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

Custom Search

Author Topic: Negative discharge effect  (Read 50103 times)

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Negative discharge effect
« Reply #30 on: September 29, 2014, 09:39:56 AM »
OK, I have built the first circuit (with a few substitutions that shouldn't matter much.) IRF630 mosfet, 1n2071 rectifier diodes, 160 uF 330V fhotoflash caps (Thanks Pirate!).
I'll give a better report a little later. Scope below shows the junction of the two caps and the coil, wrt mosfet source.

ayeaye

  • Hero Member
  • *****
  • Posts: 866
Re: Negative discharge effect
« Reply #31 on: September 29, 2014, 03:07:46 PM »
OK, I have built the first circuit
Oh great, thanks :)

So what it shows, a 3 V voltage spikes when the gate is switched on. These are likely higher, the scope may not show the full height. What is weird is the constant coil ringing, maybe due to a slow zener diode of the mosfet. But seemingly no back-emf. As i have seen, the effect occurs only with a certain frequency and duty cycle, which may even be different with the same components. And only then there is a significant back-emf.

Oscilloscope, great thing. I cannot get one, the old oscilloscopes they sell here seem to be only the ones which are so hopelessly failed, that no one can repair them. I even tried to make an ascii oscilloscope with my microcontroller, wrote the code, and even tested it. 500 ksps and 16 bits is the best one can get with that anyhow. Because of high voltage spikes it cannot be made without an op amp. And even with an op amp there are too many interferences, so who knows what else should be made to protect against these. It's like stable, but then it jumps to some who knows what value, then jumps back. So i found it too difficult, and not good enough.

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Negative discharge effect
« Reply #32 on: September 29, 2014, 07:07:19 PM »
No, I could find no trace of a narrow, higher voltage spike. This surprised me because I expected it to be there.  I'm using a yoke that I wound for another purpose, it doesn't have quite 900 turns on it. I tried another coil of around 3 H and it behaved almost the same except with a much lower ring frequency at the TP1. Still no higher voltage, narrower spike showed up. So today I'll wind a proper 900 turn yoke (I only have #27 wire though).

I deliberately used the slowest diodes in my box. I am going to start changing diodes to see if faster diodes make any difference. I have a bunch of diodes from TV and monitor chassis but I don't recall seeing your exact diode in there, I'll have to look again. I'll also change to a faster scope, in case the 60 MHz Tek 2213a is missing something.

I know money is tight these days but you really need an oscilloscope for this kind of work. You should be able to get a decent analog scope in the 60 MHz bandwidth range for 200 dollars US or so on Ebay, and I have recommended the Hantek PC-based DSO several times as a reasonable choice for a "first scope", as it is only about 100 dollars or even less and comes with 2 decent probes.

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Negative discharge effect
« Reply #33 on: September 30, 2014, 07:41:05 AM »
OK, I've wound a proper yoke with 900 turns of #27 magnet wire. I wound it all on half the yoke using my recently-built coil winder. It makes quite a lump on the yoke half!

Then I reassembled the yoke and measured its inductance on the ProsKit MT-5210 RLC meter. It measures 600 milliHenry. Is it possible that you misplaced a decimal point when you calculated the inductance using your measurement method? (That method is valid, I have checked it myself and when it's done properly it produces a good answer.)

If I am understanding your negative discharge effect properly I am able to reproduce it with this setup. We are in the non-linear behaviour region of the mosfet for sure! The oscilloscope reveals so much interesting behaviour that I am going to have to make a video to show it all. I'll be putting that together over the next little while.

I'm using the second circuit, as below.

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Negative discharge effect
« Reply #34 on: September 30, 2014, 08:19:03 AM »
The IRF630 data sheet from Vishay has the characteristics of the body diode.
At the moment I am tending to believe the following: The device might actually be picking up power from the house mains! Here's what I'm seeing. The 3.2V signal to the gate is indeed critical. If I go a little bit above this value the voltage does not accumulate on the capacitor and the signs of line power pickup on the scope decrease. If I go a little bit below this value the mosfet isn't stirred up enough to allow the voltage to accumulate on the cap. Pulse width is also critical but the effect is harder to explain, I'll just have to show it. The pulse width determines the shape of the spike response and if it's too wide the peak spike droops and the rate of voltage accumulation on the cap decreases or stops. I think that the coil acts as the pickup for the line power and the mosfet in its just-barely-turned on state allows the negative discharge effect to happen on the capacitor.
Maybe. I'm not sure about any explanations yet. I am sure that at low Gate drive voltages, right around and below the 3.2 V value, I definitely am picking up power from the mains somehow. I don't know if this is what is being stored on the capacitor though.

nelsonrochaa

  • Hero Member
  • *****
  • Posts: 653
Re: Negative discharge effect
« Reply #35 on: September 30, 2014, 11:08:19 AM »
The IRF630 data sheet from Vishay has the characteristics of the body diode.
At the moment I am tending to believe the following: The device might actually be picking up power from the house mains! Here's what I'm seeing. The 3.2V signal to the gate is indeed critical. If I go a little bit above this value the voltage does not accumulate on the capacitor and the signs of line power pickup on the scope decrease. If I go a little bit below this value the mosfet isn't stirred up enough to allow the voltage to accumulate on the cap. Pulse width is also critical but the effect is harder to explain, I'll just have to show it. The pulse width determines the shape of the spike response and if it's too wide the peak spike droops and the rate of voltage accumulation on the cap decreases or stops. I think that the coil acts as the pickup for the line power and the mosfet in its just-barely-turned on state allows the negative discharge effect to happen on the capacitor.
Maybe. I'm not sure about any explanations yet. I am sure that at low Gate drive voltages, right around and below the 3.2 V value, I definitely am picking up power from the mains somehow. I don't know if this is what is being stored on the capacitor though.


Hi ,
if you put a cap of 200nf in parallel with the coil the result will be better .:) and the output in large capacitor have to be a load , without a load the circuit will not work optimal and maybe will fry the mosfet because the collapsed magnetic of the coil.
If you you monitor the charge in the cap when the voltage increase you will observe a defective commutation of the mosfet . 
When the coil collapse will fill rapidly the cap , but if the cap  is already full i observe that high voltage peake produce in the coil will try to find the path to the ground and return by the gate create a mistaken pulse  and the fault of the mosfet.
Another think that i test with good results : if you put a full bridge rectifier after the fast diode and connect the big cap in the bridge you will see that cap will charge more fast and the mosfet will work better.If you put the full bridge without the diode the result will be poor 
So far my best result is with a coil  3 ohm resistance. Can i ask how much resistance have the coil in your tests ?

thanks

ayeaye

  • Hero Member
  • *****
  • Posts: 866
Re: Negative discharge effect
« Reply #36 on: September 30, 2014, 03:01:31 PM »
So far my best result is with a coil  3 ohm resistance. Can i ask how much resistance have the coil in your tests ?
Thank you for repeating.

The static resistance of my coil, measured in the 200 ohms range, is 20.5 ohms. But the resistance of the crocodile wires is 1.3 ohms, so the resistance is 19.2 ohms.

I measured 80 mH on an inductor on which it was likely written 8.2 mH. I also calculated that the inductance of my coil is 0.16 H, assuming that the relative permeability of that core is 100. So the inductance of my coil may indeed be 0.66 H, which is 660 mH. I still cannot understand how could i make a mistake one decimal point. Then the relative permeability of the core is approximately 400, which is possible, but quite low for ferrite. The relative permeability of steel is 100 and, as i understand, the permeability of ferrite 3C90, common for toroid cores, is 2300 http://www.ferroxcube.com/FerroxcubeCorporateReception/datasheet/3c90.pdf .
« Last Edit: September 30, 2014, 05:35:34 PM by ayeaye »

ayeaye

  • Hero Member
  • *****
  • Posts: 866
Re: Negative discharge effect
« Reply #37 on: October 01, 2014, 03:29:41 AM »
What concerns measuring the inductance with a resistor in series, i have seen 3 different equations, yes 3, and all claimed to be about sine. But in my simple mind, coil's impedance with a sine waveform is 2 * pi * f * L , so R = 2 * pi * f * L and thus L = R / (2 * pi * f) , simple. So this i think is the right equation of these 3. Measuring inductance with an AC adapter is not so reliable though, because it assumes that the waveform in the main power supply is sine, when it differs from it anyhow, then there would be an additional coefficient. So wrong equation together with not so perfect sine, likely caused in my case a 10 times error.

Nelsonrochaa, if you did an experiment, then you may put the results up somewhere. The best in a video, so that everything would be known about the experiment, some small details may be important.

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Negative discharge effect
« Reply #38 on: October 01, 2014, 05:12:07 AM »

ayeaye

  • Hero Member
  • *****
  • Posts: 866
Re: Negative discharge effect
« Reply #39 on: October 01, 2014, 04:02:33 PM »
Many thanks TinselKoala, and looks beautiful too. I added a reference to this image of your circuit to the description of my video, and said that you are not conclusive yet about where the energy comes. This i found the best way to say what the state of the things are so far.

My video https://archive.org/details/ndischarge

ayeaye

  • Hero Member
  • *****
  • Posts: 866
Re: Negative discharge effect
« Reply #40 on: October 01, 2014, 09:08:08 PM »
TinselKoala, i saw you made a video too https://www.youtube.com/watch?v=qUMb6e6QQIA&list=UUZFlznLV3IyePfbc2TfDetA , thank you, great video, great work :) This video helped to learn a lot of new about that circuit. And the presence of the effect is now confirmed, an effect is often considered valid only after repeated the first time by another person, so it's like a part of finding it. It is all now about how it is interpreted, and which of these interpretations is more correct.

Now maybe i would like to stick to my interpretation, forgive me, as this was the idea why i started it at the first place. So this can be taken as my interpretation, others have different interpretations of their own. But this is what i would like to say.

Notice these things. It picks the frequency out of the mains, right, some kind of induction. But this does not occur when the circuit is not in resonance. Also the voltage on the multimeter almost does not rise when the gate voltage is low, and there are no spikes in the coil. Even in spite that this induced mains voltage sometimes goes negative.

The ringing of the coil, 20 kHz, this is caused by the mosfet's output capacitance, the amplitude of that is very small, and this is likely as much there is leakage from the mosfet, this voltage is not much and not likely to cause the effect.

But the main thing is, there is almost no back-emf on the coil. And thus it can be no way explained how the capacitor can charge with the polarity how it does. The voltage on the capacitor is related to the voltage of the spikes, because these are the only things which can provide high enough voltage. So this is where comes my suggestion of negative discharge. It is about that a positive voltage spike in the coil, causes current to flow from the capacitor, and when there is no positive charge in the capacitor, it charges negatively. It may seem naive but, this is nothing bout the first thing i thought when i first saw the effect.

There are always many interferences, and if we say that when there are any of them present, then this must be the cause of the effect, then we can dismiss whatever effect. I also succeeded to get higher voltages, up to 2.6 volts, which is much higher than the amplitude of that mains induction, but i could not repeat it on the same frequency and duty cycle.

But one more thing which this inducing voltage by the mains may say. It says that there are things which interfere with the circuit. This may be another reason why the effect may occur on different frequency and duty cycle even when all the components remain the same. It may be enough that the frequency of your mains power changes slightly, and the effect is not on the same frequency any more.

ayeaye

  • Hero Member
  • *****
  • Posts: 866
Re: Negative discharge effect
« Reply #41 on: October 02, 2014, 04:36:32 PM »
Maybe i should explain more what i mean by negative discharge. For example when charging three capacitors in series, then the middle capacitor charges by negative discharge. Because the plates facing each other of two capacitors have zero charge, but after charging they have instead equal and opposite charges. And they take that charge from each other, like when taking positive charge, as a result the plate where they take that charge, would have a negative charge. So this is not charging, but negatively discharging.

  | +
  =
  | 0
  | 0
  =
  | -

  | +
  =
  | -
  | +
  =
  | - 

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Negative discharge effect
« Reply #42 on: October 03, 2014, 10:17:56 PM »
Well, isn't it obvious that any two plates that are connected together (Plate B of Cap 1 is wired together with Plate A of Cap 2, etc) have the same charge?

At any rate I've been testing a few different diodes. Most interesting is when the "direct" setting -- no diode -- is used.


ayeaye

  • Hero Member
  • *****
  • Posts: 866
Re: Negative discharge effect
« Reply #43 on: October 04, 2014, 07:00:09 PM »
It's really great what you do, TinselKoala, and i'm thankful to you, but then with your experiments you create more questions than answers...

TinselKoala

  • Hero Member
  • *****
  • Posts: 13958
Re: Negative discharge effect
« Reply #44 on: October 04, 2014, 10:14:29 PM »
It's really great what you do, TinselKoala, and i'm thankful to you, but then with your experiments you create more questions than answers...

I think that's the nicest thing anyone has said to me in a long time!

 :)