Picture of supercharged lemon
build a lemon-powered flashlight!

normally it takes 3 lemons to get an LED slightly glowing...

with this design you can make a single-lemon-powered flashlight that will run for weeks!!!


it was developed during the exhibition "Cooking and Constructing" at Platform21

joule thief design
Remove these adsRemove these ads by Signing Up

Step 1: Prepare the components

Picture of prepare the components
to make this lemon light up you'll need the following tools and components...

- multimeter
- soldering iron
- steel scissors
- pliers
- sanding paper
- AA battery (for testing)
- knife
- pen

- lemon
- 1 kOhm resistor
- NPN transistor
- ferrite bead
- copper wire
- sheets zinc & copper
- white / blue LED

Step 2: Wind the transformer

Picture of wind the transformer
this transformer is the crucial element to make joule thief work with lemon. it requires much more winding then in the normal joule thief design and only plain ferrite works - all colored rings failed.

1. take about 1.5-2 meters of copper wire, bend it in half and wind the coil with it. in this case it took around 50-60 windings arranged in two layers.

2. after the winding is done - cut the double end, so that you have 4 loose single tips.
3. clean the tips from the isolation lacquer with sanding paper
4. with a multimeter set on conductivity test, find two separate windings
5. twist two opposing ends of different windings into one contact
6. pre-solder the tips of the transformer.

your transformer is ready!

Step 3: Prepare the transistor

Picture of prepare the transistor
take the transistor and bend it's legs:
the middle one - goes straight backwards
the side ones - go forward and a bit more to the sides

afterwards - pre-solder all the legs

Step 4: Solder & test the joule thief

Picture of solder & test the joule thief
now we're going to build the joule thief itself

solder the resistor to the middle leg

the short leg of the LED (the minus) goes to the rightmost leg of the transistor, and the long (the plus) leg goes to the LEFTmost leg of the transistor

the transformer gets one of it's single-wire tips soldered to the loose end of the resistor, and the other single-wire tip goes to the long leg of the LED

to test the joule thief - connect the twisted end of the transformer to the plus of an AA battery, and the short leg of the LED - to the minus of the battery

if the LED doesn't light up - check your circuit

Step 5: Make copper electrodes

1. process copper plates with sanding paper
2. cut pieces that would fit nicely in your lemon
3. pre-solder spots on the electrodes
4. cut a length of copper wire about twice the length of you electrodes combined
5. remove the lacquer from the wire in the same way you did it for the transformer
6. solder the wire to the electrodes
7. check everything is soldered properly with the conductivity test

Step 6: Make zinc electrodes

Picture of make zinc electrodes
as zinc is not easy solderable, we'll have to use some force here

1. process zinc plates with sanding paper
2. cut pieces approximately the same size as copper ones
3. make small in the top of every piece and bend them
5. prepare the wire in the same way as with copper electrodes
6. clamp the wire with zinc pieces using pliers
7. make the conductivity test

Step 7: Stuff the lemon

Picture of stuff the lemon
here comes the juicy part...

1. to reduce your lemon's internal resistance (thus boosting it's current output) you have to smash the lemon several times and roll it on the table until it's all soft an juicy inside
2. mark 8 cuts with as much space between them as the lemon size allows
3. make the cuts as vertical as you can and to the bottom of the lemon
4. insert electrodes in a sequence copper-zinc-copper-zinc... making sure that they don't touch each other
5. measure the voltage between electrodes
copper - "+", zinc - "-"
it should be around 0.8-1.0 Volts
6. measure short-circuit current output
in my case it was around 10 miliAmps - that's a lot for a lemon!

Step 8: Finalize!

Picture of finalize!
solder the joule thief to the lemon, and you're done!
the twisted transformer wire goes to copper electrodes, and the minus leg of the LED - to zinc electrodes.

the last photo is the comparison between the freshly made lemon and the one that was running for a whole month by now.
1-40 of 184Next »

Hello, what if I used pennies and nickels, will it work? so that I'm not going find for the copper and zinc sheet.

Toasty22222 years ago
Would it be possible to use galvanized nails, pennies or even copper wire itself instead of the metal sheets? (As I have quite limited access to them)
s8 (author)  Toasty22222 years ago
The main idea here to get the LED running is to get as much current from the lemon as possible, which means maximising electrode surface. If you manage to stuff enough copper wire, pennies and nails - it might work, but it might be tricky making sure that they don't touch each other.
Toasty2222 s82 years ago
That makes sense, thanks!
iceng3 years ago
This should be featured..

ashleloo2 years ago
how come there are four legs in the second picture?
s8 (author)  ashleloo2 years ago
the fourth is not the leg, but the solder wire.
ashleloo2 years ago
do u have to have gigantic sheets of zinc and cooper inside lemon?
s8 (author)  ashleloo2 years ago
they are no more gigantic than the lemon itself. They're just pretty densely packed.
ashleloo2 years ago
never mind
So is it a plain ferrite bead or a ferrite toroid bead, because the instructions say you need to use a ferrite bead, but I thought ferrite toroid beads are used in joule thiefs.
.A.2 years ago
This just gave me an idea. If it works i'll post an instructable.
geeklord6 years ago
im pretty sure its not a transformer, it two diferent inductors, it might even be called a choke(look it up on wikipedia).
s8 (author)  geeklord6 years ago
it is a 1:1 transformer.
geeklord s86 years ago
you sure?, i thought i heard that these work by storing very small amounts of charge in the toroid part of it and then releasing it; all of this happening thousands of times per second, of course.
True. The toroid has "special properties" Something about EMP, EMF, and magnetic field resistance.
It is a toroidal transformer. And yes, the coil stores energy and releases it when the time is right.
rayfalcon4 years ago
so if i have a pre- wrapped torrid from an old computer monitor that has the plastic coating on it then i have to remove the coating before the joule thief or the transformer will do anything???
Well...if plastic is on the ferrite, it shouldn't do much...but try to remove it anyway.
alex_jines6 years ago
transistor serves as amplification stage, it amplify the current generated from lemon
s8 (author)  alex_jines6 years ago
not really - transistor here acts as a very fast switch.
waterlubber s83 years ago
Ever take a relay and wire it so it flicks on and off so fast it goes "beep"? Fun...
The transistor acts as a switch and the 'transformer' is just like a really small flyback transformer found it modern CRT TV's
blackghost3 years ago
Awesome instructable

Could this be powered by salt water ? or even urine?

Salt water-Yes. Urine...no way I'm gonna test that.
s8 (author)  blackghost3 years ago
Thanks, blackghost. I'm pretty sure it will run on salt water and urine. Please post here the results if you get to try it
Rosierap5 years ago
Please help!
Following your instructable, my first joule thief didn't work. It does light the led with a 3 volt battery, just not a 1.5. It is a 3 volt led.

Some questions, what kind of 1kohm resistor? The one I bought is 1/4 watt since that's all radio shack had. The transistor was a "general purpose" one. The toroid was large, but uncoated. The wire was 9 feet of 20 gauge.

Does this look right?

emenke Rosierap5 years ago
Try testing it out with the LED ends switched out... when i first tried mine, it didn't work because the LED ends were soldered backwards.  When I tried again with  the anode and cathode ends switched around, and tested it out, the LED finally lit up!  Try using a battery that is 1.5 Volts too, then use one that has progressively lower voltage.  Also, is it possible that you got the ends of the wires wound around your bead mixed up?  Try changing that around too, and perhaps the right combination would make your Joule Thief work.  Good LUCK!
Rosierap emenke5 years ago
After some research, a friend of mine got one working with 7 windings of insulated wire on a breadboard! I removed that wire and added the 60 windings of  bare copper wire (this time I used 30 gague so it would be easier ... and it didn't work.

I'm thinking that the bare wire is to blame, so I ordered 26 gauge enamel coated wire (30 seemed really puny). You mentioned you used bare wire but you had to sand off the coating before soldering so I think you are using coated wire?

Now Im racing the clock before the science fair...

-max- Rosierap3 years ago
ya, youl neefdto sand the ends, you can also scrach it off with a sharp peice of medel, of burn it off with a match (then clean off the char, of coarse!). the center tabed lead goes to to + side of battery and the two ends go to the transistor. make sure your transister is a 2n2222 or 2n4011, (2n3904 is a bad choice, their are better ones out there)

the - side of the battery goes to the emitter
the + side goes to the center tab
the led goes to the emiter and colecter (check polarity)
the center tab of the transister goes to the resistor which goes to tone end of the coil

and the other end of the coil goes to the colector on the transistor
s8 (author)  Rosierap5 years ago
yep, the wire has to be enameled. could be with normal plastic insulation as well as long as you manage to fit enough windings through your coil.

as far as i remember now - it was quite tricky to get the transformer winding right. particular ring material would work slightly different with particular wire.

i suggest you to try to approach your particular coil as systematic as you can. make first 10 windings, then 20, then 30 and so on - this will be time-consuming but the most certain way to get it running.

good luck!!!

-max- Rosierap4 years ago
have you tryed to put the battery in the other way? if it still doesn't work, make sure the toroid was wound right. when i was building one, that was always the case. make sure the transistor is connected correctly.
alright rosie, first thing that i noticed is that you have the resistor on the middle lead that is where your positive input goes (+) which goes to the center leg of your transistor, if im not mistaken its the Base its really early atm but thats what im seeing, the center (two wires on your toroid go to the positive, check your legs either by useing a digital meter and putting it on continuity or run some power through it put the positive of a battery in the middle two legs then test it to make sure it has 1.5v's on the right side if its a 1.5v battery then check the other side and make sure again its 1.5v for the example once you know that both legs are hot (they have power) then you are in bussiness, the base goes to the resistor then to one leg on the outside, not the center. hopefully that helps.
The resistor is supposed to go on the center leg of the transistor.
Tinker 13 years ago
A small wiring diagram to support the good pics would help experimenters and educate a little!

Pipper Tinker
ARJOON4 years ago
can i use ferrite electrode
Adam Manick4 years ago
Maybe add a switch to your circuit so you can turn it off when you don't want it to be lit.
eranglr6 years ago
I tried to built it and has a problem: When I'm connecting the joule thief to the lemon, the led lights up for about half a second (even less) and then stop working.. when I disconnect it and reconnect it, the same result appear... How do I manage to keep the led light up? Thanks Eran
1-40 of 184Next »