Introduction: Joule Thief With Motor Coils

About: Andrew is a software engineer by trade and prefers projects that are simple yet effective. Andrew's areas of interest include software systems that do complex things from simple input, aesthetically pleasing k…

Want a Joule Thief circuit in a slim shiny package? Scoring serious geek points is high on the agenda of the forward thinking tinkerer, and what better way to do so than with the recycled innards of a floppy drive, toy motor or precision stepper? None Spring to mind... So with that Lets get on with it.

This project is basically a "Joule Thief" but with more scrap parts reuse and unfortunately less efficiency. The basic Idea is to use the core of a motor as both the "toroid" part of a "joule thief" (with the rest of the circuit concealed in and around it) and as a nice light reflector (which , if you have access to a pancake motor, is conveniently reminiscent of a flower or the sun).

As previously stated it is very inefficient, and the reason I chose to do it this way is that it uses an otherwise scrap part as a functional and decorative component. Obviously, if you so choose, you can put a hand wound toroid in but it will probably require a bit more room than is easily available so you might lose out on Prettiful Points. If you want to go with a normal joule thief circuit I recommend 1up's excellent Instructable here. Since the Circuit build has already been covered many times before I will focus in on reusing the motor and quickly cover the rest of the circuit. If you need help please leave a comment.

For a few more pictures and discussion please see my blog post

Step 1: Bill of Materials & Equipment

1 x 1k resistor
1 x NPN transistor (the 2N3904 is adequate, however 2N4401 or PN2222A will give better light output)
1 x LED
- x Enamled Copper Wire (0.315mm is fine)*
1 x Reasonably sized electrical motor. DC and stepper motors are both fine.

*(other insulated wire should work fine, I used this and it looks OK)

Soldering Iron & solder
Needle Nosed Pliers/tweezers
Screw driver

Step 2: Get Your Motor Open

If you are disassembly something with a motor in it I cannot really help, each disassembly process is a whole Instructable in itself. To bypass the complexity; pulling off plastic and sheet metal covers and take care to unscrew where you can, until you find something similar to the picture below. This is a stepper motor, its usually decoupled from the main board to allow vibration dampening to stop it damaging connections (Which is ideal for us because we have a nice complete unit to work with). Normally then we can pull out a motor connected to a small piece of circuit board, see image one and two for floppy drive motors, image three and four for PC fan motors,  and images five and six for DC toy motors.

Step 3: Disassemble the Motor

Due to the bewildering array of possible motor types I cannot hope to cover how to disassemble them all. A good piece of general advice is to post in the forums if you need specific advice on getting the stator or rotor out of your motor. I will cover below how to remove a stator from a floppy disk drive because this will normally be the type of stator you want. As noted later in this document you can use the rotor from DC motors, but the effect is a little underwhelming visually. Image two is the rotor from a DC motor, with the contacts section highlighted.

Unscrew any retaining screws and keep in a safe place. (Look for Screws going through the core, you don't want to be tugging away at it while its still secured down). Once all the screws are out there should be more "give" (freedom of movement) in the core, pull it up and get a lever underneath it, be very gentle, you don't want to snap those thin wires connecting it to the board because it will be near useless if you cannot easily access them.

Removing the core of the motor is a tricky business, use your soldering iron and just heat up each pad you can see connected to the coils and keep the unit under gentle upward pressure. Heat the pads in turn or use a wick to remove the solder, if you can. You may need to iterate heating and pulling but it should come away after a little while.

Congratulations, you have your "toroid" component.

If some of the wires broke off try to unravel them a bit to get access, we need two coil pairs, so if you lose one or two wires all is not necessarily lost.

Step 4: Work Out the Wiring

We now have to find two sets of wires (two coils) and connect them up in the right way. I am unsure whether other units will be wrapped or wired differently, I have dismantled 3 and the way they are hooked up does seem to differ, so be prepared to tinker with the connections a little. Generally the coils seem to be either six, three or four wires, normally these are connected as shown in the images.

One type of configuration has each coil tied to it's neighbours (lets call it the Ring Configuration) as represented in image one. Another type of configuration has no connections between any of it's coils (lets call this a Disjointed configuration) as represented in image two. Yet another configuration has a common ground or high pin (lets call it the Common Configuration) as represented in image three.

In any of these cases figuring out which configuration you have is easy, just get your ohmmeter and a pencil and paper. Label each wire and test the resistance between each one. If the resistance is immeasurably high then don't draw a connection. If the resistance is very low we can say that the two points are probably connected by one coil. If it is a little higher then it's probable that we are measuring two or more coils. Once you have the connections drawn out then you will have an image much like images one, two or three.

Ring configuration (fig.1)
The ring configuration is commonly found in DC motors, and a little more rarely in pancake motors. It is typified as having three coils each connected to it's neighbours. All three coils are wound in the same direction. In DC motors it is common for the coil to be wound from a single wire. Typically ring configuration stators and rotors will have 3 wires.

Disjointed configuration (fig. 2)
The disjointed configuration is common (in my experience) in pancake motors and not in many other applications. Each coil has two wires that are only connected to the mounting board. They can normally be identified quickly in that they will typically have 6 wires. It will pay to double check with an ohmmeter just to be sure.

Common configuration (fig. 3)
This configuration is commonly found in pancake motors and computer fan motors. Each coil has one side connected to a common wire (to which all other coils are also connected) and the other side is connected to the board and nothing else. The number of wires in a common configuration is normally 3 or more, but they can be easily identified because one wire will clearly be connected to a number of other wires, normally twisted together.

Now that you have identified the type of your motor please jump to the relevant section. Please note that differently coloured coils and wires in the diagrams are just to make referring to them easier.

Step 5: Ring Configuration

Ring configurations are normally used in brushed DC motors and pancake stepper motors that can be found in floppy disk drives. They can be identified either by the fact that they typically have three wires, or by the fact that each of the connected wires is connected to two adjacent wires by one coil separation, for all of the wires.

This configuration is easy to deal with. We are starting with what is effectively one large coil with three centre taps (fig 1). In we need to make a single break in the "loop" in order to get two "end" wires and one tap in the middle. This needs to be done because otherwise the third coil (blue in this example) will disrupt the operation of the coil and prevent it from oscillating.

If you would like to see what we are doing electrically please click through images one, two, three and four in turn. Images two, three and four are equivalent electrically but demonstrate the removal of the blue winding.

DC motors
It is common in DC motor windings to use a single piece of wire all the way around the rotor, for all three coils. What we want to do is disconnect a single "in" or "out" from the contact pad (fig. 2). If you wish you can go ahead and unravel this one length of wire from the rotor. When you get to the other end of your unwound wire it will be welded to the next pad around, you simply need to cut the wire off before the solder joint. This should leave you with a length of wire completely disconnected from the rotor that you can re-use, and a space that is possibly large enough between magnetic stacks to insert your transistor (the Joule thief in picture five uses this trick). The two pads where you disconnected the "blue" wire are the two "end" wires. The one pad that has not had wires detached is therefore the centre tap.

Keeping track of which wire is which, jump to the "Time To Test" step.

Pancake motors
With a ring configuration pancake motor we simply need to make a single break. Each of the three exposed pieces of wire will consist of two wires soldered together. Pick any one and break the connection (fig. 2) between the two wires. You probably want to leave the windings on the stator because it looks better this way, also the wires are inter-weaved and you would (in attempting to unwind the redundant coil) risk damaging the functional coils. Select one side of the break that you just made (in fig. 2 I chose the green coloured side) - this is one "end" wire. .

Referring again to fig.2 we can see that the "blue" wire side of the cut is not needed, and so can be taped away. We now need to know which of the two remaining connections is the end wire, and which is the centre tap. Note that you cannot tell by their position on the coil, the best way is to use an ohmmeter, checking the resistance between each connection and the "green" end point. Using the example as coloured (fig. 3) green/yellow is half the resistance of green/red - so yellow is the centre tap. Put another way, the resistance between your end point and the other end point will be X, and the resistance to the centre tap will be one half X.

Keeping track of which wire is which, jump to the "Time To Test" step.

Step 6: Disjointed Configuration

Disjointed configurations are probably the hardest configuration because you need to keep tract of winding directions. Commonly this configuration has 6 wires (three coils) although there could be more coils. For our purposes we need two coils.

The first task is to identify two coils and the four wires connected to them. The is easy, using your ohmmeter, take any wire and measure it's resistance to every other wire. It should only be connected to one other wire. Good, you have your first pair. Now pick a different wire from the two you have already identified and repeat. We now have four wires connected to two seperate coils. Tape down all the other wires, we don't need them.

Next, mark any of the four wires as "start 1" with a sticky label. Look at the direction the other wire for this coil ("end 1") is wrapped around (is it going clockwise or anti clockwise?). On the second coil pick the wire that is winding in the same direction ("start 2"). Connect "end 1" and "start 2" (fig. 3). The join you just made is the "centre tap" as shown in fig. 3. The other two wires start 1 and end 2 are either end of the coil. Any other wires than the four are superfluous and you may want to tape them out of the way to save confusion.

I strongly suggest you use sticky labels to track which wire is which. Also, experiment with the circuit, testing it out before gluing it in place. If it doesn't work, fret not; you may have gotten confused and connected the wrong wire, just retrace your steps and try again.

Keeping track of which wire is which, jump to the "Time To Test" step.

Step 7: Common Configuration

By far the configuration that I see the most is the "Common" configuration (fig. 1). I call it common configuration because each coil has one end free and the other connected to a common wire (to which all other coils are connected too).

This configuration is by far the easiest configuration to use. No extra work is required, all we need to do is work out which wire is which.

There will be one wire that upon closer inspection is many wires soldered together. This is the centre tap. Pick any other two wires. You now have your two "ends". In figure two we are simply ignoring the "red" coil, you may ignore more or none - the number of coils on a "common" configuration varies, I have seen two and three coils, but I see no reason why there couldn't be more.

That's all that you need to do for this step, so keeping track of which wire is which, jump to the "Time To Test" step.

Step 8: Time to Test

Now comes the time to test your coil. Use the circuit diagram below to create a joule thief with your coil. I will cover briefly how to connect the inductor (your scavenged motor part) here, if you need more instruction please refer the Joule thief Instructable. Remember that you can skip the hand winding toroid section.

Firstly, please look at the circuit diagram below. The "centre tap" of our stator is connected to the + end of the battery. The two remaining ends connect to the collector and base(via a resistor) of your transistor. For the resistor I recommend a variable resistor with the range of something like 0 Ohms to 5Kohms, although I have never needed to use a resistor larger than 1kOhms in a joule thief circuit. The emitter is connected directly to the negative side of the battery. Finally, an LED is connected across the transistor; positive leg on the collector and negative leg on the emitter.

I would thoroughly recommend having a joule thief circuit breadboarded and tested with a normally wound inductor first. After you know that your circuit is working it becomes a lot easier to diagnose problems.

Common Problems

The circuit works with a normal inductor but not with my scavenged stator/rotor.
-Have you connected the stator correctly? (are the windings pointing the correct way? Remember that direction, i.e. anticlockwise/clockwise matters).
-Have you tried varying the resistance? Your value should be between 300 and 3000 ohms.
-Have you tried a lower power LED (red are the lowest )?
-Have any of the fragile connections on your stator/rotor come loose?

The circuit lights only red and orange LEDs (The Joule thief is not stepping up the voltage as much as it should, this means that only low voltage (normally red) LED's can light up on the available voltage)
-Have you varied the amount of resistance on the (variable) resistor?
-Has the battery lost most of it's charge? If so try a new one.
-It may be that in this circuit the inductor cannot step voltage any more, have you tried with a normal inductor?

Step 9: Creative Flourish

Now that we have the circuit done, here's a note on aesthetics;

Disk Drives
 If you got your stator from a CD/DVD/Floppy disk drive it will probably be the flat "pancake" type. If this is the case, one or two red/yellow/amber LED's illuminating the coil (as shown below) gives a nice effect reminiscent of the sun with rays coming out of it.

Computer Case Fans
Computer case fans are a little more compact and don't look very sun-like when illuminated. However they have a hole in the middle that a small LED fits into quite well, giving a more Iron Man ark reactor-esque appearance. Since the hole is normally inside a recessed disk a dab of hot glue could diffuse the LED light for a more mini-fusion reactor feel to it :P

Toy DC Motors
Toy DC motors are (visually) a different beast entirely. They look good unilluminated and trying to illuminate them is often very difficult because of their shape. You may want to point your LED(s) outwards  rather than trying to illuminate them, because the effect is not as good as "pancake" stator illumination.

And Finally
These all work well as necklace pendants, you are only dealing with 1.5 to 3 volts, so safety is not really a concern provided you are sensible with sharp edges and pointy stuff. In the Sun Dials I have put the battery on the pendant but a good idea is to put the battery holder on two wires used as the necklace loop. The battery behind the users neck counterbalances the pendant.

Important: always properly shield the battery, sometimes they go pop and spray acid, which is BAD! Also, no sharp Edges! Also also, put a weak point in the wire loop/string of the necklace, if you snag your necklace on something you want the string to go snap, not your neck! Play nice...

Really Finally
Some furtherideas;
-Use UV LED's and fluorescent pigments to really bring the design alive. Bear in mind water soluble stuff may rub off!
-Use bits of the circuit board to further decorate the design. Remember, no sharp edges!
-Add an on/off switch
-Use a more efficient version of the joule thief circuit

Finally Finally
If you do follow these instructions and make something cool please post pictures in the comments.

Okay Really Finally, Seriously
I find it helpful to cover the wires of the exposed coils with a thin layer of PVA glue. This helps prevent snagging the wire and breaking your joule thief. However in my experience this this seems to exacerbate the high pitched whine that you can sometimes here from joule thieves... I suspect it is something to do with increasing the capacitance in the coil with the water retained by the glue or something similar. Be careful not to put glue across any exposed solder joints, specifically the base of the transistor, since the glue is slightly conductive this can upset the circuit and make it sulk (I.e. not work).

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