Joule Thief

[Pirate88179]

Why do you need a reed switch?  A 2N3055 works well with the Bedini bifilar coil and you can get 16,000 rpm pretty easy.  Folks using sphere magnets have hit over 300,000 rpm.

I know many folks use reed switches on the Bedini but I have never understood why they use a mechanical device when a transistor will do the job with very low power input.

Bill

[crowclaw]

Why do you need a reed switch?  A 2N3055 works well with the Bedini bifilar coil and you can get 16,000 rpm pretty easy.  Folks using sphere magnets have hit over 300,000 rpm.

I know many folks use reed switches on the Bedini but I have never understood why they use a mechanical device when a transistor will do the job with very low power input.

Bill
Hi Bill, It's all about  maximising the base current of the 2n3055 so that you achieve high collector switching currents, a reed switch is the simplest way of achieving a very  high base current for the gain of the transistor. But I agree with your comments... you can of course use other means of driving the base as a reed switch is not the ideal device being mechanical and prone to wear etc.  One of my pulse motor designs  use a slotted opto coupling device which drives a Mosfet gate (BTS117)... very reliable. Kind Regards

[dasimpson]

yeah i only just found the reenginered joule thief idea most videos showed the read switch you see
i do like the transister idea better and if i do think of going bedini i will use it

[dasimpson]

ok i just read this and worked out that if the winding gor the base of transister ic clock wise it is better to wind the secondory clock wise to get best power draw as the flyback is higher then the forwed pass of voltage would i be correct ?

I found this so i thought i would post it here. i hope this may help out

THE TRANSFORMER
The secret of this circuit is the transformer.
We normally think of a transformer as a device with an input and output, with the voltage on the input and output being connected by a term called "turns ratio."
If the output has more turns than the input, the output voltage will be higher.  This is called a setup
transformer. If the output has less turns than the input, the output voltage will be lower.
This applies to "normal" transformers where the voltage is rising and falling at a regular rate, commonly called a "sinewave."

But the transformer in this circuit is different.
The voltage applied to it is not rising and falling smoothly, and thus it does not work in normal "transformer mode."
The voltage is being applied and then turned off. When the voltage is applied, the primary winding (the 90 turn winding) produces magnetic flux. When the voltage is turned off, the magnetic flux collapses and produces a VERY HIGH voltage (in the REVERSE DIRECTION), in all the windings.
Our transformer is really a coil in flyback mode with a feedback winding.
The feedback winding delivers a voltage to the transistor to turn it on HARDER. If the winding is connected around the wrong way, the circuit will not work.

The other important factor about the transformer is the core material. There are many different types of
ferrite. Ferrite is a type of iron which is powdered very finely so that the magnetic lines that pass through the particles do not create eddy-currents. These eddy currents absorb the magnetic flux.
The circuit also employs a term called RE-GENERATION. This is the effect where a circuit is turned on slightly by a component (the base resistor in this example) and then the transistor turns itself on more and more until it is fully turned on. The feedback winding is configured so that the voltage it produces (actually the current it produces) is fed into the base to turn the transistor on. Thus the feedback winding is very clever. It produces energy and is delivered in a particular direction - in
other words it can be a positive or negative energy. In this case it produces positive energy, to turn the
transistor on harder.
This is called POSITIVE FEEDBACK as it turns the transistor ON during the active part of the cycle.
Now we come to the MAIN, PRIMARY or FLYBACK winding. This winding produces a high voltage during part of the cycle (the FLYBACK part of the cycle) and this is passed to the LED.
If the LED is removed, the transformer produces a high voltage with a low current, but when the LED is
inserted, an amazing thing happens. The energy from the transformer is converted to a lower voltage with a higher current. What actually happens is the LED absorbs the energy and turns it to light as soon as the voltage rises to 3.6v. We could achieve the same low-voltage, high current requirement, with less turns, but the number of turns has to be determined so the core does not saturate.
The voltage for the LED is produced when the transistor is switched off and the magnetic flux in the ferrite core collapses. The speed of the collapse produces a very high voltage in the OPPOSITE DIRECTION and that's why a positive voltage emerges from the end connected to the LED. These two facts are important to remember. The other important fact is called "transformer action." This is the action of magnetic flux. When a voltage is applied to a winding of a transformer or a coil of wire, a current will flow and this will produce magnetic flux. If another winding is present, the magnetic flux will cut the turns of this extra coil and produce a voltage in it. However, there is a very important point to remember. The magnetic flux can be: EXPANDING, STATIONARY or CONTRACTING.
When the magnetic flux is expanding, a voltage will appear in the second winding mentioned above.
When the magnetic flux is stationary, NO VOLTAGE will appear in the second winding.
When the magnetic flux is contracting a voltage will appear in the second winding with REVERSE
POLARITY. The size (the amplitude or "value") of the reverse voltage will depend on the speed of the collapsing magnetic flux. If the flux collapses quickly, the amplitude will be very high.
That's how the transistor turns itself on and on until it is fully turned on. At this point the current flowing through the circuit is a maximum but the flux is not expanding so the base of the transistor does not see the high "turn-on" energy and thus the transistor suddenly turns off.
The magnetic flux collapses and the transistor sees a reverse voltage on the base to keep it turned off until the flux is fully collapsed. The current through the resistor enters the base to start the cycle again.
From this you will be able to see how the transistor and transformer work.

[guruji]

Why use rotors on bedini when it can be done solid with just adding  two resistors to the original circuit and a very high oscillation.