Author Options:

6 volt LED lantern joule thief Answered

I'm about to embark on a project to build a joule thief to power my new 6 volt LED lantern. I'm going to replace the lantern battery with the same volume of half dead AA batteries, which I have a bowl-full. My mice and cameras reject the AAs when they are only half done. The joule thief should finish them off.
My question is if I might be just as well off to wire my AA four battery packs in a series/parallel circuit. First start parallel, then series as the batteries run down. This would give me a high/low control for the light, too.
The joule thief will only draw the batteries down so far, and the LEDs have a low voltage threshold. Since the light is engineered for six volts, I'm just wondering which way to go.



8 years ago

A jewel thief as I believe they work are meant to use an inductive component
and trans form a low voltage from a single battery to a  higher voltage to
light an LED that the battery alone could not.  
Jewel thiefs come in many configurations.  This one is is more complex and runs a battery down to 0.7VDC.
I provide the circuit, the PDF of the IC and the pointer to the instructable.

Hope this is a learning experience 4U. . . . . . .   A


Answer 8 years ago

Thanks for the reply, iceng. I'm going to pick up a DTDP switch with a center off position to see if that can wire up my series/parallel circuit. I'll sketch it up to see. I'll take the lantern to Radio Shack to see how many AA four-packs I can fit in. I figure the batteries are already down to .7 volts already on average. Four in series in the four pack should make 2.8 volts. Two packs in series should make close to the six volts the lantern wants. If I can get eight packs in the lantern, I'm hoping the series/parallel trick will suck the batteries even lower than a joule thief.
I may see what a joule thief can do with the circuit after the series setting has drawn all it can. That would take another switch.
It will be interesting to see just how much juice can be sucked out of a bunch of AA batteries that otherwise would be tossed.


Answer 7 years ago

Making progress. I'm using two 8-packs of AAs, with a series/parallel switch I found only right here in Instructables! I just hooked it up to a standard joule thief, and it draws .10amps off the parallel setup @ 7&7.5 volts respectively from each pack.
The control LED lantern with a 6 volt lantern battery draws .08amps.
The control LED lantern with a joule thief and a 6 volt lantern battery draws .076 amps.


Answer 7 years ago

I wonder what purpose the 100 ohm resistor is for? It seems just a waste of power that would otherwise go to the LED. Also I wonder if the chip has a way to sense the current so the current through the LED could be constant. Obviously I haven't checked out the datasheet for this chip yet. I've checked other Maxim chips and found that they seldom have a DIP version, most are tiny SMD which makes it really difficult to experiment with. That's another reason why most experimenters stick to the Real JT, with a single transistor.


Answer 7 years ago

This is a much more efficient jewel thief able to start as low as 0.7V.
In fact you can run it off of two cells in series 3Vand run that down to
0.7V which means you can suck each cell down to 0.35VDC.

The MAX1675 is a constant voltage output device and a series resistor is
necessary unless the LED is designed to use ½ Amp.  Another reason for
the 100 ohm resistor is to make it easy for a scope current measurement.

IF you have a look at this ible where it says in step one,
That "Sorry, but this project requires advanced soldering skill to build !". 
Yes, there are many easy JT projects for beginners. 
This JT project however gives advanced users a chance to strut their stuff,
and besides the very detailed learning instructions the ible allows the user
to make a very tiny unit.