I received a Google Alert for a Youtube video called “Joule Theif (sic) meets ABHA Coil!!” and I have some comments that I’d like to share, but I’m not going to put up with Youtube’s extremely lame text limitation of 512 characters.
The two batteries in series show 2.5 volts on one DMM, and I’m guessing that the other DMM is showing current, but after watching it a couple times, I didn’t pick up anything about what that current was. It may have been the battery current. If so, then 2.5V times 0.025 amps is 0.0625 milliwatts. That’s a lot less than what a typical Joule Thief draws. A typical JT draws 80 milliamps at 1.5V which is 120 milliwatts, about double what his is drawing.
I have to thank him for doing this interesting video. But if he reads this, I hope I don’t disappoint, because life is tough when you’re a JT, and it’s difficult to do the JT job efficiently. He keeps on saying that the JT is amazing, but he may not like reading the truth. A typical JT has an efficiency of 40 to 60 percent, or about half the input is lost and doesn’t get to the LED. He doesn’t give the output current but I’m sure his JT circuit is not any more efficient than a typical JT.
He said that all 24 LEDs are in series, at 3.4 volts per LED. That’s a total of 81.6 volts. That’s awfully high voltage; the TIP31A is rated at a maximum collector voltage of only 60 volts (by the way, the G after the A stands for lead free or ROHS). He should be using the TIP31C, which can handle 100 volts max. It would be better to break the 24 LEDs into two parallel strings of 12 LEDs each for a maximum voltage of about 31 volts.
It’s much easier for a JT to convert a voltage from 2.5V to 3.4V than is is to convert from 2.5V to 81V. The higher the conversion ratio, the harder it is for the JT. That’s why I said that I’m sure his JT is no better than 40 to 60 percent efficient. My guesstimate is that it is even lower than this. Another very important point is connecting all the LEDs in series is not a good idea. If one fails open, then the whole string will go dark. It is much more reliable to connect the LEDs in series – parallel so that if one fails open, only a fraction of the LEDs will be affected. If the lamp is to be used in an environment (such as a tropical climate) where the weather is wet, there is a high probability that there will be corrosion in anything electrical. So choose a design where a single point of failure such as a single LED in a series string will not totally disable the light.
ABHA Coil
Okay, now for the mystery ABHA coil. I’ve never run into this term, even though I have a lot of experience with RF and inductors. It’s probably an acronym someone came up with to describe his method of winding the coil. I’ll have to Google it and see what turns up. I can say that after seeing how broad the field was, that this is not good for making an efficient coil. When we wind a toroid, the donut shape contains the magnetic field so that very little gets outside, and this makes for a good high Q, low loss coil. His ABHA coil obviously doesn’t exhibit this quality. Update: I Googled it and watched a Youtube movie about the ABHA coil. Looks like it’s from the same Youtube account. I heard something, but it didn’t sound like any valid scientific explanation. He gave no valid measurements. He compared two currents, but the current is only half of the power, the other half is the voltage. When you measure the power output and the power input and then divide the power output by the power input, you will get a fraction that when multiplied by 100 gives the efficiency in percent. This movie had none of that.
Back to the original movie. He talks about packaging the circuit up with a solar cell and selling it to third world countries where they have no electricity. With a coil that big, it’s going to be really difficult to package it into a reasonable sized enclosure, and with an external field that is that strong, the magnetic field may be absorbed by the case or other parts if they are metal. I also must mention that at least one other entrepreneur has already created a similar piece of equipment and is trying to introduce it to the countries without electricity (more on this in the note below).
I’ve given just a few of the many ways to improve the conversion efficiency of a conventional JT. My ‘Supercharged Joule Thief’ circuit increases the efficiency to 70 percent or more. It’s a simple circuit and I’m dismayed that no one seems to recognize its merits. Could it be that once they have built a conventional JT, they are so dazzled and ‘blinded by science’ they believe it’s the be-all and end-all of lighting a LED from a single 1.5V cell? Believe me, if they try the ‘Supercharged Joule Thief’ circuit they will never go back to the conventional JT again.
I googled ABHA coil and came up with more hits. This one is just stunning. I got more than halfway through this balderdash and gave up. He takes 36 paragraphs to say nothing of any value.
Note: the justification for introducing a simple rechargeable light is to allow children in school to study at night after sunset. At the present time, they have to use a kerosene lamp, and the fuel is expensive and pollutes the air in the house. The rechargeable electric lamp would eliminate the pollution.