joules thief « Mad Scientist Hut Blog

A Very Nice Steam Engine Powered Carousel Project That Uses The Joule Thief

By Kirk, on September 26th, 2012%

Jerry built this great little home made steam engine and the carousel that is powered from the steam engine. He posted a video of it in operation on you tube. He runs the Carousel and a little generator from the steam engine, the generator is putting out ~900mV that is then boosted using a Mad Scientist Hut Joule Thief board that lights some LEDs that are around the Carousel.

Jerry repairs old vacuum tube radios. If you are in need of getting an old vacuum tube radio back in functioning condition just send me an e-mail at madscientist@madscientisthut.com I will be sure to forward your request to Jerry.

Here are some of the still shots of the carousel in development: ( To see a large format picture, click the picture on this page then on the next page click the image there and the next page will open a full size picture)

Jerry’s Steam Powered Carousel with Generator and Joule Thief Boost

One Winding Joule Thief

By Kirk, on February 19th, 2012%

We had some high permeability toroid cores shipped in. The permeability is so high that it can achieve somewhere between 3-5uH per each winding. This allows for us to make a High Power Joule Thief with just one winding on each side of the transformer.

The new one winding Joule Thief is very stable, starts up at below 600mV, and runs very bright at 1.5VDC leaving spots in your vision if you happen to glance at the LED while it is on. These units are assembled, tested, and can be purchased here.

High Power Joule Thief 1 Watt Cree LED

Here it is running off of a single AA battery.

High Power Joule Thief 1 Watt Cree LED

Introducing the Cree 1 Watt LED High Power Joule Thief Kit

By Kirk, on December 4th, 2011%

We are very excited to introduce our newest Joule Thief kit. This kit is a higher power Joule Thief kit that includes a Cree 50 Lumen XLamp 1 Watt white LED. See our energy harvesting product section to purchase this kit .

1 Watt Cree LED Joule Thief

You can also purchase these Cree XLamp XL LEDs as an individual unit by going to our components section.

Make a Joule Thief Battery Charger

By Kirk, on January 19th, 2011%

Recover the last bit of energy from a “dead” alkaline battery. When your modern electronics gadget turns off because the alkaline batteries are “dead” it just means the voltage in the batteries has dropped below a usable level for that gadget, which depending on the electronics that voltage could be around 0.9 VDC to 1.2VDC per cell.

I found this nice graph on http://www.powerstream.com/AA-tests.htm that shows the discharge curve for alkaline batteries. You can see that when the alkaline battery is below 0.9VDC there is not much usable energy left, but if there is 1.2VDC left in the battery there is about 28% of the energy left in the battery.

AA Alkaline Battery Discharge Curve @ 100mA

So what can I do with this “dead” alkaline battery? I can use a Joule Thief to make a battery charger that depletes the remaining energy from the alkaline battery and recharges a NiMh battery.

To make a Joule Thief battery charger is a quick and easy project. Here is the Joule Thief battery charger schematic:(to view full size images click image then click image on following page)

Joule Thief Battery Charger Schematic

I am in the process of building a battery charger this week and will put data about this project as I charge batteries.

Some notes about using the Joule Thief to charge NiMh batteries:

1) This probably is not the most efficient way to recover the energy, but hey it is quick, cheap, and easy to do. The batteries were going to the trash so I might as well try to recover the lost energy from them.

2) The LED in the schematic probably uses half of the energy that would be recovered, but it is the only good way to see if the circuit is still running. You could also modify the circuit and charge up to 4 NiMh batteries in series (of course this will reduce the charge current, since the boost voltage has to increase).

If you use a white LED the circuit can be used as a night light, but the white LED (3.5V forward voltage) will consume about 79% of the energy when you are charging one NiMh Cell. If you charge four NiMh batteries in series the white LED will consume about 41% of the charging energy, the LED will be dimmer since the current will drop.

If you use a standard red LED (1.7V forward voltage) the LED will consume about 57% of the charge energy when you charge one NiMh cell, with four series NiMh cells the red LED will consume about 25% of the charge energy.

3) This circuit, if built properly, will run the alkaline battery down to 350-400mV which will truly make it a dead battery.

4) As long as your NiMh battery has a high enough capacity you will not overcharge it with this circuit, provided you do not exceed its C/10 rating (capacity/10). I found this on http://www.powerstream.com/NiMH.htm
“The cheapest way to charge a nickel metal hydride battery is to charge at C/10 or below (10% of the rated capacity per hour). So a 100 mA/Hr battery would be charged at 10 mA for 15 hours. This method does not require an end-of-charge sensor and ensures a full charge. Modern cells have an oxygen recycling catalyst which prevents damage to the battery on overcharge, but this recycling cannot keep up if the charge rate is over C/10. The minimum voltage you need to get a full charge varies with temperature–at least 1.41 volts per cell at 20 degrees C. Even though continued charging at C/10 does not cause venting, it does warm the battery slightly. To preserve battery life the best practice is to use a timer to prevent overcharging to continue past 13 to 15 hours.”

5) It can take several “dead” alkaline batteries to recharge a 1500mAH NiMh battery, before I experiment I am going to estimate that it will be somewhere between 6-15 batteries.

Update: I built the circuit to charge 4 batteries in series. The battery charger circuit was working great for several days until the charged batteries got up to around 5.4v then they started to discharge. I was really perplexed for a while as to why this was happening. I finally figured out what went wrong, the LED reverse breakdown voltage was somewhere around 5.4V and it ended up destroying the LED and discharging the NiMh batteries. I have a new circuit design that will be more efficient and will charge the batteries quicker.

I have ordered parts for the new higher power joule thief circuit. I will build some and try them out, if they work out well I will add them as a new high power joule thief kit.

Using a Joule Thief to Harvest Energy from a Candle

By Kirk, on January 8th, 2011%

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? )

TEC Joule Thief Generator Components

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.

TEC Generator

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

TEC Generating 1.8VDC

And here the circuit is operation, producing ~14VDC to light four white LEDs. :

Joule Thief TEC Generator in Operation

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.

A Very Nice Steam Engine Powered Carousel Project That Uses The Joule Thief

One Winding Joule Thief

Introducing the Cree 1 Watt LED High Power Joule Thief Kit

Make a Joule Thief Battery Charger

Using a Joule Thief to Harvest Energy from a Candle

Joule Thief

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