"Joule Thief" Experiment, Need Help (For Unlimited Power Flashlight) - Page 1
Forum section: electronics / projects

author: Undweeber
author_rank: Regular Contributor
timestamp: March 11, 2018, 06:43:00 am
content: Hello guys.Spring break came and since I need to unwind from biology I decided to build the ultimate joule thief circuit and thus an "unlimited power" flashlightI just need some pointers.Goal:-shaker torch (hollow tube with a strong magnet inside, and copper wrapped around creating alternating current, going through a rectifier into the supercapacitor-charged supercapacitor would feed the power into the "joule thief" circuit (trademark ofbigclivedotcom)-the circuit would power a 10mm White LED @3.4V and 0.2mA (if I perfect the joule thief circuit and become a joule wizard i may play with more powerful LED's)Rough plan:-I will be using deadish batteries to test the joule thief circuit and once that is good to go I will build the "alternating shaker pipe"-I currently do not have a supercapacitor, and I am looking into some options on ebay, there is a2.7V 500Fcapacitor on eBay for very cheap, but unless someone here can confirm its not chinese garbage I will be gettingMaxwell BCAP0350 - 2.7V 350For maybe something even cheaper with less Farads, the capacity is not of importance at this stage.Tools on hand:-I do not have an oscilloscope for troubleshooting, but I should imagine if I end up really needing it, my physics department at school might have one, or a hundred.-I have scavenged 3 different transistors-I have a nice rectifier i scavenged from some power supply (though not needed at this time)-I only have 5mm LED's on my hands at this time ordering 10mm soonTransistor 1:http://pdf1.alldatasheet.com/datasheet-pdf/view/410739/JSMC/3DD4128PL-O-Z-N-C.htmlTransistor 2:https://www.infineon.com/dgdl/Infineon-SPD_U04N60C3-DS-v02_06-en.pdf?fileId=db3a30433f12d084013f1a0318e31921Transistor 3:http://www.mouser.com/ds/2/149/FQP33N10-109249.pdfMy Question:What transistor do I pick? Which one would be more efficient for this circuit? What kind of coil would go with it?So instead of guessing and experimenting, is there a way to calculate the number of turns needed for most optimal efficiency? do i have to match the # of wingdings to the spec of the transistor?

author: Don Hills
author_rank: Regular Contributor
timestamp: March 11, 2018, 07:30:24 am
content: Consider using a handcranked generator. But instead of the usual geared DC motor, use a small stepper motor salvaged from an old scanner or printer etc. For example:http://www.siliconchip.com.au/Issue/2004/February/Our+Fantastic+Human-Powered+LED+Torches

author: Undweeber
author_rank: Regular Contributor
timestamp: March 11, 2018, 08:01:00 am
content: i have several hand crank type generators with DC though, problem is to charge lithium it would take an insane amount of time, ive looked into some options on amazon, there is even something called "pocket socket" that thing puts out 120V, but you need serious muscle to to charge your phone with it for example.What I am after is less of how to get power, but more of how to store and extract it, so making a torch along with something that can suck out every bit of power be it a supercap or an old battery would be what i am after, I am open to options and suggestions

author: soubitos
author_rank: Frequent Contributor
timestamp: March 11, 2018, 09:33:04 am
content: I think the path to go is something like thishttp://www.ti.com/product/BQ25504

author: abyrvalg
author_rank: Frequent Contributor
timestamp: March 11, 2018, 10:01:59 am
content: Shaker and crank both have their disadvantages (two-handed operation of crank and "usage pause" while shaking). There is a different mechanical design popular in exUSSR free of these limitations:

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 11, 2018, 09:22:16 pm
content: Neither of those transistors is very suitable. What about old fashioned 2N3904 and the like?This uses a low-Vce(sat) BJT for 67% efficiency,Similar parts might be salvaged from an LCD monitor backlight (CCFL) power supply.You won't get very far without a regulator, though. These circuits work best with a stable alkaline or NiMH cell. With a supercap, something has to make up for the voltage varying with charge.Tim

author: Undweeber
author_rank: Regular Contributor
timestamp: March 12, 2018, 02:31:15 am
content: Progress:So I have built my first Joule thief circuit, testing it with 1V and 0.7V batteries.The transistor from the CFL seems to work well (4128PL), but I do have 2 of those small transistors that i can remove from some circuit-boards, I know that the beefier the coil - theI made a is ringing i can hear it, but when i put a strong magnet against it, the ringing stops, and the LED lights up even brighterAn interesting thing I discovered, when I touched other LED terminal while holding the (-) charge coming from the coil, the current seemed to travel through my body and was able to light up the LED!!@T3sl4co1l surprisingly the circuit is very verstile, it powered up my 5mm LED, and also powered up (dimly) a 12V LED thing from china, plus i saw tutorials on youtube and supercaps have been used successfully, but you are right, problem is that efficiency varies depending on the draw or input, im not quite sure. I am using an unidentified resistor as i couldnt find a single resistor (i used to have a baggy of them from radioshack) so the rough idea works, but i would love to have formulas so i could see what is happening, when i put a strong neo magnet against my coil, the light brightens up, can you confirm this with your build? any explanations about this?@abyrvalg the pause in operation is not a big deal, the beauty of super-capacitors is that they charge quickly, and a tiny super-capacitor is capable of 20 minutes of light, a large supercap could horse a lot longer, I agree that crank is nice, but there isnt a crank on the market of that design anymore, its all crappy plastic they dont even bother using Teflon or anything, maybe i will go for a crank of some sort, i will consider it, but for now i want to concentrate on getting formulas to see how the joule thief works and how to build the most possibly efficient oneAttached picture: 1.0V battery powering 12V LED as if it was a dead 9V battery. +magnet on the coil (makes the light brighter somehow)

author: BravoV
author_rank: Super Contributor
timestamp: March 12, 2018, 02:47:42 am
content: Though its fun draining the battery till the last drop of it's energy, becareful as Alkaline will leak like hell when drained down to very low volt.Also don't use rechargeable like NiMh or worst LiIon, the circuit will kill them permanently as it will suck down beyond the safe low threshold voltage allowed.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 12, 2018, 03:03:15 am
content: Quote from: BravoV on March 12, 2018, 02:47:42 amYou're SUPPOSED TO fully empty NiMH/NiCD batteries. It's when you DON'T deplete them and then charge them that starts weakening them over time. But they'll regain they're full charge (or at least most of it) when fully cycled.Lithium batteries will not die immediately if you drain them, they just get weaker if you keep doing it (or leave them shorted). It's when you have them series and try to drain them all then it could cause a cell to reverse which does fry it.EDIT: You can damage NiMh/NiCd batteries by leaving them on a purely resistive load, but there are semiconductors here so it will cut off below the junction voltage. So it's perfectly safe to use them here.

author: BravoV
author_rank: Super Contributor
timestamp: March 12, 2018, 03:17:33 am
content: Quote from: Cyberdragon on March 12, 2018, 03:03:15 amSince you sound so knowledgeable, what level of "empty" that Ni based cell needs to drained to ? Zero volt ?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 12, 2018, 03:45:53 am
content: Quote from: BravoV on March 12, 2018, 02:47:42 amI've scraped away the remains of many an alkaline that was discharged only a little over its lifetime.The problem seems to be sitting after modest discharge. Fresh cells are basically good until their date (which is a pretty amazing accomplishment in itself). Discharged cells have little left to leak (that's the point), though they may still do so from leftover zinc content that wasn't connected to the terminals.But really, there are experts on these matters, and it seems neither of us are one.QuoteNiMH has no "minimum safe voltage", though they last longer when not discharged.Common high leakage NiMH typically comes discharged off the shelf, because it's so damned leaky it's gone in a month's time anyway. They must be used quickly for the same reason.Low leakage NiMH come charged, and store a charge very well. They will last for years when treated well.Simple Google for NiMH:https://photo.stackexchange.com/questions/27836/is-it-necessary-to-fully-drain-ni-mh-batteries-before-recharging-themLithium ion does become unsafe when discharged below 3V or so.Quote from: Cyberdragon on March 12, 2018, 03:03:15 amCheck the above link.QuoteLithium can grow dendrites or some BS like that, becoming unsafe after undervolting. They may recover, they may be shorter life, they may go up in smoke...Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 12, 2018, 03:53:57 am
content: Quote from: Undweeber on March 12, 2018, 02:31:15 amLEDs are visible with mere nanoamperes, if your vision is dark adapted.It's not exactly useful light output though.QuoteWell, so what? Put some numbers to it. You can light an LEDvisiblyfrom static electricity, but that doesn't mean it's useful.Get some kind of meter, at least a VOM or DMM first, by the looks of it. Start putting numbers to things. What value resistor? How much voltage? How much current? How much brightness? (Photometer tip: use an LED as a solar cell, by measuring its short-circuit current. Calibrate against indoor lighting sources and sunlight, to get a feel for how many microamperes match with so-and-so brightness!)It's very easy to get a JT circuit that lights an LED, but the traditional circuit also runs at about 20% efficiency. You're better off taping three or four flat cells together and wiring them to the LED straightaway. It'll last longer!It takes a bit of design to make one with high efficiency (which is maybe >50% at this voltage). Not hard, but you have to follow a procedure, or build the circuit exactly as given (which, I don't think any of the online instructions do anything other than the basic crap version, so beware).QuoteNo freaking clue.Measure, measure, measure!I can tell something about an inductor just by looking at it, in some detail; but a blurry photograph in a poorly lit scene, it might as well be another UFO. Know what I mean?Tim

author: alsetalokin4017
author_rank: Super Contributor
timestamp: March 12, 2018, 04:01:10 am
content: Here is a comparison of several different transistors in the "standard" JT circuit, comparing voltages needed to start the oscillation and the voltages at which oscillation stops.

author: IanB
author_rank: Super Contributor
timestamp: March 12, 2018, 04:08:54 am
content: Quote from: BravoV on March 12, 2018, 03:17:33 amI believe that if you look up some NASA technical documentation on the subject, they recommended carefully and slowly draining NiCd cells down to zero volts and then placing them in long term storage with a shorting bar across their terminals. So yes, zero volts. The intuitive reason being that if you remove all the stored energy from the cell, then there is no energy left to drive any kind of degradation process over time. The cell effectively becomes chemically and physically inert.I do not know if this applies equally to NiMH cells, but I have observed no harm in draining single Eneloop cells down to zero volts and then recharging them later. So as long as you don't reverse the polarity I do not think there is much harm in draining NiMH cells down to very low voltages.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: March 12, 2018, 04:09:40 am
content: And here's my "favorite" JT using a 10F supercap:And just for fun, a "bonus" mini-JT on a rudimentary PCB:And in case you were wondering... here's a HV JT powering 6 ea. NE-2s in series, from a single AAA battery, using a 2n3055.

author: BravoV
author_rank: Super Contributor
timestamp: March 12, 2018, 04:42:19 am
content: Quote from: IanB on March 12, 2018, 04:08:54 amI'm not claiming an expert, but I did deep discharge test on NiMh cell in the past, too bad I didn't take note, particularly an Eneloop by using vintage Germanium transistor as it has lower junction voltage at these popular "Joule Thief" circuit does, and my finding was the Eneloop deteriorated really fast. Actually I sacrificed two cells for repeatability to confirm my finding.Also this test looks like to confirm my finding too for Eneloop ->http://aacycler.com/post/deep-discharging-nimh-lsd-cells/, and take note as its only discharged down to 0.9 Volt, not down to low say like 0.6V as Silicon junction or near zero volt.Edit : Just remembered you use Eneloop a lot too from previous posts if I'm not mistaken, suggesting to bookmark this site, it has nice infos imo.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 12, 2018, 04:54:28 am
content: .9V for a 1.2v cell? That's nowhere near deep disharged!They used an LED flashlight, no wonder they couldn't drain them!Plus, how were you charging these cells you fried? How long did you leave them on the charger?

author: BravoV
author_rank: Super Contributor
timestamp: March 12, 2018, 05:06:10 am
content: Quote from: Cyberdragon on March 12, 2018, 04:54:28 amSon, watch & read the saga of Batterroo will ya ?

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 12, 2018, 05:51:10 am
content: Quote from: BravoV on March 12, 2018, 05:06:10 amIrrelivant, that's usable power remaining.You guys are confusing current capacity with remaining voltage.You have to get rid of most of the voltage on NiMh and NiCd cells (or at least for NiCd), regardless of whether most of the current is gone. This is why NiCd batteries are stored shorted and why you guys keep killing your batteries.

author: Undweeber
author_rank: Regular Contributor
timestamp: March 12, 2018, 06:06:41 am
content: Quote from: BravoV on March 12, 2018, 02:47:42 amOMG thanks for reminding me about the alkalines leaking i totally forgot about it! What if I drain those non-rechargeable energizer lithiums? are those safe to drain?My long term goal is to use this circuit with a super-capacitor, I do not plan on doing this with nearly dead batteries, unless under supervision etc.

author: Undweeber
author_rank: Regular Contributor
timestamp: March 12, 2018, 07:02:16 am
content: @T3sl4co1l I am trying to put numbers to it, but I have no idea what to measure, I have a crappy analog multi-meter old thing made by Philips or something, the only thing I can comprehend on the display that shows everything at once is the volts, no idea what amperes say, this is why I was asking for mathematical formulas so i could design what i want without relying too much on measuring. The circuit i just built was more of a proof of concept for myself to see what ill be dealing with. The picture was just to show that I built it and it works, not much more to it. I started with a 1V alkaline battery 3 hours ago and it is still dimly lighting up a 12V LED bulb, only few LEDs are still on within the bulb, not useful light, but this thing is sucking the battery dry!@blueskull I do not plan on using batteries at all, I people have sort of went off topic, but my goal is to use this circuit with a supercapacitor, I just orderedBCAP0350 E270 T11it's Maxwell 350F 2.7V so this will be my energy storage. The reason there is a battery in the picture I posted is because I am using deadish batteries to see if the circuit works, and it does.@alsetalokin4017 if you take the most "capable" transistor and explore the limits of the coil, does the result improve? Secondly, you have the starting and ending voltages, isn't it possible to predict such voltages based on the calculation formulas and datasheets for those transistors? I love experimenting and tinkering, but having solid data and equations would make everything so much easier! This is a huge physics problem which needs to tackle every single variable of this circuit, but once its done, we could have a single equation and we could each create a perfect joule thief circuit to our needs.@alsetalokin4017 that is awesome i want details on that JT circuit that's powering those neon bulbs!!! please explain how you are using that coil, ive seen those coils but they usually only have 2 terminals and you need to have 3, i have a few of those lying around, and i actually made another fat inductor using a large ferrite and thicker wire, what is that huge transistor with the heat-sink? By the way when i feed 3 or more volts into my circuit my transistor is getting hot and the light is dimming, seems the crappier the battery the brighter is the light, but it has a "range" where the LED is the brightest, but if you go too low or too high the LED will not shine as brightly, i don't understand why this is and how to circumvent this, or is this the flaw of the circuit or what.Guys I love the enthusiasm and I am actually learning a lot about Nickel batteries lol, but please help me with my joule thief.These are the updates so far:~My joule thief I made works, I started with a 1V alkaline powering a 12V LED bulb(dimly, maybe like a candle), it started dying 3 hours later only few LEDs were on so i switched to a single blue 5mm LED and back shining. The battery has dropped to0.8Vand the joule thief is still draining it. The point is, it sort of works, but now I need to start building a second one, but this time I would prefer to use some formulas so that I don't do it blindly or trial and error, lets solve this once and for all using actual data, @alsetalokin4017 has posted some data on transistors, I think it should be possible to derive the numbers using datasheets and be able to predict most optimal coil designs.-I have just ordered Maxwell 350F 2.7V supercap, this will be my work horse, so I think the further design of the circuit should be built around this supercap-The top voltage the circuit should handle is 2.7V and the minimum, well, it should be able to go down to at least 0.5V. I have just checked and my joule thief can handle 6V (i haven't tested above that)-Transistor I am using is "Transistor 1" from the head post.-Ferrite core inductor + piece of magnet can be seen in the attachmentRight now, I would really like to have a big fat equation, with the power source being a supercap, and transistor being transistor, I feel like the only variable is the coil itself, but my major is biology so .. my feelings are not facts

author: soubitos
author_rank: Frequent Contributor
timestamp: March 12, 2018, 08:03:30 pm
content: Quote from: BravoV on March 12, 2018, 02:47:42 amNot if they have over-discharge protection...This is what my SCLD4056 does... i designed it with solar in mind, it charges a lithium battery during the day and during the night it uses a slightly modified single inductor joule thief to light a 12V led strip (i currently use a single 1m 12v led strip but plan to "split" it into 5cm/3LED segments to provide indication lights around a house!!!). With a 12V/3W cheap solar panel and a 1400mAh recycled 18650 from an old laptop it keeps the leds on all night and it recharges even during a cloudy day.. at full sun it recharges the battery in a matter of 2-4hrs and from what i can tell it is good for a couple of nights.. )

author: Undweeber
author_rank: Regular Contributor
timestamp: March 13, 2018, 10:55:23 pm
content: The joule thief was able to take the battery down to 0.5/6 V at which point i terminated the test, the LED was still lit

author: Undweeber
author_rank: Regular Contributor
timestamp: March 17, 2018, 06:39:00 pm
content: UPDATEI have received 350F Supercapacitor, from Maxwell, its the size of a D-cell, 2.7V, I connected it through a small DC generator I made and tried charging it, the load was pretty high on the generator, it was pretty significant, but I quickly found out a big problem.The point of a hand shaker torch or even a hand crank generators and LED diodes themselves and this whole joule thief circuit is - quick and easy light for free without batteries. The goal of a supercapacitor is to get from 0V to 2.7V within a reasonable amount of time.Problem #1:Because of the insane capacity of 350F, getting from 0V to 2.7V is taking an unprecedented amount of energy and time, so hand cranking it... maybe with a stepper motor + rectifier and an actual crank handle.Problem #2:I am not sure what voltage to charge this supercapacitor at. I have a 18650 which can put out 30A of current (LGDAHB21865), it was charged to 2.4V and was able to charge the supercap to 1.8V relatively quickly at the same time overheating the thin alligator leads, but at least I got the polarity correctly etc. Thing is I still don't know what maximum voltage and current I should be charging this thing at. The Supercap is (BCAP0350) 350F 2.7V Maxwell.Problem #3:The capacitor puts out insane amperage, it was charged to 2-1.8V, I fed it into myjoule thiefcircuit, the LED flashed and went dim within 1 second, the coil started heating up, and the transistor was impossible to hold it was that hot. I ascertained that it is probably pumping out insane amperage into the circuit, I then connected my circuit to the 18650 I used to charge the supercap, and it gave the same exact effect of brief LED light before going dim and overheating the transistor, all within 1 second as well.Conclusion:my circuit cannot handle high current, I need to limit the current flowing into the circuit somehow I don't know how, at the same time I need to make my joule thief be able to operate at 0.2V at least to make this supercap even work with this circuit, or get a smaller capacity supercap like a 10F 2.7V also made by Maxwell. But for now I would really like to make this large supercap work and I would greatly appreciate some input from you guys.I have made 2 extra coils, one with a large ferrite core and thick wire, another with the same size ferrite core but with much much thinner wire and way more winding, this thread is so thin that i may have a problem with soldering it, but ill do my best.

author: Undweeber
author_rank: Regular Contributor
timestamp: March 17, 2018, 06:40:54 pm
content: UPDATEI have received 350F Supercapacitor, from Maxwell, its the size of a D-cell, 2.7V, I connected it through a small DC generator I made and tried charging it, the load was pretty high on the generator, it was pretty significant, but I quickly found out a big problem.Seems like my joule thief has a limit of 1.5V top, and will drain until the output is at 0.4V, but if I disconnect the circuit at 0.8V and try to turn it back on, the circuit will not fire up so it seems that it needs at least 1V to fire up, but then takes much less to operate, and will shut off at 0.4V.The point of a hand shaker torch or even a hand crank generators and LED diodes themselves and this whole joule thief circuit is - quick and easy light for free without batteries. The goal of a supercapacitor is to get from 0V to 2.7V within a reasonable amount of time.Problem #1:Because of the insane capacity of 350F, getting from 0V to 2.7V is taking an unprecedented amount of energy and time, so hand cranking it... maybe with a stepper motor + rectifier and an actual crank handle.Problem #2:I am not sure what voltage to charge this supercapacitor at. I have a 18650 which can put out 30A of current (LGDAHB21865), it was charged to 2.4V and was able to charge the supercap to 1.8V relatively quickly at the same time overheating the thin alligator leads, but at least I got the polarity correctly I was charging it by connecting the 18650 in parallel, correct? Thing is I still don't know what maximum voltage and current I should be charging this thing at. The Supercap is (BCAP0350) 350F 2.7V Maxwell.Problem #3:The capacitor puts out insane amperage, it was charged to 2-1.8V, I fed it into myjoule thiefcircuit, the LED flashed and went dim within 1 second, the coil started heating up, and the transistor was impossible to hold it was that hot. I ascertained that it is probably pumping out insane amperage into the circuit, I then connected my circuit to the 18650 I used to charge the supercap, and it gave the same exact effect of brief LED light before going dim and overheating the transistor, all within 1 second as well.Conclusion:my circuit cannot handle high current, I need to limit the current flowing into the circuit somehow I don't know how, at the same time I need to make my joule thief be able to operate at 0.2V at least to make this supercap even work with this circuit, or get a smaller capacity supercap like a 10F 2.7V also made by Maxwell. But for now I would really like to make this large supercap work and I would greatly appreciate some input from you guys.I have made 2 extra coils, one with a large ferrite core and thick wire, another with the same size ferrite core as original but with much much thinner wire and a lot more winding, this thread is so thin that i may have a problem with soldering it, but ill do my best.

author: helius
author_rank: Super Contributor
timestamp: March 17, 2018, 07:10:37 pm
content: https://en.wikipedia.org/wiki/Mechanically_powered_flashlighthttps://www.aliexpress.com/item/3leds-Dynamo-LED-Lantern-light-Hand-pressing-powered-charge-Wind-Crank-Press-Flashlight-Torch-for-hunting/32674910643.html

author: Undweeber
author_rank: Regular Contributor
timestamp: March 17, 2018, 07:21:25 pm
content: @helius yes I am aware of mechanical torch existence, there are even some that are powered by a tiny 1F supercaps, problem is those supercaps are too small, the circuit is so basic that a lot of energy is left behind, and others use lithium batteries. I am thinking of getting one of those torches to use as the main body for my build, using either current supercap or a smaller 10F supercap, but before I get there, I want to get the joule thief circuit right, and make it efficient, and be able to handle large current and low voltage - a characteristic of supercapacitors I was not aware ofPS. offtopic a funny fact, this would be a great survival tool, a charged supercap with the insane current it can put out, you can easily start fire with it without matches, and theoretically it should work forever pretty much

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 18, 2018, 11:42:32 pm
content: If it's shorting out and overheating, your coil is probably wound wrong.http://cs.yrex.com/ke3fl/htm/JouleThief/JouleThief.htm

author: Undweeber
author_rank: Regular Contributor
timestamp: March 22, 2018, 03:56:12 am
content: @Cyberdragonmy coil is wound correctly, and thanks for the link i'm going to read it tonightUpdate:So I have done more testing, I did not collect any data as I don't really have the means, but I have observed the exact same behavior of the circuit thatGreatScott!was trying to troubleshoot in his video hereMy observations:- my circuit operates in the range from 0.4V-1.3V, giving a decent amount of brightness down to 0.5V and from .5 to .4 its unusable brightness.- for my circuit to be able to utilize higher voltages I had to beef up the resistor, and then my circuit could take 2.7V-1.3V, if the resistor stayed the same - the TRANSISTOR would overheat and LED would go dim- I have observed using multi-meter that at higher voltages the charge of the capacitor drops much quicker because a LOT of energy is wasted as heat in the transistor, to mediate this i used a beefier resistor and the circuit could operate again, however this raised another issue where the joule thief could not operate at lower voltages which is the point of this build.- I also observed that circuit was able to extract more energy more efficiently at lower voltages WITHOUT a resistorMy Conclusion:- I have harvested some beefy coils from my old power supply as well as transistors etc, I will try using different beefier coils to see if there is any benefit- I have also came to the conclusion that a circuit like this will require a constantly variable resistor, and that scares me a bit, because it does in fact seem that if only one type of resistor is used - you will only have a very narrow range where the efficiency is in 90's% where everywhere else it would be much lower.- With variable resistor, constantly controlled current going through the circuit would be able to more efficiently extract the energy stored in the supercap- my LED should be lit up brightly for ~350 minutes considering the 22F supercap can light the LED for 20 minutes.. Will have to test this.- I will also test the circuit using FET instead of BJT as some say thatFET can operate down to 0.1VQuestions:- is there a chip that could be pre-programmed to vary the resistance automatically?- is there an easy solution to this besides a potentiometer? I want the light to be on on its own without having to tinker with it constantly to make it work, so this part is kind of important.- I am looking at these thingshttp://www.ti.com/product/BQ25504/descriptionbut how efficient are they, I haven't looked for ones that would operate from 2.7V down to 0, but don't think they have them at a quick glance, not sure if they would work as well as joule thief either so don't really feel like paying for it if it doesn't work

author: Siwastaja
author_rank: Super Contributor
timestamp: March 22, 2018, 06:58:11 am
content: Quote from: IanB on March 12, 2018, 04:08:54 amWhile this is AFAIK indeed true for NiCd (I don't know about NiMh), this kind of "intuitive" reasoning is wrong and dangerous; it just happens to go right in this particular case. For example, in lithium ion chemistry, voltage over about 1.5-2.0V is needed to prevent copper foil dissolution.Intuitively, when chemicals required to build a battery are put together, they rarely are "inert" in any way, in any state-of-charge. How the state-of-charge or open-circuit voltage affects the rate of unwanted side reactions, is case-by-case dependent of the actual chemistry involved: for example, lead acid requires 100%, li-ion is happiest between about 0-40%, and NiCd is best long-term stored at some negative SoC value (0V OCV). I bet it's not completely "inert" even then.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 22, 2018, 08:03:30 am
content: 1. You're probably now at the point where you need therightcircuit!As I mentioned earlier, the common circuit seen most anywhere on the internet is bad. A subtle change is all that's needed. This is the basic building block:The LED is still connected between Output and GND, as usual.Rbias controls how often the circuit pulses. If it delivers enough bias current, the circuit can run continuously, at which point it's more or less delivering maximum power. Further increase in bias only modestly increases output power, while greatly increasing losses (mainly due to wasted bias current).Rb controls how much current is pulsed into the base, during conduction. In the common circuit, Cbb = 0 and Rbias + Rb sets turn-on current. It will usually run full wave in this condition, somewhere between class D (good) and class A (bad) operation, because base current is strictly limited by the resistor value. That's why the common circuit is naught but a toy.With Cbb, much more peak current can be delivered, by the transformer, into the base, saturating the transistor hard, forcing class D (efficient) operation.Explanation:Cbb is sized so that, drive current (which acts to discharge Cbb) peters out, just as the inductor's current reaches the design peak current. This causes the transistor to turn off the quickest.Approaching the peak, the transistor is already beginning to open up. Collector current continues to rise, while base current is falling. As it falls below hFE(sat), Vce begins to rise (coming out of saturation). When Vce rises, transformer action slams the base voltage off, hard.During the off phase, the inductor discharges into the LED, until its current reaches zero. Voltage (across the inductor) returns to zero, with a bit of undershoot. If Cbb has been charged up to about Vbe (~0.6V) in this time, the next cycle will begin immediately. If not, and the undershoot isn't extreme, then the transistor will remain off until Cbb charges to that point.2. Component values.This is where you must design the oscillator.The basic circuit can only operate usefully over a modest range, maybe 2:1. If your criteria is much looser (e.g., it lights up at all), maybe 3:1 or 4:1.Do not try to fully discharge the capacitor: it is folly. A 350F capacitor charged to 2.5V contains E = 0.5 * C * V^2 = 1093J of energy. Charged to 0.5V, it contains only 43J, or 4%. Who cares. In fact, you get 80% at 1.12V, a much more reasonable target -- nearly in that 2:1 range of useful operation!- The transformer winding ratio is determined by the flyback voltage, and the base 'on' voltage (Vbe) and reverse limit (Veb(max)). The smaller the ratio is (secondary (base) to primary (collector) winding turns), the less drive voltage (and current), until the oscillator stops from not having enough gain at all. Typically 0.5-3V is a good target. The higher the ratio, the more drive voltage and current, until the voltage goes so high that it causes E-B breakdown (the B-E junction looks like a ~6V zener diode), which pushes current back into Cbb, and the circuit runs away like a Diesel engine with leaky seals...Obviously, adjust this limit depending on what the transistor datasheet says. Faster transistors tend to have lower voltage ratings (3V or even less), while general purpose transistors are usually 6 to 8V.For a 2.5V supply attached to a 3V LED, a 2:1 winding will be fine.- Operating frequency. This is fairly arbitrary. It must be many times smaller than the transistor's fT, otherwise it won't be able to switch on and off sharply. (Most have fT > 50MHz, so this isn't a problem until you're pushing over ~1MHz, which would be pretty fast for a converter like this.) Likely, you'll pick the frequency based on how many turns you can fit onto some random core, and what inductance that gives. That's perfectly fine.- Inductance. This can be calculated, if the core is known. Ferrite beads and powdered iron cores can be looked up. Cut cores, their size and shape can be measured, and their value calculated (with some supporting assumptions). Open cores (rods, bobbins, etc.) can be estimated, calculated, or measured.Example: take a bobbin inductor, that's printed with its known value, and unwind it. Count N turns as you unwind it. Calculate:A_L = L / N^2(A_L is the inductivity of the core). UseN = sqrt(L / A_L)to find the number of turns needed for inductance L, orL = A_L * N^2to find the inductance for some turns N.Preferably, for a 2:1 transformer, wind half the primary turns, then the secondary (which, by the way, can be finer wire than the primary), then the rest of the primary. Use tape if you like, to insulate layers; especially if you're using salvaged wire that's probably nicked and cracked.- Capacitor. Now that we have a transformer, how much drive do we need for it?This depends on desired power output, transistor hFE, and transformer inductance.Power goes up as L and F go down. Obviously, current goes up with power. So, Cbb goes up as power goes up and frequency goes down.Say the LED is 20mA nominal. It's receiving pulsed power, let's say 80mA peak. (So that, during the pulse, it receives 80mA ramping down to 0mA, an average of 40mA during the pulse; and it's pulsed for about half the time, so the average overall is 20mA.)Say the transistor has an hFE(sat) of 50, so we bias it at (80mA/50) = 1.6mA, or an Rbias of (1V / 1.6mA) = 625 ohms, say 470 or 680 for the next closest common value.Say the transformer primary has an inductance of 50uH. This ramps up to 80mA in 2us (giving around 250kHz operating frequency). Cbb needs to deliver about a volt in that time, or C = I * dt / dV = (1.6mA) * (2us) / (1V) = 3.2nF. 2.2-10nF would be typical values to try.And we set Rb = 0. Some is okay, up to maybe 100 ohms; the typical effect is dampening ringing on the base, and reducing oscillator gain and saturation (again, the whole reason why the common circuit sucks so bad -- it's all resistor!).3. Stability.The average characteristic is roughly resistive. That is, more input voltage --> more input current --> squared more output power. (It's worse than that, really, because as Vin exceeds LED Vf, the oscillator still tries to oscillate, but the supply is dumping current directly into the LED, and the transistor can only sit there melting. But it's more or less square-law between nominal supply voltage and whatever voltage it shuts off at.)To get constant intensity, or at least reasonably constant, until the capacitor discharges too far to be useful, you need to effectively adjust Rbias. Varying resistors is hard (unless you want to put a potentiometer or switch on there and do it by hand), so it's convenient to have a control circuit do this for you.Here's a rough example (maybe not a working one, for a number of reasons):Note that:- Rbias is replaced by a PNP transistor (general purpose), which delivers a variable current instead of a variable resistor (this is actually better than a resistor, so that's nice).- The transformer and NPN (in this case, a PBSS303NX or similar would be typical) are wired as normal, and, instead of the schottky diode and output, you could attach the LED here (sort of).- Instead of an LED, there's an output filter cap (10uF), and another PNP with a zener diode and bias resistor.This way, instead of the output pulses driving an LED direct, they charge a capacitor, causing its voltage to rise. When that voltage exceeds Vref + Vbe, the PNP turns on, shunting the 2.2k that's turning on the other PNP, thus reducing power output, and limiting the output voltage.To adapt this to an LED, you'd want to control LED current instead of voltage. And you'd want to do it with a small voltage drop, so as not to waste power -- probably needing two or three additional transistors to work with the small voltage.4. FETs, ICs.JFETs: kinda. JFET oscillators have been demonstrated to operate at single-thermoelectric-junction voltages (tens of mV). They don't make any big JFETs, so the current is pitiful (10s of mA), and the power even more pitiful! I've personally demonstrated a circuit that runs at 0.2V and is able to deliver 5V... into a 100kohm load resistor. Well, it will "visibly" light an LED, in a dimly lit room... that's about it.At more reasonable voltages, JFETs don't have any advantage over BJTs. And at still higher voltages, MOSFETs.If you're into boutiques, germanium power transistors are still fairly easy to find, and can run much lower, 0.2V perhaps. You still have the problem of crap efficiency, and not being able to draw enough current to make useful power.JFETs can sort of be used in the same kind of circuit, with the difference that, instead of Rbias being from +V to Cbb, it goes from GND to Cbb. Cbb can be smaller too, it doesn't matter much. Rbias doesn't need to deliver much current (as you might guess from returning it to ground!), it can be 100k or more. The oscillator won't really have any setting but full throttle.MOSFETs can be used in a somewhat similar circuit, but without base current discharging Cbb, some other method needs to be arranged to cause it to cycle efficiently. (Maybe a diode and resistor from Cbb to drain?) MOSFET gain is lower than BJT, so (for this case) a 1:1 or even 1:2 winding would be needed. For the same reason, the minimum startup voltage will be higher as well.To get much more elaborate, a JFET oscillator could be used to just barely power a controller circuit, which operates a MOSFET; in this way you could draw significant power from a low voltage load (amps+). Once started up, it runs off its own output power (bootstrap!). But this is going well beyond the scope of this thread...HTH,Tim

author: Audioguru
author_rank: Super Contributor
timestamp: March 22, 2018, 03:54:23 pm
content: I opened my cheap Chinese cranking flashlight and saw that it did not have a super capacitor and it did not even have a rechargeable battery. Its "generator" was not connected to its ordinary throw away battery. With its switch one way the battery lights the LEDs and becomes dead in a while. With the switch the other way then the generator lights the LEDs while your hand is wearing out.A capacitor voltage drops fast when it is loaded but a battery voltage remains fairly constant when it is loaded.A Joule Thief uses a low voltage and a low current, not the much higher voltage and current from a super capacitor.

author: Undweeber
author_rank: Regular Contributor
timestamp: March 23, 2018, 01:20:44 pm
content: @T3sl4co1lthat is exactly what I needed thank you I will go through this and report back@Audioguru, seems you’ve never played with supercapacitors, they don’t discharge quickly, they actually discharge very slowly, and the current they provide can be limited, so it’s not a big deal, my supercap acts like a 30A 18650 that can only go up to 2.7V and down to “0V” which is enough to power a bright LED for several hours. I just need to perfect it for efficiency etc. then attach a hand crank.If your light was hooked up right and had a small 22F capacitor, you would have 20 minute power reserve with the joule thief. Watch the video I posted few posts above.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 23, 2018, 08:09:42 pm
content: Quote from: Undweeber on March 23, 2018, 01:20:44 pmWhat's the ESR...I smell something funny...Here's some from mouser with 3.5 and 3.2mESRhttps://www.mouser.com/Passive-Components/Capacitors/Supercapacitors-Ultracapacitors/_/N-5x76s?P=1yfrn65Z1z0x2ud

author: Undweeber
author_rank: Regular Contributor
timestamp: March 23, 2018, 08:21:19 pm
content: @Cyberdragon yeah and? what are you hinting at? I do not get your sarcasm as I am very very new to all this, I am bio major, so explain and don't patronize please

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 24, 2018, 01:53:01 am
content: Supercaps, especially that big, normally discharge fast enough to blow up or melt things. That's the whole point of being capacitors, they're supposed to have way more current output than batteries. On Kasyan TV he put a small supercap across a razor blade and it instantly turned yellow hot where it touched, yours should do the same thing.WARNING: If the capacitor is working and you have long leads, they may melt off or weld if you short it. (Not entirely sure, but seeing a piece of metal heated like that, just be careful not to get it welded)EDIT: If it doesn't heat a small piece of metal, it might be faulty.

author: Undweeber
author_rank: Regular Contributor
timestamp: March 26, 2018, 04:21:00 am
content: ughh firstly please delete that unnecessarily huge picture, I am aware what sparks look like, and I am aware of the current it can put out, what I have been doing so far does no harm to anything, it does turn shorted wires yellow instantly but I don't do it unintentionally, don't flame please

author: BravoV
author_rank: Super Contributor
timestamp: March 26, 2018, 04:36:00 am
content: When working with these supercapacitors, especially the big ones, if not used, keep the terminals shorted, as the cap's dielectric absorption possibly will generate enough energy that is fire hazard if its shorted by accident and/or unattended, say like in your drawer.Just short the two terminals with a piece of wire.

author: Undweeber
author_rank: Regular Contributor
timestamp: March 27, 2018, 03:12:05 am
content: I didn't know about having to do it, but I have been doing it anyway myself because i saw wires turning yellow hot instantly

author: Undweeber
author_rank: Regular Contributor
timestamp: March 29, 2018, 03:30:00 am
content: @T3sl4co1lWow I finally got the balls to read your post, read it to the end, good news is I could follow to the end, and I have a few things on my mind.I see what you mean with designing the coil instead of mindlessly winding it, it sort of just works if you do, but yeah we learned it in highschool physics that you design a coil with the number of coils you need instead of mindlessly winding one, so I will have to design one myself.I like the idea of using a PNP instead of a variable resistor potentiometer, that is exactly the goal to keep as steady brightness as possible, and I will definitely start looking at your formulas. I will try to write everything down that you said in a more visual way for myself and once I see the full picture in its entirety I might bother you with further questions1. You have listed several extra components that I would need, I have pnp's, problem is, soldering it all does not sound like a proper way of testing, its time consuming for me as I am sort of working on this in secret so I have to put all that stuff away in shoe boxes otherwise my parents will give me a ton of shit, so I was wondering if I could use those breadboards where you push components into the holes and push wires from hole to hole to connect them, or would this circuit in its more or less entirety be too complex for that? I would prefer to swap components for a quick test and then solder together a working prototype.2. Do you recommend I get a variable power supply, I think I would be able to test the circuit in a better way that way, I could better see the useful light brightness etc. If you do recommend it, what should the power supply definitely be capable of besides the obvious, should I get one that can pump out 30Amps to simulate a supercap?3. I agree with you that discharging the supercap down to 0 is pointless, and I am perfectly fine with the operating range being 0.4/0.5V - 2.7V, that would give me 2.2V range which is plenty.Also, I noticed that charging the supercap from 0V-0.4V is practically impossible with 1A, I had to use iPad charger which is 13W 2.4A for it to budge at that level, but after 0.4/0.5 it happily uses 1A, but flies on iPad charger anyway.Anyway please answer 1 and 2 if you can, in the meantime I will get a large piece of paper and try to draw a big picture for myself, will be a few days.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 29, 2018, 05:28:30 am
content: 1. Yes, solderless breadboard is adequate here.2. It would help, and be safer than having a charged supercap rolling about. A battery might be more convenient, like a 2 x AA pack, less available current (and still operates over a wide voltage range as it empties). Get a selection of power resistors, so you can artificially reduce the voltage.One of those adjustable buck regulator modules from China might be a fine way to get started. Without a scope, you don't have any way to tell how godawful noisy it is...Tim

author: Undweeber
author_rank: Regular Contributor
timestamp: March 30, 2018, 03:33:26 pm
content: Hmm actually I have some Duracell D batteries I could solder together to simulate a 3V power supply which would last for a while. And using resistors for artificial voltage drop sounds sound too, but there is no way to simulate the insane current, I connected a resistor across the terminals and it turned lava hot instantly, I wanted to see how long it would take to heat up. I looked up Dave’s variable resistor thing it costs $100-200, maybe chinese have one for cheaper, but will it work.I’ll look into power supplies, maybe I’ll build one myself, Dave has a tutorial, some other youtubers do as well, I need it to be small and somewhat powerful I think, will see.Max current 840AMax continuous current at 40°C: 34A; at 15°C: 21A