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Registered Member #14432
Joined: Sat Apr 20 2013, 01:18PM
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Posts: 18
Hi again Proud Mary and thank you for the paper. I have read lots of papers about the LOPT and my brain doesn't have enough ghz to still grasp how exactly it in details works but I am going to deep analyze that useful paper:) I don't know but it seems to me that tesla coil basic operation theory is so much easier to understand IMO.. I could be wrong(I mean the traditional tesla coil.., the SSTC technical side could be much different though)
Alright:) I have now tried 3 things across the flyback with moderate power 3.5vPSU input(probe is 1ft from +terminal):
1- A diode between 0v and ground(both diode sides tested) 2- A capacitor 3 A diode and a capacitor(diode hooked to 0v of flyback)
In short it seems that the waveform didnt change much.
1- First 2 pics.Amplitude decreased dramatically when hooking the diode. Only thing that happened here almost as it should was: the damped ringings turned only almost into one directed DC directed pulses as you can see in pictures. However there was still AC(perhaps its because the diode isnt perfect...ha?)
2- Third pic. Tried both 850pf and 4700pf ceramic disc caps, with one terminal end of cap and flyback 0v to the ground. Other end of cap hooked to + of flyback. Both caps caused the amplitude decrease a lot. With the 4700pf ceramic disc test as you can from the picture the 4700pfcap only smoothed very little of the ringings but amplitude was towards the negative side?? I am confused to what to make out of this. Is this how it suppose to look like?
3- When hooking both the diode(tried both sides) and 4700pf together, I get no result at all at the oscilloscope.
I am a little puzzled, the diode situation could be explained by imperfection of diode but what a about the smoothing capacitor that didnt smooth the out put?
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Modern LOPTs are almost all of the 'diode split' type, which produce a DC output, so I'm not clear why you are adding an extra rectifier to its output. It doesn't need one.
If you could post a picture of your circuit arrangements, together with a circuit diagram, it would reduce the amount of guesswork in helping you sort it out.
Registered Member #14432
Joined: Sat Apr 20 2013, 01:18PM
Location:
Posts: 18
Proud Mary, hehe no no, oh yes I know it is a DC dst flyback type and it charges my capacitors when I tested so it is DC certainly. However, I put the diode in accordance to the sugestion made by Sigurthr "I think you are seeing ringing and the AC signal from the HV return. Try placing a forward biased HV diode between the HV Return and your scope ground probe."....to see why the output wave in the first place have AC components I put the capacitor here to see if the output would be smoothed but as you can see from the waveform, it wasnt so smoothed ..
The driver circuit is a basic typical feedback one. the probe is 1ft from the + of flyback. Here are the 4 arrangements I made in my testing. The capacitor was a 4700pf ceramic disc type. The diode connected to ground was a HV fast diode and I tried both ways, with cathode to ground and with anode to ground. So now I wonder why the waveform was as it was and was never smoothed with the 4700pf cap connected, even with different size caps, all that happened was higher or lower amplitude of the same waveform
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Good, now I think we can understand what is going on.
1. Forget what I said about the waveforms to be expected in TV service, and we will assume that the primary waveform is crudely sinusoidal.
2. Once every cycle, the voltage across the series diode-split secondaries climbs high enough to break down the air at the end of your EHT lead, probably as a corona discharge with streamers.
3. Until the voltage needed to break down the air is reached, no electromagnetic energy is generated that can cross the one foot gap to your probe.
4. As soon as the voltage falls below the ionisation voltage, the radiated electromagnetic energy will stop.
5. This is why you are seeing pulses at your probe. It would look very different if you were able to monitor the voltage across a load, such as a resistor, when you would see much more like the true waveform. I do not recommend you try this until you have got more experience, as an oscilloscope can very easily be ruined beyond repair by voltages of this order.
6. I have been a bit vague about 'electromagnetic energy', because I think that at a distance of one foot the signal arriving at your probe will have a mixed content. Some of it may come from the differential voltage gradient between the EHT terminal and your probe - thinking of the air being a resistor - a potential divider - in this case. And some of it will come from the detection of electromagnetic waves - i.e. radio waves - which no doubt are causing interference across a wide band of frequencies from VLF to UHF.
Your probe setup is completely unable to remotely detect DC appearing at the LOPT output. This is why the signal disappears when you put a larger capacitor across the output - the pulses have been smoothed out.
To sum up, the air around your EHT terminal is acting a bit like a zener diode. No current can flow until a certain (high) voltage is reached, and it will stop again at once when the voltage falls below the level needed to ionise the air. This is what is giving rise to the pulse wave form.
Thank you for showing us a very interesting experiment!
Registered Member #14432
Joined: Sat Apr 20 2013, 01:18PM
Location:
Posts: 18
Aaah, thank you, finally some solving to make me sane. I made sure to minimize any corona discharges at the terminals by adding big spheres but obviously that isnt near enough then. I was nearly pulling my hair into baldness:) I suspected what you said right before I did the testing experimentation but I had no other way to test. Best would be to directly connect the probe across the terminals but the oscilloscope would go to heaven ofcourse.
(BTW when I connected the capacitors the waveforms still were there, and if I connect a diode the waveforms were still there but when I connected the diode and capacitor.. thats when all signal is 100% lost :) )
So the only way now is to measure directly somehow which would need at least a very high resistance added to the probe( to make the probe a 1000x and lots of other variables...).. BUT! Hmmm isn't this "remote probe testing" I just used, also used successfully in reading HV devices like Tesla coils or am I wrong, That's why I thought it would be good to use this remote probing in the first place hmm.., the method seems to be working fine with many Tesla coils if not all I have seen .. yet a tesla coil isn't exactly "electromagnetically silent" if you know what I mean.
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
If you don't have anything connected to the flyback transformer output, the waveform there is almost not affected by the internal diodes, that charge just the small distributed capacitance of the transformer and external cables. The coupling to the oscilloscope probe is capacitive, so no DC can be seen anyway. The transformer rings with its distributed capacitance after the main pulse, and this is what you see. Connections as shown with external diodes or capacitors should not change this, but the extra wiring can change the coupling to the oscilloscope probe and change what is seen.
Registered Member #14432
Joined: Sat Apr 20 2013, 01:18PM
Location:
Posts: 18
Antonio wrote ...
If you don't have anything connected to the flyback transformer output, the waveform there is almost not affected by the internal diodes, that charge just the small distributed capacitance of the transformer and external cables. The coupling to the oscilloscope probe is capacitive, so no DC can be seen anyway. The transformer rings with its distributed capacitance after the main pulse, and this is what you see. Connections as shown with external diodes or capacitors should not change this, but the extra wiring can change the coupling to the oscilloscope probe and change what is seen.
Thanks for the good explanation. But what about Mary´s explanation that its actually the pickup of the corona discharges EMF at the leads that are affecting the probe, maybe it is both but which do you think is dominating?
Without a direct connection you're just getting capacitive coupling, which only passes AC signals (most of which are radiated from the HV return lead, external components won't change this as they will appear to be in parallel and not in series with the "dc-block air capacitor").
Registered Member #14432
Joined: Sat Apr 20 2013, 01:18PM
Location:
Posts: 18
I now also decided to confirm the source of waves. I picked up the grounded probe with my hand and carefully wiped half a ft above and across the entire circuit all way from the insulated big spherical terminals of flyback, over the cables and above the bad boy flyback itself. Indeed the signal was much stronger and absolutely strongest exactly across and above the flyback with its big secondary. As I start now to move further away from the center of flyback and move along the grounded 2ft HV return cable all the way the signal diminishes extremely to a very small amplitude. I tried now the other way. I started now to move away from the flyback center along the red + terminal wire of the flyback and also indeed the signal diminishes the further along the wire I move away from flyback center. But the diminishing here is not nearly extreme as that of the HV return. However as I reach the end of the + terminal the signal picks up a little more. But the signal is 10 times stronger exactly above the flyback. So from all what I understand now the signal is the original ac source before the inbuilt connected diodes, so the signal must therefor come from either or both: 1:the entire secondary winding itself, 2: the lead that hasnt the diode connected across it directly.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
I just recently saw this thread, been in north Dakota flying drones for academic purposes, but know im back.
exactly what is your goal here? are you wanting to measure the magnetic waveform from the core, or the electrical waveform from the HV output?
there are many factors that can muck-up what appears to be just another transformer. Flybacks are wonderfully complicated, with internal diodes, multiple windings with inter-winding capacities coupled all over, stray inductance, and so forth.
once you include a airgap to your probe, your effectively getting all kinds of bogus data appearing, and real data goes missing.
really, if you want an accurate electrical waveform, youll need an HV oscope probe (good luck getting one ). but if you want just the magnetic conditions of the core, you could wind your own coil, or find a good one to hi-jack just for measurement purposes.
EDIT: a step below the cost and difficulty of an HV probe, would be a resistive voltage divider, maybe tuned maybe not, depends on your needs. As others have said, that low side, isn't really a faithful ground, there's a whole bunch of garbage on it too around 1-3kv, at a blur of frequencies too.
you can find several of my related threads too, I have a benchtop HV PS using a feedback winding, and external resistors. and ive posted numerous threads on HV measurement... youll be able to learn from my mistakes if you like...
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Strange DC Flyback output waveform?
). but if you want just the magnetic conditions of the core, you could wind your own coil, or find a good one to hi-jack just for measurement purposes.