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Author Topic: Joule theif : try out !  (Read 22072 times)

Offline MarkE

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Re: Joule theif : try out !
« Reply #15 on: January 21, 2014, 01:46:21 PM »
omdano that transistor will have a hard time starting at low voltage.  For low voltage designs you want a transistor that conducts at zero voltage, like a JFET, or a depletion mode MOSFET.

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Re: Joule theif : try out !
« Reply #15 on: January 21, 2014, 01:46:21 PM »

Offline omdano

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Re: Joule theif : try out !
« Reply #16 on: January 21, 2014, 01:57:47 PM »
omdano that transistor will have a hard time starting at low voltage.  For low voltage designs you want a transistor that conducts at zero voltage, like a JFET, or a depletion mode MOSFET.
In short , it wont work to light the led  ?

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Offline TinselKoala

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Re: Joule theif : try out !
« Reply #17 on: January 21, 2014, 04:12:14 PM »
omdano, why don't you start, like many of us did, by making a common Basic Joule Thief as a testbed. Use a common NPN transistor; almost any will work in the Basic circuit and will run on a depleted AA or AAA battery, down to 650 mV or so, lighting one or two or three LEDs brightly.

Then you can start experimenting on your own, by substituting in different transistors, different values for the base resistor, different winding ratios on the inductor (doesn't need to be a toroid) and circuit geometry variations. This way you will learn what does what in the circuit and you will be able to tell whether you are actually getting any improvements, since you will have a basis for your own comparisons.

Please start with something you know will work, and make your variations from that point. In that way, you may discover something on your own and actually _add_ to the JT base of hard-won knowledge.

The extremely low voltage JTs will also, unfortunately, only give out a small amount of light. That they work at all is an electronic "miracle". To get a brilliant, steady light from a 0.025 V JT.... will be an even greater miracle.

For your amusement: JT with 4 blue LEDs in series, running on a depleted AG4 (LR626) button cell, recharging with heat from the soldering iron:

http://www.youtube.com/watch?v=K7msKzlNzKw

Offline MarkE

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Re: Joule theif : try out !
« Reply #18 on: January 21, 2014, 04:21:13 PM »
In short , it wont work to light the led  ?
No it won't.  All JT and JT like circuits can be coarsely described as having two states:  transistor (mostly) conducting, and transistor (mostly) not conducting.  In order to get energy into the transformer so that the transformer will immediately boost by the turns ratio, or so that the transformer can fly-back, we have to initially turn the transistor on.  All that we have available at that instant is the supply voltage.  If the transistor will not turn on then no energy goes into the transformer and we can never boost the supply voltage.


Offline TinselKoala

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Re: Joule theif : try out !
« Reply #19 on: January 21, 2014, 04:25:07 PM »
No it won't.  All JT and JT like circuits can be coarsely described as having two states:  transistor (mostly) conducting, and transistor (mostly) not conducting.  In order to get energy into the transformer so that the transformer will immediately boost by the turns ratio, or so that the transformer can fly-back, we have to initially turn the transistor on.  All that we have available at that instant is the supply voltage.  If the transistor will not turn on then no energy goes into the transformer and we can never boost the supply voltage.
It may also be important to note that a JT circuit can oscillate, but without sufficient amplitude to turn the LED on. It will still be radiating RF, though. The DALM JT shown above, with BC337-25 BJT,   has been observed to oscillate off and on for many days, as the battery spontaneously regenerates (starting oscillations) and depletes (ending them), over and over, but without enough "boost" actually to light its LEDs.

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Re: Joule theif : try out !
« Reply #19 on: January 21, 2014, 04:25:07 PM »
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Offline MarkE

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Re: Joule theif : try out !
« Reply #20 on: January 21, 2014, 04:34:49 PM »
That's where a flyback variant would do better.  One could wind the 100T or so secondary bifilar with one winding directed at the output rectifier and LED load, and the other winding directed soley to drive the transistor gate timing circuit.

Offline Farmhand

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Re: Joule theif : try out !
« Reply #21 on: May 22, 2014, 12:31:53 PM »
I realize this thread hasn't been posted in for a while but I thought I would post here because this is my first Joule Thief and I'm trying to work out if I have it right or working as it should.

I got a newer set of shots after some alterations and also made a drawing of what I "think" will work ok, the only things on the drawing that I have not got in the circuit is, I'm only using the 1 K resistor, I haven't tried it with 12 volts but I imagine with more resistance on the trigger and more load it could. I took out 2 LED's and am charging two AAA's in their place, so 4 LED's and the batteries in series.

Any hints on what I may be doing better ? 

First is collector to ground, second is base to ground and circuit proposed. I'm using 5 nF in series with the base at the moment.

.

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Re: Joule theif : try out !
« Reply #21 on: May 22, 2014, 12:31:53 PM »
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Offline MarkE

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Re: Joule theif : try out !
« Reply #22 on: May 22, 2014, 02:51:44 PM »
I recommend two changes to your design:

Change the 1N4007 diodes to 1N4148 diodes.
insert a Schottky diode sucn as a 1N5819 in series with the LEDs.

Both changes are to reduce losses due to the reverse recovery of the diodes.

Offline Vortex1

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Re: Joule theif : try out !
« Reply #23 on: May 22, 2014, 03:30:38 PM »
I recommend two changes to your design:

Change the 1N4007 diodes to 1N4148 diodes.
insert a Schottky diode sucn as a 1N5819 in series with the LEDs.

Both changes are to reduce losses due to the reverse recovery of the diodes.

Those are worthy changes. Additionally ,few people give thought to the function of the two windings in a blocking oscillator. Since there is current gain available, this can be used to advantage to get fast switching of the transistor. Study some old schematics by Tektronix where blocking oscillators were properly designed. You will find that the base drive winding is properly sized to effect good switching, but not wasting power by over driving.

There are alternative circuits to the usual practice used in most JT's of a power wasting resistor in series with the base winding. This does not produce the best switching. You want a circuit which biases the winding to the base threshold yet still allows sufficient current flow into and out of the base, but not excessive. The base winding should have lower turns ratio than the collector winding.

In an ordinary poorly designed blocking oscillator such as a JT, switching can be improved by adding an series R-C speedup network across the bias resistor, but this is not the best improvement that can be made, as the circuit itself is not optimized topologically.

Offline MarkE

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Re: Joule theif : try out !
« Reply #24 on: May 22, 2014, 03:34:27 PM »
Those are worthy changes. Additionally ,few people give thought to the function of the two windings in a blocking oscillator. Since there is current gain available, this can be used to advantage to get fast switching of the transistor. Study some old schematics by Tektronix where blocking oscillators were properly designed. You will find that the base drive winding is properly sized to effect good switching, but not wasting power by over driving.

There are alternative circuits to the usual practice used in most JT's of a power wasting resistor in series with the base winding. This does not produce the best switching. You want a circuit which biases the winding to the base threshold yet still allows sufficient current flow into and out of the base, but not excessive. The base winding should have lower turns ratio than the collector winding.

In an ordinary poorly designed blocking oscillator such as a JT, switching can be improved by adding an series R-C speedup network across the bias resistor, but this is not the best improvement that can be made, as the circuit itself is not optimized topologically.
I agree that the base drive as it is is wasteful.

Free Energy | searching for free energy and discussing free energy

Re: Joule theif : try out !
« Reply #24 on: May 22, 2014, 03:34:27 PM »
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Offline mscoffman

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Re: Joule theif : try out !
« Reply #25 on: May 22, 2014, 04:52:59 PM »
A Self Boostrapping Manual Start Circuit.

It might be fun to use a manual SPDT switch as a multipress trigger AC source
from a low voltage DC higher current supply to a small Crockroft Walton Voltage
Mutiplier. Once a client higher voltage Joule Thief starts running it could serve as
AC clock source for running the voltage multiplier itself.

This could serve as a stardard way to deep six carbon/zinc primary batteries from
"emergency" circuit designs for a crystal cell battery per spec.


:S:MarkSCoffman

Offline TinselKoala

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Re: Joule theif : try out !
« Reply #26 on: May 22, 2014, 05:00:38 PM »
Two of my JTs:

The NE2HVJT lighting up six NE-2s in series from a depleted AAA battery, and another HVJT lighting up an incandescent bulb and a NE2 simultaneously, on 3V input.

So I'm going to say that "performance" depends on what you are trying to do. If you are trying to see how long you can get a visible glow in an LED or operate at the lowest possible input voltage that's one thing, or maybe two. If you are trying to get max voltage and fast rise-fall times in the oscillator's output, that's another. If you are trying to operate the transistor at its best efficiency (max gain for minimum base-emitter current) that is something yet again different.

The JT problem space was pretty completely explored back in the old JT threads where Jeanna was posting a lot of her research. People even stripped turns one at a time off coils to find optimum winding ratios for what they were doing. Some remarkable results were achieved, lighting up CFLs to very reasonable brightnesses on tiny input voltages and currents. Before anyone starts re-inventing the wheel, I suggest digging out those old threads and skimming over them, you might discover that the dedicated JT builders know more than you think, already.


Offline Vortex1

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Re: Joule theif : try out !
« Reply #27 on: May 22, 2014, 06:28:56 PM »
Two of my JTs:

The NE2HVJT lighting up six NE-2s in series from a depleted AAA battery, and another HVJT lighting up an incandescent bulb and a NE2 simultaneously, on 3V input.

So I'm going to say that "performance" depends on what you are trying to do. If you are trying to see how long you can get a visible glow in an LED or operate at the lowest possible input voltage that's one thing, or maybe two. If you are trying to get max voltage and fast rise-fall times in the oscillator's output, that's another. If you are trying to operate the transistor at its best efficiency (max gain for minimum base-emitter current) that is something yet again different.

The JT problem space was pretty completely explored back in the old JT threads where Jeanna was posting a lot of her research. People even stripped turns one at a time off coils to find optimum winding ratios for what they were doing. Some remarkable results were achieved, lighting up CFLs to very reasonable brightnesses on tiny input voltages and currents. Before anyone starts re-inventing the wheel, I suggest digging out those old threads and skimming over them, you might discover that the dedicated JT builders know more than you think, already.

I agree it all depends on what you want to do. In addition to digging out those old threads, I suggest folks dig out some old books, because this subject was fairly thoroughly engineered before most of us were born, back when it was called an inductively coupled oscillator, saturating core multivibrator,  or blocking oscillator (and many more names) in the vacuum tube days.

I built my first miniature blocking oscillator using a CK722 transistor in the mid 50's,(when it went to $0.99) to make a portable 4' flourescent tube light and before that, several versions of a vacuum tube blocking oscillator.

Quote
The CK722 was the first low cost junction transistor available to the general public. It was a PNP germanium small signal unit. Developed by Norman Krim, it was introduced by Raytheon in early 1953 for $7.60 each; the price was reduced to $3.50 in late 1954 and to $0.99 in 1956.

Offline Farmhand

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Re: Joule theif : try out !
« Reply #28 on: May 22, 2014, 11:11:56 PM »
Reading through old threads is unfortunately a good way to waste time and read a lot of misconceptions, these sites have lots of threads with lots of posts not worth the time to read and a few good posts in amongst them. Ever tried it ?

I just want a low part count easy to make setup that can drive some LED'S to get usable light from old AAA and AA alkaline batteries, as well as charge some odd tiny batteries with low current.

I take on board the diode advice.

Considering if I was to stick to under 4 volts input. Can I ask why it is that the base drive is inefficient ? Like what are the reasons, is the voltage applied to the base too high or is the current too high or too low ?

The circuit has been running for 24 hours now driving 4 x 5 mm LED's and trickling a pair of AAA 700 mAh, with two old 900 mAh NiMH AAA batteries as supply, now considering that the garden path lamps using one 5 mm LED deplete the 1 x 700 mAh battery before dawn, but in this setup the two 900 mAh AAA's are still at 2.44 volts which is still over the nominal 1.2 volts of the batteries, I think it is doing ok. Now I do realize that the solar garden lamps probably do not charge the battery well because it seems this circuit (like other pulsing circuits) apply a better charging voltage and it doesn't drop off like the sun so charging is not halted and the batteries gain some working condition, the tiny 20 mAh NiMH batteries I have responded well to charging by JT but not so well with DC.

I think the AAA NiMH batts I'm charging now will take a charge from the wall charger better after trickling on the JT for a day or two.

When I make the little PCB I'll use a connector to attach the load LED/s so it can be swapped out for the load battery or the load battery can be connected in series with other loads ect.

..


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Offline Farmhand

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Re: Joule theif : try out !
« Reply #29 on: May 22, 2014, 11:52:05 PM »
One of the main problems as I see it on these sites is that the discussion and chit chat gets mixed in with the technical info. In reality the entire sites are a big "chat box" with "sub sections" of chat that may or may not contain "chat" that has information relative to the issue a person is dealing with.

There is an inherent problem with suggesting folks lookup old "chat" and that is that it is just that "chat" how does a new experimenter differentiate between "chat" and technical info when the technical info is stuck in the middle of thousands of words of chat ?

Until a solution is found people will just continue to ask new questions and chat, increasing the issue.

Along with oversized images it make reading the threads difficult and time consuming.

..
.

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Re: Joule theif : try out !
« Reply #29 on: May 22, 2014, 11:52:05 PM »

 

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