Great Idea - Gravity Powered Light - Page 1
Forum section: electronics / general

author: SLJ
author_rank: Frequent Contributor
timestamp: January 10, 2013, 11:38:33 am
content: Here's a great idea. Coo Coo Clock power meets high efficiency LEDs:http://www.indiegogo.com/projects/282006Heck, I'd get some of these for around my house.

author: Dago
author_rank: Frequent Contributor
timestamp: January 10, 2013, 12:13:49 pm
content: Does not seem terribly useful when you do the math. Assuming the bag weighs say 5kg and its raised to a height of two meters, it will contain about a hundred joules of potential energy. Assuming a (low powered) LED light that uses 1W and no conversion losses the light would light up for about 1min and 40 seconds. In reality it will light up for maybe half or at max 2/3 of that time.And it scales linearly so hanging 50kg to two meters would make the light light up for a maximum of around 17minutes.

author: amyk
author_rank: Super Contributor
timestamp: January 10, 2013, 12:47:24 pm
content: Looks a little more realistic thansome previous attemptsbut still,QuoteI doubt it.

author: FrankBuss
author_rank: Unknown
timestamp: August 01, 2015, 05:41:27 am
content: There is a new campaign with an improved version,GravityLight 2. From the FAQ: "A 6ft [1.8m] drop gives over 20 minutes of light.". Sounds useful. You can lift it in seconds to recharge.

author: PlainName
author_rank: Super Contributor
timestamp: August 01, 2015, 09:35:30 am
content: QuoteMaths isn't everythingI bought into the original and acquired one. It does what it says on the box and provides gravity-powered light. It is useless in my office or home, but it was brilliant during out bonfire night party to light between the pools of light out the back. Well, providing someone lifted the weight as they went past so it didn't run down.And that's where this is aimed. It's not to be compared with lights as we know them, but with no light at all. Once acquired, it is free light - nothing to charge, no fuel to use, just a weight to lift five feet twice an hour. And the light it puts out may not be enough to read by from ten feet away, but it's a hell of a lot better than nothing and allows you to do stuff you'd otherwise not be able to do. Or just sit there andseethings.I have a couple of issues with mine (not waterproof, so not so hot in the garden, for instance, and the bags could be a little bigger to allow for less dense packing material than soil) but it is a brilliant idea and execution of same IMO.

author: FrankBuss
author_rank: Unknown
timestamp: August 01, 2015, 09:57:58 am
content: @dunkemhigh, cool, can you post some photos what's inside? I guess nothing interesting, a rectifier, capacitor and maybe not even a voltage regulator, because the description for the old version says it is brighter if the weight is higher. I could already think of some improvements, like blinking when the weight is at the bottom (could use a bigger storage capacitor and measure the power source), because if you are focussed on doing your homework or something (as intended for Africa), you might not notice the position of the sand bag and then I guess it shuts off quickly.I just backed the new version.

author: rs20
author_rank: Super Contributor
timestamp: August 01, 2015, 10:05:04 am
content: Quote from: dunkemhigh on August 01, 2015, 09:35:30 amAim your criticism the right way at least; the faulty assumption was a 1W led. The maths was fine. Evidently, the LED actually runs on less than 80mW, so it must just be a pretty excellent LED.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 01, 2015, 10:18:37 am
content: The eye is very good at adapting - if there is total darkness, 100mW will easily provide enough to see where you're going, and read by if reasonably close.

author: bookaboo
author_rank: Frequent Contributor
timestamp: August 01, 2015, 11:02:44 am
content: In addition to that effect all LEDs become really efficient towards the bottom of their drive current curve. So you have both these working together.As for the project it's a neat idea and all but for a lot of the developing country applications I don't see what's wrong with a solar solution.

author: PlainName
author_rank: Super Contributor
timestamp: August 01, 2015, 11:15:31 am
content: QuoteSure, but not for a while - I am tied up elsewhere for a bit.

author: Zero999
author_rank: Super Contributor
timestamp: August 01, 2015, 11:37:07 am
content: Quote from: rs20 on August 01, 2015, 10:05:04 amYes, I thought that was a faulty assumption too. 10mA or so into an LED can provide enough light to see and is much better than total darkness.

author: matseng
author_rank: Frequent Contributor
timestamp: August 01, 2015, 11:41:38 am
content: Quote from: bookaboo on August 01, 2015, 11:02:44 amNot sure if you're being serious or just joking... Solar requires an expensive battery that needs to be replaced every now and then, and it requires *enough* sun during the day to last during the dark hours - if not you're out of luck until the next day. I'd say that those two arguments against solar powered lights are more than enough to dismiss them compared to "wind-up" lights.

author: bookaboo
author_rank: Frequent Contributor
timestamp: August 01, 2015, 11:52:27 am
content: Quote from: matseng on August 01, 2015, 11:41:38 amThe indigogo unit was $25.00, you can get a lot of solar rechargable LED for that. Alibaba is full of them. Granted the batteries will probably only last a few years but then that's all I'd expect from this thing.Furthermore, proper micro generation small scale solar with quality batteries is a very feasible solution to bring "proper" lighting solutions.As for needing "a lot of light" you can get similar units that work as garden lights that work fine in northern European winters.So yeah Im serious.

author: rs20
author_rank: Super Contributor
timestamp: August 01, 2015, 12:20:20 pm
content: Quote from: bookaboo on August 01, 2015, 11:52:27 amI agree, and don't forget that this gravity thing only puts out 80mW for 20 minutes, vs an 18650 cell which can power 13 of these LEDs for 8 hours. So saying "rechargeable batteries are hard to get into developing countries" might be looking past just how miniscule these batteries could be while still outperforming the GravityLight.

author: EEVblog
author_rank: Unknown
timestamp: August 01, 2015, 12:40:59 pm
content: Quote from: mikeselectricstuff on August 01, 2015, 10:18:37 amYes, there are whole bunch of ultralightweight bushwalking nerds who obsess over weight so much they custom design their own torches and headlamps for long treks, shaving every last gram. That means lasting weeks of nighttime walking and camping and reading etc on a single AAA or whatever. And yes they swear you can navigate with bugger-all light, and certainly read.I've gone nighttime canyoning with my princeton Tec Eos on the lowest setting, and it would be way under 100mW IIRC.

author: EEVblog
author_rank: Unknown
timestamp: August 01, 2015, 12:42:09 pm
content: 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?

author: EEVblog
author_rank: Unknown
timestamp: August 01, 2015, 12:46:35 pm
content: Quote from: EEVblog on August 01, 2015, 12:40:59 pmI just checked. The EOS gets 50hrs regulated and 120hrs total on 3xAAA's on the low setting.1.4Wh per AAA = 4.2Wh = 84mW.So yes I can (not so easily, but I can) do nighttime canyoning with less than 100mW of light. And that was 5+ years ago, LED efficiency has improved much since then.

author: nctnico
author_rank: Super Contributor
timestamp: August 01, 2015, 01:11:14 pm
content: Quote from: FrankBuss on August 01, 2015, 05:41:27 amSuddenly I picture streets lights with weights hanging from the top and a cord to rewind them...Still I doubt it's well to wheel efficiency isn't that great because our bodies aren't very energy efficient.

author: LukeW
author_rank: Frequent Contributor
timestamp: August 01, 2015, 02:18:00 pm
content: QuoteKerosene energy density: 46 MJ/kg.Gravitational "energy density" (at 1 meter displacement): 9.8 *10^-6MJ/kg.

author: amyk
author_rank: Super Contributor
timestamp: August 01, 2015, 02:27:16 pm
content: 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.

author: rs20
author_rank: Super Contributor
timestamp: August 01, 2015, 02:38:58 pm
content: Quote from: LukeW on August 01, 2015, 02:18:00 pmHeh, so kerosene can lift itself 4693 kilometers vertically (assuming the engine and the oxygen weighs nothing and gravity remains constant). I guess that proves that rockets are feasible!Interesting to note that the potential energy required to reach geosynchronous orbit is about 50 MJ/kg, incredibly close to the energy density of kerosene. Clearly staging is required for an actual kerosene rocket to get there!

author: PlainName
author_rank: Super Contributor
timestamp: August 01, 2015, 03:48:40 pm
content: QuoteWrong.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.

author: PlainName
author_rank: Super Contributor
timestamp: August 01, 2015, 03:54:26 pm
content: QuoteEver 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...Battery torch is probably OK if you have a charger, but when it runs out at 10pm that's your day gone. The gravity job never runs out at the wrong time (or, rather, it doesn't matter when that happens because 2 secs later you have another half hour of output).And... how many peeps are going to buy one of these nice torches and send them, sight unseen, not even an unpack video made, to some 3rd world place? I dont' think you'd run out of fingers working that one out.

author: nitro2k01
author_rank: Frequent Contributor
timestamp: August 01, 2015, 04:25:51 pm
content: Quote from: LukeW on August 01, 2015, 02:18:00 pmNow if only we could increase the energy held by 1 kg of kerosene by 46 MJ, by lifting it 1 m, the world would no longer have any energy problems...

author: bookaboo
author_rank: Frequent Contributor
timestamp: August 01, 2015, 05:50:40 pm
content: Quote from: dunkemhigh on August 01, 2015, 03:48:40 pmI 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.

author: Zero999
author_rank: Super Contributor
timestamp: August 01, 2015, 06:02:14 pm
content: Quote from: bookaboo on August 01, 2015, 05:50:40 pmI agree. Solar is a much better solution.The batteries should last a long time, especially if they're never completely discharged.

author: ez24
author_rank: Super Contributor
timestamp: August 01, 2015, 07:19:53 pm
content: Quote from: EEVblog on August 01, 2015, 12:42:09 pmGood 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#AskIf 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.

author: Mechanical Menace
author_rank: Super Contributor
timestamp: August 01, 2015, 07:30:36 pm
content: Quote from: ez24 on August 01, 2015, 07:19:53 pmI'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.

author: rs20
author_rank: Super Contributor
timestamp: August 01, 2015, 11:03:51 pm
content: Quote from: dunkemhigh on August 01, 2015, 03:54:26 pmQuote from: ez24 on August 01, 2015, 07:19:53 pmHave you considered that you might be comparing a cheap,badly implementedwind-up torch vs awell implementedgravity 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.

author: PlainName
author_rank: Super Contributor
timestamp: August 02, 2015, 12:59:49 am
content: QuoteFair cop - I was thinking wind-up battery rather than spring. Ididhave 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.

author: matseng
author_rank: Frequent Contributor
timestamp: August 02, 2015, 02:25:57 am
content: 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....

author: EEVblog
author_rank: Unknown
timestamp: August 02, 2015, 02:27:29 am
content: Quote from: amyk on August 01, 2015, 02:27:16 pmThat 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.

author: EEVblog
author_rank: Unknown
timestamp: August 02, 2015, 02:29:49 am
content: Quote from: dunkemhigh on August 01, 2015, 03:54:26 pmNo 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?

author: ez24
author_rank: Super Contributor
timestamp: August 02, 2015, 04:46:09 am
content: QuoteI think you mean mW a minute, my guess is 1 mW per minute at full forceI 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

author: vk6zgo
author_rank: Super Contributor
timestamp: August 02, 2015, 06:38:20 am
content: 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".

author: rs20
author_rank: Super Contributor
timestamp: August 02, 2015, 06:58:35 am
content: Quote from: matseng on August 02, 2015, 02:25:57 amIf your only only benchmark is powering an 80mW LED, you don't need a big solar panel at all, even in northern locations.

author: PlainName
author_rank: Super Contributor
timestamp: August 02, 2015, 07:47:03 am
content: Quote from: EEVblog on August 02, 2015, 02:29:49 amSurely 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?QuoteI 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 andactuallywind 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...

author: rollatorwieltje
author_rank: Unknown
timestamp: August 02, 2015, 10:55:52 am
content: Quote from: ez24 on August 02, 2015, 04:46:09 amRiding 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.

author: EEVblog
author_rank: Unknown
timestamp: August 02, 2015, 11:38:28 am
content: Quote from: ez24 on August 02, 2015, 04:46:09 amA 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?

author: george graves
author_rank: Super Contributor
timestamp: August 02, 2015, 11:55:06 am
content: 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?

author: VK5RC
author_rank: Unknown
timestamp: August 02, 2015, 12:00:02 pm
content: 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.htmlThis implies you might get up to the 100W range esp with a good cranking position.

author: lewis
author_rank: Frequent Contributor
timestamp: August 02, 2015, 12:00:09 pm
content: Quote from: ez24 on August 01, 2015, 07:19:53 pmI had one of those wind up radios once, I used to charge it using a power drill. That was really easy.

author: SeanB
author_rank: Super Contributor
timestamp: August 02, 2015, 12:06:11 pm
content: 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.

author: EEVblog
author_rank: Unknown
timestamp: August 02, 2015, 12:34:23 pm
content: Quote from: VK5RC on August 02, 2015, 12:00:02 pmThanks 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.

author: amyk
author_rank: Super Contributor
timestamp: August 02, 2015, 01:45:54 pm
content: Quote from: EEVblog on August 02, 2015, 12:34:23 pmIn short bursts, humans can produce over 1kW:https://en.wikipedia.org/wiki/Human-powered_transportArticles likethis oneshow that hand-cranks can produce ~50W continuously.

author: rs20
author_rank: Super Contributor
timestamp: August 02, 2015, 01:52:24 pm
content: Quote from: amyk on August 02, 2015, 01:45:54 pm50W = 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!

author: PlainName
author_rank: Super Contributor
timestamp: August 02, 2015, 04:38:11 pm
content: QuoteInteresting, thanks. but I note the abstract says:QuoteEr.. 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 lightI 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.

author: ez24
author_rank: Super Contributor
timestamp: August 02, 2015, 06:27:21 pm
content: QuoteI 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)

author: lewis
author_rank: Frequent Contributor
timestamp: August 02, 2015, 07:25:46 pm
content: Quote from: ez24 on August 02, 2015, 06:27:21 pm

author: zapta
author_rank: Super Contributor
timestamp: August 02, 2015, 07:31:05 pm
content: Quote from: ez24 on August 02, 2015, 06:27:21 pm+1.Anybody has a gravity device to send to Dave?

author: continuo
author_rank: Frequent Contributor
timestamp: August 02, 2015, 08:03:39 pm
content: I would be more interested in the teardown of an anti-gravity device

author: Dave Turner
author_rank: Frequent Contributor
timestamp: August 02, 2015, 10:47:44 pm
content: I suspect that for the targeted recipients this gravity powered light would be ideal, particularly if one considers nomadic people, where a solar installation would probably be completely impractical.What concerns me is the product's longevity.In comparison to a laboratory these devices are being targeted for use in a relatively very dirty environment. From the description I assume that there is some serious gearing up involved in order to spin the generator fast enough similarly to the spring powered devices. What material is being used for the bearings, gears etc?