Joule Thief

[Jason Walters]

Hello. Im trying to make a very simple Solar Powered LED Light. Basically....Im trying to make a Solar Powered Garden Light....but in a different enclosure. I know I can go buy one and rip it apart....but Id rather make it from Scratch. I have messed around with some Schematics I found on Instructables.com....but just cannot get it to work. So...I decided to join the Forum. Why can't I get my Joule Thief to work. I need to boost 1.5v to 3v to power some Super White LED's. I wrapped insulated wire about 8 times around and connected 1 wire from each pair together just as instructed....but still no power out of the LED. This is what Im trying to follow. Thanks for your help in advance! http://www.instructables.com/id/Solar-LED-Light-Bulb/?ALLSTEPS

 

[Harald Kapp]

Welcome to electronicspoint.

Apart from the finer details of corretcly building the transformer, this circuit will operate only if there's no light to the solar cells. As soon as the solar cells become active, the upper 2N3906 will tiurn off due to the positive base voltage via the 5k resistor.

To get the basic Joule thief working, replace the 2N3906 by a short circuit from emitter to collector.

 

[Jason Walters]

Thanks!!!!!

Actually I want it to work that way. This way when the sun goes down....the lights turn on. I just dont think Im getting the Voltage. Ive tried it even with just using a AAA Alkaline as the power source and nothing!

Welcome to electronicspoint.

Apart from the finer details of corretcly building the transformer, this circuit will operate only if there's no light to the solar cells. As soon as the solar cells become active, the upper 2N3906 will tiurn off due to the positive base voltage via the 5k resistor.

To get the basic Joule thief working, replace the 2N3906 by a short circuit from emitter to collector.

 

[Harald Kapp]

Actually I want it to work that way. This way when the sun goes down....the lights turn on

That's o.k., but I recommend you split the problem into snippets you can tackle separately. Therefore exclude the solar-power-plus-switch part and get the basic joule thief working.

Once you've got this running, you can re-attach the solar-power-plus-switch part.

I wrapped insulated wire about 8 times around

Around what? You will need an iron core, preferably a toroidal core.

Here is a much better (in my view) explanation how to build one. Do you realize that the small dots at the windings of the transformer are there for a reason? They indicate the start of the winding, assuming all windings are made in the same direction. Otherwise the induced currents/voltages will have the wrong phase. In the link I gave they show this rather detailed.

I once build such a Joule thief as in my link using a toroidal core and it worked fine from a 1.5V AA battery.

Once you've got this running, you can re-attach the solar-power-plus-switch part.

I wrapped insulated wire about 8 times around

 

[Jason Walters]

Thank you so much for your help. This is exactly what I have been trying. Just to get the light to turn on with a AA battery. I have attached a photo of what I just did after you sent me your link. I tried to make it EXACTLY the same and still no luck. Everything is brand new. The only thing I can thing of is the Toroid isnt the right one. How does it look to you??

That's o.k., but I recommend you split the problem into snippets you can tackle separately. Therefore exclude the solar-power-plus-switch part and get the basic joule thief working.

Once you've got this running, you can re-attach the solar-power-plus-switch part.

Around what? You will need an iron core, preferably a toroidal core.

Here is a much better (in my view) explanation how to build one. Do you realize that the small dots at the windings of the transformer are there for a reason? They indicate the start of the winding, assuming all windings are made in the same direction. Otherwise the induced currents/voltages will have the wrong phase. In the link I gave they show this rather detailed.

I once build such a Joule thief as in my link using a toroidal core and it worked fine from a 1.5V AA battery.

Once you've got this running, you can re-attach the solar-power-plus-switch part.

 

[Jason Walters]

Here is another view

 

[Harald Kapp]

Looks o.k. from the pictures. Check your components separately:

• Check the LED: Does it light when attached to a 3V battery with a small resistor (22Ω...47Ω) in series?
• Check the transistor: Use a 3V battery in series with a small resistor (see above) with the circuit. When you connect base to "-", the LED should light. When you connect the base via the 1kOhm resistor to 3V (detach the resistor from the coil first), the LED should be off.
• Check the resistor: measure the resistance to verify it is ~1kΩ.
• Chek you solder joints, they don't look extremely bad, but not too god either.

Also it may help to use wire with a thinner insulation and put more windings on the toroid. The toroid itself is imho not that critical (as long as it is made from ferrous material, not paper )

 

[BobK]

Try switching the leads from one of the coils in your transformer. They must be connected correctly for the Joule Thief to work.

Also, typically you would use more windings that that. The one I built used 22 turns of enameled wire.

Bob

 

[Jason Walters]

YOU GUYS ARE FANTASTIC!!!

It was all in the toroid. I purchased a much bigger one and wrapped it more times and wallah. Thank you so much!

 

[Colin Mitchell]

Measure the current.
Now put a 10n between the join of the transformer and the 1k and the negative of the battery and measure the current.

Then try 30 turns and 30 turns without the ferrite and see it will work just as well.

 

[Jason Walters]

Thank you Colin...You lost me at "without the ferrite" are you telling me I can boost the voltage without using a toroid???

Measure the current.
Now put a 10n between the join of the transformer and the 1k and the negative of the battery and measure the current.

Then try 30 turns and 30 turns without the ferrite and see it will work just as well.

 

[BobK]

Certainly you can, but I think the coil would have to be significantly larger.

Bob