Joule Thief circuit with Wireless LED

Thread Starter

abrahamkkk

Joined Apr 6, 2024
9
I wonder why LED1 is turned on in the Joule Thief circuit and wirelessly connected LED2 is not.

Someone said "In Joule thief circuit the transformer is would around a ferrite core. This is to make sure that the magnetic coupling between the two coils is strong. In your image you seem to have done this by winding the coils very close to one another. However the coil associated with LED2 is not wound in such a way and so the magnetic coupling is weak, ie leakage of magnetic field from the two coils is weak resulting in an induced emf/current in the third coil connected to LED2 which is insufficient to light LED2."

Is this valid answer? The LED2 didn't light up even if I placed it close enough.

Capture.PNG
 

ThePanMan

Joined Mar 13, 2020
800
Welcome to AAC.

I have no experience with Jewel Thieves (JT's). So let me just ask a stupid question: Is the diode installed correctly? Or is it reversed? Try swapping it around and see what happens. Worst outcome is 'nothing happens.'

Oh, and it's not "Wireless" it's magnetically coupled. Wireless implies it being separate from all other components by some marginal to distant location.
 

MrChips

Joined Oct 2, 2009
30,946
LED1 gets enough current and voltage from the 1.5V battery to light up. The voltage has to exceed 2V.
LED2 does not get sufficient current and voltage to turn it on.
 

Thread Starter

abrahamkkk

Joined Apr 6, 2024
9
LED1 gets enough current and voltage from the 1.5V battery to light up. The voltage has to exceed 2V.
LED2 does not get sufficient current and voltage to turn it on.
Why? If the transistor is turned off in the circuit on the left, electromagnetic induction will cause a large voltage in the secondary coil, which will also induce a large voltage in the circuit on the right. If the induced voltage in the circuit on the right was not enough, shouldn't LED1 also not be turned on?
 

MrChips

Joined Oct 2, 2009
30,946
Why? If the transistor is turned off in the circuit on the left, electromagnetic induction will cause a large voltage in the secondary coil, which will also induce a large voltage in the circuit on the right. If the induced voltage in the circuit on the right was not enough, shouldn't LED1 also not be turned on?
You need to have better magnetic coupling into the external coil in order to get enough energy transfer.
 

BobTPH

Joined Jun 5, 2013
9,149
Take led1 of out the circuit. When it conducts, it limits the voltage the led2 sees.

It might still not light, but worth a try.

How are the two coils coupled? The should be on the same core for maximum coupling.
 
Last edited:

BobTPH

Joined Jun 5, 2013
9,149
Oh, and it's not "Wireless" it's magnetically coupled. Wireless implies it being separate from all other components by some marginal to distant location.
So are wireless phone chargers. How do you know the coils are not separated? The schematic indicates they are not on the same core, though I would not trust that.
 

MisterBill2

Joined Jan 23, 2018
18,986
You need to have better magnetic coupling into the external coil in order to get enough energy transfer.
At all times the voltage supplied to LED1 has the battery voltage added to it, while LED2 does not. In addition, the signal voltage for LED1 is greater. because the source resistance is less. The theory about induction produced voltages does not match the reality because the model is a bit off.
 

Thread Starter

abrahamkkk

Joined Apr 6, 2024
9
Take led1 of out the circuit. When it conducts, it limits the voltage the led2 sees.

It might still not light, but worth a try.

How ste the two coild coupled? The should be on the same core for maximum coupling.
LED2 did not light up even when LED1 was taken out of the circuit. Also, LED2 did not light up even when the two coils were put on at the center without any interval.
 

Thread Starter

abrahamkkk

Joined Apr 6, 2024
9
At all times the voltage supplied to LED1 has the battery voltage added to it, while LED2 does not. In addition, the signal voltage for LED1 is greater. because the source resistance is less. The theory about induction produced voltages does not match the reality because the model is a bit off.
I didn't understand it very well. As far as I know, the transistor is off, and the secondary coil in the left circuit has a voltage of about 20V, so LED1 can be lit. If so, shouldn't the coil of LED2 also have about 20V generated by coupling and be turned on?
 

MisterBill2

Joined Jan 23, 2018
18,986
It may also be that LED2 is connected with the wrong polarity. Besides all of that, itis also possible that your two coils and the core they are on simply is not able to store enough energy to light LED2 Without a magnetic material core the energy transfer will be provided by the magnetic field in air. Air is very difficult to magnetize, BTW.
Where did you get the information about those coils????
 

Thread Starter

abrahamkkk

Joined Apr 6, 2024
9
Thanks for agreeing with me.
It may also be that LED2 is connected with the wrong polarity. Besides all of that, itis also possible that your two coils and the core they are on simply is not able to store enough energy to light LED2 Without a magnetic material core the energy transfer will be provided by the magnetic field in air. Air is very difficult to magnetize, BTW.
Where did you get the information about those coils????
There are no specific information about those coils. When I eliminated LED1 like below figure, LED2 turned on... Then, isn't it possible to see that sufficient energy is transferred to the coil of LED2?
 
Last edited:

MrChips

Joined Oct 2, 2009
30,946
There is only so much energy generated by the Joule Thief. Maybe there is not sufficient energy to light both LEDs at the same time.
 

BobTPH

Joined Jun 5, 2013
9,149
Read my post #7 again. I suggested exactly that, and explained why I thought it might work.

You have to understand what happens when current is stopped to an inductor. Its voltage rises to whatever it takes for the current to continue and the energy to be removed. When led1 conducts in the original circuit, the voltage across the primary does not go high enough to light led2 before led1 conducts. With led1 out of the circuit, it has to rise higher, then led2 lights. Increasing the windings in the coil connected to led2 might reverse the situation, since led2 would light at a lower primary voltage.
 

Thread Starter

abrahamkkk

Joined Apr 6, 2024
9
Read my post #7 again. I suggested exactly that, and explained why I thought it might work.

You have to understand what happens when current is stopped to an inductor. Its voltage rises to whatever it takes for the current to continue and the energy to be removed. When led1 conducts in the original circuit, the voltage across the primary does not go high enough to light led2 before led1 conducts. With led1 out of the circuit, it has to rise higher, then led2 lights. Increasing the windings in the coil connected to led2 might reverse the situation, since led2 would light at a lower primary voltage.
Do you mean LED1 limit the secondary coil voltage in original circuit?
 
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