Frequency

[Alberto]

Hello.

I bought theese and I don´t understand one thing. If I run the transformer with the PCB, and I measure the frequency in the primary, it gives 214 Khz, both of them. And 2,6V



But, if I try to run  the transformer alone, with my own oscillator, at 214Khz the arc is almost inexistent. The best performance is at 30 khz

Why that difference?

Thank you

Kind regards

[John123]

Can you post a schematic? Maybe the drive waveform isn't correct with your circuit perhaps.

[Alberto]

[John123]

How were you measuring the original 214khz? Is this for an actual flyback transformer from a CRT? 214khz sounds way too high if it is.

[davekni]

The circuit shown should generate ~12-16kHz.  The 214kHz reading was likely counting ringing cycles of the transformer.  An oscilloscope is the best way to measure complex waveform shapes.  If using a frequency-counter or meter, measure 555 pin 3 rather than the transformer.

[Alberto]

Sorry!!

I have just realise that I forgot put the images of the coil and the driver!!



In the picture they are the drivers and coils I bought and it works at 214khz

And the diagram is about my oscillator with wich they work better at 30Khz

[John123]

Sorry!!

I have just realise that I forgot put the images of the coil and the driver!!



In the picture they are the drivers and coils I bought and it works at 214khz

And the diagram is about my oscillator with wich they work better at 30Khz

Oh they look interesting, have you scoped the original circuit to see what drive waveform is being applied to it and in what topology?

How are you measuring that 214khz? Like Dave said if you're using a multi meter then you might just be measuring ringing. Scope/measure on the gate/base pin of the drive transistor of the original board.

[Alberto]

Please, don´t kill me, but my most advanced instrument is an 25$ DMM.

One question. I bought theese things in aliex****. They don´t put anything in the description most of the times. How can I know the maximun voltage to run this coils? I dont even know the diameter of the wire of the primary...

[John123]

Hey that's fine, just put the black probe on the transistors source/emitter and red on the output of the thing driving the gate/base for measuring frequency. Trying to measure across the primary coil usually doesn't work due to ringing.

So there wasn't a max input voltage listed in the description?

[davekni]

I bought a couple of those circuits before discovering someone selling just the transformers.  I did not use the circuits that come with the transformers.  They are simple single-transistor (BJT) oscillators using a second primary winding for feedback.  I expect the frequency is well below 214kHz, but can't say for sure.  I'm using the transformers for my small plasma-globe (two in series):
https://highvoltageforum.net/index.php?topic=924.msg6187#msg6187

[Alberto]

This is a great forum, I always learn grat things. Thanks for your answers.

You were right. When I measure the frequency in the way you say it gives 30 khz (Sorry davekni, I didn´t understand the first time you told me)

And on the voltage, looking up, I found that the circuit is rated at 12v, but I prefer to run the transformers on my own. There is no typical voltage for those transformers, right?

[davekni]

Not much in the way of real specifications on these.  Some of the listings say 10kV or 15kV for the secondary, but also say not to run them without forming an arc.  In other words, they won't survive 10kV for long - just enough to strike an arc.

Mine measure 24uH primary and 470mH secondary.  Winding resistance is 0.16ohms primary and 2.1k secondary.

Correction to my previous post:  The single-transistor oscillator version I'd purchased used a different transformer on a tiny U-core.  I didn't buy oscillators with these, so don't know what circuit they use.  I use them with a ZVS oscillator circuit.

[Alberto]

Not much in the way of real specifications on these.  Some of the listings say 10kV or 15kV for the secondary, but also say not to run them without forming an arc.  In other words, they won't survive 10kV for long - just enough to strike an arc.

Mine measure 24uH primary and 470mH secondary.  Winding resistance is 0.16ohms primary and 2.1k secondary.

Correction to my previous post:  The single-transistor oscillator version I'd purchased used a different transformer on a tiny U-core.  I didn't buy oscillators with these, so don't know what circuit they use.  I use them with a ZVS oscillator circuit.

Thank you for your answer. Yes, that is my question. What voltage do you apply with the ZVS?

[davekni]

I use 15-19V into the ZVS for two of these in series.  This generates about +-8kV.  You could probably run higher for short periods of time.  My goal was to handle continuous operation without overheating nor insulation breakdown.

[Alberto]

I use 15-19V into the ZVS for two of these in series.  This generates about +-8kV.  You could probably run higher for short periods of time.  My goal was to handle continuous operation without overheating nor insulation breakdown.

Ok, thank you so much!

[Alberto]

I use 15-19V into the ZVS for two of these in series.  This generates about +-8kV.  You could probably run higher for short periods of time.  My goal was to handle continuous operation without overheating nor insulation breakdown.

Another question. You say you run them in series. Do you mean the primary in series  and also the secondary in series to get more output right?

I thought it would be better in parallel.

And, could you put a diagram of a simple ZVS to run them? I have made a mazili driver, but I don´t know how to connect it to thak kind of transformers. I use it for flybacks

[davekni]

Yes, both primary and secondary are in series.  Parallel would increase current, series increases voltage.

I have the project documented here:
https://highvoltageforum.net/index.php?topic=924.msg6187#msg6187
Ignore the left half of the circuit.  That is a buck-converter to add current limiting and adjustable power.  Right half of the schematic is a ZVS oscillator.

[Alberto]

Yes, both primary and secondary are in series.  Parallel would increase current, series increases voltage.

I have the project documented here:
https://highvoltageforum.net/index.php?topic=924.msg6187#msg6187
Ignore the left half of the circuit.  That is a buck-converter to add current limiting and adjustable power.  Right half of the schematic is a ZVS oscillator.

Thank you very much. It has worked!



I´m dumb in electronics (I´m teacher of economics) and I didn´t realize that if I coupled the to coils ther primary behave like the 2 primaries I use in the flyback.

And the arcs where a little bit shorter, but more powerfull. When I run one of these coils with the 555 oscillator my skin only burns, but this time I have felt the current.

And no, I donñt use to touch electricity. 

And your plasma globeis NICE!

[davekni]

Great to hear that it is working for you.

Yes, the center of the two series-connected primary windings works well as the power-feed point for ZVS oscillators.  Coupling-factor is low between the two windings compared to normal center-tapped winding halves.  Low primary coupling is not an issue for ZVS oscillators.  Many ZVS oscillator circuits use two separate inductors for power feed (zero coupling).

[Alberto]

Great to hear that it is working for you.

Yes, the center of the two series-connected primary windings works well as the power-feed point for ZVS oscillators.  Coupling-factor is low between the two windings compared to normal center-tapped winding halves.  Low primary coupling is not an issue for ZVS oscillators.  Many ZVS oscillator circuits use two separate inductors for power feed (zero coupling).

Ok ok, thank you for all your help. I have just bought the NiZn ferrite to a better coupling.

[John123]

Bit late now but there's another iteration of the ZVS driver which does away with the requirement for a center tapped primary coil.

Source: http://www.kiblerelectronics.com/bob/app_notes/note11/note11.html

[Alberto]

Not late. I´m always building things. I´ll try that one. Thanks!

[Alberto]

Hey that's fine, just put the black probe on the transistors source/emitter and red on the output of the thing driving the gate/base for measuring frequency. Trying to measure across the primary coil usually doesn't work due to ringing.

So there wasn't a max input voltage listed in the description?

Hello. I tried this in a new set up. A ZVS to run a AC flyback

It has 2 MOSFET and I measure the frequency in the source and the gate. If there is no arc, I measure 12 Khz and if I bring closer the wires of the secondary and the arc starts, i measure 50Khz   Wich one is the good one? For example, if I put a cockcroft-walton, wich frency is the good one to make the calculations for the cockcroft-walton?

And another question, if a use another DMM if there is no arc, the frequency measured is 12kHz, but when there is an arc, the frequency goes to 100kHz

Thank you

[davekni]

If there is no arc, I measure 12 Khz and if I bring closer the wires of the secondary and the arc starts, i measure 50Khz

For ZVS oscillators feeding transformers, it is normal for frequency to increase at high load.  Oscillation changes from transformer's normal parallel inductance to transformer's leakage inductance (inductance with secondary shorted).

And another question, if a use another DMM if there is no arc, the frequency measured is 12kHz, but when there is an arc, the frequency goes to 100kHz

Arcs are erratic loads.  And they create EMI that can confuse local electronics such as low-cost DMMs with minimal internal shielding.  However, given the 2:1 ratio, perhaps more likely that second DMM is measuring a harmonic frequency.  Even first may be measuring a harmonic, with actual frequency being perhaps 25kHz.

Are you using the primary winding built into this AC flyback?  Or are you winding a new primary on the other leg of the ferrite core as most people do when using ZVS drive?

[Alberto]

Thanks for your answer.

I'm winding cable around the ferrite

[davekni]

I'm winding cable around the ferrite

In that case a jump from 12kHz to 50kHz is likely not real either.  Perhaps either 16.66kHz or 25kHz.

Best way to measure upper frequency may be with transformer secondary shorted rather than arcing.  Primary should have a more stable waveform that way.

Wich one is the good one? For example, if I put a cockcroft-walton, wich frency is the good one to make the calculations for the cockcroft-walton?

For a CW multiplier, starting frequency will be higher one.  Capacitors are not charged, so present a high load.  As capacitors charge, frequency will switch to lower 12kHz.
If transformer coupling is too high (frequency ratio above 1.88x), ZVS oscillators are prone to drop out of oscillation and burn out during the frequency transition region of loading.

[Alberto]

Thank you!