joule thief transformers can be built with a small number of turns.

But of course the frequency will be higher. Depends on the toroid material. There are some which are only specified for very high frequencies.

 

Wrapped 30 gauge wire, which took a while since it's so thin. Made 29 turns.

Still didn't work. I double checked the circuit, everything appeared correct.
I thought maybe it's the toroid.
But then realized the 1Kohm resistor affected the performance.

I kind of connected the transistor without a resistor (shorted it basically) and the light bulb just lit up.
The transistor did get hot, so I'm sure a resistor is necessary.

How do I determine which resistor value I need?

 

What resistors do you have? And what transistor are you using?

 

What resistors do you have? And what transistor are you using?

Transistor: 2N3904 T-NPN, SI-Gen AMPW, SW ROHS. Brand: NTE Electronics

Resistors: I don't have that many values lol. But I can combine resistors to reduce or increase resistance.

 

The toroid could be unsuitable. Normally you can increase the resistance to at least 20 K Ohm.

By the way, I do offer Joule Thief kits, containing most if not all components: TOKO transformers, Toroids (tested), thin wire wrap wire, high efficiency LEDs, Transistors.

I have 3 online, and releasing a 4th soon.

Also the windings ratio 1:1 is not neccessarily correct or the best. I'd try 2:1 and 1:2, maybe it works better.

 

Which toroids do you use?

I tried with a 270 Ohm resistor, worked flawlessly. Is that value too low for the transistor? I wonder why it doesn't work with 1Kohm like for you guys.

Also where can I find your kits online?
On a curious note: what is the purpose of the TOKO transformer? (Is TOKO a brand or is it a type of transformer?)

 

As long as your transistor's not getting hot and the LED is lighting the right color, the worst thing that'll happen is that your battery will run down sooner than it would, otherwise. Base current isn't being used to light the LED, so it's theoretically "waste current." The bigger you can make the resistor, the more your battery's being used to light the LED!

 

Maybe what you thought was a 1kΩ resistor was not 1kΩ.
Double check.

 

Which toroids do you use?

I tried with a 270 Ohm resistor, worked flawlessly. Is that value too low for the transistor? I wonder why it doesn't work with 1Kohm like for you guys.

Also where can I find your kits online?
On a curious note: what is the purpose of the TOKO transformer? (Is TOKO a brand or is it a type of transformer?)

270 Ohms is a bit on the low side. Does the transistor heat up?
You can find my shop via my blog here on AAC (link in the side bar).

Also I can customize the components kit, remove some parts you dont need, add others. There you can see the toroids too, I dont sell single pieces, it would be much less than $1.

Or you could try a small ferrite rod too.

TOKO is a brand for small HF Transformers, originally used in AM Radios. It is just common, people know what kind of small transformer you mean. Of course, not all work for joule thiefs.

I got a new batch wire wrap wire which I also sell in small quantities, so I can supply all whats needed. Just for one Joule Thief, the shipping would be most expensive, so the kits are designed you can build a few from them.

 

Maybe what you thought was a 1kΩ resistor was not 1kΩ.
Double check.

Double checked. Br/Bl/Red/Gold and verified with multimeter.

 

Doubled checked. Br/Bl/Red/Gold and verified with multimeter.

Ok, thanks.

 

I give a try to this project and found the following:

1) the resistor is not critical. I tryed values from 330 ohms up to 10K and the led just dim with high values. Transistor used: 2N2222.

2) the coil is not critical, providing you do not wrap more the 20 turns. 10 turns seems to be the optimum.

3) use a single peace of wire (gauge is not critical) and bend it in the middle, so that when you wrap it around the toroid you will wrap both primary and secondary at the same time. Wrap 10 turns.

4) joint together the end of the secondary with the start of the primary. Double check the connection with a DVM, if connection is corrected you will read continuity between the two single wires. (since the ratio is 1:1 primary and secondary are the same)

Assemble the circuit and you are done. Interesting I could lit 5 white leds in series with a single AAA battery with only 0.98 volts, and when connected to the circuit the voltage dropped to 0.7V (DVM reading), and left on all night on the following morning was still on and bright.

Alberto

 

Alberto, thanks for sharing your observations.

5 white LEDs with 1 volt? Nice!

I observed something also: when the circuit works it only works with low voltage such as 1.5 V. If you use a voltage too high such as 3 volts then the LED won't stay lit (and the LED did not get damaged, I checked again with 1.5 V and it worked). Why not?

 

Try raising the resistor value when you use the higher voltage?

 

Alberto, thanks for sharing your observations.

5 white LEDs with 1 volt? Nice!

I observed something also: when the circuit works it only works with low voltage such as 1.5 V. If you use a voltage too high such as 3 volts then the LED won't stay lit (and the LED did not get damaged, I checked again with 1.5 V and it worked). Why not?

Maybe that toroid would work better with 30 turns thin wire, and 20 for the feedback.

 

Takao21203 sent me some torroids and they work amazingly well compared to my previous toroid. 6 wraps of wire, could probably use less wraps, but with 6 wraps the LED lit up brightly. As far as resistor values, used various up to 10K into the base and the LED was still pretty bright.

Also for experimental purposes, I tried something else. If I plugged the negative lead of the LED into the base of the transistor, it would still light up though not as bright.