Joule Thief

[dog812]

On a bifilar jt , the pickup coil needs to be starting and ending at the same location , if the pickup coil goes over the end

What does this mean??

[jeanna]

I think this just means you must not have the secondary/pickup wire on top of (or under) the place where the primary wires begin their turns - or end their turns. I think the primary 's job is to make the oscillations happen, and then since the secondary is actually oscillating, the secondary oscillations could negate the primary ones if they meet at the all important turning point of the primary coils.

Does this make sense?

I am glad to hear the resistors work.
I think it is your pot. I have one that cuts off the circuit when it gets to a max spot.
Maybe you have one like that too.

A bunch of us have been able to take the resistance very high. I went to 50K and xee2 took his to 500k.

The frequency just gets higher and higher with more ohms in the base resistor. (well we have not found a limit yet.)

Great stuff dog812,

thanks for describing your work.

jeanna

[electricme]

@Xee2
Your post is very timely indeed, last night I completed removing the copper wires off the torrids, what a job that was, I have strained my right arm, the wires were around 2mm to 2.2mm diameter (thats right, built for amps). Story and picks below.

@ dog812 
Interesting test. I would think that it would work OK but it doesn't. That is the value of experimentation. Some people say that coils work better when they are tight against the ferrite, but I have made many coils with turns not tight (like your white wires) and they worked. I never did any tests to see if they worked better when tight. However, I do think that the way you have made it may be reducing the coupling between the collector coil and the base coil, since both of them are probably more tightly coupled to the secondary than to each other the way you have made it. I do not know why that would make using a resistor a problem though. I would think that it would make it necessayr to use a larger resistor. Which is another example of why testing is the only way to tell if it will work.

As I mentioned above, I removed the wires, I was left with a torid which has a white plastic shell covering the torid itself.
I pulled off the covers and could see there is no way that the previous windings could be in touch or be as closely wound a plastic encased torid as is in other cases.

There must be a reason for this, but I dont know at the moment, I have to phone up a fello (electrical design engineer) who is very high up in the power supply mob in Toowoomba in a couple of minutes about another torid question and I willl ask him what is going on here.

Enjoy the photos.
jim

[Mk1]

@all

I hope this will make sense .

[Pirate88179]

@ All:

Great work folks!

Just a note.  Stefan said on another topic that he will be switching to another software and server tomorrow.  This is good news.  He also said that the site may be down for about 24 hours. (the bad news)  but, when back up and running, it will be a lot better.  I just wanted to pass this on.

Bill