I didn't mean to use a supercap to charge a battery; that would be silly. I was wondering if a supercap could be the energy storage device instead of a battery. Caps aren't energy sources anyhow.
I asked him how much energy he needed to store. If the gadget is human-powered, it can't be much.
If this is for lighting, it may not need much power. Useful lighting can happen at a few milliwatts.
Most car alternators need a lot of field power. Something smaller, with permanant magnets, would be better, a motorcycle or bicycle generator.
On Tue, 24 Nov 2015 08:47:53 -0800, John Larkin Gave us:
A surplus generator from the military radio days of WWII. 220 V IIRC.
My idea for third-world lighting is phosphorescence. Ship them a jug of a good phosphor paint and let them paint whatever is available: cardboard, bark, rocks, dried bundles of leaves. Put it out in the daytime and take it in at night.
The best stuff now is strontium aluminate, which is pretty impressive. It would be cool if someone could invent something even better, if the physics allows.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
I have a night light that runs a good LED at 1 uA, which is enough to find it in the dark. The lithium battery should last 30 years or so.
A good white LED, at 1 mA and 2.6 volts, is blindly bright when you're dark-adapted. Plenty of light to, say, read a book by.
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Problem with motors is the higher speed required to get significant output. Gearing is expensive and has lots of friction. Have you considered something like a violin bow? Wrap the string around the motor pulley and play it like a violin. No mechanical structure required, low friction.
Do the math to consider a PTC for the series resistor. An incandescent light bulb makes a great PTC. Problem is finding one that has the "sweet spot" at the voltage and current you need. I've used them in the 70mA region for battery charging. Maybe the lamps used in xmas tree light strings would work. You just need to protect the LED against someone hooking up fully charged cells. That generally won't be an issue. It's a long shot, but maybe worth a few minutes of math.
Another math area is the charge efficiency of cells vs state of discharge. These will be used in the region from dead, dead, dead to 1% charge. Standard assumptions about how cells behave may not apply.
I missed where you stated where you're deploying these. If they have sun, there are compelling arguments for solar. Local dollar store sells an outdoor path light for a buck. Manufactured in some third world, shipped thousands of miles, through several levels of distribution and they still sell it for a buck.
Problem with many of these is that the boost chip turns the light on as soon as the sun goes down. These have a switch...but they won't charge with the switch off. I put a diode across the switch so they would charge and I'd have control of when they're on. Some loss of efficiency, but I can always turn on the switch for faster charge.
Snap off all the plastic and they're a puck 2" in diameter and an inch thick. I leave them sitting in the window. When the power goes off, I have a supply of "candles".
I can't imagine building ANYTHING for less than what these would cost direct from the source.
It works better made into a decent plastic binder. Thin sheet plastic being probably the most effective form to maximise surface area.
Isn't that much scope for improvement. The stuff is already good enough to last all night after a decent charge of sunshine and dark adaption means that as it fades your eyes get more sensitive.
It is an impressive phosphorescence. Way better than the old ZnS based junk that used to last a few minutes of faint green on a good day.
-- Regards, Martin Brown
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?
Don't give up on the gearing; there's LOTS of very clever options and even 'third world' folk can benefit from economies-of-scale. Planetary gearing , with self-lubricated plastics, and a generator, will just have to be prebui lt.
Clock-style chains/weights is high-tech, but a rock, a rope, and drum isn't .
Matching the source with the load is the hard part: your 'generator' has to produce enough back-torque to nearly stop the falling rock, or that gravity system doesn't store energy long.
How do we make that work? 2 solar panels onto one light? There still isn't much light output. Guess I should try one, see if one can navigate a room & read with it.
$30 is about 20x over budget. A bike even more so.
Sorry, it's far too expensive. Too many zeroes!
battery.
I don't see how that would work practically
I'm liking that. Not sure if LiIon is abusable enough, it would be hammered during charging
A repeating supply of those is too expensive. I will look at a joule thief type circuit later to use discarded cells.
I'll have to do some experiments. Looks like a variable R would be of use.
NT
n via rubber band gear, rectifier, 3xAA 0.6Ah, resistor, 2x LEDs. The AAs w ould need to be bought, and sometimes the LEDs. Combining a bought white LE D with a scavenged colour one could trim cost a bit.
t.
I like that
that could solve LED overcurrent. 40mA at a fraction of a volt...
yes
anywhere & everywhere in the 3rd world
maybe adding a hand cranked motor wuold get those things to be good enough, I'll have to play with one.
All my 3rd world projects so far have had zero BOM. I'm needing on this one to accept a budget of upto about $1.50.
Since that doesn't allow 2 solar lights, I wouldnt say no to a way to get m ore energy from the panel. A simple white bowl would probably help. Mountin g them on ali might even permit some al foil to put 2 suns on them.
NT
I have done one of these for an Xmas lecture based on coaster CDs and post office rubber bands and a small electric motor. Modern LEDs are so good now that it isn't hard to make it glow brightly.
And at 10uA it is good enough to see around a room once dark adapted. Bridging the switch on a LED torch makes a great emergency light since you can always find it in the pitch dark. Our village lost power on Sunday after the milk tanker totalled a mains and phone line pole.
But I think we are both fans of doped strontium aluminate which has the obvious advantages of no moving parts and a very long service lifetime.
The other choice would be tritiated fishing floats. Again no moving parts and a 12 year half life.
Indeed. I suspect in these countries the price of primary cells is low enough that the most important thing is just to have a choice of series resistors and diffusers so that the thing can light a room dimly or a book brightly with the lowest current compatible with the task in hand.
The battery miser to run old "spent" batteries completely into the ground might be a better choice for this market.
-- Regards, Martin Brown
I did the opposite. The 1M resistor is alongside the Tadiran lithium cell, which sets the normal current. If I want brighter, I bridge the resistor with damp fingers (or tongue, for a hands-off light.)
-- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
I was thinking more in terms of cutting the output, to make the battery's charge last longer.
These were $1 at a local store:
The 3x3cm panel produces about 30mA s.c. and 2.4V o.c. in full sun. The unit draws 7mA from its single 50mAhr AAA NiCd when lit.
This means it'll run, with charge efficiencies, about three hours for every hour of full sun.
It's *easily* enough to read with, even lights up a room well enough to navigate once you're dark-adapted.
When you're in the bush and can't see *anything* after eight o'clock, this would be a godsend.
If anything I'd throttle it back to get more run-time, not increase it.
You're being too literal. The generator would be scrap, not costing anything close to $30. Use a random permanent magnet motor, if you've got one.
Junk car, junk motorbike alternator, etc.
No need to hammer it--junked cellphone chargers are everywhere. Worn out cellphone cells that are useless for cellphone use (hi-Z) will serve years more in micro-power lighting use.
Yes, and yes. Prepare to be impressed. Very roughly, 1mW = 1/2 candle, which is more than plenty to turn nothingness into a somethingness.
Cheers, James Arthur
Have you considered pulleys for low speed, gears only for the high-speed part? Pulleys are pretty low-tech, and using them only for the low speed part reduces the length of cord (fishing line?) needed, while avoiding the need for high strength gears (for low speed).
On Tue, 24 Nov 2015 10:52:59 -0800, John Larkin Gave us:
Except there are longevity issues. No matter how much daylight you excite them with they will not endure through the night and the light output degrades the entire time as well..
On Tue, 24 Nov 2015 11:07:14 -0800, John Larkin Gave us:
There is a single white LED keyboard illuminator at the top of the display on a certain model of Lenovo laptop, and it lights the whole room when you enter it at night after being acclimated to darkness.
It definitely lights the entire keyboard and you if using skype.
On Wed, 25 Nov 2015 11:46:25 +1100, Clifford Heath Gave us:
Build a 3 meter crank wheel at the top of a tower and wrap the cord holding the rock to that. Build two side by side and while one is falling generating work, a person could be cranking the other back up. Both can feed the same down shaft from opposite sides. Pegs could work for gears "Da Vinci" style. The bottom of the down shaft could be geared up to directly drive a generator or geared down to drive a generator which already has a spool up gear set in it.
Exercise equipment is basically a generator and many have constant power modes. When I was doing cardiac rehab last spring, one of the exercises I was doing was basically a hand-cranked generator with a constant power load (don't slow down!). After the twelve weeks, I was able to do 85W for 15 minutes.
I now (well, about an hour ago ;-) do about 750 (nutrition) Cal in an hour on a treadmill. If I haven't screwed up the conversion that's something like 825W.
You're obsessed with the crank. This is proposed as an alternative! But it requires sun. I expect that there are regions of "everywhere in the world" where that's a problem. But maybe regions where sun is plentiful. One size doesn't have to fit all.
Would be interesting to see the BOMs for your 3rd world projects.
I missed the leap to 2 solar lights??? It's already got three LED's if you wanted to put wires on 'em.
Go to the MANUFACTURER and see if you can get just the internal puck without all the plastic that makes it a walkway light or shipping for a quarter...in quantity.
I've emailed you
Those last 2 both have their place and will be addressed. But I expect there are nowhere near enough discarded batteries to light a billion people, and there are certainly many for whom the cost of new cells is prohibitive.
Tritium & glowsticks I don't know much about beyond the basics. I'll do some experimenting.
NT
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