Joule Thief Made With A Ferrite Bead From An Old CFL Light Bulb

Here I make use of an old burnt out CFL light bulb for a Joule Thief light circuit. The ferrite bead/core from the CFL is at most 1/4 inch diameter and can fit in the core of my last circuit with a bit of room to spare. I used about 22 turns of fine (bi-filar=2 parallel wires) insulated wire. Comparing it to #30 gauge as shown in my last Joule Thief light circuit video, this wire seems about only half as wide (maby close to #40 gauge or so: seems slightly thicker than a human hair). If I used #30 gauge wire for this ferrite core then only 15 or so turns on it would be possible and may or may not have worked could of since the inductance would probably be about the same as the recommended circuit.

A Joule Thief circuit is basically like a "voltage step-up/increase" circuit. Voltage basically is the force that will be available to push the current around a circuit. 1.5V is not enough force or potential to push the current through a white LED light, so a Joule Thief increases that to about 3 to 6 V approximately, but can be more.

I put a round ceramic magnet near the coil/transformer of the Joule Thief circuit, and the LED dimmed a bit. I guess the inductance of the coil went up leading to a higher reactance (ie. resistance) in the coil, which would diminish the available current.

Some more notes for the value of R, the resistor in this circuit: 1K is the reccomended value (but could be a bit less). The circuit will work, produce some light, and diminishing/lessening brightness up to 300K ohms (300,000 ohms of resistance). For the apparent half-brightness use 50 to 100K, and for 1/3 or 1/4 apparent brightness use 100 to 200K. Expect better battery "life time"/lower current drain as you reduce the LED brightness level. You can use a "variable resistor", perhaps 100 or 200K ; just be sure to put the 1K resistor in series with this as a "safety resistor" incase the knob on the variable resistor is set to 0K for max. LED brightness for the given circuit. This 1K will prevent the transistor or other circuit elements/components from being damaged.

So far, with the smaller ferrite/coil/transformer circuit element, than the last circuit, the results seem a bit better so far with this circuit, perhaps less drain on the battery. Probably a more efficient coil construction when the number of turns happens to take up all the available space.

Advanced usage: There are some circuits here on YouTube, that basically replace the coil or LED with a stepup transformer (high voltage type I guess) that can light a CFL from a 1.5 volt battery.

Someone is selling some nice projects/kits for Joule Thiefs. This is very nice since winding that small coil is not so easy, and even nerve wracking when you have to solder the wires to the rest of the circuit, so it's a good deal::
You may even use wires to extend the LED off the circuit board if using this inside some box/holder. This kit above seems to be a very good project for anyone, especially since you don't need to know much about electronics other than hooking/soldering things up to work right, as in an electronic kit maker. You can often get an inexpensive soldering iron at some "dollar stores". This may truely be one of the most "neat and useful" circuits (besides a crystal radio circuit, and simple laser communicator circuit) available. Its good to have some things also like "alligator clip hookup test wire", and a Digtal Multimeter (DMM), for all kinds of circuit measurements and testing, which can be had for under $5 such as from Harbor Freight, etc. I've seen some nice once at Kmart/Sears that have some nice "extra functions" on them such as temperature and capacitance metering to name a few. Later you might even consider an oscilloscope to see the voltage "waveforms" and frequencies to test circuits.

A nice Earth Battery / Joule Thief:

More data: Voltage source 2500mAh NiMh, 1.2V rechargeable battery: Stays at near about 1.2V area for about 3 days (36 hours.... seems to want to "maintain" this voltage), then drops quickly down to about 0.575V in a matter of 6 hours about, and stays in that voltage area for quite a while (just above 0.5V). At this voltage, the light from the LED has not much use, and it will eventually start pulsing (due to the battery and/or the LED?) at a fast rate, and then more slowly over several hours. This 0.55V is the battery voltage while under load/circuit working, and the battery voltage at that point is about 0.875V without the load/non-working circuit at that point. If this is ran off a 0.5 V solar cell, then the circuit would have to be designed to boost the voltage more....or hook up 2 or 3 small solarcells in series.

[ March 11, 2011, update: someone else has a previous similar video: watch?v=ZnNQrYy_Bw4 ]
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