Joule Thief 101

[MileHigh]

Brad:

As far as your Joule Thief scope captures go and your power in to light out data goes, I really have nothing to say.  Again, I made a long posting stating that there are many parameters associated with that issue and just throwing your two circuits out there and showing some numbers does not say much.  In addition to that, your two circuits are running at about 130 kHz, which is way too fast.  Almost certainly you are losing some light output efficiency because they are running so fast.

If you want to play the light output efficiency game, then a Joule Thief clearly sucks because of the sloped current discharge waveform through the LED which is inefficient.  A long time ago I said that a brand new circuit that keeps a large cap charged to the optimum LED voltage for maximum light output efficiency while part of the circuit flashes the LED on and off to reduce power by taking advantage of the persistence of human vision would be a great circuit.  I said that chances are that it would beat the pants off of a Joule Thief for power in to light output efficiency even if it was a more complex circuit.

But the problem with that circuit is that you actually have to design something yourself, right?  There is no more being an "experimenter automaton" copying a Joule Thief schematic and building the same stupid circuit for the thirtieth time.  You actually have to THINK and develop a circuit all by yourself from scratch.  You actually have to invent something YOURSELF.  Mums the word there.

I said that a great pulse motor build-off would be to have a sueprcapacitor energy store and to build a pulse motor with a design goal of outputting the maximum mechanical energy.  The goal would be to use the pulse motor to lift up a weight and the winner would be the person that had the best lifting energy to capacitor energy ratio.  Another great idea that requires that you have to THINK and INVENT something YOURSELF from SCRATCH.  You had nothing to say about that.

I asked you how you would measure your supercapacitor value and any other paramaters and I got one nearly useless response from you.  So you apparently don't even know how to come up with your own system to measure the value of a bloody capacitor that you made yourself.  I actually would not be surprised if Robert Murray Smith told me to piss off when I asked him for his own measurements on his devices because he is in the same boat as you.

When you are asked to show how you measure the output impedance of a battery you balk.  You are given an opportunity to show your own powers of reasoning and you chicken out.  There is a decent chance that what you would have to say would be riddled with errors and be a farce.

So your BS fake preening is not impressing me at all.  Like it or not, you clearly did not understand how a simple Joule Thief works as of a few months ago, and I am not even sure if you understand how one works now.  Like I have already told you several times, if you are serious about your hobby, the best thing you could do for yourself would be to buy yourself three or four books on basic electronics and lock yourself in a room for a month and read them and understand them.  Then you won't be saying ridiculous gaffes like there is no voltage drop across a resistor.

MileHigh

[TinselKoala]

OK... Brad says that transistor type and coil turns don't matter as long as they are the same for both circuits. I don't fully agree with this but it certainly makes things easier for me. So for all tests, until further notice, I will be using the circuit I built and described in the other thread: MPSA18 transistor, 20+20 turns on the pot-core inductor, low-side current sensing using 0.1 ohm non-inductive CSR, and one of the LumiLed ultra-efficient LEDs for the load. I connect the LED, which is fixed to the inside end of my lightbox, to the circuit with a jumper cable about 18 inches long. All I have to do to switch between circuits is to change the pins where the jumper connects to the circuit board, so the LED isn't touched and remains in the exact same position during testing. These circuits runs at between 9 to 14 kHz or so, depending on voltage.

Lately though I have decided to use an ultracapacitor for the power source. I'll be using a Nesscap 10F 2.7V rated capacitor with 30mOhm (0.030 ohm) equivalent series resistance. See the data sheet attached below (which by the way describes an easy method to determine the actual capacitance of a test capacitor.)

Using the capacitor as power supply has several advantages. It eliminates noise caused by the power supply, it has a much lower impedance than the battery, and it allows one to track changes in light output over time as the voltage drops while running the circuit. Plotting the Lux value against seconds of runtime will allow one to generate a "lux vs. seconds" curve, the area of which will correspond to the total light output in Lux-seconds. Selecting a certain end-point voltage, say 0.450 V, and timing the time taken to reach that voltage from a given starting voltage, say 1.500 V, will give a consistent set of boundaries for measurement. Input power vs. Lux output readings can also be made along the way.

I've already done a couple of sample test runs using the ultracapacitor, charged to 1.5-1.6 V, and it works quite well. It's hard to get valid power readings from the scope at the lowest voltages due to the small current, but the input voltage and Lux values can be read quite precisely. It takes about 11-12 minutes for the voltage to go from 1.500 V to 0.450 V using Circuit 2 (LED across coil). The LED still produces measurable light output down to below 0.420 V after over 17 minutes.

[poynt99]

TK,

Would you mind re-sizing your images, they are way too big and it forces us to widen the browser window just to read the posts. Sorry, but it's a pain and Stefan apparently can't fix it. If you need hi-res as well you could zip them up and add them as attachments in addition to your reduced-size image.

Thanks.

[TinselKoala]

TK,

Would you mind re-sizing your images, they are way too big and it forces us to widen the browser window just to read the posts. Sorry, but it's a pain and Stefan apparently can't fix it. If you need hi-res as well you could zip them up and add them as attachments in addition to your reduced-size image.

Thanks.

Sure, sorry, it's something that I often complain about too, but 1200 pixels wide is perfect for my monitor. I forget that other people may not have widescreen monitors. So I'll keep them to 800 pixels wide in the future. Thanks....

Meanwhile here is some raw data taken with the ultracap as power source. Every 30 seconds I recorded the Lux reading and the voltage in mV. These data can be used to generate curves and get total light output in Lux-seconds as I described earlier. It will take me some time to graph the data as I have to take the dog to the dogpark and do some other things. But if anyone else wants to do it..... welcome to it.

[tinman]

Here Brad, reality check #1 for you copied from the other thread:

Okay Brad.

Let's just sample some approximate numbers and work out a very simple problem for illustrative purposes.

Let's say we have a source voltage of 1.5 volts and an output impedance of seven ohms.
Let's say that we have circuit #1 that draws 50 milliwatts from the power supply and draws continuous DC current.
Let's say that we have circuit #2 that draws 50 milliwatts from the power supply and draws current with an 80% ON time and a 20% OFF time.

Let's examine these two circuits.

Circuit #1:

The current is 0.050/1.5 = 33.3 milliamps
The power lost in the internal resistance of seven ohms is 0.0333^2 x 7 = 7.78 milliwatts

Circuit #2:

We know from above that the average current is 33.3 milliamps.
Therefore the ON current for 80% of the time is 0.0333 x 5/4 = 41.7 milliamps.
The power lost to the internal resistance of seven ohms is 0.0417^2 x 7 x 4/5 = 9.72 miliwatts

Well look at that Brad.  When you put the two circuits on an even playing field where they draw the same amount of power from the fixed 1.5 volt power supply, circuit #2 that has the 80% ON, 20% OFF duty cycle has more losses due to the internal resistance of seven ohms.

Brad, I have made this very easy for you to follow and understand.

MileHigh

This example just illustrates a basic principle.  If you can't use your brain and apply it to the two Joule Thief circuits that's your problem not mine.

Well you screwed that up MH.
Nice try,but far from an even playing field.
Both inductors are supplied with the same(thats right MH--the same) amount of energy,and they are the same inductor. How you ever decided to make the input energies different--well who knows where your head is at some times.

The inductors now have the same  !SAME! amount of stored energy.
So now tell us,which of the two circuits will deliver the most of there stored energy to the LED.

That is how simple it is MH.
God knows how you keep screwing these things up


Brad