Joule Thief Charger Mod

[twofortheroad]

I've been experimenting with the joule thief for awhile, mainly as a charger and discovered a way to significantly increase its output. I looked around the internet and couldn't find anybody else who had configured the joule thief this way. So if someone has already done this, I'm not trying to take credit for it, I just discovered it myself and thought I should share it if nobody has already done so.

I realized there was a significant amount of back EMF coming off of the secondary winding of the bifilar coil. Normally only the primary winding is tapped for the back EMF. I tapped both windings and it increased the output. It increases charging current by 30% and increases open circuit voltage by 104%.

See the attached schematic for details and info on how to best charge batteries with this mod.

[sucahyo]

That is significant gain, nice .

Have you compare battery charging temperature?

[twofortheroad]

I tried to edit my original post but it wouldn't let me. Anyway, sorry about the pic of schematic. It got trashed during upload. Here is a link to it at imageshack.

ImageShack® - Online Photo and Video Hosting

[twofortheroad]

@sucahyo

Charging with a joule thief doesn't generate any noticeable heat when charging lead acid batteries. I haven't charged single celled batteries over a long period of time to notice any heat. I normally only charge rechargeable NiMh batteries long enough to recover them when they wont charge with a normal charger.

[sucahyo]

@sucahyo

Charging with a joule thief doesn't generate any noticeable heat when charging lead acid batteries. I haven't charged single celled batteries over a long period of time to notice any heat. I normally only charge rechargeable NiMh batteries long enough to recover them when they wont charge with a normal charger.

No, I mean comparing charging with single diode and your solution.

Because I found that sometime FWBR solution can heat up the battery more. Easier to notice when charging single nimh with 350mA output or more, measured with amp meter in series with the battery.

It is a pity that you don't charge your nimh with radiant charger. Mine 2500mAh has standing voltage of 1.40V now and can run 50ma load continuously for three days, or at least 48 hours.

[sucahyo]

Can you post input and output current with amp meter in series with the source battery and charging battery?



BTW, press go advance to edit your post.

[twofortheroad]

@sucahyo

I haven't noticed any difference in heating with single celled batteries and lead acids don't heat up noticeably.

Normal joule thief
Input 100mA, output 60mA

Joule thief mod
Input 100mA, output 78mA

I just chose 100mA for testing. I've had input current as high as 680mA but it loses efficiency due to generation of heat in transistor and coil.

[sucahyo]

@sucahyo

I haven't noticed any difference in heating with single celled batteries and lead acids don't heat up noticeably.

Normal joule thief
Input 100mA, output 60mA

Joule thief mod
Input 100mA, output 78mA

I just chose 100mA for testing. I've had input current as high as 680mA but it loses efficiency due to generation of heat in transistor and coil.

Thanks, that is good efficiency . Hopefully more people would try your circuit .

[twofortheroad]

@sucahyo

I believe the efficiency if this circuit comes from the toroid core material. I used a F-240-W toroid from CWS ByteMark. The "W" core material has a high permeability rating of U=10000. Cores with high permeability are used a lot in battery desulfation circuits because it increases the voltage spike or BEMF created when the magnetic field collapses inside the coil. I chose this core in hopes it would work well with this circuit and I am very pleased with its performance. There is a company in Germany that makes Nanoperm toroid cores with a permeability of U=200,000 that I would love to try but I haven't found a USA distributor yet. If anyone knows of one or knows of an equivalent or better core material let me know.

[sucahyo]

I see. Many thanks for the info . I tried toroid but never have big gain, only more reliable oscillation.

What is the frequency of your circuit, is it audible?

[twofortheroad]

The frequency varies with potentiometer setting, 2.2-3.5 kHz and it is very audible, annoying at times. I ran the sound it makes through a spectral analyzer because it sounded a little strange and it showed harmonics from operating frequency up to about 20 kHz. I wish I had an oscilloscope to see if these harmonics exist inside the circuit (like its ringing) or if it is just an audible anomaly.

[sucahyo]

The frequency varies with potentiometer setting, 2.2-3.5 kHz and it is very audible, annoying at times. I ran the sound it makes through a spectral analyzer because it sounded a little strange and it showed harmonics from operating frequency up to about 20 kHz. I wish I had an oscilloscope to see if these harmonics exist inside the circuit (like its ringing) or if it is just an audible anomaly.

I see. thanks. Very interesting if yours really produce harmonic. Mine clean.

Do your circuit consumption increase without load? Or if you afraid to broke the transistor, would neon bulb load consume less current than battery load?

[twofortheroad]

At 200mA under load it drops to 80mA when load is removed.

[Watson]

I've been experimenting with the joule thief for awhile, mainly as a charger and discovered a way to significantly increase its output. I looked around the internet and couldn't find anybody else who had configured the joule thief this way. So if someone has already done this, I'm not trying to take credit for it, I just discovered it myself and thought I should share it if nobody has already done so.

I realized there was a significant amount of back EMF coming off of the secondary winding of the bifilar coil. Normally only the primary winding is tapped for the back EMF. I tapped both windings and it increased the output. It increases charging current by 30% and increases open circuit voltage by 104%.

See the attached schematic for details and info on how to best charge batteries with this mod.

Please repost the image, it was so blurry that I couldn't read the text. Thank you.

[ewizard]

Watson, Check his post #3 - image there is clear as a bell