Today I made a compact thermal electric generator ( TEG ) using a thermal electric cooler ( TEC a.k.a Peltier device ) and a Joule Thief.
This TEC produces about 1.8VDC when heated on one side and cooled on the other (this setup uses a candle as the heat source and cooling is from ambient air). The advantage of using the Joules Thief circuit in this setup is that it will boost low voltages to higher usable voltages. The open circuit output voltage of the Joule Thief in this circuit was about 31V Peak. It takes about 14VDC to forward bias and light the four LEDs.
The down side of this circuit is that there are conversion losses, but still it costs a lot less to buy one TEC then to buy nine of them and put them in series to get to the voltage required.
From the time I light the candle it takes ~36 seconds to light the LEDs, and they continue to get brighter from there. The LEDs stay lit for ~2 minutes after I blow the candle out, as the residual heat moves from the bottom heat sink through the TEC to the top heat sink, not shown in the video.
Here is a video of the circuit in operation:
Here is a picture of the major components, from left to right: top heat sink, thermal electric cooler, Joule Thief, bottom heat sink, and candle. (to see full size images click images, then click image on following page, still have to figure out why you have to do this to get a full size image? )
Here is a picture of the assembled cooler and heat sinks, I added several pieces of 12AWG solid wire and a 3/4inch copper coupler to direct the heat.
Here is a picture of the TEC Generator connected directly to a DMM without the Joule Thief boost circuit. The DMM is reading 1.792 VDC
And here the circuit is operation, producing ~14VDC to light four white LEDs. :
This Joule Thief Kit is available as a thru-hole board kit. This kit allows you to substitute components and includes all parts and a quality PCB. The PCB is double sided with extra copper around each hole on both sides, all traces are redundant top and bottom of the PCB. The PCB design allows for the components to be replaced many times as long as good soldering practices are followed. Substituting components will allow the experimenter to try for different voltages or efficiency.
* 40 inches red magnet wire
* 40 inches green magnet wire
*1ea – NPN TO-92 transistor
*1ea – torroid
*1ea – 1/4watt axial resistor
*1ea – PCB
*1ea – Ultra bright white LED
BIG educational discounts on kit quantities of 20 or more. Educator kit also includes 1 assembled and tested Joule Thief, please contact us at firstname.lastname@example.org for more information on customized kits.
A little info on the Joule Thief for those of you that have not heard about it. In the article “One Volt LED – A Bright Light” written by Z. Kaparnik from Swindon, Wilts, UK published in the November 1999 issue of the magazine “Everyday Practical Electronics” in the section “Ingenuity Unlimited”; described how to make a “Micro-torch circuit” using a very compact high frequency, high efficiency DC-DC converter design. The circuit consisted of a hand wound micro toroid, a 10K resistor and a ZTX450 transistor. The circuit was designed to run a LED that had a forward voltage drop greater than 1.8VDC from a single cell battery (1.5VDC) and could run as low as 750mV, this meant it could run from nearly dead batteries. This circuit has been propagated, experimented with, and changed at numerous sites and discussion boards and most significantly can now run white LEDs that have forward voltages greater than 3V. Someone nicknamed the circuit “Joule Thief” and it has stuck ever since.
A Joule Thief circuit is a simple three component, low Voltage DC-DC boost converter. The circuit can run on voltages as low as 300-400mV depending on the transistor used and windings on the transformer. The output voltage and current depend on the three components used in the circuit. As a minimum the transistor must have high enough gain and should have a collect-emitter voltage rating that is well above the maximum output peak voltage on the secondary winding ( I like at least a 25% margin ). The resistor is chosen so that it limits the maximum circuit current, by limiting the current to the base of the NPN transistor. The transformer can be wound 1:1 for simple operation or can be wound with more than two coils ( A third winding may be wound to create high voltages for running EL devices, Nixie tubes, neon bulbs, etc… ).
I decided to try and experiment with this circuit myself. I have made many variations of the circuit, some that could run to voltages as low as ~350mV and still produce 12V out (not much current though with such a low input voltage). In making the circuit, I decided it would be nice to have a PCB so that I did not have worry about problems that I was having with the air wired experimental circuits. The air wired circuit had several problems due to wiring shorts or opens, and was not robust enough to carry around. I thought it would be nice to produce some kits for other experimenters so that it would be easy to assemble and not have to worry about wiring problems. Visit the products page or see Joule Thief kits here: http://www.madscientisthut.com/Shopping/agora.cgi?product=Energy%20Harvesting&user4=Joule%20Thief%20Kits Read the rest of the Joule Thief Blog for circuits, simulations, and experiments.
Using the Joule Thief with Stepper Motors at Low RPM to Generate Useful Power
When ever I took apart old equipment like dot matrix printers that were heading for the trash heap I saved the stepper motors, slide rails, etc… I have tried using the stepper motors in projects like making generators, but you have to spin them fairly fast to get any useful voltage out of them, so I never did much with them other filling up a box in the garage.
Since I have been playing with the Joule Thief and low Voltage energy harvesting experiments, I thought well lets see what we can do with a stepper motor. So I took one of the stepper motors out of the garage this morning and made a circuit with a stepper motor that has both coils connected to two bridge rectifiers feeding a 8200uF 10VDC capacitor. The capacitor then feeds a Joule Thief circuit that is running 4 white LEDs in series. The generator is able to light the LEDs at very low RPM. ( I stopped at 4 LEDs because this is around the target voltage I would like to use this circuit at which is 14VDC, I am sure that this will run more LEDs in series.)
A Joule Thief is a perfect circuit for this application. The circuit is a simple 3 component, low voltage DC-DC boost converter. The circuit can run on voltages as low as 300-400mV depending on the transistor used and windings on the transformer. Specifically in this application I am rectifying the low output of the stepper motor and storing the energy in a capacitor then using the Joule thief to boost low voltage stored in the capacitor to about 14VDC. The final application for this Joule Thief circuit will be to charge 12V sealed lead acid batteries using a low speed windmill.
So here are some applications this could work in (be aware that these circuits would have to be redesigned with some protection to prevent failures):
* Low wind speed generator.
* Low speed water generator using a water wheel setup or a small Pelton wheel with low water head.
* A machine that converts linear motion to rotary motion could also use this type of setup (like the old sewing machines that were run from foot power pushing a pedal).
Here is the Schematic: (If you want to see a full size image click the image, and then click on the next page image)
Here is a picture of the Joule Thief Generator Circuit as built:(If you want to see a full size image click the image, and then click on the next page image)
And in the following short video of the circuit in operation, I am spinning the stepper at a very slow rate of less than 100RPM and you see the Voltage generated by the stepper never gets above 2VDC, but it is lighting 4 white LEDs in series at about 14VDC: