Joule Thief using Starship coil, lighting 36 LEDs from one AA
At Sunrise:Off-Grid I ended up mentioning this fascinating little circuit to many people, but hadn’t taken an example with me. The Joule Thief allows a single 1.5 volt battery to power one or more 3volt LEDs for many hours. The light won’t stop until the battery drops to approx 0.4 volts.
The construction is very simple indeed, and quite fun – you have to wind a little torroid with wire and a ferrite ring. You need one transistor, one resistor, an LED and your battery. You can also use a Rodin Starship coil in place of the torroid, allowing the whole thing to use wire with no ferrite ring. The image here shows a Joule Thief made this way. The picture shows a single AA (reading about 1 volt) lighting 36x 3 volt LEDs. I would have tried more but I ran out of LEDs! Interestingly, the whole lot were only drawing about 20 milliamps at 1 volt – less than the normal load of a single 3 volt LED!
Below is a diagram of the build of the Joule Thief. You will need the following parts:
- 3volt white LED
- 1kohm resistor
- Transistor 2n3904 or 2n2222
- Small ferrite ring
- 1.5v AA or AAA battery
- Some insulated wire
It is easy enough for a child to make and intriguing enough to keep an adult entertained and bewildered for hours…
good job man….
I want ask how many turn if I built with rodin starship coil
Thanks for your comment satria – I have used starship coils with only six turns, and normally only use 3 to 5 LEDs, for wire sculptures. The one in the picture has a lot more turns (18? I don’t remember) but I made it just to make a fat small starship, not specifically for the JT. I don’t know how the number of turns may effect the number of LEDs that can be lit. I thought I’d experiment one day but I haven’t yet…!
Hello TonyRambler. I am using the torrid solution and I have 10 LEDs in parallel, but cannot get them to light unless I plugin a 3V batt. (and it draws 26mA). Even 1 LED doesn’t light and my AA batt. measures 1.3V and I measure .6mA. Can you give me a tip?
Hi Perchman, thanks for reading. Well, I’m not sure, but I have seen one not work because the torroid winding was messy and crossing over itself. Once that was sorted it worked fine. If it doesn’t work with a single AA then it’s not working at all – don’t bother trying with 3 volts as that would light the LED conventionally anyway. I can only suggest you double check all your wiring (especially the transistor pins and LED polarity are correct), and make your winding neat on the torroid. It’s a reliable and simple circuit so if I’ve ever had one not work straight away it’s been a simple building error. Hope that helps.
Hello again TonyRambler and thanks. I double checked everything and now it works. It looks like I had a connection issue. I now have all 10 LEDs running off of a AA battery (measuring 1.12V and drawing 21mA). I have seen setups where people have hooked the LEDs in series off of a Rodin coil, do you have any experience there?
That’s great news. I’ve never made a proper Rodin coil – it’s a much more time consuming job than a starship coil. Maybe one day…
I have another question. Are you using a dual circuit Starship coil? and when interleaving the two circuits, is there anything special that has to be done? (I’ve tried a starship with twisted pair and it didn’t work with the Joule thief)
The starship was wound with 2 wires simultaneously, then the end of one linked to the beginning of the other, just as with the torroid, so the two runs end up used in opposite directions. Haven’t tried a twisted pair but I don’t see why it shouldn’t work.