7 ms·

Make a Joule Thief (2002)

69 points by bariumbitmap 5y ago

bariumbitmap 5y ago
Related submissions, although none have any comments: Joule Thief (June 17, 2021) https://en.wikipedia.org/wiki/Joule_thief https://en.wikipedia.org/wiki/Joule_thief https://news.ycombinator.com/item?id=27540614 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/ http://aeguana.com/blog/the-joule-thief/ https://news.ycombinator.com/item?id=9451484 https://news.ycombinator.com/item?id=9451484 Joule thief – A minimal boost converter (January 25, 2015) https://en.wikipedia.org/wiki/Joule_thief https://en.wikipedia.org/wiki/Joule_thief https://news.ycombinator.com/item?id=8941971 https://news.ycombinator.com/item?id=8941971
hasmanean 5y ago
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.
- datameta 5y ago
  Is it possible to build a circuit that keeps the same voltage while letting the current drop?
  - yetihehe 5y ago
    Yes and no (your question is invalid/underspecified), with voltage source (constant voltage), current is consequence of device power demand at required voltage. More power required at a given voltage, more current will flow. Less power required, less current will flow, but voltage stays constant. So, ALL voltage regulators are "dropping" current, so your question could be answered by "any voltage regulator, for example LM7805". But if some device requests some power and your regulator's power source can't provide that power, your voltage will drop.
    - datameta 5y ago
      Thanks for the explanation!
  - hasmanean 5y ago
    You mean a voltage regulator? That is possible to build but not with this circuit (Joule thief). The Joule thief charges an inductor in one half of each cycles, and let’s it discharge into the load in the next half. Inductors like to emit a constant current and will kick up the voltage to maintain the current, so it’s more like a current source. Because it drops to 0 quickly before the transistor starts charging it again, it delivers its output as a series of pulses. So it’s a pulsed current source. The only way to get a constant voltage out of it is to 1) feed the current into a fixed resistance load 2) filter the output via a capacitor. I thought about how to make a single transistor voltage source but I gave up. Transistors are so cheap there’s not much point. The world has a bizarre preference for voltage sources (maybe due to the fact that early batteries were DC, or maybe it’s just Edison’s ghost). Most real-world loads have useful outputs proportional to current (LEDs, magnetic fields) and the voltage is just a secondary variable.
spapas82 5y ago
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!
- koala_man 5y ago
  Why don't you use rechargeable batteries? I stopped using them in the 90s but switched back a few years ago. More convenient and less wasteful than single use batteries, higher capacity and longer device life than built in batteries.
  - p1mrx 5y ago
    Rechargeable AA/AAA batteries were always limited to 1.2 volts, which works poorly in some devices. Now you can buy lithium ion cells that regulate down to 1.5 volts, so NiMH is basically obsolete. Alkaline can still make sense for things with multi-year battery life, like remote controls.
    - Maursault 5y ago
      > Now you can buy lithium ion cells that regulate down to 1.5 volts, so NiMH is basically obsolete. NiMH is a lot safer, cheaper, and has slightly better capacity. It's been a few years since first available, but any posters even heard of anyone using 1.5V Li-ion cells? Once you know enough to even be aware of them, you'd be using 3.6V Li-ion instead, so really it's the 1.5V Li-ion that was instantly obsolete, yet still somehow hangs on due to extremely specific circumstances of boutique users that want a flat-regulated 1.5 volts.
      - p1mrx 5y ago
        Are you sure NiMH has better capacity? You have to look at mAh * voltage (or just mWh) for a fair comparison. NiMH is safer, and cheaper for now, but those factors are irrelevant when 1.2V is insufficient for a particular device. If a device accepts 3.6V with overdischarge protection, then regular Li-ion makes sense, but there are a lot of 1.5V-3.0V AA/AAA devices out there.
veganjay 5y ago
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://www.gigaparts.com/etow-humanalight.html - https://aa7ee.wordpress.com/2014/08/18/the-humanalight-a-flashlight-that-uses-your-dead-aa-batteries/ https://aa7ee.wordpress.com/2014/08/18/the-humanalight-a-fla... - https://swling.com/blog/tag/etow-humanalight/ https://swling.com/blog/tag/etow-humanalight/
ricksunny 5y ago
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.
- Animats 5y ago
  It is a DC/DC converter. It's a basic switching power supply. I was hoping, from the name, for something that would pick up ambient RF and deliver a milliwatt or so. That would be useful for things that need minimal power and are a pain to connect to a power source. Such things have been around for decades. There's an Instructable for this.[1] Newer designs try to use more of the available spectrum.[2] [1] https://www.instructables.com/RF-Energy-Harvester/ https://www.instructables.com/RF-Energy-Harvester/ [2] https://www.teratonix.com https://www.teratonix.com
  - kragen 5y ago
    Agreed, though it's an impressively simple DC-DC converter. A whole milliwatt is a lot to hope for from ambient RF (you can do it if you get lucky or make the device big enough), but it's easy to get from solar cells. The purple amorphous kind are less efficient in sunlight but provide more power under the dimmer lighting we use indoors.
tzs 5y ago
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.
- p1mrx 5y ago
  If you search for "1.5V rechargeable", there are lots of lithium ion batteries with electronic voltage regulators now. Some designs will step down to ~1V when nearly depleted, so that low battery indicators still work. I'm not sure if an NiMH sleeve was ever practical given the space constraints, but it's kind of moot now that better technology exists.
- Nextgrid 5y ago
  What you're talking about is the Batteriser/Batteroo. It would actually work fine as a voltage stabilizer delivering a constant voltage all the way to the end, but the inefficiencies in power conversion would probably be a major downside (you're losing some energy on the conversion even if the device itself is powered off).
nickcw 5y ago
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 https://www.youtube.com/channel/UCtM5z2gkrGRuWd0JQMx76qA
- randombits0 5y ago
  * Anticipated explosions managed with the fire containment pie tin. Big Clive is an electrical engineer from The Isle of Man and has a very unique English accent, complete with local slang and idioms. He’s a very engaging character and passes as entertainment, even without the electronics content. Genuine and occasionally heartfelt and up-lifting. :)
  - gm3dmo 5y ago
    His accent is quite common in Scotland. What's really cool is he has a brother "Ralfy" who also has a Youtube channel specializing in reviewing Whisky: https://www.youtube.com/watch?v=DWRyIShLRO0 https://www.youtube.com/watch?v=DWRyIShLRO0 They are the Tappet Brothers of the 21st Century.
    - lscotte 5y ago
      I love your Tappet Brother's analogy - it's spot on. The videos they do together are hilarious in a way that only two brothers could be.
- lscotte 5y ago
  Big Clive's channel(s) (he has a separate one for live streams) have some of my favorite content on YouTube. He's super down to earth and just has fun with what he does, never taking himself too seriously while being very knowledgeable.
- agumonkey 5y ago
  beside clive there's a bunch of special electrical oriented channels: - photonicinduction (warning, absurd levels of everything up to 11, borderline insane at times, but if you want to see ultra high everything, here's the channel) - styropyro, spiritual son of the above, but for everything lasers
HPsquared 5y ago
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) https://youtu.be/1uEmX5XClPY https://youtu.be/1uEmX5XClPY
kragen 5y ago
> The one shown was sourced from Maplin Electronics in the UK RIP, Maplin. Glad Big Clive's still alive and kicking.
fencepost 5y ago
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.

69 points by bariumbitmap 5y ago

Related submissions, although none have any comments: Joule Thief (June 17, 2021) https://en.wikipedia.org/wiki/Joule_thief https://en.wikipedia.org/wiki/Joule_thief https://news.ycombinator.com/item?id=27540614 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/ http://aeguana.com/blog/the-joule-thief/ https://news.ycombinator.com/item?id=9451484 https://news.ycombinator.com/item?id=9451484 Joule thief – A minimal boost converter (January 25, 2015) https://en.wikipedia.org/wiki/Joule_thief https://en.wikipedia.org/wiki/Joule_thief https://news.ycombinator.com/item?id=8941971 https://news.ycombinator.com/item?id=8941971

hasmanean 5y ago

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.

datameta 5y ago
Is it possible to build a circuit that keeps the same voltage while letting the current drop?
- yetihehe 5y ago
  Yes and no (your question is invalid/underspecified), with voltage source (constant voltage), current is consequence of device power demand at required voltage. More power required at a given voltage, more current will flow. Less power required, less current will flow, but voltage stays constant. So, ALL voltage regulators are "dropping" current, so your question could be answered by "any voltage regulator, for example LM7805". But if some device requests some power and your regulator's power source can't provide that power, your voltage will drop.
  - datameta 5y ago
    Thanks for the explanation!
- hasmanean 5y ago
  You mean a voltage regulator? That is possible to build but not with this circuit (Joule thief). The Joule thief charges an inductor in one half of each cycles, and let’s it discharge into the load in the next half. Inductors like to emit a constant current and will kick up the voltage to maintain the current, so it’s more like a current source. Because it drops to 0 quickly before the transistor starts charging it again, it delivers its output as a series of pulses. So it’s a pulsed current source. The only way to get a constant voltage out of it is to 1) feed the current into a fixed resistance load 2) filter the output via a capacitor. I thought about how to make a single transistor voltage source but I gave up. Transistors are so cheap there’s not much point. The world has a bizarre preference for voltage sources (maybe due to the fact that early batteries were DC, or maybe it’s just Edison’s ghost). Most real-world loads have useful outputs proportional to current (LEDs, magnetic fields) and the voltage is just a secondary variable.

spapas82 5y ago

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!

koala_man 5y ago
Why don't you use rechargeable batteries? I stopped using them in the 90s but switched back a few years ago. More convenient and less wasteful than single use batteries, higher capacity and longer device life than built in batteries.
- p1mrx 5y ago
  Rechargeable AA/AAA batteries were always limited to 1.2 volts, which works poorly in some devices. Now you can buy lithium ion cells that regulate down to 1.5 volts, so NiMH is basically obsolete. Alkaline can still make sense for things with multi-year battery life, like remote controls.
  - Maursault 5y ago
    > Now you can buy lithium ion cells that regulate down to 1.5 volts, so NiMH is basically obsolete. NiMH is a lot safer, cheaper, and has slightly better capacity. It's been a few years since first available, but any posters even heard of anyone using 1.5V Li-ion cells? Once you know enough to even be aware of them, you'd be using 3.6V Li-ion instead, so really it's the 1.5V Li-ion that was instantly obsolete, yet still somehow hangs on due to extremely specific circumstances of boutique users that want a flat-regulated 1.5 volts.
    - p1mrx 5y ago
      Are you sure NiMH has better capacity? You have to look at mAh * voltage (or just mWh) for a fair comparison. NiMH is safer, and cheaper for now, but those factors are irrelevant when 1.2V is insufficient for a particular device. If a device accepts 3.6V with overdischarge protection, then regular Li-ion makes sense, but there are a lot of 1.5V-3.0V AA/AAA devices out there.

veganjay 5y ago

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://www.gigaparts.com/etow-humanalight.html - https://aa7ee.wordpress.com/2014/08/18/the-humanalight-a-flashlight-that-uses-your-dead-aa-batteries/ https://aa7ee.wordpress.com/2014/08/18/the-humanalight-a-fla... - https://swling.com/blog/tag/etow-humanalight/ https://swling.com/blog/tag/etow-humanalight/

ricksunny 5y ago

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.

Animats 5y ago
It is a DC/DC converter. It's a basic switching power supply. I was hoping, from the name, for something that would pick up ambient RF and deliver a milliwatt or so. That would be useful for things that need minimal power and are a pain to connect to a power source. Such things have been around for decades. There's an Instructable for this.[1] Newer designs try to use more of the available spectrum.[2] [1] https://www.instructables.com/RF-Energy-Harvester/ https://www.instructables.com/RF-Energy-Harvester/ [2] https://www.teratonix.com https://www.teratonix.com
- kragen 5y ago
  Agreed, though it's an impressively simple DC-DC converter. A whole milliwatt is a lot to hope for from ambient RF (you can do it if you get lucky or make the device big enough), but it's easy to get from solar cells. The purple amorphous kind are less efficient in sunlight but provide more power under the dimmer lighting we use indoors.

tzs 5y ago

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.

p1mrx 5y ago
If you search for "1.5V rechargeable", there are lots of lithium ion batteries with electronic voltage regulators now. Some designs will step down to ~1V when nearly depleted, so that low battery indicators still work. I'm not sure if an NiMH sleeve was ever practical given the space constraints, but it's kind of moot now that better technology exists.
Nextgrid 5y ago
What you're talking about is the Batteriser/Batteroo. It would actually work fine as a voltage stabilizer delivering a constant voltage all the way to the end, but the inefficiencies in power conversion would probably be a major downside (you're losing some energy on the conversion even if the device itself is powered off).

nickcw 5y ago

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 https://www.youtube.com/channel/UCtM5z2gkrGRuWd0JQMx76qA

randombits0 5y ago
* Anticipated explosions managed with the fire containment pie tin. Big Clive is an electrical engineer from The Isle of Man and has a very unique English accent, complete with local slang and idioms. He’s a very engaging character and passes as entertainment, even without the electronics content. Genuine and occasionally heartfelt and up-lifting. :)
- gm3dmo 5y ago
  His accent is quite common in Scotland. What's really cool is he has a brother "Ralfy" who also has a Youtube channel specializing in reviewing Whisky: https://www.youtube.com/watch?v=DWRyIShLRO0 https://www.youtube.com/watch?v=DWRyIShLRO0 They are the Tappet Brothers of the 21st Century.
  - lscotte 5y ago
    I love your Tappet Brother's analogy - it's spot on. The videos they do together are hilarious in a way that only two brothers could be.
lscotte 5y ago
Big Clive's channel(s) (he has a separate one for live streams) have some of my favorite content on YouTube. He's super down to earth and just has fun with what he does, never taking himself too seriously while being very knowledgeable.
agumonkey 5y ago
beside clive there's a bunch of special electrical oriented channels: - photonicinduction (warning, absurd levels of everything up to 11, borderline insane at times, but if you want to see ultra high everything, here's the channel) - styropyro, spiritual son of the above, but for everything lasers

HPsquared 5y ago

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) https://youtu.be/1uEmX5XClPY https://youtu.be/1uEmX5XClPY

kragen 5y ago

> The one shown was sourced from Maplin Electronics in the UK RIP, Maplin. Glad Big Clive's still alive and kicking.

fencepost 5y ago

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.