Hello,
I have seen numerous Youtube videos on super high voltage Joule Thief projects. They are using small one inch ferrite toroids and from single 1.5 volt AA battery power a 3-5 watt 110-220 volt cree LED brightly consuming merely 200 mA of current from the battery! The following link will help you understand it better:
https://www.instructables.com/id/Make-a-SUPER-Joule-Thief-Light/
However, all such similar links do not specify the specific inductance of the Toroid being used or the Permeability. All they suggest is to use high permeability ferrite toroid! The authors also do not provide the answer.
Now, I want to replicate such a project at low cost. For that purpose, I have procured the following Toroids from Element14 (India):
As, per the above mentioned link with the "Instructible", which suggests there should be 1 volt per turn induced in the secondary of the JT, I am wondering what should be the correct toroid selected for this purpose? The toroids I have already purchased do not give me such result.
- Manufacturer: FAIR-RITE; Ferrite Toroid: 25.4mm x 15.5mm x 12.7mm; Core Material Grade: 77; AL (nH) : 2700 ±25% (I have procured)
- Manufacturer: FERROXCUBE; TN25x15x10; Core Material: 3E25; AL: 5.62µH (I have procured)
- Manufacturer: EPCOS; Toroid; 25.3 × 14.8 × 10.0; Core Material Grade: T37; AL (nH): 6970 ±25% (yet to procure based on your advice)
Therefore, I will be more than happy if you can guide me accordingly on this.
Thank you,
With best regards,
Raj Mukherji
I cannot help but think that this little project is on a par with much of the other madness which is published on the "Instructables" website.
Using a 1.5v battery to generate 130 volts, to light an LED. Is that sensible?
If you want to light an LED from a 1.5v battery you only need 4 or 5 volts, surely?
JimB
I agree with JimB's comments. There will be two conversions. first from 1.5 volts to about 200 volts. then another conversion within the bulb from about 200 volts to about 11 volts (Assuming 3 LEDs driven in series) Both conversions will involve losses. It would be better and simpler to just step up the voltage to that required to drive the LEDs You would not need to wind a large number of turns for a secondary winding as it would not be required. The LED would be connected directly between the collector and the - Ve rail. There are many slight variations of the design if you search for "joule thief" I suspect the cores removed from a CFL lamp would work.
Les.
Your example seems strange, with the LED, because we never get anything for nothing. We often look at the 100 percent efficiency numbers to be able to quickly see what might be going on, so doing that, we see that if we have 200ma at 1.5v going in and we have 150v on the output then the MAX current available to the output device is 2ma because the ratio of input voltage to output voltage is 100 and so the input current can only produce one one-hundredth (1/100) of the input current, which in this case is 2ma. THAT however is at 100 percent efficiency, so most likely we would see 1.5ma if we were lucky. That may or may not be enough to drive whatever it is we have on the output like a higher voltage LED.
The idea behind the Joule Thief is that when the core starts to saturate the transistor is forced out of saturation...
When the core saturates the collector current rises but what causes the transistor to turn off is the decrease in base drive because the core has saturated and there is no transformer action and thus no positive feedback.when the core starts to saturate the transistor is forced out of saturation, and that means the collector voltage rises suddenly and that turns the device off.
The core saturation happens when the drive current forces the core up high on the BH curve where the inductance falls sharply and so the current rises sharply too. The time it takes to get there is based on the inductor, but the value of the inductance has a lot to do with this because of v=L*di/dt, or rearranged, di=v*dt/L. In this last equation you see L in teh denominator, so di grows less with time as L is made larger. This helps set the oscillation frequency, and it cant be too high or the transistor doesnt have enough time to switch in and out of it's saturated base region mode. di cant be allowed to go too high or the core saturates too fast. Large value inductors will saturate faster because they have a lot of turns, but if you buy an inductor then they tell you the saturation level and current handling ability of the device. Knowing the saturation level and the inductance you can calculate the time to core saturation, and that cant be too fast.
Probably 50kHz would be a good starting point, but even 20kHz would not be bad.
You'll have to buy an inductor that has an open frame so you can add the secondary winding.
To get a rough idea how all this works you can simulate it. Choose a transistor, choose an inductor value, see what happens.
No marks for MrAl
The question of efficiency has already been done to death
The idea behind the Joule Thief is that it accepts a low voltage, typically from a single solar cell or discharged primary cell, and converts it into a usable voltage. It uses a relaxation oscillator to do this. Relaxation oscillators of all types are used for many applications.
When the core saturates the collector current rises but what causes the transistor to turn off is the decrease in base drive because the core has saturated and there is no transformer action and thus no positive feedback.
No. The higher the inductance the less current will flow and the slower the core will take to saturate. This is because the transformer has a voltage drive, not a current drive.
These inverters typically oscillate at 10Khz. Any higher and the losses rise exponentially.
The OP already has a core which can be easily wound
I doubt the OP would have the skills to simulate the design- inappropriate simulations have already caused enough havoc recently on ETO.
spec
Hi there,
What ??????
Yeah this is a funny one. I was describing the 'other' Joule Thief, probably because i've used that one much more often. That's the two transistor version that does not require a transformer just a single inductor. Much simpler to build because we only need an inductor. Maybe i should post that schematic, if the OP is interested.
I jumped right into that one for some reason probably because i used it much more often. I have used the transformer version too though but yes that is somewhat similar to a Royer. I used it to build an islolated low current power supply (transformer was good for that).
I'll put a note in my original post:
"[The following notes are about the two transistor version with single inductor not the transformer version]"
But i should at least get an "E" for "effort"
Or a "B" for "too much Beer".
Hi All,
Many thanks for your time in replying back to my query.
I have noted your comments and advice and would request MrAl to furnish the 2 transistor converter circuit for our reference here.
Let me also inform you that I have already made a JT using 3E25 core mentioned above with 400T of 30 SWG as Secondary, 15T and 60T with 26SWG and it is able to drive 3W 220V LED bulb. However, I am not very happy with the brightness of it. There is yet another JT circuit which I have made with the 77 toroid with 300+T using 30SWG, 4T using 22SWG and 14T using 24SWG. This also lits up the same LED bulb. The brightness of the light with both the two circuits seems to be same. To me, it can be useful as a night lamp but I want to increase the intensity more. I have tried using 2n2222, TIP41C, BD139...all give me fairly the same result!
The first circuit using 3E25 core gives me around 30 volt pulsed DC output without any load from a fuuly charged 1.5 volt AA 2100 mAH NiMH battery where as the second circuit gives around 50 volt output. I am not able to increase the voltage beyond this. I know that the LED bulb brightness will increase when the secondary output reaches 110 volt. I will try the above circuit suggested by SPEC and revert with my results. Please find the screenshot of the circuit for "Super JT" attached here.
However, any suggestion as how I can achieve 110 volt output from the secondary coil will be appreciated.
Thanks and regards,
Raj
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