A few years ago there was some new company (I vaguely recall that it may have been a Kickstarter or similar) touting something like this built into a shell that you could put an AA battery in, and the shell would still fit in most AA slots.
They were way overselling its benefits, claiming you would get something like 6 times as much runtime out of your batteries, and it got a lot of negative reviews and debunking at EE tech sites.
I wish someone would make one of these with that sleeve approach, not as some sort of miracle energy extended scam but rather as a voltage curve adjuster.
A common non-rechargeable alkaline battery starts at about 1.5 volts and over its useful life drops fairly steadily to a little over 1 volt, and then rapidly drops to near zero.
A NiMH rechargeable starts at around 1.4, fairly quickly drops to about 1.3, then over most of its life drops fairly smoothly to about 1.2, then starts dropping faster to around 1.1, then rapidly to near zero.
This is why you can use NiMH in devices designed for alkaline batteries even though nominally alkaline batteries are higher voltage. The device has to actually be designed to handle 1 to 1.5 volts, and the NiMH is in that range for nearly all of its discharge curve.
This is also why some devices designed for alkaline report low battery on NiMH long before the batteries actually need changing, and still report low but useful battery level right up until the device stops working. They are estimating battery life by looking at the voltage and fitting that to the alkaline discharge curve to estimate how far the battery has discharged, and it makes the batter level meter on many devices close to useless if you use NiMH.
It would be great if there were a sleeve you could put around your NiMH batteries that would dynamically raise or lower the voltage as the battery discharges to make it match the alkaline curve. Then your battery level indicator on your devices that were designed only for alkaline would work.
I built a joule thief flashlight as part of a workshop at a security conference in 2018. We bought a kit that had all the parts, and then soldered them together. For a beginner soldering project, this is excellent.
Unfortunately, I don't think the kit I built is still available.
Here's some information I could dig up:
- https://www.gigaparts.com/etow-humanalight.html
- https://aa7ee.wordpress.com/2014/08/18/the-humanalight-a-fla...
It would be great if this was available for purchase from somewhere. And if it also included an on off button! I've got a lot of dead batteries (because children toys) and it would be nice using them to get some light for night reading!
Related submissions, although none have any comments:
Joule Thief (June 17, 2021) https://en.wikipedia.org/wiki/Joule_thief https://news.ycombinator.com/item?id=27540614
How to steal every last bit of juice from a battery (April 28, 2015) http://aeguana.com/blog/the-joule-thief/ https://news.ycombinator.com/item?id=9451484
Joule thief – A minimal boost converter (January 25, 2015) https://en.wikipedia.org/wiki/Joule_thief https://news.ycombinator.com/item?id=8941971
This circuit is intriguing…a single transistor power converter that steps up the voltage to any value the load can take. It’s more like a pulsed current source.
It might be suitable for miniaturization.
I love that it's easily small enough to fit into a flashlight bulb base, which would also make it feasible as a replacement for an emergency flashlight. You might not get a lot of light, but you'd almost always get some.
Curious now whether some of the little garden path solar cell lights use these to get maximum output from 4-5 square inches of cheap solar cell and a small nicad battery.
Reminds me of this video about LED light bulbs that continue to draw power even with the switch off. (Something to do with capacitance of the house wiring, the capacitive coupling is enough to make the bulb glow faintly even with the switch turned off)
What are some of the most practical applications? I work in off-grid energy (solar) and would be interested in when/whether a JT can be more viable than, say, a boost DC/DC converter / linear current booster.
> The one shown was sourced from Maplin Electronics in the UK
RIP, Maplin. Glad Big Clive's still alive and kicking.
Big Clive's YouTube channel is worth a watch if you like seeing electrical items disassembled and critiqued. It also has the occasional explosion and unusual cooking videos!
https://www.youtube.com/channel/UCtM5z2gkrGRuWd0JQMx76qA