myweb.wit.edu/ELDERF/Human_power_page.html
This implies you might get up to the 100W range esp with a good cranking position.

Thanks for the confirmation. Seems my gut feeling was correct.
I've produced circa 400W on a bike myself, and knowing how much relative biomechanical energy can be had by the arms/shoulder/torso combination, half of the legs seems about right. Would vary a large amount depending upon angle of application, and total muscles used etc. e.g The Karate kid "wax on wax off" lateral technique would probably be 1/5th the output of a good double hand side stance crank that engaged the shoulder and torso etc.
In short bursts, humans can produce over 1kW:

https://en.wikipedia.org/wiki/Human-powered_transport

Articles like this one show that hand-cranks can produce ~50W continuously.
 

Offline rs20

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Re: Great Idea - Gravity Powered Light
« Reply #45 on: August 02, 2015, 01:52:24 pm »
Articles like this one show that hand-cranks can produce ~50W continuously.
50W = 1000J every 20 seconds; or the energy in 50kg at a height of 2 metres in 20 seconds or so. Which makes sense, because we all know that you can lift 50 kilos up 2 metres in 20 seconds or so (maybe in two 25 kg pieces if you're me). Nice thing about a spring is that you can keep on winding!
 

Offline PlainName

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Re: Great Idea - Gravity Powered Light
« Reply #46 on: August 02, 2015, 04:38:11 pm »
Quote
Articles like this one show that hand-cranks can produce ~50W continuously.

Interesting, thanks. but I note the abstract says:

Quote
The experimental setup consisted of an altered cycleergometer which was adjustable in height. We measured the subjects' (eight young males) maximum power output and the time to exhaustion at different power levels. The research showed a sustained power output from cranking to be: 54 ± 14 Watt (mean ±
SD).

Er.. so we can get 50W if we use fit males on a rig built especially to maximise their output and run 'em into the ground. I suspect that's not quite practical for most applications of the gravity light :)

I would have thought that if it is this simple, at least one of those wind-up torches would fit the bill. But, AFAIK, none of them do.
 

Offline ez24

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Re: Great Idea - Gravity Powered Light
« Reply #47 on: August 02, 2015, 06:27:21 pm »
Quote
I would have thought that if it is this simple, at least one of those wind-up torches would fit the bill.

I think a scientific approach to the answer would make a good eevblog.  There might be something on the market that would work.  I know the one I had would not.

If so I would look for:

- long crank arm  (mine was 2 inches)
- efficient LED  (mine was when LED first hit the market and I do not know if it was efficient or not)
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Offline lewis

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Re: Great Idea - Gravity Powered Light
« Reply #48 on: August 02, 2015, 07:25:46 pm »
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Offline zapta

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Re: Great Idea - Gravity Powered Light
« Reply #49 on: August 02, 2015, 07:31:05 pm »
I think a scientific approach to the answer would make a good eevblog.

+1.

Anybody has a gravity device to send to Dave?
 


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