help with Joule thief please

[robhho123]

hi everyone

im new to electronics and hope to learn alot i have tryed to make a simple joule thief well i say simple but have not been able to make it work and im not sure what i am doing wrong.
if anyone can help me i would be very greatfull.
i have attached a picture of what looks like it has a toroid ring with 8 turns of insulated copper wire, 1ohm resistor, BC547 transistor and a 3v green LED.

please help

ROB

 

[BobK]

hi everyone

im new to electronics and hope to learn alot i have tryed to make a simple joule thief well i say simple but have not been able to make it work and im not sure what i am doing wrong.
if anyone can help me i would be very greatfull.
i have attached a picture of what looks like it has a toroid ring with 8 turns of insulated copper wire, 1ohm resistor, BC547 transistor and a 3v green LED.

please help

ROB

I looked up joule thief, cool project!

1. I assume you meant a 1K resistor, not 1 Ohm, right?
2. Did you connect a battery with the + terminal to the two twisted wires coming out of the torroid and the negative terminal to the emitter of the transistor?
3. Are you sure your LED leads are not backwards?
4. You are using a green LED. This circuit is designed for a white or blue LED which have a much higher voltage drop, and it might not work correctly with a green LED.

Bob

 

[(*steve*)]

Another possibility is that one of the windings may need to be reversed.

I'd double check that the transistor is correctly wired too.

Do you have a link to the instructions that you followed? Do you have a circuit diagram?

 

[robhho123]

thanks for the reply's it could be the led were im going wrong i have wired it exactly how it show's on this website:http://www.emanator.demon.co.uk/bigclive/joule.htm. i will try wiring it up with a white led and see if this solves it.

thanks ROB

 

[robhho123]

still aint working i thought it was somthing to do with the solder being the wrong type or somthing but it turns out it wasn't ive been trying all day different config's to see if i have done it wrong.the transister im using is rated slightly different to the one that is said to be used.if i put somthing conductive over E and C turminals it flashed the bulb.im not sure if it could be that i have the wrong resistor in even though i have a 1k resistor.

please help

ROB

 

[robhho123]

still aint working i thought it was somthing to do with the solder being the wrong type or somthing but it turns out it wasn't ive been trying all day different config's to see if i have done it wrong.the transister im using is rated slightly different to the one that is said to be used.if i put somthing conductive over E and C turminals it flashed the bulb.im not sure if it could be that i have the wrong resistor in even though i have a 1k resistor.

please help

ROB

 

[jackorocko]

Another site says to try and use thinner wire if the circuit won't work. Maybe you could try that...

 

[robhho123]

i have tryed lots of different types of wire but it still won't work does anyone know if the transistor and resistor im using should work?

 

[robhho123]

it works at last i was about to give up on it.it lights up a 3v green led but the only thing i dont get is why when i put my DVM on it it only reads 1.5v still and not 3v?

 

[Resqueline]

1st; a green LED does not have a Vf of 3V - it's more like 1.9V-2.3V (see here), and 2nd; a joule thief like that delivers pulses - not a steady DC - so the average is lower.

 

[BobK]

it works at last i was about to give up on it.it lights up a 3v green led but the only thing i dont get is why when i put my DVM on it it only reads 1.5v still and not 3v?

So what did you change that finally made it work?

Bob

 

[nepow]

it works at last i was about to give up on it.it lights up a 3v green led but the only thing i dont get is why when i put my DVM on it it only reads 1.5v still and not 3v?

Well done...your persistance has paid off!! all the advise given here so far is important to remember when building circuits. Now try a white LED but take note that many devices are polarity sensitive! Don't just copy circuits... try and understand how the circuits and components work...plenty of help available by searching the net. Kind Regards

 

[robhho123]

cheers guys for the help.
I used a different transistor a 100ohm resistor instead of a 1k resistor.
Im just trying to work out how i can use this to have a constant voltage i was thinking capacitor.if anyone has any idea's it would be much appreciated

regards ROB

 

[(*steve*)]

Connect the anode of a shottky diode to the collector of the transistor and to the cathode connect the +ve end of an electrolytic capacitor. The other end of the capacitor goes to ground (the emitter of the transistor).

You will get a high(er) voltage across the capacitor.

Without some sort of load, the voltage may get quite high, possibly high enough to exceed the breakdown voltage of the transistor (not good).

If you connect a LED to this (across the capacitor), you would need to use a small series resistance and be careful not to connect the LED while the capacitor was charged.

 

[robhho123]

thank you for that i will try that today and see how it goes.

regards rob