Joule Thief 101

[resonanceman]

This  thread is intended  to be a place for  people to learn the basics of how to make a JT ( Joule Thief )  and  what can  be done with them .

This thread is not to be used for asking  questions or  casual  dialog .   This thread is to be kept short  and clean .  The  goal  is to pack  as much  knowledge into a few dozen pages .

With the  recent turn of events  and  the possibility  of  proving  OU new people are bound  to show up .      It is not reasonable  to expect them to read 1000 pages  before asking a questions .
It is also not reasonable  for  the new people to expect us  to drop everything and answer  the most  basic questions .........over and over .

The schematic  below  is  a basic JT
It is shown  using  a 2n3904  but  2n2222s  and many other  transistors  have a proven  track record .   

The schematic  shows  a 1K resistor going to the base of the  transistor   I recommend using a potentiometer   ( Pot ) in  place of the  resistor .  In  real  life it is  a good idea to  sweep the whole  range of the  pot  each time  you make a change in the circuit .

ALmost any toroid can be used .
Low permeability  toroids are easier, they require less turns of the primary .
By the way .......the  2 windings shown  in this drawing  are the JT primary . 

One  thing that  causes alot  of  confusion   with new people  are the dots  drawn  at the top and bottom of the  coils .
I do not know the technical name for them .   I call them marks.
When  you are winding  your  toroid  use something to mark  either the starting end or the finishing end of both wires ..   Magic marker,   nail  polish, paint ........anything to mark the end.

WInd both wires together   as if they  were one . Try  6 or 8 wraps at first .   A very high perm toroid may  need more, a low perm  toroid  will work with less.

When  you  are  donw winding   find  the marks you made on the ends of the wire.

You should  have  2 wires on each  side of the toroid .
One side  will be wires with marks.   The other side  will be wires with no marks.
Take   one of the wires with marks and connect it to  one of the other wires with no marks .

The  Positive  side of the battery  is connected to  the 2 wires you  just  connected together.

The end  of one of these coils  is connected  to the longer  lead on your LED.
The other  coil connects to your pot  which  then connects to the base of the  transistor.

You now have  one of  the 3 wires of the  transistor  connected.
Connect  the  one of the other  wires  on the transistor  to   the same  end of the coil that you connected  the long lead of the LED to  ( at the same spot )

Connect  the  short lead  on your LED  the 3rd wire on your transistor   and   the negative side of your battery together ....... If you did all this  right  , you now  have a working JT

I will leave the  technical  terms to others .   In  theory   you have to  have the  transistor  hooked up  properly ..... in real life it  works  either way . Just  make sure you get the  base  hooked up right . ( at least  with a 3904 and 2222 )

[resonanceman]

This  schematic  shows the basic  JT  with  a capicitor ( cap )  added  across  the  resistor  to make   a simple  RC tank .   
I always  have  use a  tank when  first  trying  a new toroid .  Some  toroids  will work without  a tank .......some will not   
I have never seen  a toroid  that would  not  work  with a tank circuit in place .     I have seen quite a few that  stop when the cap is removed .
I usually  start  with  a 1uF cap  but  a .1 sometimes  is better .


Another thing added to the basic  JT in this  drawing is a secondary .
A  JT  by itself is a novelty .     
It is the secondary that  makes  the JT interesting.
What  can  you get done with it ?
How much  voltage can you make ?

There may  be  many  secondarys  on  a JT
The  secondarys   are always  closed loops in and of themselves.  There is no electical connection to the  primarys.
The primarys ( the original 2 windings of the JT )  are called primarys  because they  are  what makes the  JT work .   
The  secondarys are also called takeoffs .......because they are used to take off power.


gary

[resonanceman]

I found these helpful

[Pirate88179]

Gary:

Great topic!  And very timely too.  You boiled it all down to simple steps.  So now, no one can say they can't make a joule thief.

Great job!

Bill

[xee2]

@ resonanceman

More recently, the "secondary coil" in the above diagram has also been called a "pickup coil" instead of a "secondary coil". Although both terms are used. This is because there can be more than one pickup coil used and it does not make sense to have several secondary coils.