(A report from the folkelectronics project.)

Introduction to the Joule Thief: (Wikipedia)

Rehab '50s penlight
The extreme simplicity and almost magical function of the Joule Thief circuit makes it an iconic resource for the practitioner of folkelectronics. We were introduced during a search for an uncomplicated 12v source from a 1.2v supply. It worked in the application, and as a side-effect infected the research with delectable little thought-balls of vectors and magnetic fields. Upgrading a 1950's penlight from the pencil drawer to a single "dead" cell driving a white led was a functional way to apply the little circuit, but it's real mission seems to be the rescue of batteries from their rejection as "dead" by modern devices. (touch pictures to expand)

Existential Discharge

A cache of joules.
Picture sent by a JT user.
For about twenty years the shop has had a bucket of batteries waiting to be recycled,-- deemed dead by the devices they once powered. Suddenly they have become a joule cache, and all have been able to bring the JT to life, including a few found in the street fifteen years ago, after they'd been run over by at least one car. It seems like a moral failure that so many of these batteries get tossed when they contain enough juice to power an led for hours, days and even in some cases, weeks.

"It's amazing what pleasure there is in getting that last electron out even though there's no practical utility to it!" -JT user

This JT will accomodate any cell, and includes six colors of leds for
various mood lighting applications.
The simplicity of the circuit allows for an enormous variety of configurations and cell types, --as long as the cell voltage is less than two volts. A higher voltage will result in undesired odors and likely tragic heat damage to the transistor. Everyone should have a JT, - and an internet search for "Joule Thief" will deliver more information than you need to know to build one.
four color desk model

"So I just went down to the basement to get some formerly, totally dead AA batteries for christ sake because the one in the Joule Thief is now really dead-third one. Now I have to have two dead battery boxes: one allegedly dead, and one Joule Thief dead. Don't experiment any more. I don't want to have three boxes." -JT user

JT at home.

The joule cache contained many shapes of cells, and included a number of "packs" of odd cells from telephones, NiCD's, NiMH, Zn-air hearing aid, and several kinds of button cell. A frenzy of design and prototyping produced some solutions, --but the research continues.
Prototypes for various size cells.

"I love the joule thief page. It makes me want to make one too." -JT user

One of the most endearing folkelectronic qualities of the JT circuit is that almost every attempt at constructing one works.

Wooden JT PNP with wood-core,
solenoid wound coil.

Firewood Joule Thief

Wooden JT by
John V. Dollhausen
The first JT here worked on the first try and was running for days before anyone noticed that the transistor collector and emitter were wired backwards. It seems impossible at first glance, is a twisty thing to figure out, and is not recommended.
The research had a few glitches, but continued through power outages.

I'm glad to have another use for my old batteries, instead of throwing them into the fireplace." -JT user

The performance of batteries in the fireplace is virtually unaffected by the JT.

Dead AA cells are ubiquitous, and need special attention.

"I carried it around and fondled it like it was a folk art treasure. Then when it wouldn't light my after-dinner cigar, I thought it could be used as a 4th of July sparkler anyway. The Joule thief does look great hanging on that nail on the wall. And it's wonderful that, it eats dead batteries, of which we have a plethora." -JT user

Prototype wall hangings.

"When I got up at 2:00 this morning, I checked the jewel thief because I knew that she/he was getting low on energy, but she/he still had a spark (and still does)." -JT user

"Have relocated the Joule Thief to a place where we can all keep track of its thieving ways." -JT user

One JT maker writes that he is currently working with a 2ft
diameter toroid core, to create a searchlight that will replace
the carbon-arc lights in watchtowers around his prison farm.

"...joule thief! I love it! I have been carrying it around with me everywhere. It's on it's second dead (rusty) battery. I can actually hear it - the LED light makes a high pitched whine. No one else that I show it to can hear it so far." -JT user

Smashed battery found in street, -20yrs in the recycle bucket.

"love this thing. Looks like I've got a year's supply of batteries." -JT user

"I just watched my very special JT suck the last bit of life out the battery, and it started blinking on and off every few minutes! It makes me smile... it's almost like it's alive." -JT user


JT built with an ancient germanium NPN,
drains battery to 0.36 volts.

JT users often assign anthromorphic characteristics to their JTs, confusing it with a "living thing" or even an artwork. This could be simply the expression of pathological features from the users, but is surprisingly consistent, and might possibly be induced as a result of the focussing of ephemeral forces in the complex magnetic patterns the JT generates. Some users have reported that they can "hear" some of the resonant frequencies generated by this ephemeral interaction. This aspect of the JT begs more research, but is beyond the scope of folkelectronics.

"I would start by stating that my Joule Thief is a most engaging art object, except I am not completely clear that that is indeed what it is. It certainly has many of the theoretical attributes that one ordinarily associates with “art object”. It was man- made with intentionality. It gives great pleasure and pride of ownership. Its value is in content rather than material. Finally, it has no reason d’etre in the practical world. So far, it sounds like Art!, except that it is alive, which has no standing in John Dewey’s scheme for deciding what is Art.
Early prototype.
I know it is alive because of the way it behaves. Its little light, glowing softly in the shadows is certainly there to attract a mate (no luck yet!) Its faint glow reassures me that all is well and time continues to pass. It asks nothing of me. I think it must be the same egoless assurance the Zen monks find in the plaintive call of the house crickets that they cherish and protect.
"Float trip with friends."
From a jt user.
When I see its light, I think of primordial species having made it through several brushes with extinction, soldiering on by consuming very little and causing no other species any grief. The Joule Thief shares some of those qualities with the large mosquito-like creatures that don’t eat or drink or bite, but fly around my house in the summer looking only for love, finally to die on the cool tile floor of the bathroom. I am sad when the light finally dims to death, but redeemed by the JT’s enthusiasm when presented another life sustaining moribund cell. It is an “easy keeper”, as all survivors learn to be. Its light is a beacon of quiet hope for love in the face of sadness (I have recently had it fixed.) If I were sentimental I would name it Abelard. Its beauty is measured in “millihelens” (the amount of beauty necessary to launch a single ship.)" -JT user

Jig for testing toroid windings.

"The Joule Thief is intriguing. It's unbelievably efficient...almost science fiction. Since I've never before seen or heard of anything like, it seems a bit subversive. And decadent. Leaving a battery-operated device on all the time seems just wrong. Fun!" -JT user

"In our bedroom a pendant lamp with a frosted glass shade hangs over a table used for reading. The Joule Thief sits on the table just below it. In the dark the LED illuminates the entire shade from below, making for an eerie, bulbous night light. A spooky shadow is cast on the ceiling. We love it!" -JT user

JT-based tester for testing.
With the ability to operate at extremely low voltages, the JT should find use in simple test equipment. Powered from one zinc and one copper probe, a JT will test any sufficiently composed electrolyte solution, and will light when the probes are inserted in various fruits.
Tester, testing.
Calibration is in the eye of the user, and with practice it is possible to distinguish between them. This could mean an end to any confusion between apples and oranges, for example.

"We are loving our little light! I found the perfect spot in the hallway. It helps guide me to the bathroom in the middle of the night." -JT user

JTs with magnetic battery contacts offer versatility and convenience in high-turnover situations and will accomodate any size cell, --but beware of voltages exceeding 1.5v.

Magnetic contacts make it easy to change batteries.

Magnetic contacts and multiple leds.
Button cell.

Magnetic contacts.

Magnetic contacts - 1watt led.

Blue Joules

CRUD on battery contact.


Batteries tend to leak when deeply discharged. The ejaculate is potassium hydroxide which is slightly corrosive and crystallizes into potassium carbonate on the battery contacts. The resulting resistance at the electrodes will stop current flow and render the JT dormant.
Fortunately, the crud is easily removed using a mild acid like vinegar, on a cotton swab. It's not a bad idea to do a light cleaning even if the JT is working because the extremely low voltge during the discharge is vulnerable to the slightest resistance.

New Discoveries

It was recently noticed that batteries that were 'drained' by the JT, -and subsequently relegated to the 'totally dead' bucket-, tend to recover somewhat after a rest period. some even recovered enough to light up a JT for a couple days. This somewhat admirable tenacity might be troubling to JT users with a propensity for empathy.
AC adaptor for emergency situations. Will power a JT for 24+hrs
during an outage.
Another complicating factor has to do with rechargeable batteries that have reached the end of 'useful' service. These, and simple 1.5v AC adapters for battery-operated electric clocks can keep a JT operating indefinitely, or forever, whichever comes first.

Hospice Care

jt jt
A neatly packaged solution to complete discharge.
jt jt
Dead battery holder made of black walnut burl.
A joule thief user came up with a system for ensuring the maximum discharge of AA cells while accomodating the propensity for the cells to recover after a rest. A major contribution to folkelectronics, this system promises to be a productive souce of data for the project.

The fifteen cell organizer, made of solid black walnut burl, would grace any decor but it is protected by its metal case from the perils of dirt and activity in the shop. A magnetic base JT can be mounted in any convenient position on the case. The case incidentally provides a Faraday shield for the cells, protecting the system from the distorting effects of ephemeral forces on the data generated.

jt jt
Up to 15 dead cells can be stored.
jt jt
Germanium transistor JT
terminal V<125mv!
This basic JT uses a fifty-plus year old germanium transistor and it can pull a cell down to 122 millivolts or less -- not a perfect zero volts but good enough for folkelectronics.

The procedure is to load the JT with any cell, run until the led is dark. Replace the cell in the holder and reload the JT with any other cell. If the new cell does not start the JT, discard it and choose another cell. Repeat until all fifteen cells have been discarded.

jt jt
Still glowing @ 193mv
jt jt
Ancient Ge transistor.
jt jt
Led fires @ 122mv.
jt jt
Extreme discharge causes impressive
leakage at the cathode.
2KOH + CO2 → K2CO3 + H2O
jt jt
Faulty toroid serves as an asshole
for a hobby horse.

Gravity cells drive leds on 1.1 volts.
Gravity cells produce 1.1v, and are ideal for keeping a JT burning. Simple to make from hardware-store parts and chemistry, a pint size will power a JT for a month. They are the subject of another folkelectronics report, not yet posted. Gravity cell wiki

This page is not finished. JT anecdotes solicited.