Joule Thief 101

[MileHigh]

This is exactly why most of my JT circuits, including the high voltage units, all have a VR on the base.  I tried to explain this earlier in the topic but, it really does work well for what you want to get out of the circuit.

Lidmotor even used this method on his replication of the Jeanna Light if I am not mistaken.  I actually used 2 VRs in that project...I think he used a rheostat if I remember correctly.

Bill

Well if you are following along with what I am saying, then it means that you start your Joule Thief with the base resistor at the higher value to keep the power drain to a minimum, and then some time later when the battery voltage has decreased to a certain value you lower the value of the base resistor by perhaps 10%-25% to ensure reliable switching to a lower battery voltage.

That's it, there is no brightness control, no twirling of pots to look for a bright spot, just a controlled decrease in the base resistor value to ensure that the switching can operate properly at a lower battery voltage.  There is no "sweet spot" at all.

However, this leads to a question, is it even worth it to go to this kind of trouble?  How much power can you really save compared to your nominal running power using a fixed resistor and how much proportionally longer a run time can you get when you do this?  What if changing the value of the resistor in two steps only saves you 2% on your nominal running power and gives you 2% more run time?  You have to think about it and crunch some numbers for that.

Supposing you crunch the numbers and a variable resistor solution only gives you a 3% overall improvement?  Most people would then say forget it, it's not worth it.  It's not worth the extra complexity or the trouble.  The better solution is to do your experimenting and analysis and determine the optimal resistor value.  The next step is to decide what standard resistor value or combination of standard resistor values to settle on for the final design.

That's the real deal - the real, serious experimentation and analysis and evaluation of the various trade-offs and design choices to arrive at a final Joule Thief design.  From what I can tell, you have never seen anything like that done on this forum.

[Pirate88179]

Well if you are following along with what I am saying, then it means that you start your Joule Thief with the base resistor at the higher value to keep the power drain to a minimum, and then some time later when the battery voltage has decreased to a certain value you lower the value of the base resistor by perhaps 10%-25% to ensure reliable switching to a lower battery voltage.

That's it, there is no brightness control, no twirling of pots to look for a bright spot, just a controlled decrease in the base resistor value to ensure that the switching can operate properly at a lower battery voltage.  There is no "sweet spot" at all.

However, this leads to a question, is it even worth it to go to this kind of trouble?  How much power can you really save compared to your nominal running power using a fixed resistor and how much proportionally longer a run time can you get when you do this?  What if changing the value of the resistor in two steps only saves you 2% on your nominal running power and gives you 2% more run time?  You have to think about it and crunch some numbers for that.

Supposing you crunch the numbers and a variable resistor solution only gives you a 3% overall improvement?  Most people would then say forget it, it's not worth it.  It's not worth the extra complexity or the trouble.  The better solution is to do your experimenting and analysis and determine the optimal resistor value.  The next step is to decide what standard resistor value or combination of standard resistor values to settle on for the final design.

That's the real deal - the real, serious experimentation and analysis and evaluation of the various trade-offs and design choices to arrive at a final Joule Thief design.  From what I can tell, you have never seen anything like that done on this forum.

I follow along with what you are saying, I just totally disagree with it.  I have easily seen 3 times the running time using a vr on the base as without.  I have JT lights here that will run for months using this method.

All of this was discussed years ago in the main JT topic area.  You can unsolder and replace as many resistors as you want during the runtime and I will just turn the vr a little bit.  This method takes less than 1 second and allows you to milk every drop of energy from the battery which was one of the purposes for this circuit to begin with.

No compromises needed...just an adjustment now and then.

Bill

[poynt99]

The phase shift video.


https://www.youtube.com/watch?v=EhpP7Bmcwhs



Brad

If you block the magnet (but don't change anything else) and run through a wide frequency sweep in the same area, what do you see in terms of the phase relationship?

[MileHigh]

I follow along with what you are saying, I just totally disagree with it.  I have easily seen 3 times the running time using a vr on the base as without.  I have JT lights here that will run for months using this method.

All of this was discussed years ago in the main JT topic area.  You can unsolder and replace as many resistors as you want during the runtime and I will just turn the vr a little bit.  This method takes less than 1 second and allows you to milk every drop of energy from the battery which was one of the purposes for this circuit to begin with.

No compromises needed...just an adjustment now and then.

Bill

What you are saying is not incompatible with what I am saying.  I am just talking about a Joule Thief in normal operating mode.  I don't know how much energy is left in a battery when the voltage falls below the minimum voltage for normal operating mode and for all I know you can still get a lot of light out of the device in that range.  It just requires more measurements and investigation.

[verpies]

The phase shift video.
https://www.youtube.com/watch?v=EhpP7Bmcwhs

I just got a PM from one of my "fans" directing me here because you are vibrating some ferromagnetic materials near coils, which is a well known pet peeve of mine
I never looked in here before because I expected this thread to contain some boring Joule Thief circuits - not an off-topic device like that.

I am too lazy to read the entire thread, so could you summarize for me what is your investigation about and what are you trying to determine?