Joul thief how to?

I've been reading some ibles about joul thief making, and most of them teach how to power an LED with a 1.5v AA battery.  That is great, if you want to power an LED with a 1.5v AA battery :)
But what if I want to keep using old, weak AA batteries, as 1.5v batteries?  How do I make a joul thief that takes whatever the battery can give it, and outputs it as 1.5v? 
I know the kind of transistor, ferrite core, number of windings and wire gauge all affect output, so how do I know what to use?


sort by: active | newest | oldest
You don't use a Joule thief for that kind of application.
Morgantao (author)  steveastrouk4 years ago
Why not?
Are you referring to the fact that it turns the DC to AC? I can always add a diode bridge to turn it back to DC.
No, because it has no regulation of the output voltage. Adding a diode bridge immediately means you need another 1..2V of extra O/P volts to drive the diodes.

There are MUCH better power supply circuits, with low start voltages.
Morgantao (author)  steveastrouk4 years ago
Ah. Let me rephrase my question then:
I have a huge bunch of used AA batteries that are too week for most applications. What is the circuit I need to make them run at 1.5v again?
I would very much appreciate as much info as humanly possible (diagrams, photos, videos, how to's and ibles will be most welcome), as I'm pretty much a dumb-dumb when it comes to electronics.
Thanks again!
When they're too weak, you won't get any more life with any loads other than a nice small one like an LED, there ain't no such thing as a free lunch: you'll find that the dry cell rechargers do something for you more effectively than trying to put a specaial PSU together.
Morgantao (author)  steveastrouk4 years ago
That explains why 99% of Joule thief (notice the spelling is correct, thanks to kelseymh) are for powering LEDs.
kelseymh4 years ago
You don't. The total energy available from the battery is the product of voltage, current, and time. You can't get more energy out than is available.

If you want higher voltage, than you need to draw very little current, which is what a joule thief does (and notice the spelling, it will help you find more information).

If you want current, then you're not going to get voltage.

If you want the battery to work they way it did when you bought it, then you need to recharge it. If you're dumb-dumb about electronics, as you say, then throw money at the problem instead of trying to solve something you don't understand, or don't want to understand.
Morgantao (author)  kelseymh4 years ago
Oh, but I do want to understand :-)
My problem is I don't know where to start... Every source I've found online has either been too simple, or too complex. Either they teach you the very basics, or the jump into more complex circuits. Not much in between.
I have basic knowledge of what each component does, but the interaction between electric components eludes me. I can read basic diagrams, but on more complex ones I get lost pretty quickly.
The thing that is most mysterious to me is how one goes to choose the right components (the right values that is). If I want to build something from scratch, I don't know what the final load will be, so I don't know what values I need for my components, so I can't start building the circuit.
Looking at component datasheets may give me a general idea of what a component is used for, but is too technical for me to understand how to use it and where.
My whole life I've been an autodidact, but electronics seems to be beyond me.
A lot of old books for radio amateurs would get you on the right track. Electronics is an engineering discipline that takes many years to master, don't be surprised you can't absorb it readily. To know what is really going on takes very advanced maths.