The idea is to use light and temperature gradients to keep an ultracapacitor charged. The flashlight would then run off of the stored charge in the ultracapacitor.
I am lookiing at an IC made by Texas Instruments that will allow this form of energy harvesting. The chip is a BQ25504RGTT. I will use a power inductor from Coilcraft, the LPS6235-223MLB. :-)
I am going to do some calculations and post the results here. This will determine if the idea is even feasible to bother with.
EDIT: Okay, some quick calculations... If I use a 400F ultracapacitor rated at 2.7 volts and the energy harvester is running at its maximum of 400mW, then it would take approximately an hour and a half to charge the cap. I know I can run a one watt, high-brightness LED for at least 15 minutes on a full charge. This may not seem like a good deal. buuut...
If the flashlight were used for quick tasks and or emergencies with lots of time between uses, it would basically always be charged. You would always get at least 15 mins of good, bright light from it just laying around or floating around in your pocket.
I am gonna try it! :-)
Comments
Neat! I have about fifty 0.6F
Neat! I have about fifty 0.6F polyacene caps I intend to use for wireless power devices. So I'm interested in what you come up with.
Steve Greenfield AE7HD
Sounds cool! I'm sure
Sounds cool! I'm sure something like that would be great to show off at the alternative energy fair, too. I wonder how many passive things like that you could capture in a small package... Heat, and light. vibration? EM? Pressure. I've been getting more interested in the "making educational items" angle, since I think those will generally play well at public events.
I'm interested in playing around with some of the beginner level energy harvesting stuff: joule thief, solar cells and related charging stuff...
on the "making things to show off at public events" tangent (i might post it elsewhere too) I had a vision last night of a CNC routed water table - a maze of CNC'ed channels, cut from a big sheet of plastic with 3d printed mechanical components, sandwiched in plexi, that takes the "electricity as fluid" metaphor to its logical conclusion.
chris guttierez was showing me an electronics book he had with diagrams of the hydraulic analog to a switch, transistor, diode, resistor, and/or/not, etc. I bet the moving parts could be produced almost entirely from the line drawings... you could construct lots of common circuits in a reasonable amount of space if you made the channels small enough. I was also thinking for digital logic gates and IC's, you could have a door flap down over them that just said e.g. AND - but when you open the flap, you can see all individual transistors inside
colored fluid would make the process nice and visible (you'd need to have a way to flush it though)
man, I've got to fix this text editor
Original Joule Thief page, no
Original Joule Thief page, no explanation for how it works
http://www.emanator.demon.co.uk/bigclive/joule.htm
This gentleman removed his explanation after I sent him a correction, but his mismarked schematic remains
http://www.pm.keirle.com/4_misc/joule/joule.htm
This gentleman -also- removed his explanation after I sent a correction
http://www.evilmadscientist.com/article.php/joulethief
Both now say essentially the same thing under How It Works: "Very well"
I think I should put up a blog that explains exactly how the Joule Thief works. No one else seems to have it correct.
It is just a blocking oscillator.
A joule thief might be used with one or two solar cells to step the voltage up to charge a LiIon battery. I did something similar with Ge transistors, stepped it up to 6V albiet at low current.
Steve Greenfield AE7HD
I am glad you understand it,
I am glad you understand it, because I think it is a cool project on several levels: cheap to build, almost free to operate, useful.
I did notice varying accounts when reading about it, but attributed it to the slightly different geometries used: most wound their own transformers; some used off the shelf inductors.
I think most hobbyists don't
I think most hobbyists don't know how what they build works, they just duplicate it.
At work, I pull dead 3.6V lithium (nonrechargeable) cells out by the dozens. I also use a pair of wireless headphones that run off of two AAA NiMH cells. I'm thinking I should build a Joule Thief with a regulator so I can use those "dead" lithium batteries, which are commonly around 1.5 to 2.5V when I pull them out.
And to make it a bit cooler (in the "ain't it neat" sense), not all bad boards go back, so I've scavenged some toroids, shottkey diodes, transistors, and misc. parts I can probably use.
I was going to talk more about a SIG meeting on wireless power and Joule Thief circuits, but I just realized I'm hijacking Keith's blog. I should go post this in mine.