energy harvesting « Mad Scientist Hut Blog

Joule Thief

By Kirk, on December 29th, 2010%

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

By Kirk, on December 24th, 2010%

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)

Joule Thief Stepper Motor Generator

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)

Joule Thief Stepper Generator Circuit

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:

Joule Thief Energy Harvesting Experiment w/Low Voltage Solar Cell

By keith, on December 13th, 2010%

Solar Cell Setup

I put a 0.5v 1A monolithic silicon solar cell on the front end of the Joule Thief circuit. Added a schottky and 2000uf cap on the output. I wanted to see how long it would take the Joule Thief to charge the cap bank. There are two 1000uf/50V caps in parallel to get the total 2000ufs. In full sun it took 3 mins 34 sec. to charge to 21.8 V.

Stored energy 1/2*C*V^2 = 0.48 Joules

Update on Homemade Zinc Copper Battery Experiment

By Kirk, on December 4th, 2010%

Here is an update on the Joule Thief Kit experiment, where I was trying to charge a NiMh battery using a homemade single cell Copper Zinc battery. See this post from October http://madscientisthut.com/wordpress/?p=46

The first experiment using a zinc plated bolt failed as the zinc plating came off of the bolt in about one day. So I set off to make a much better zinc plate. I found a certain unnamed Copper coin made after a certain date was greater than 97 percent Zinc. Zinc has very low melting point of 787.15 degrees Fahrenheit. I have a wood burning stove that makes for a nice melting furnace. I took about 50 coins and stuck them into a tin soup can and inserted them into the fire and after about 10 minutes I had a nice molten Zinc soup. ( I do not recommend doing this because it is dangerous )

I carefully removed the soup from the fire and poured it slowly (to prevent the copper chunks from coming out of the bottom of the can) onto a large #10 sauce can that was inverted. I let it cool for a long while before removing the zinc slug from the can.

I put this battery together using a plastic peanut butter jar, a 3/4inch x 8 inch Copper pipe and the zinc slug. added some water, salt, and vinegar. I connected the Joule Thief Kit with clip leads to the Copper and Zinc. Took the output from the Joule Thief Kit and rectified it with a 1N4001 diode and put that into a completely depleted NiMh battery ( I use a white LED in series to indicate if the circuit is operating). This is the same schematic circuit from the late October post. This battery charger has been running since November 1st and the NiMh battery Voltage is up to 1.237V. Since I am not exceeding the 1/40th current rating this battery will not overcharge.

The only maintenance I have been doing is adding a little vinegar every time the liquid level drops from evaporation (that is about 1/16th cup a week), I will post another update when I find time.

I suspect that I can charge 4 NiMh batteries in series with this circuit, and that might be a future experiment.

I know many of you think how can this be useful since it takes a month to charge the NiMh battery, but there are many situations where I think this could come in handy. This low cost circuit provides a source of light as well as being a battery charger. There are plenty of places in the world where electric power is not a luxury of life, and there are plenty of things that you can make low voltage sources with that the Joule Thief circuit will happily run off of. This is what energy harvesting is all about, lets make some use out of something that we could not use before.

Joule Thief Copper Zinc Battery Low Voltage Energy Harvesting Experiment

By Kirk, on October 30th, 2010%

I was thinking what else could I use this Joule Thief kit for? It dawned on me that I could harvest energy from a homemade battery. So this morning I set out to make a zinc copper vinegar battery. I took a piece of copper pipe and a zinc coated bolt from my junk pile. Cleaned the copper pipe with a sanding sponge. Placed the two pieces in a plastic container, poured in some vinegar, connected to the JT_kit001b and wow it worked!! There was light coming from the LED!!! I measured the voltage coming from the homemade battery at ~550mV and the battery current was somewhere around 15mA.

Next I thought, well I could remove the LED and put a rectifier diode on the output of the Joule Thief board to see what kind of voltage I was getting. I put a 220uF capacitor on the rectified output and it charged up to >10VDC in a few seconds.

Well onto the next experiment, trying to recharge a depleted AA NiMh battery with the Joule Thief harvesting energy from the zinc copper battery. Will update with results at a later date as I think this may take a couple of days. Here is the Joule Thief schematic showing what I was doing.

Joule Thief Circuit Battery Charger

Update: 6:40AM Oct 31st : Last night I started with completely depleted NiMh (520mV with 10mA load) After charging overnight the static value is sitting at 1.210V. The Zn Cu battery is not fairing so well the output voltage is sitting at 425mV and the output current is now at a paltry 2.9mA (the JT circuit is still running, LED is still lit) The bucket of vinegar is looking really ugly. I think I may have to find a more robust source of Zn or another material to make the ‘battery’ out of.

Update: 9:20AM Oct 31st after running the JT charger circuit on the Zn Cu battery for about 12 hours the input voltage dropped too low (about 390mV) to keep the circuit running. The NiMH static voltage is at 1.225V. Time to try a different input battery.

Another experiment will be trying to harvest the low voltage output from a thermal electric cooler (TEC, Peltier device or Peltier cooler) when heating one side and cooling the other.

Joule Thief

Using the Joule Thief with Stepper Motors at Low RPM to Generate Useful Power

Joule Thief Energy Harvesting Experiment w/Low Voltage Solar Cell

Update on Homemade Zinc Copper Battery Experiment

Joule Thief Copper Zinc Battery Low Voltage Energy Harvesting Experiment

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