Joule Thief 101

[tinman]

Would seem a med imbalance...
the auditory hallucinations should calm down in a day or two..."I can hear the sounds of the frying pans clanking off in the distance.".

Might take longer for the others to stop...["steaming Brain Fires" and such]

I suggest a few days off and  lay off the Old Star trek marathons ...

and definitely no old Pink panther marathons!!

could make the  twitching much worse !!




Oh and back to crayons for the time being no "pens" or other sharp objects.

MH seems to have missed the fact that the circuit resistance changes during the on time,regardless of that of the batteries internal resistance,due to the inductor. I mean,he just spent months on the ideal coil thread explaining this ,but now there seems no need to take that into account-hmmm.

TK asked MH a valid  question in regards to having a series resistor when using a cap,so as to mimic that which would be had with a battery,but MH played dodgem.

Anyway,should get the light box  built tonight,to match that of TKs.


Brad

[tinman]

I can hear the sounds of the frying pans clanking off in the distance.

I tried to repeatedly to explain to you what the base resistor was for you but you would have none of that.  I tried repeatedly to explain to you that your test that showed a limited amount of brightness change in the LED was just a distant secondary effect of changing the value of the base resistor but you wouldn't have any of that.  Just like the YouTube clip explaining how a Joule Thief works got you all confused, frustrated, and mad, you clearly have no understanding about how a Joule Thief works even though it must have been explained to you at least a dozen times.

Here is your big bamboozle moment:

The chances of TK changing the value of the base resistor in the second circuit to bring the Lux output to the same level as the first circuit while maintaining proper Joule Thief circuit operation are essentially nil.

Here is your big bamboozle moment II:

Okay!  So the supercapcap drops from 1.5 volts to say one volt.  You measure the output impedance of the battery when it also has dropped to one volt driving when the Joule Thief and say for illustrative purposes the output impedance of the battery is measured as being 10 ohms.

Here is where Brad's brain is on fire!

He takes his supercap which is outputting one volt, then adds the series resistor of 10 ohms, and then connects the Joule Thief load.  "We have the technology."

Then he sets the setup off to run, and WHOOPS!, he is not measuring one volt at the Joule Thief now.  He is only measuring 0.85 volts!

What's going on?  Brad says, "I know when my supercap is at one volt I must put a 10-ohm resistor in series.  But then the voltage at the Joule Thief is 0.85 volts."  "I am confused, because I know when my battery voltage is 0.85 volts, the output impedance is 12 ohms and I am supposed to put a 12-ohm resistor in series."

"But I just put a 10-ohm resistor in place but now I have to put a 12-ohm resistor in place??"

The steaming she is a starting, the sizzling sound she is a crackling.  Get your marshmallows out!

The fans from Bizarro World start up a chant, "More discombobulator!  More discombulator!" with the clanking sound of frying pans in the background.

The moral of the story:  Avoid the Logic Discombobulator and think first before you leap into the forum.

MH

Perhaps you should have a rethink about that wonderful post again,only this time ,take into account the impedance of the inductor-as we do have one in a JT you know.
Now,the instant the transistor switches on,what would be the voltage across the series capacito/resistor ,and as the impedance of the inductor decreases over time (per pulse),what would happen to the voltage across our series capacitor/resistor?
Now we do the same test,but with a battery that has that same resistance value and same voltage of our series capacitor/resistor--what do you suppose would be the outcome?.

Yes,it pays to think before splattering stuff all over a forum.


Brad

[MileHigh]

Yes, Brad, what you probably aren't realizing is that your model is wrong.

The proper model would be a fixed voltage source in series with a variable resistor, and of course the value of the resistor increases over time to model the battery getting discharged.

That simple model takes care of everything.  The voltage will drop over time under load with this simple model.  That's the model for a battery.

Your incorrect model is a dropping voltage source (the capacitor) in series with a variable resistor.  That model is no good because the lower voltage in the capacitor already represents the voltage drop associated with the impedance, but the actual output impedance is not correct.  Then when you tack on the variable resistor to match the impedance you cause another voltage drop that you don't want.  That new voltage drop represents another impedance and you end up chasing your tail around and around.  <<<  From below:  Or you can write a software control system if you wanted to torture yourself, perhaps some spaghetti code.  Or, you could do a table look-up and dumb it down.  >>>

All that you really need to do is write a simple litte microcontroller program, like in an Arduino.

The Arduino monitors the voltage and the current from the power supply which is set at 1.5 volts.  The program will monitor how much energy has been put into the load.  The microcontroller is connected to a little stepper motor that connects to a 10-turn pot. The 10-turn pot is used as the series output resistance for the 1.5 volt power supply.

So as the energy is delivered to the load the Arduino will adjust the 10-turn pot to emulate the increasing output impedance of the emulated battery.  So with not too much effort you can make a decent little battery emulator that also monitors energy delivered to the load.  You could even load in different battery profiles, regular, alkaline, etc.

Then there are some cat-calls from the Bizarro World supporters.  "Put a stepper motor on the voltage control also!!"  And indeed, if you had perhaps a bench power supply with a voltage control input, you could connect an Arduino D/A channel to the bench power supply.  Then you would hear the clanking from the rabid frying pan crowd.  You now have a Bizarro Whackadoo II self-monitoring power supply with variable voltage output and variable output resistance all under software control.  It can even play an mp3 song at the same time (Or perhaps maybe a software waveform generator perhaps??).

You see Brad, I can invent a project off the top of my head in five minutes that is probably more interesting than anything you have come up with over the past six years.  If I was so inclined I could build it too.

The pen is mightier than the bench.

https://www.youtube.com/watch?v=3zdcMXl3J0Q

[TinselKoala]

Isn't anyone going to analyze the graphs? Oh well....

Both Circuit 1 and Circuit 2 data were taken until the voltage dropped below 0.450 V, which was the predefined endpoint of the trials. Looking at the Lux - Seconds graph we can see something very interesting. While a rough integration using numerical methods shows that Circuit 1 is the _overall_ winner in terms of Lux-seconds, this is only due to the first three minutes of the data. Considering only the data after 210 seconds (corresponding to a voltage of somewhere around 0.9-1 volt), we see that Circuit 2 produces more total light.

In terms of (lux-seconds) per Joule, for the total data, we have :
Circuit 1 produces 8698.8 Lux-seconds of light and uses 11.16 Joules, for an energy efficiency of 779.15 LS/J.
Circuit 2 produces 7483.2 Lux-seconds of light and uses 11.77 Joules, for an energy efficiency of 635.60 LS/J.

But considering only the data from 210 seconds on, we have :
Circuit 1 produces 2035.8 Lux-seconds of light and uses 2.54 Joules, for an energy efficiency of 801.1 LS/J.
Circuit 2 produces 2698.2 Lux-seconds of light ....  but uses 3.82 Joules, for an energy efficiency of 706.9 LS/J.

Please check my math and my reasoning....

[MileHigh]

TK:

Very interesting numbers.  It's apparent that circuit $1 is giving you more Lux-seconds per Joule, even after that 210-second cross-over point on the Lux-duration chart.

To me it suggests if you could lower the consumption of circuit #1 then you could possibly be in a position where circuit #1 runs at approximately the same power levels and the same Lux levels at circuit #2.  Considering the data we have seen so far, then it looks like this hypothetical circuit #1A would blow circuit #2 out of the water.

So that raises an interesting question, doesn't it?  If you are working within the basic architecture of the Joule Thief, and you have a fixed supply voltage, what is the best way to lower the average power consumption but keep roughly the same instantaneous current levels flowing through the LED?

What I am seeing is that the basic timing is determined by the inductance of the main power coil.  So if you increased the number of turns of the main coil, that should slow down the energizing cycle.  However, this will change the turns ratio for the feedback coil also, and you might have to add turns to the feedback coil to maintain the proper EMF to the base resistor to keep the feedback switching circuit operating properly.  However, you might be able to get away with less feedback coil turns if you lower the value of the base resistor a bit.

So, let's assume that you now have a longer inductor energizing cycle and the Joule Thief slows down.  Let's assume for the sake of argument the initial current through the main coil is approximately the same when the Joule Thief switches and starts the discharge through the LED.  So, you have approximately the same instantaneous brightness but it's a bigger and longer burn from a bigger main coil.  Slower pulse repetition rate but a bigger pulse, have you really lowered your average input power?  I am not sure.  Has the Lux brightness changed a little or a lot?  What about the actual human eye?  I am not sure.

And in the background is the problem of whenever you add more turns to a coil, the more wire resistance losses you have.

So, I am not sure how easy it is to slow down a Joule Thief and keep other parameters where you want them to be.

Then the other approach, assuming that you have a blank slate, is to try to manipulate the size and overall relative permeability of the core itself to try to throttle down the power consumption.

Anyway, I am just musing here.

MileHigh