capacitor and diodes. Voltage values for a CW

[Alberto]

Hello. I´m making a CW multiplier. I want it to last, so I´m carefull with the values.

I´m using 40Kv 1nF capacitors and 2 20kv diodes in series. It will have 9 stages and I´n going to put in in a pipe filled with paraffin oil.

I don´t wat to put in more than 10kV AC 20 kHz, so what do you think of the voltage of the capacitos and the diodes?

Thank you

[MRMILSTAR]

Those look like very workable values. You may want to go higher in frequency. Use this calculator to try out some designs.
https://www.extremeelectronics.co.uk/calculators/cw-voltage-calculator/

[Alberto]

Thank you for your answer and the link, it is very useful.

My idea it is to put 10 stages to keep at minimum the voltage input.
I'm going to run a high frequency 300watts transformer with a ZVS. The gates are powered by an independent power supply and the rest of the circuit with a variable power supply, so I can vary the output. Is that a good idea? I mean in terms of voltage and current output and safety of the components.

I need to check the voltages at the secondary of the HF transformer, but I think with just 1 or 2 volts at the primary I can get around 1 or 2 kV at the secondary, so starting with around 40kV at the CW and more

Thank you

[MRMILSTAR]

My CW multiplier sounds very similar in concept to yours. You may want to take a look at my posting detailing my device here.
https://highvoltageforum.net/index.php?topic=1524.0

One problem with using a ZVS driver is that the input voltage output has to be at least around 10 volts before you apply power otherwise the transistors may latch-up and burn out. Once you have it oscillating you can then vary the input voltage to change the output voltage. Just be certain that you don't let the input voltage fall below about 10 volts.

[Alberto]

My CW multiplier sounds very similar in concept to yours. You may want to take a look at my posting detailing my device here.
https://highvoltageforum.net/index.php?topic=1524.0

One problem with using a ZVS driver is that the input voltage output has to be at least around 10 volts before you apply power otherwise the transistors may latch-up and burn out. Once you have it oscillating you can then vary the input voltage to change the output voltage. Just be certain that you don't let the input voltage fall below about 10 volts.

Yours look amazing!! And a very good finishng.

I'm not sure about what you say of the 10 volts input..I'm using this circuit



First I put 12volts in point A. And them y put between 1 or 12 volts in the red square. Is that what you mean

[MRMILSTAR]

Yes. You want at least 10 volts at point "A" from the DC power supply before you switch the power to the ZVS driver. I use a minimum of 12 volts just to be safe.

[Alberto]

Yes. You want at least 10 volts at point "A" from the DC power supply before you switch the power to the ZVS driver. I use a minimum of 12 volts just to be safe.

Thanks for your answer.

Yess I learnt that in this forum some time ago asking about a ZVS for an induction heater.

And another question. About measuring the output of the HF transformer. Could I do it using a bridge rectifier (HV diodes), capacitor to filter and a voltage divider using HV resistors? Let's say 260Megaohms. What should be the value of tha capacitor?

I use a basic needle voltmeter because my DMMs are cheap and got crazy measuring these things so I think it is a good idea to use a capacitor to know the peak value of the output. And should I use in the output of the transformer (I have some HV caps if around 10nf) or I can do it in the output of the voltage divider which would allow me to use a regular capacitor ?

[MRMILSTAR]

Look further down in the comments of the link to my CW multiplier that I supplied. I describe the method that I used to measure the HV output of the flyback transformer using a full-wave bridge rectifier, smoothing capacitor, and a COTS HV DC voltmeter.

[Alberto]

Look further down in the comments of the link to my CW multiplier that I supplied. I describe the method that I used to measure the HV output of the flyback transformer using a full-wave bridge rectifier, smoothing capacitor, and a COTS HV DC voltmeter.

Even to just measure the transformer output you make a neat and clean set up!!

Thanks for your answer. My concern is about the reduction of the voltage. I see you are using a HV probe right? I made a DIY probe with 10x 26Mohm resistor for a 1000:1 ratio. So can I use it with a 2nF capacitor to obtain the measurement of the peak voltage?

[Alberto]

Yes. You want at least 10 volts at point "A" from the DC power supply before you switch the power to the ZVS driver. I use a minimum of 12 volts just to be safe.

And another questión. I´m going to use one 24V power supply. I have put a 220ohm resistor in point A to use the 24Volts directly. And to power the ZVS driver, I put in the 24V power supply a DC-DC converter to vary the output. There is no problem taking the current for the gates and to power de ZVS from the same power supply right?

I have instaled a relay that allow to power the ZVS only when the gates are already with the 24volts to be safe.

Thabk you

[MRMILSTAR]

I don't know what the purpose of the resistor is. You may have trouble with the DC-DC converter. You are cascading two SMPSs. At the minimum, the DC-DC converter must be capable of supplying sufficient current, probably at least 10 amps. I would try and find a single adjustable SMPS.

[davekni]

And another questión. I´m going to use one 24V power supply. I have put a 220ohm resistor in point A to use the 24Volts directly. And to power the ZVS driver, I put in the 24V power supply a DC-DC converter to vary the output. There is no problem taking the current for the gates and to power de ZVS from the same power supply right?

I have instaled a relay that allow to power the ZVS only when the gates are already with the 24volts to be safe.

Yes, that should work well.  Presuming the existing 470ohm gate pull-up resistors are rated for 2 watts as listed in schematic, they will handle 24V directly.  No need for 220-ohm resistor to reduce power.  As a bonus, with 24V directly to gate resistors the FETs will switch faster so dissipate a bit less power.  Removing 220-ohm resistor also increases startup oscillation amplitude before relay closes, making startup even a bit more reliable.

[Alberto]

And another questión. I´m going to use one 24V power supply. I have put a 220ohm resistor in point A to use the 24Volts directly. And to power the ZVS driver, I put in the 24V power supply a DC-DC converter to vary the output. There is no problem taking the current for the gates and to power de ZVS from the same power supply right?

I have instaled a relay that allow to power the ZVS only when the gates are already with the 24volts to be safe.

Yes, that should work well.  Presuming the existing 470ohm gate pull-up resistors are rated for 2 watts as listed in schematic, they will handle 24V directly.  No need for 220-ohm resistor to reduce power.  As a bonus, with 24V directly to gate resistors the FETs will switch faster so dissipate a bit less power.  Removing 220-ohm resistor also increases startup oscillation amplitude before relay closes, making startup even a bit more reliable.

Thank for your answer

I added the 220 ohm resistor because de 470 ohm resistor, despite being 2watts get too hot and they where close to the MOSFETs in the PCB.

Since I'm going to enclose everything, I'm going to remove the 470 ohm resistor from the PCB and put th near the fan what pull the air from.the enclosure and they will get cooler

[Alberto]

Done! I had an accident with the cyanocrilate and the lid is a mess, but is sturdy



You can turn the pipe to obtain a positive or negative output

The worst part what making the lids of the pipe. Some acrylic sheets glued and later lathe and drill press. M3 screws in 5mm thick acrylic. A bit of silicone to seal it and paraffin oil.

I need to increase the output of the HF transformer. It is ran by a ZVS and 5+5 turns in the primary. Should I put 4+4 or 3+3? If I´m correct that should increase the output rigt? But does it affect to the current of the output?

Thank you

[MRMILSTAR]

Looks great. You have to experiment with the number of turns and the capacitance. I would start with 5+5. What kind of output do you get?

[Alberto]

Looks great. You have to experiment with the number of turns and the capacitance. I would start with 5+5. What kind of output do you get?

I tried to measure the voltage like you but I don't know why it doesn't work. But with 5+5 turns and a 16volts input the arcs in the secondary of the HF transformer starts at let's say 5 or 6mm so I think it is 5 or 6kv peak