Overunity motor, part3, all 4 recharging bats reading at 1.400 volts now.

[Pirate88179]

Bill:

The answer to your question is that in a JT circuit you are not supposed to change the value of the base resistor.  In any generic transistor switching circuit, the base resistor value is normally chosen to provide the minimum amount of current to fully switch on the transistor.  It's a standard design exercise when designing a switching circuit.  How much current does the transistor need to switch?  What is the current gain of my transistor?  How much voltage is available behind the base resistor?  What is the voltage drop across the base-emitter diode?  Add a 10% margin of safety and then you can determine the value of the base resistor.

When you varied the value of the base resistor you varied the way the JT circuit responded.  The way to answer why the LED got brighter would be to look at the waveforms with your scope, construct a timing diagram, and then analyze the timing diagram.

Without analyzing the timing timing diagram and making proper measurements you are just observing.  Think of a small transistor radio.  As long as you stay away from the tuning section, chances are that varying the value of any other capacitor, resistor, or inductor in the circuit will make the sound from the speaker get louder or softer.  Do you know why?  Assume the answer is no.  So does that mean that there are 15 "volume controls" in a transistor radio?  Obviously the answer is no.  By changing the value of a random component you were skewing the circuit with an observable effect:  The volume got softer or louder.  However, the right component value to change is the setting of the volume control pot.

There are no "rules" saying that you can't change the value of the base resistor.  However, there are real design principles:  In a switching circuit you choose the value of the base resistor to ensure that your transistor is fully saturated when it switches on and there is minimum amount of power expended to do that.  So in theory there is truly a "right" value of base resistor for a given Joule Thief configuration.

If you want to change the brightness in a Joule Thief chances are varying the value of many of the individual components will do that.  But the point is to make an intelligent design choice as opposed to the transistor radio example where you just change values willy-nilly and observe the effects without actually knowing why the effects are happening.

Going back to your example, you were not "tuning" the circuit, but it more like you were "skewing" the circuit.  It's very possible that when the LED got brighter than normal the overall efficiency of the JT circuit went down.  Certainly you were not finding any "resonance" because a JT circuit does not resonate.

You also mentioned that when the battery voltage got lower you could play with the base resistor value to bring the LED brightness back up.  That's all fine but the true JT circuit is not normally changed as the battery voltage lowers.

All of the answers to the question of why the LED gets brighter or dimmer come from using your scope and making good measurements and analyzing the timing diagram.  In a generic sense the LED gets brighter because the (inductor + battery) is dumping more average power into the LED.  So you start by looking at your timing diagram and observing the charge/discharge timing for the main inductor.

MileHigh

Thank you for the explanation.  Back then, all I was using was a DMM but I will dig out some of my older circuits and put them on my scope.

Thanks,

Bill

[sm0ky2]

When you varied the value of the base resistor you varied the way the JT circuit responded.  The way to answer why the LED got brighter would be to look at the waveforms with your scope, construct a timing diagram, and then analyze the timing diagram.

MileHigh

Are you implying that operating a JT at resonance by using the transistor switching function,
would have a different result than operating the transformer in an LRC circuit of the same frequency?

[sm0ky2]

Permit me to ask you a litmus test question about a JT:  A JT can light up a series string of 20 LEDs just as easily as it can light up a single LED.  Why is that?  In other words, please explain the mechanism for that.

No, it actually can't. At least not "just as easily"
  As you will find, that adding each successive series LED will slightly decrease the voltage  until you reach the limits of the circuit.  Also, doing this will affect the operating frequency, which will bring the JT out of resonance. Which will significantly reduce the run-time if you are using batteries or a charged capacitor.

[MileHigh]

Are you implying that operating a JT at resonance by using the transistor switching function,
would have a different result than operating the transformer in an LRC circuit of the same frequency?

Sorry, but if you want to flesh that out and make it clearer, then I may be able to answer your question.

[sm0ky2]

Sorry, but if you want to flesh that out and make it clearer, then I may be able to answer your question.

ok...   Where you assume that the resistance value should be calculated to the transistor - this is not the case with the JT.

Because the batteries do not have enough voltage to turn the transistor on.
The first cycle (which is microseconds) it is reversed biased through the inductor.
(and yes this is true, even though theres a diode..)
the next cycle, and every one after that, the voltage is fed from the transformer, and the resistance should be determined from that value instead. At resonance, the voltage is the highest, and so is the current, because reluctance is (near) 0.
This will also affect the capacitance of the transformer, which is a function of each coil, as well as the inductor material.