Language: 
To browser these website, it's necessary to store cookies on your computer.
The cookies contain no personal information, they are required for program control.
  the storage of cookies while browsing this website, on Login and Register.

GDPR and DSGVO law

Storing Cookies (See : http://ec.europa.eu/ipg/basics/legal/cookies/index_en.htm ) help us to bring you our services at overunity.com . If you use this website and our services you declare yourself okay with using cookies .More Infos here:
https://overunity.com/5553/privacy-policy/
If you do not agree with storing cookies, please LEAVE this website now. From the 25th of May 2018, every existing user has to accept the GDPR agreement at first login. If a user is unwilling to accept the GDPR, he should email us and request to erase his account. Many thanks for your understanding

User Menu

Google Search

Custom Search

Author Topic: Joule Thief  (Read 5815836 times)

Offline Pirate88179

  • Moderator
  • Hero Member
  • *****
  • Posts: 8366
Re: Joule Thief
« Reply #16875 on: February 18, 2016, 08:25:20 PM »
We are seeing more AC power point mains outlets available with single or twin USB sockets incorporated...good idea. No doubt you guys over the pond have them also?

By the way how are you Bill haven't looked in for a while.


I am fine, how are you doing?  It has been a while.  It seems the days are flying by much faster now...ha ha. 


I have not seen what you have described with those outlets around here but, that does not mean anything.  It could be they are incorporated into new construction, of which I have not had any reason to see.  I will look around to see if they are available at the home supply stores next time I go.  It would be a good idea if they did have them.  I wonder how much noise they have in them from the transformation of the AC and also, being surrounded by the ac?


Take care,


Bill

Offline Pirate88179

  • Moderator
  • Hero Member
  • *****
  • Posts: 8366
Re: Joule Thief
« Reply #16876 on: February 18, 2016, 08:31:27 PM »
Here is a Joule Thief issue that has been in the back of my mind for a long time.  See the attached portion of a Magluvin scope capture of his Joule Thief collector-emitter voltage.  Of course the collector-emitter voltage is the voltage across the LED.  Naturally there is an unknown current waveform associated with the voltage waveform that will have a similar decaying waveform shape.

So the issue is this:  You can clearly see the declining voltage across the LED.  So how bright is the LED as a function of the voltage?  What if the LED is bright for the upper half and very dim for the lower half?  I don't know if this is true but it merits an investigation.

If if the lower half light output from the LED is very dim then presumably it does not contribute to the visible light output of the LED to the naked eye and there is a lot of "wasted energy" in the inductor discharge.  If that's true it is arguably an "issue" and it suggests you can build a better mousetrap Joule Thief.

So, what if, for the sake of argument, that half of the energy in the coil discharge is essentially wasted because it barely lights the LED?

MileHigh


MH:


I would think that it would depend upon the values associated with those points.  In other words, and I just read this around here somewhere in the past few days, the basic JT can put out 40 volts but it does not fry the led because it can handle the high freq. HV pulse and responds by lighting brightly.  So, if the lower point you indicate has the voltage dropping to 4 volts, 1/10 of the original value, that led will still burn brightly no?


I will try to find where I read this as it confirmed what I had been saying about the HV high freq JT's and leds for many years now.  It is something we found out during our experiments and playing here on this topic.


Maybe I did not understand what you were meaning and went off in another direction...if so, I am sorry and will look at this again once I get home.


Bill

Offline MileHigh

  • Hero Member
  • *****
  • Posts: 7600
Re: Joule Thief
« Reply #16877 on: February 18, 2016, 09:01:58 PM »
Bill:

I think you read about the "40 volts" in one of my copy-pasted descriptions of how a Joule Thief works.  That is somewhat of a misnomer because the coil never outputs 40 volts when the LED load is connected.  It's the same old issue - the discharging coil is a current source and not a voltage source but mentioning that in any kind of magazine or online article, apparently even an article written for "hobbyist keeners" would throw too many people off and cause more confused people than enlightened people.

The real test to check how the LED responds to different voltages would actually be to slowly change the current through the LED and then measure the resulting voltage across the LED and compare that to the voltages you see in the scope shot.  It might be quite a surprise if the lower half of the voltage curve was barely lighting the LED.  My gut feel is telling me that "barely lighting" is an exaggeration but the proof is in the testing pudding.

I am willing to bet you that this investigation was never done in all 1126 pages and six year's worth of this thread.  Not bad for a guy leaning back in his Laz-Z-Boy eh?

MileHigh

P.S.:  And the follow-up to that is if it truly is a problem, what can be done to alleviate it?

Offline Pirate88179

  • Moderator
  • Hero Member
  • *****
  • Posts: 8366
Re: Joule Thief
« Reply #16878 on: February 19, 2016, 01:57:09 AM »
Bill:

I think you read about the "40 volts" in one of my copy-pasted descriptions of how a Joule Thief works.  That is somewhat of a misnomer because the coil never outputs 40 volts when the LED load is connected.  It's the same old issue - the discharging coil is a current source and not a voltage source but mentioning that in any kind of magazine or online article, apparently even an article written for "hobbyist keeners" would throw too many people off and cause more confused people than enlightened people.

The real test to check how the LED responds to different voltages would actually be to slowly change the current through the LED and then measure the resulting voltage across the LED and compare that to the voltages you see in the scope shot.  It might be quite a surprise if the lower half of the voltage curve was barely lighting the LED.  My gut feel is telling me that "barely lighting" is an exaggeration but the proof is in the testing pudding.

I am willing to bet you that this investigation was never done in all 1126 pages and six year's worth of this thread.  Not bad for a guy leaning back in his Laz-Z-Boy eh?

MileHigh

P.S.:  And the follow-up to that is if it truly is a problem, what can be done to alleviate it?

I think you are correct about where I had read that.

Waay back Gadgetmall was using a ceramic cap on the base of his transistor.  My thoughts are, that if indeed it is wasting energy by having a moment of low voltage to the led then what about using a decent sized supercap, say 1 F, in series with the led?  This way, the voltage would never drop as the cap would absorb all of the pulses, both high and low.  Sort of a smoothing operation but not exactly the same.

Does this make any sense?

Bill

Offline MileHigh

  • Hero Member
  • *****
  • Posts: 7600
Re: Joule Thief
« Reply #16879 on: February 19, 2016, 04:26:13 AM »
Putting a cap in series with the LED doesn't make any sense.  But we all know that putting a cap in parallel with a weak battery as an example can keep the voltage steady when the load momentarily increases as compared to the weak battery alone which would crap out.  So you are in the ballpark in the sense that somehow a smoothing cap could be part of the solution.

Offline Pirate88179

  • Moderator
  • Hero Member
  • *****
  • Posts: 8366
Re: Joule Thief
« Reply #16880 on: February 19, 2016, 05:04:23 AM »
Well, I gave this some thought.  If you put the supercap in parallel with the led then you run the risk of over charging the cap if the energy flows into the cap faster then it is being drained by the led.  This is why I used series so the pulses get absorbed and leveled out on the way to the led and since the led is a diode we do not have to worry about any energy returning back into the cap.

I believe I did this very thing a while back and I will see if I made a video of it...if not, I will make another circuit to attempt to demonstrate what I am saying...or trying to say.

Bill

PS  This has to do with something I found out about supercaps (or possibly any caps?) in that when you hit them with spikes or pulses, they do a much better job of retaining that energy than a battery which makes them very good to use with catching spikes from a JT circuit or the pulses from my earth battery.

Offline Pirate88179

  • Moderator
  • Hero Member
  • *****
  • Posts: 8366
Re: Joule Thief
« Reply #16881 on: February 19, 2016, 05:40:47 AM »
This guy made a JT using some SMT inductors:   https://www.youtube.com/watch?v=g2jMrNFV4nQ

I have seen some like this but they are so small I can barely see them.  Now, if he used an SMT transistor and mini led it could be even smaller.

Bill

Offline Nink

  • Sr. Member
  • ****
  • Posts: 393
Re: Joule Thief
« Reply #16882 on: February 19, 2016, 05:57:04 AM »
This guy made a JT using some SMT inductors:   https://www.youtube.com/watch?v=g2jMrNFV4nQ

I have seen some like this but they are so small I can barely see them.  Now, if he used an SMT transistor and mini led it could be even smaller.

Bill


Nice 2 * Ferrite Bead SMT Inductors back to back with and an NPN transistor. Clever. Wouldn't mind seeing a comparison. 


Offline AlienGrey

  • Hero Member
  • *****
  • Posts: 3709
Re: Joule Thief
« Reply #16883 on: February 19, 2016, 04:59:02 PM »
Have a look at this Joule thief the current draw is 50 ma at 2 volt in this case
Have a look at this device it can be tuned for optimal brightness in this case the voltage is 2v at 45 ma in  this case.

Re scop shot freq 95 khz, width +10.25, with - 240, period 10.6 us, 20v cm x10 probe
« Last Edit: February 19, 2016, 07:04:12 PM by AlienGrey »

Offline Pirate88179

  • Moderator
  • Hero Member
  • *****
  • Posts: 8366
Re: Joule Thief
« Reply #16884 on: February 20, 2016, 01:49:44 AM »
That looks like a straw hat led...I have some of those and they are very bright for their size.

Well done.  Will that run on 1.5 volts or lower?

Bill

Offline sm0ky2

  • Hero Member
  • *****
  • Posts: 3721
Re: Joule Thief
« Reply #16885 on: February 20, 2016, 04:30:57 PM »
Well, I gave this some thought.  If you put the supercap in parallel with the led then you run the risk of over charging the cap if the energy flows into the cap faster then it is being drained by the led.  This is why I used series so the pulses get absorbed and leveled out on the way to the led and since the led is a diode we do not have to worry about any energy returning back into the cap.

I believe I did this very thing a while back and I will see if I made a video of it...if not, I will make another circuit to attempt to demonstrate what I am saying...or trying to say.

Bill

PS  This has to do with something I found out about supercaps (or possibly any caps?) in that when you hit them with spikes or pulses, they do a much better job of retaining that energy than a battery which makes them very good to use with catching spikes from a JT circuit or the pulses from my earth battery.

I made some that charged caps using a 1/2 wave rectifier off a secondary coil. Just be sure to drain the cap with some kind of load, or it could blow up!

Offline AlienGrey

  • Hero Member
  • *****
  • Posts: 3709
Re: Joule Thief
« Reply #16886 on: February 20, 2016, 06:45:41 PM »
That looks like a straw hat led...I have some of those and they are very bright for their size.

Well done.  Will that run on 1.5 volts or lower?

Bill

Yes it will, i just tried it with an old AA duracell ! and it's about as bright too.


Offline Pirate88179

  • Moderator
  • Hero Member
  • *****
  • Posts: 8366
Re: Joule Thief
« Reply #16887 on: February 21, 2016, 05:16:57 PM »
MH:

Here is one of my first earth battery videos: https://www.youtube.com/watch?v=mq9ZKDKDclY
(This was before Pirate Labs)

I didn't know it at the time but I was using a .5 farad 5.5 volt supercap in series with the led.  The led would
not light without it in the circuit.  This is where I first learned how the caps can gather up the spikes and allow them to be used.  This is where I got the idea to use them later on the JT circuit.  The cap is charged by the spikes from the earth battery and later, the cap is charged by the JT spikes.

Does this make any sense now?  I knew next to nothing about electronics when I did this 9 years ago (not that I am an expert now, ha ha) but I stumbled on to something that has been helpful ever since.

Bill

Offline MileHigh

  • Hero Member
  • *****
  • Posts: 7600
Re: Joule Thief
« Reply #16888 on: February 21, 2016, 05:51:50 PM »
Bill:

It's the corroding magnesium rod that generates the voltage and associated current.  The current is quite low and that translates into saying that as a voltage source, the corroding magnesium has a very high output impedance, too high to drive the LED reliably.  There are no spikes produced by the magnesium.  But it is reasonable to assume that the current produced by corroding magnesium is variable.  It depends on what is happening at the boundary layer between the magnesium and the soil and how much moisture and salinity there is at every point of contact, etc.  That is presumably quite variable and therefore the output impedance is also variable.

So the capacitor just absorbs the variable current and smooths it out to drive the LED.  It effectively converts the variable output impedance from the corroding magnesium rod into a more constant impedance such that the LED is driven with a more constant current.

MileHigh

Offline Pirate88179

  • Moderator
  • Hero Member
  • *****
  • Posts: 8366
Re: Joule Thief
« Reply #16889 on: February 21, 2016, 06:43:59 PM »
Bill:

It's the corroding magnesium rod that generates the voltage and associated current.  The current is quite low and that translates into saying that as a voltage source, the corroding magnesium has a very high output impedance, too high to drive the LED reliably.  There are no spikes produced by the magnesium.  But it is reasonable to assume that the current produced by corroding magnesium is variable.  It depends on what is happening at the boundary layer between the magnesium and the soil and how much moisture and salinity there is at every point of contact, etc.  That is presumably quite variable and therefore the output impedance is also variable.

So the capacitor just absorbs the variable current and smooths it out to drive the LED.  It effectively converts the variable output impedance from the corroding magnesium rod into a more constant impedance such that the LED is driven with a more constant current.

MileHigh

Well, we later learned some other things about this type of set-up.  For example, I hooked up my scope to the E.B. and you could see all of these high voltage spikes jumping all over the place.  They could have be coming from anywhere...leaking ac line, radio waves in the ground (noise) or possibly lightning strikes from distant storms?  Who knows...but...those spikes were there and that is why I could charge up my large cap (650 F) to 2.7 volts when I was only measuring around 1.9 volts using several different meters. (Analog and digital)

This is about the time I began calling this arrangement an earth energy receiver rather than an earth battery.  Maybe the energy was man-made...who knows?  I just know it was there otherwise, I could never have made enough power to run my Bedini motor or those Fuji circuits.

I will look for some photos of the spikes if I can find some and will edit this post later.

Here is the video showing the spikes jumping all over the screen...they are hard to see but they are all over the place.

https://www.youtube.com/watch?v=qjBAU4HAMfs


Bill