I've concluded that producing gearing for a gravity powered light looks unw orkable (in the 3rd world, from nothing but junk) (would need around 1000:1 ). That leaves one other just maybe - a handle driven motor which charges a 2.4v battery at a very high rate for under a minute. Question is, how do N iMH cope with such charging? Is it workable?
NT
How much power do you need, for how long?
Supercap?
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
nworkable (in the 3rd world, from nothing but junk) (would need around 1000 :1). That leaves one other just maybe - a handle driven motor which charges a 2.4v battery at a very high rate for under a minute. Question is, how do NiMH cope with such charging? Is it workable?
You can charge NiMH at 4C with no problem, probably faster. 10C for a
1,800mAH cell is 18A. 18A for 2 minutes x 1.3V = 23W, maybe too hard for a hand-cranked generator. (50W is easy walking, 200W is killer.)23W for two minutes is 390mWHr. If you got 300mWHr stored, you'd have enoug h for 10 hours @ 30mW.
I wouldn't use two cells--they're guaranteed to be ruined quickly, being ru n down regularly into the dirt until one reverses. Even I have such accident s, and I *know* it's bad.
Before giving up on your original idea, have you considered clock escapements and music box mechanisms for inspiration?
How about a weight hanging from a string, wound around an axle, driving a bicycle wheel? The wheel could friction-drive a 2nd stage, which drives a generator. Worn-out tires would be good. Each stage gives 25:1 easily.
But Chinese solar night lights are only $1. Modifying one of those would be a lot simpler, and more reliable in use. That's my vote.
Just a few wild ideas.
Cheers, James Arthur
The 2004-2010 Honda Civic Hybrid has essentially 120 NiMH D cells in series. The traction motor is 20 Hp. So, you have 20 Hp flowing in and out of a
150 V battery pack. So, that's 15 KW / 150 V = 99 A. This is REALLY tough on the cells, but they absorb this abuse for 5 years or so!Jon
So, a bicycle-powered generator making 50W for two minutes works. Bike-->car alternator-->battery charger.
But, then you need all those things, and have to build it, ship it, house it, in primitive conditions.
Cheers, James Arthur
I have a couple of hand-crank lights and cellphone chargers that work. Most of the ones I pick up at garage sales have the crank busted off. That oughta be a clue. I did some experiments to determine if they worked as a flashlight. I cranked them till my hand hurt every week or so. Still couldn't get runtime sufficient to do normal flashlight stuff. They seem to have two series lithium cells at 8.4V. Since they sit dead most of the time, they quickly fail. Series resistance is so high that the light won't come on at all.
Best I can get out of 'em is 250mA. At a reasonable crank force/rate it's more like 100mA. That's .24W. Depending on how much power you need to run that unspecified lamp and the efficiencies you can get in the conversion process with random parts, you might just keep up with continuous cranking. And these are devices designed/optimized for that exact purpose.
To put it into context, I tried to reverse engineer your gravity system. Round numbers...scale to suit. If you have 100kg with 1 meter drop distance, you have 980 joules. That's .98 watts for 1000 seconds, if you could get 100% efficiency with random parts left by the side of the road. To keep the numbers round, assume the wildly optimistic efficiency of 60%, you'd have to raise the weight back up every 10 minutes. Consider a crank/pulley system that could raise that 100kg up a meter every 10 minutes. That's the order of magnitude of the effort required, no matter how you get there. And that's only one watt.
It's not clear that excess charge rate is your biggest problem. You probably don't have a supply of supercaps. People are gonna run the light until it quits. Overdischarge or cell reversal might be a bigger issue, depending on how you're translating from 2V to something the LED likes. Might be more efficient overall to use 3.6V and waste some energy in a resistor.
The elephant in the room is that you need a design that works with whatever junk you find by the side of the road. Makes it really tough to design.
If you had such a device that was really a game changer, it would probably be taken from you at gunpoint.
nworkable (in the 3rd world, from nothing but junk) (would need around 1000 :1). That leaves one other just maybe - a handle driven motor which charges a 2.4v battery at a very high rate for under a minute. Question is, how do NiMH cope with such charging? Is it workable?
Unfortunately, ANY battery OTHER THAN a sealed lead acid (SLA) would degrade very fast in a tyical Third World environment -- dust, extreme humidity and heat, Please take that into account in tour design.
Would it not be SLIGHTLY less expensive to ship the construction drawings, and have the device made there; the parts are rather common...
Why would you want to charge it so fast? It is much easier to sustain a few watts or tens of watts mechanical output from a human.
For use in the third world wilderness to provide minimal lighting where none would otherwise exist I reckon the passive luminous 3M plastic used for GloTorches would be ideal. Just hang it up where it gets the sun in daytime and come the nighttime it glows all night long.
Good enough to see by dark adapted but not to read by. They are rare as hens teeth these days. Great product but terrible marketing.
This is one where solar powered LED garden lamps would win hands down. (perhaps with a better LED)
One thing that might be useful in the third world is a tweak to turn broken former transistor radios and ear buds into crude deaf aids.
-- Regards, Martin Brown
On Mon, 23 Nov 2015 17:51:25 -0800 (PST), snipped-for-privacy@gmail.com Gave us:
Set up a car alternator, which does not require a high rpm to put out and does not require high HP if the load is light (as in not a car battery) and feed a simple 12V to USB charger device readily available with it.
On Mon, 23 Nov 2015 17:53:48 -0800, John Larkin Gave us:
If they were viable energy sources for recharging a device battery, they would be in use as such.
Since all standby or backup battery devices are batteries themselves and have 10 to 25 some odd thousand mA/H capacities (which is how they get listed. I know that is A/H, but "XXk mA/H" is how they are declared typically), I doubt that a supercap solution will work without a huge, expensive bank of them.
On Mon, 23 Nov 2015 20:42:26 -0800, mike Gave us:
Quite simple. A car alternator works at low rpm and up. If not driving into (charging) a car battery, the mechanical load will be low and easily managed "by hand". So a simple hand crank setup from an old tricycle or bicycle should work.
Drive into a simple cigarette lighter driven 12V to USB charge current device, easily obtainable, and you are done.
No elephants plowing over trees needed.
You always end up saying stupid shit.
Bad form to followup own post but actually they do have one thing using the plastic but it is insanely overpriced and as such not worth buying:
-- Regards, Martin Brown
On Tue, 24 Nov 2015 09:58:13 +0000, Martin Brown Gave us:
If one is near a river, erect a water tower and hand pump water into it by day and use a gravity fed water turbine to drive an alternator at night.. Drain into a trough if you want to keep and return the water to the tower, drain back to the river if not.
A person on a bicycle driven pump could sit and pump for an hour, then let another person take over.
The water in the tower is stored kinetic energy. This system is scaled up and uses entire reservoirs in some nations to drive megawatt generators (at much larger flow rates, of course).
On a sunny day (Tue, 24 Nov 2015 11:12:24 +0000) it happened Martin Brown wrote in :
Martin you really got to get to know ebay. Typing 'glow tape' in the search window found many. This is 1 $ 39 cents free shipping:
Light lasts 8 hours.
I'm afraid an SLA won't last long either, as it probably will be discharged too deeply. And if you put a discharge controller on it aiming at preventing just that, I'm sure some 'clever' townsman will shows up bypassing the whole thing. After all it must be broken as it doesn't give light anymore while the battery clearly isn't empty yet.
joe
nt:
nworkable (in the 3rd world, from nothing but junk) (would need around 1000 :1). That leaves one other just maybe - a handle driven motor which charges a 2.4v battery at a very high rate for under a minute. Question is, how do NiMH cope with such charging? Is it workable?
John Larkin:
Gravity light was, if I could come up with a functional design, going to pr oduce about 0.1w for 30 minutes. 0.1w is about the minimum that would make a gravity or hand cranked light useful.
5F 2.7v 90p is affordable to some, but won't give 0.1w for long. Q=CV = 13.5coulombs If it's usable down to 1v, that's an average of 1.85v, so 0.1w = 54mA Of the 13.5C we get to use 1.7/2.7 = 8.5C 54mA from 8.5C gives 157 seconds = 2minutes 37s. With inefficiencies one might get a minute. 2x 0.6Ah AA cells could deliver, for similarish cost: at 2.4v typical, 0.1w = 42mA 42mA 0.6Ah gives 14hrs operation.dagmarg...:
agh
Yes, hand cranking is doable for low lighting power
un
ts,
If one used 3xAA wth a pair of white LEDs, the LEDs would quit before the b attery went into partial reverse charge, and no electronics would be needed , beyond a rectifier, resistor and maybe a zener.
I'm not seeing how either would work for a gravity light
A 25" bike wheel would need to drive a 1" shaft/wheel to get 25:1. Possible , and the inefficiency of tyre friction drive might be workable, but the co st of a bike wheel isn't. My conclusion with gravity lighting is that any t ype of gearing I could come up with that's robust enough is simply too expe nsive. 1000:1 is roughly what's needed, able to take 20kg weight plus abuse for years.
Tempting. But there are issues. The panel would probably be prone to being stolen. The LED doesn't give out enough light. They might make a reasonable supplementary generator & battery.
Jon Elson:
s.
ugh
just what I need to know!
snipped-for-privacy@yahoo.com:
Yes, and any of those 3 is just too expensive.
that bit's no problem. Some people will build their own, some will build & sell them.
Shipping is more a case of carrying it home. So it's affordable often enoug h.
mike:
0.1W for 30mins is 0.05 watthours, or 3w for 1 minute. Double or triple tha t for inefficiencies, that should be doable.that shouldn't be an issue with NiMH
Something tells me these are devices optimised to be as cheap as possible, regardless of result.
Was looking at 2m & 0.1 watt.
no.
agreed. The LED then protects the battery against overdischarge
mike:
People are welcome to the plans for free, if I figure them out. They can pu t the machetes away.
snipped-for-privacy@gmail.com
I doubt there's much I can do about battery life. Having concluded that bat teryless gravity, supercaps & watertowers are too expensive, NiMH is about the only option left.
Robert Baer:
that's the plan. Figure out how to do it, build one to test, and ship bits of paper. If this design works out it'll be one of many bits of paper going to many places.
Martin Brown:
that's the plan. that's fast charging for AA or AAA.
that's a problem. The possibility to read is a big plus for education.
I like that.
DecadentLinuxUserNumeroUno
A car alternator is over an order of magnitude too expensive.
they would be in use as such.
I'm looking at cheap 0.6Ah AAs as the prime choice
That lot's about 2 orders of magnitude too much cost.
DecadentLinuxUserNumeroUno
pumps can probably be made from junk. But the rest is way over budget.
lotu
I'm doubtful but I'll have to try these things.
thank you everyone! At the moment I'm thinking random small motor driven vi a rubber band gear, rectifier, 3xAA 0.6Ah, resistor, 2x LEDs. The AAs would need to be bought, and sometimes the LEDs. Combining a bought white LED wi th a scavenged colour one could trim cost a bit.
NT
SLAs are way too expensive
NT
I didn't mean shipping in from out-of-country, but rather shipping a bulky, awkward contraption in-country, from the assembly point to the end-user.
I still like the solar night (garden) light best, mod'd to last longer than their normal few hours.
Another idea: a classic 6W bicycle alternator, mounted to a bicycle, used to charge a NiMH 'AA' cell.
They're current sources, which is almost ideal. People could charge their own batteries with a few minutes' riding during the day. Someone could also easily set up a business by putting their bike in a stationary stand, and offering a few days' charge on people's NiMH night-light cells.
If massively ambitious they could set up a pedal-powered car alternator and do it with ten minutes' pedaling (or let the customers have at it themselves!), but the classic friction-drive 6W unit is the Volkscharger--it sets up instantly, is light, cheap, and (at least formerly) ubiquitous.
Three more quick ideas: - If the town has the occasional vehicle, they could charge from the 12v battery.
- Old cellphone LiIon cells. Chargers are everywhere. The cells can drive LEDs through a resistor, or simple constant-current source.
- 'AA' alkalines are universal, world-wide. They're about 15 cents, which is a pretty penny in some quarters , but might be a good backup system for times of no charging sources. (Be sure to make it *last* -- $2 is a decent day's wage in many places.)
BTW, you don't need 100mW. 10mW is more than plenty for one person to read by, and would be a massive contrast to the spooky dead black of a moonless African night. BTDT.
Cheers, James Arthur
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