Joule thief circuit issue

Thread Starter

woozycactus

Joined Jan 4, 2021
56
Hey guys,

So I am making a little joule thief robot looking thing with my son. I should have done a test circuit first but for some reason when I connect the battery I get a tiny little blink and that's it until I disconnect and reconnect then a little tiny blink again. Any ideas on what the problem is here? Its unfinished so please don lt judge but pics are attached.f811b342c671090927cb133dd76b2e88.jpg20210515_213530.jpg
 

DickCappels

Joined Aug 21, 2008
7,434
I cannot tell from your drawing whether the red and blue windings are properly phased. Try swapping the polarity of one of them. This is a nearly foolproof circuit.
 

BobTPH

Joined Jun 5, 2013
3,315
It looks like you have created a lot of extra inductance by winding the wires around the frame. This could possibly affect the circuit.

Bob

Edit: I see someone beat me to it!
 

DickCappels

Joined Aug 21, 2008
7,434
I think the most common error in connecting transformers wound this way is that the collector winding goes in the opposite direction of the base. The two windings are supposed to be in series, not parallel as I suspect.

1621163127186.png
Look carefully at the color codes of the wires coming off the nail. The positive battery terminal (using an NPN transistor) is connected to the finishing end of one winding and the starting of the other winding. (It is not connected to two starting ends or two finishing ends.)

1621163335267.png
You probably used this schematic Notice the phasing dots. On the base winding the base goes to the undotted end and on the collector winding the collector goes to the dotted end.

Below is my preferred way of drawing the tapped inductor. No confusion about phase here.
1621163528519.png
 

Thread Starter

woozycactus

Joined Jan 4, 2021
56
I think the most common error in connecting transformers wound this way is that the collector winding goes in the opposite direction of the base. The two windings are supposed to be in series, not parallel as I suspect.

View attachment 238627
Look carefully at the color codes of the wires coming off the nail. The positive battery terminal (using an NPN transistor) is connected to the finishing end of one winding and the starting of the other winding. (It is not connected to two starting ends or two finishing ends.)

View attachment 238629
You probably used this schematic Notice the phasing dots. On the base winding the base goes to the undotted end and on the collector winding the collector goes to the dotted end.

Below is my preferred way of drawing the tapped inductor. No confusion about phase here.
View attachment 238630
Ok I see what your talking about. I will try this when get a chance. Thanks.
 

Thread Starter

woozycactus

Joined Jan 4, 2021
56
Ok I see what your talking about. I will try this when get a chance. Thanks.
Ah man, thank you very much. I literally just had to switch 2 wires. Wish I knew before I dismantled that entire thing and started testing. Now I run the 2 leds all the way down to 0.32 volts. Again. Thank you!
 
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