My DIY Joule Thief Hurricane Lamp Project: Lots of pics!

[PCC]

I wonder what circuit they use in the old Nite Ize 3-LED Mini-Mag drop-in? Mine will power up just fine on batteries that won't light up my datiLED made toroid Joule Thief. I won't even try using them in 2AA Mini-Mags anymore because they'll run down the AA alkaline cells so badly that it's a guaranteed leak waiting to happen. I have them in cut-down MMs.

 

[Darvis]

http://www.candlepowerforums.com/vb...boost-driver&p=3546854&viewfull=1#post3546854

That's just plain amazing!! I wish I was that good at this... I've gotten mine down to some pretty small tube sizes for some nice compact lights now and have found some great LED holders and such, never dreamed they could be that small, though.. I gotta see if I can replicate those.

 

[Justin Case]

A Joule Thief installed within an MES bulb base.

 

[tylernt]

Yeah, I like the ZXLD381 because it's uber-small and only requires one other component. Cheap too. However, a pair of helping hands is really indispensable.

For my SMD inductor, I used 587-2053-1-ND / LBR2518T220K (22uH). You could also use a 15uH with the ZXLD381, but you risk blowing or fading a 5mm emitter as peak current (120mA) exceeds the LED's rated maximum... for a high quality Cree or Nichia I suppose that's less of a concern than with cheap noname LEDs.

 

[eternity]

Okay gotta make myself one of these in case another hurricane swings by my place. Of course I don't know if I can trust my own handy work in an emergency. Guess I'll have to save up for another light, just in case.

 

[Justin Case]

I built a JT on perf board (not one of the above super miniature JTs) using the classic circuit. It can light a 5mm LED down to Vin=0.55V.

 

[cnjl3]

Does that mean that you check the voltage across the battery when you turn the JT circuit on? Or do you measure the voltage before you turn the JT circuit on?
I just made one of these little jewels and it made me smile when I powered up the 5mm LED. I used the website recommended above [FONT=&quot]http://www.kitsandparts.com/toroids.php[/FONT]
and bought 50 transitors and 25 ferrite coils dirt cheap so I guess I will be make a "few" if these JT circuits.

Thanks! Daryl for the info.

I built a JT on perf board (not one of the above super miniature JTs) using the classic circuit. It can light a 5mm LED down to Vin=0.55V.

 

[Justin Case]

Vin with the circuit running, i.e., under load.

 

[Darvis]

Tylernt, where do you source your parts? I found the ZXLD on mouser, but not the inductor... maybe I just got the part numbers wrong?

Ah.. nevermind, digikey!!

 

[tylernt]

I got my stuff from Digi-Key, but I'm sure Mouser sells several suitable inductors -- just look for one that can handle the peak mA you intend to push through the LED with a comfortable safety margin. For a 22uH inductor, for example, the ZXLD381 needs an inductor that can handle at least 80mA+. Once you find some inductors that can handle the juice, then just look for the one with the lowest resistance. Should work fine.

 

[Darvis]

Thanks!! I found the parts.... So, wow, I really think I'm going to give this a try... the parts are cheap!!! And your thread was great as well...

I may need to ask you some questions when I get the parts, though, as I am just learning this stuff and I'm not entirely sure I'll know what to solder to what. My perfection of the lamp has purely been cosmetic and I've made my basic circuit more compact, figured out a few things here and there, but have not yet deviated from the classic JT parts as of yet...

You have all been a great help with this, I need to get some newer pictures up of some recent builds, including my dual circuit, dual LED lamp with selector switch and both warm and neutral LEDS!! Woohooo!!

 

[Darvis]

Complete and utter success with my first ZXLD circuit... unreal!!! Man, it really reduces the footprint. I have to admit, I was not prepared for how small the components really were and probably made this first one bigger than it needed to be, but it works!!

Here it is next to a traditional JT circuit:

This may be a totally bad practice, but I was having trouble getting everything to stay in place to solder, even with the helping hands, to, er... help, so I simply used a drop of crazy glue to hold the parts in place and it worked great...


Now I just gotta get it into a host.

 

[tylernt]

Yeah I was a little surprised when I got my first ZXLD381 too, sneeze and that thing is gone!

 

[Justin Case]

I'm interested in how low the Vin can be and still start up the ZXLD381 and how low the Vin can be to keep the ZXLD381 running. I've gotten startup and good output from a AA alkaline with less than 0.9V open circuit, and 0.549V under load using the basic JT circuit.

 

[Darvis]

So I was able to get the new circuit integrated into a host....

From right to left: A 1.25" compression host with 2 JT circuits each driving one LED with a single pole, double throw switch with center off. This allows the use of one neutral LED (brighter) and one warm LED (low mode) depending on the needs. If you look close, you'll see the second LED towards the front, in front of the rear (lit) LED

Next to that is what was my standard build using a 1" compression fitting and an on/off toggle... this was about as small as I was getting it...

Enter the ZXLD (third from the right) and now I'm in a 1/2" compression fitting and have eliminated the switch all together... Small, clean, awesome!!!!!! (well, awesome to me anyway)

For size reference next to a 6P and an 18650:

I have gotten my taditional JT down to .58-60v before in a straight run, but found it needed about .90 (as you noted) to actually start the circuit. Not yet sure about the ZXLD, but I aim to find out.


Oh, and here's a reading lamp that only a mother can love:

 

[Justin Case]

Mine will start at ~0.5V from a bench power supply. The 0.9V referenced before is the OCV for a "spent" AA. I can run such a AA cell so that it sags to ~0.55V under load. Turn off the JT and immediately turn on the JT again. The circuit clearly starts back up since the LED lights up with a nice, bright, steady beam. Within that brief period of time, the AA cell certainly has recovered its OCV to no more than perhaps ~0.6V.

 

[Darvis]

Makes sense. My guess is that I've duplicated your results without knowing it, if that makes sense. Because I've not actually measured anything other than the voltage of the battery going in and then coming out, I've not seen the the OCV recovery part of it, etc.

I did experiment with different sized ferrite beads and windings to see if it would improve output or runtime (in other words, could I get down to .30v?) and found no real difference. There seems to be no gain from using more winds, or larger diameter wire- a good wind is a good wind it would seem... A bad, or crossed winding however, makes for some truly weak (or no) output!!! I learned that lesson the hard way. It has to be done right, but over doing it gains nothing...

I can say that with my traditional JT circuit, the light does start to dim around .70v (this is based on me pulling NiMH batts for recharging) It's my indicator of when they need to be dropped into the old charger. I've run alkalines all the way to almost off and towards the very end, they're just barely glowing. But honestly, until that ~.65-.70 mark, there is really no perceptable change in brightness, so the circuit does provide some degree of regulation as well.

This has become quite the cool learning project!!!

 

[Justin Case]

Do you know anything about the ferrite you have, e.g., AL value? How many turns are you using? It does seem to me that the basic JT circuit is fairly insensitive to coil inductance, as long as you are "in the range". I wound a powdered iron coil (Micrometals T44-52) with calculated inductance of only 2.8 uH and that circuit was very squirrely. It would work "bare" -- the parts all soldered directly to one another. But if I mounted the parts neatly onto perf board, it wouldn't turn on. Just a little change in how tightly the coil was wound seemed to affect the JT. When I wound more turns on the powdered iron core to get about 6 uH, the JT became reliable. I also have some ferrite cores (Epcos B64290L0044X038 -- T38 material) with very high AL (5100) and only 4 turns give a calculated inductance of about 80 uH.

Depending on what ferrite formulation you have, you might try something extreme like just one turn to get the min inductance to see if your JT will still work.

A Si transistor is not going to work well (i.e., at all) with only 0.3V. You'd have to go to germanium.

 

[Darvis]

I do, this is straight off of the website I got them from and I'm getting 9 turns on mine using standard twisted pair phone wire (22ga?):

OD(A) = 0.5 in / 12.7 mm +/- 0.25 mm
ID(B) = 0.281 in / 7.15 mm +/- 0.20 mm
Ht(C) = 0.188 in / 4.9 mm +/- 0.25 mm AL=440 [SIZE=-1]+/- 20 %[/SIZE] uH=(AL*Turns2)/1000
Actual measured AL using 10 turns #28 wireTemperature Stability (ppm /°C) = 12500Color Code = shiny blackApplication Freq Range
Wideband Transformers 5 - 400 MHz
Power Transformers 0.5 - 30 MHz
RFI Suppression 5 - 500 MHz

Now, I admit, I have NO idea what any of this means, I literally bought them based on their size. The website is actually pretty cool, it's called "kits and parts" and this bead is part number FT50-43

I will try what you suggested above and report back on what I get. I have the circuit rigged on a breadboard, so I can play with it as needed.

 

[Justin Case]

FT50-43 means a ferrite core, 0.50" outside diameter, material formulation 43. #43 looks like it is spec'ed for EMI/RF suppression. For the JT application, you probably care most about the AL value, which relates the number of turns to the inductance. For 9 turns, the inductance is 440*9^2/1000 ~36uH (+/-20%). To explore the low end, I might try 2, 3, and 4 turns to see if the JT still works.