Joule Thief

[nievesoliveras]

@spinner

Hmm, this circuit (a very basic transistor oscillator with an inductive coupling) is called "The Joule Thief"? Lol,  I can assure you it's more like a "Joule waster"...

Yes, it works with only a few (easy to get or make) components, but that's about all it can do...
It actually works as a (quite inefficient) DC to AC/frequency converter, wasting at least half of the Energy available.

Maybe it's the rather low input voltage where LED is still working that fascinates you?

There are serial (three/four pin "transistor like") components on the market, which allows you >85% efficiency (DC/DC chips, usually needing only a few external low-tech components to work). They all beat this circuit (in efficiency) at least by the factor of two... And they're still not Unity.

Joule Thief? Yeah, sure...

I built a joule thief circuit " http://www.overunity.com/index.php?topic=6123.msg139345#msg139345 "
And as today it is still working.  It lights 4 leds with a 1.5v battery that only has 0.35volts left.
also if I connect a 0.00v AA battery, it charges it by increments of 0.01v every three hours.

Just build it and see for yourself. The schematic is included.

Jesus

[Yucca]

Hmm, this circuit (a very basic transistor oscillator with an inductive coupling) is called "The Joule Thief"? Lol,  I can assure you it's more like a "Joule waster"...

Yes, it works with only a few (easy to get or make) components, but that's about all it can do...
It actually works as a (quite inefficient) DC to AC/frequency converter, wasting at least half of the Energy available.

Maybe it's the rather low input voltage where LED is still working that fascinates you?

There are serial (three/four pin "transistor like") components on the market, which allows you >85% efficiency (DC/DC chips, usually needing only a few external low-tech components to work). They all beat this circuit (in efficiency) at least by the factor of two... And they're still not Unity.

Joule Thief? Yeah, sure...

I would agree that although it operates on low voltages it burns more current in the coil chargeup than is captured as BEMF by the LED, but I think if you make the coil out of very thin wire then more efficiency can be had, the coil gauge will need to be matched to the load. Basically up the gauge until the LED stops getting brighter. Or maybe make a very high impedance coil with exceptionally fine wire and many more turns and have a high voltage and incredibly low current light the LED, a bit like a Stiffler SEC. In this scheme the trigger coil ratio will need to be lowered so as not to upset the transistor base.

But it is in it's current form a bit of a Joule waster as you put it, but as I see it plenty of room for improvement.

I think the circuit is a good thing to play with because it helps the experimenter gain a more intuitive understanding for electronics than just buying a 80% efficiency DC-DC converter. The DC-DC converter packages you speak of can any of them operate down to 0.3V input voltage?

Yucca.

[spinner]

I built a joule thief circuit " http://www.overunity.com/index.php?topic=6123.msg139345#msg139345 "
And as today it is still working.  It lights 4 leds with a 1.5v battery that only has 0.35volts left.
also if I connect a 0.00v AA battery, it charges it by increments of 0.01v every three hours.

Just build it and see for yourself. The schematic is included.
Jesus

Ok, empty batteries still have some juice left (chemical potential) before they're really dead. (as no output current).
The internal resistance of the battery rises tremendously, while the electrolyte decayes...

Measure the voltage of your battery in circuit. Measure unloaded battery with a DMM. Any difference? Use scope to see the waveforms in the circuit,... Digital V-meter is a nice instrument, but has some limitations... You cannot measure pulses of any kind...

You can try using a charged el. cap instead of the battery. Or, use a (low ohm) resistor divider connected to a good battery () and try your circuit (setting up the output at 0,35V). Add filter cap,...

Ah, I see. This circuit "sucks energy" from otherwise "dead" batteries (the ones considered empty after the normal use). So it actually is a Joule Thief...


@Yucca
Any component in this circuit is lossy. Especially semiconductors. Therefore, this circuit cannot be OU.
But it's interesting and educational to play with, indeed.
It may pump the energy from somewhere... 

Yes, DC/DC circuits need much more than 0,35V.  This circuit, too. Transistor cannot operate with CE voltage that low, but with suitable inductive coupling and a voltage superposition while oscillating it obviously works...


I'll leave all the practical and useful solutions to you, guys!
Cheers!

[WilbyInebriated]

Hmm, this circuit (a very basic transistor oscillator with an inductive coupling) is called "The Joule Thief"? Lol,  I can assure you it's more like a "Joule waster"...

Yes, it works with only a few (easy to get or make) components, but that's about all it can do...
It actually works as a (quite inefficient) DC to AC/frequency converter, wasting at least half of the Energy available.

Maybe it's the rather low input voltage where LED is still working that fascinates you?

There are serial (three/four pin "transistor like") components on the market, which allows you >85% efficiency (DC/DC chips, usually needing only a few external low-tech components to work). They all beat this circuit (in efficiency) at least by the factor of two... And they're still not Unity.

Joule Thief? Yeah, sure...

ummm... thanks Captain Obvious....

the serial component you speak of are not more efficient, and for sure not by a factor of 2, as tested here...
http://www.talkingelectronics.com/projects/LEDTorchCircuits/LEDTorchCircuits-P1.html

all that aside, my JT lamp uses 3x2 led's 3.3V 19mA each. 310mA drain @1.5V (81%)
now if you buck it instead of boost, and feed the "extra" V back to the smoothing capacitor, gets you closer to 90% efficient.

[nievesoliveras]

@all

I put a capacitor 2200uf 50v to the circuit and after an hour it was filled with 2.44volts. The thing is that it gets empty again somehow and it start it all over again.

The strangest thing is that it is filled with the same battery and circuit. The battery now oscillates between 0.35 and 0.44 volts. I peeled the battery cover to diferenciate it from the other batteries I have.

When I put it back to the circuit, it took about 10 seconds to light the four LDs again without the capacitor.

??

Jesus