UCVC

[resonanceman]

The circuit in the schematic  is the basic voltage control circuit.
For simplicity  I did not add a  means for  charging the cap.


This is  a very simple circuit ......but I thought I would break it down  for the people here that are fairly new at building circuits.

This schematic  is  of the U cap potentiometer and LED.
The dots on the ends of the lines coming from the U cap should  be considered  as connection points  for  the original means of charging the U cap.
The potentiometer  is used to drop  a variable amount of voltage , the LED is chosen  to provide an indicator light  and drop a more or less consistant  amount of voltage .

gary

[resonanceman]

This  shows that the negative  side of  the U  cap and  the battery are kept at the same voltage.
The battery is shown as a separate battery  it can also be the source battery for the JT charging U cap.

gary

[resonanceman]

This schamatic shows that the transistor acts as a simple switch that enables or disables the control coil

If  the transistor  is conducting then the impedance of the control coil drops .
If  you  have ever used more than one secondary on a JT you know that they must be matched very carefully.
If they are not matched most of the power will go to the lower inductance winding.
This circuit just takes advantage of  this simple fact.

As the voltage that remains after  the LED and pot reaches a level that starts turning on the transistor  the impedance of the winding drops effectively loweing the ability of the JT to charge the U cap.

This turns out to be a VERY soft switch. It  is not easy adjusting the pot because the LED does not come on all at once.
I like this quirk because it shows  more about the actual charge state then a simple on or off condition.

A zener diode would probably provide a much sharper transition than the LED .

So far the control coil is a secondary on the JT used for charging  the U cap.
I plan to test using a separate coil soon.

gary

Edit

I will  try to get a few pictures posted  in the next few days.

[resonanceman]

I recommend using small supercaps in place of  U caps while  building and adjusting this circuit.
I  hooked 2   5.5V supercaps in series so I pretty much don't have to worry about going over rated voltage.

gary

[nievesoliveras]

Is this just the secondary of the Joulethief?