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Joule thief efficiency evaluation

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fernando_g

New Member
As a way of saying thanks to this forum, which has taught me some valuable info, I wanted to provide a little contribution myself.

Essentially, I wanted to investigate what circuit mods improve the efficiency of the joule thief.

This is preliminary work, and I'm sure that it can be improved.
 

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Sceadwian

Banned
All you need to do is come up with a V/I curve of the LED's at the currents you measured and use that diode drop calculated against your equivalent MA comparison and you'll get a true efficiency comparison, all it would take is to plot the diode drop with the initial calibration currents you did.
 

fernando_g

New Member
Your suggestion is a good one, but...isn't light output efficiency the desired output?
 
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Sceadwian

Banned
No.
You need power in power out calculation's at those light output levels. Otherwise your numbers don't mean anything as far as efficiency goes.
 

mneary

New Member
Nice experiment. Would be nice to see what an older alkaline (1.0 or 0.8V) or typical NiMH (1.2V) cell looks like.
 
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RODALCO

Well-Known Member
Interesting research you are doing.

I have succesfully used the diode and capacitor option in parrallel with the LED and it will very reliably run a astabile flip flop.

See my YouTube link attached.

YouTube - Joule Thief with Flip Flop

It still works at the moment at 0.5 volts although the led on - off ratio is a lot faster.
 
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sPuDd

New Member
Some of the Joule Thieves I made ran as high as 600kHz. You will need special gear to measure the current drawn at this frequency, as the system behaves like a low power factor load.

sPuDd..
 

Hero999

Banned
I don't think power factor is a problem because it's DC voltage but it is true that you cant use a DC DVM to measure the current because the current is AC. You could use an oscilloscope and calculate the RMS current from the waveform.
 

fernando_g

New Member
The filter circuit of page 4 filters out completely the AC ripple component. I verified the voltage drop across the 0.47 ohm resistor with an oscilloscope and it is essentially DC.
 
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