Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Messages - davekni

Pages: 1 2 [3] 4 5 ... 139

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: 160mm DRSSTC II project | Questions

« on: March 15, 2024, 08:06:08 PM »

Quote

1) If i use 2 GDTs is it better to use one for each of the bricks or one for top IGBTs and other for bottom IGBTs?

One GDT per brick (one per half-bridge) is better. Uniform load on both edges for each GDT, one gate rising while other gate is falling. Keeps dead-time uniform. And some pulse-skip drivers require 2 GDTs connected this way (one per half-bridge).

Quote

2) If i use signle wires instead of a cat5 cable is it better to have as many primary wires as secondary wires on the GDT? And having them twisted together

Yes. Twist each pair (one primary and one secondary) together within coil winding. Twist each primary winding lead pair separately. Parallel the four (or two) primary windings at driver.

Quote

3) How much for coil this size does GDT wire crosssection matter and is there optimal crossection for a GDT.

Don't think wire gauge is very critical, but get other opinions too. Ratio of wire diameter to insulation diameter does matter some. Thicker insulation is best combined with larger wire diameter too. That keeps parasitic (leakage) inductance from rising. (Leakage inductance for twisted pair windings is proportional to log(wire spacing / wire diameter).

Quote

4) Am i correct to assume that its better to keep the GDT wires as short as possible and use shielded wire for the primary? (GDT would be way closer to igbts than the driver circuit)

If primary leads are twisted, shielding shouldn't be needed.

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: Bleeder resistor for MMC

« on: March 15, 2024, 06:20:47 PM »

Quote

It is rare, however I think relying on luck to prevent destruction of IGBTs is not the path I'd take

Rare is a relative term. For normal axial-leaded wire wound power resistors, I think "rare" is close enough to never. Meteorite impacts are rare too. I spend no time being concerned about coil destruction by meteorite impact.

Beginners / Re: No Corona Discharge with ZVS Driver

« on: March 15, 2024, 12:00:51 AM »

Quote

What do you mean by a capacitor value which is used in which original circuit?

HV flyback transformers were mostly built for CRT displays (TV sets and computer monitors). When used in CRT circuits, drive looked close to your 555 circuit, but with a capacitor across primary winding terminals. Unfortunately I have no way to know what value was actually used for any given flyback primary. Probably less than 0.68uF, perhaps between 10nF and 100nF. If you have an oscilloscope, proper value can be estimated by checking waveforms.
Without any capacitor, IRFP260N FET is going into avalanche breakdown on every on-to-off transition. Wastes power and heats FET.

Quote

I have added the circuit diagram of my Flyback as an attachment.

I presume IRFP260N source connects to ground rather than +7V as shown in your 555 schematic.

Quote

I used the coil between pin 1 and 2 as the internal coil for the 555 Circuit.

Do you have a specification for this flyback transformer? There's no way to tell from the schematic which pins were intended for primary drive. Primary winding likely has low resistance (larger wire diameter) than most other windings.
Have you tried swapping pins 1 and 2? For flyback drive into rectified secondary, output voltage will be much higher with one polarity than the other.
Most CRT flyback primaries are designed to be driven by higher voltage FETs, usually 900V to 1500V FETs. Other primary windings may work well with lower voltage FETs, but also may have higher DC resistance and over-heat with continuous operation.

Quote

Now i can create much more corona discharge, but is it possible to create the same result with the zvs driver?
It is still much more efficient.

By "efficient" do you mean it draws less current? That would be expected for a circuit generating less output power.

Because ZVS waveforms are symmetric AC sine waves, flyback output can't reach quite the same voltage as with proper flyback drive (555 style drive) into correct primary coil with correct FET voltage capability and parallel capacitor. However, ZVS can likely achieve enough for your interests. Difficult to debug without a scope. I'd suggest first selecting ZVS cap value to hit desired frequency, say 20kHz. Then increase voltage to ZVS circuit until output reaches what you want.

General Chat / Re: Welcome new members, come say hello and tell a little about yourself :)

« on: March 14, 2024, 11:23:20 PM »

Quote

I've since purchased a cheap oscilloscope

Almost any issue can be figured out with proper scope captures. Much harder to guess what an issue may be through just pictures and DMM measurements.

Good luck with your bridge build! Mads site has lots of great information. A couple tutorials I've posted here might be helpful too:
https://highvoltageforum.net/index.php?topic=1854.msg13949#msg13949
https://highvoltageforum.net/index.php?topic=1324.msg9795#msg9795

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: Super flat QCW simulation (does this look reasonable?)

« on: March 14, 2024, 05:03:41 AM »

Quote

I simulated this thing and seem to have soft switching on both legs of the bridge? I thought this was not possible?

Yes, it is possible and desirable. With correct dead time phasing, one FET turns off, remaining (small) primary current causes Vds to rise, then opposite FET turns on as its Vds approaches 0V.

Quote

Currently using CoolMOS C7 as Quorvo models don't want to converge.

Yes, some models have trouble converging, especially IGBT models. Often the old LTSpice IV converges much better than any version since then. I use LTSpice IV most of the time. Haven't found any advantage to newer releases.

Beginners / Re: No Corona Discharge with ZVS Driver

« on: March 14, 2024, 04:56:51 AM »

Quote

I actually have a few more pictures of the circuit and the corona discharge, but when uploading und attaching pictures I always get "Invalid Attachment".

I've occasionally experienced the same issue. However, ignore the message and attach anyway. Image shows up at the end of message instead of where it was inserted, but still is there. Images would be very helpful. (I presume you are using an allowed image file type. Mine are always ".jpg".)

Quote

I can also set the frequency of the 555 circuit. But I can't get to a frequency that you can't hear and that allows the transformer to work at the same time. So I can only operate the transformer with a loud annoying noise.

Most DC flyback transformers are designed for at least 15.625kHz (old analog PAL TV standard). Likely to work OK to 20kHz with proper drive.

Are you using primary winding built into flyback transformer? Or are you forming a new primary on other leg of flyback's ferrite core? Added primary winding works best with ZVS drive. For 555 drive (conventional flyback drive), internal primary works better. Typically requires a high voltage FET for drive when using internal primary, and a resonant capacitor across primary roughly matching value used in original circuit.

Voltage Multipliers / Re: Bleeder resistor in CW multiplier

« on: March 10, 2024, 06:58:51 PM »

B5 to ground

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC Questions

« on: March 10, 2024, 06:49:36 PM »

Quote

Looking at the thundermouse's page, it lists on time up to 20ms. This is more likely why its max arc length is so good.

You may not need 20ms, but long on times match well with high coupling. The high coupling allows primary-to-secondary energy transfer for longer (over a wider frequency range as arc loading reduces secondary frequency). That's the key advantage of high coupling.

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC Questions

« on: March 10, 2024, 03:42:28 AM »

Quote

So I guess the question is, is a DRRSTC with such high coupling realistic?

Short answer: Yes, I think so.
AFAIK, DRSSTCs are better with as high coupling as possible without creating racing sparks along lower part of secondary. Low secondary aspect ratios (height/diameter) allow higher coupling without racing sparks. Low aspect ratios are common for short coils such as this. I think I've seen several such small DRSSTC examples with similar coupling on the forum, but don't recall any specific ones to mention.

Transformer (Ferrite Core) / Re: Frequency

« on: March 07, 2024, 11:35:01 PM »

Quote

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.

Quote

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.

Beginners / Re: Unknown Diode Replacement

« on: March 07, 2024, 10:55:40 PM »

Quote

What is the purpose of the diode and resistor connected to the gate of the IGBT? I would be very grateful for some help in finding a suitable replacement diode.

Purpose is to speed up on-to-off transition of IGBT (falling edge of Vge). Schottky diodes are normal here, as confirmed by your 0.245Vf measurement. Perhaps something like DSS16U or SMD16PL-TP for SMD options. 1N5819 is a common through-hole part used. Any ~1A 40V or higher schottky diode is likely to work fine.

Electronic Circuits / Re: CM400 Induction Heater

« on: March 07, 2024, 10:46:42 PM »

Quote

Meanwhile I managed to track down an issue that has been plaguing me during the last few days:

Looks like you need a bleed resistor across H-bridge output. That way startup will be consistent. Without resistor, leakage current of IGBTs defines initial bridge output voltage. If output happens to be at same level as first half-cycle drives it, no current is generated.
Yet faster startup can be achieved if two resistors are used to bias initial H-bridge output to either + or - Vbus. However, that requires checking which polarity first half-cycle drives H-bridge, then adding resistors to bias output to opposite polarity.

Quote

I gave the smaller crucible a try though (empty), and it presents a very light load. At 12V / 50% duty cycle it takes ages to heat up and only gets to the point where it is glowing a bit.

Any non-magnetic load is likely to be less effective (higher Q), so require higher voltage (higher current and/or higher frequency).

Transformer (Ferrite Core) / Re: Frequency

« on: March 07, 2024, 10:23:27 PM »

Quote

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).

Quote

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?

Electronic Circuits / Re: CM400 Induction Heater

« on: March 07, 2024, 05:12:31 AM »

Quote

I don't understand why the tank current would rise "after the temperature reaches the curie point". What ferrous metals are you heating at that time?
In my humble (ZVS induction heating) experience, current DECREASES as ferrous metals in the work coil reach the curie point.

Yes, same load change at Curie point causes opposite power change. ZVS drive (parallel drive resulting in fixed voltage across coil) consumes less power when load Q increases. H-bridge drive in series with coil consumes more power when load Q increases.

Quote

I notice a graphite crucible sitting beside the work coil in one picture, but that isn't ferrous, so "curie point" wouldn't apply. Right?

I was wondering the same thing. Depends on crucible electrical conductivity and geometry and drive frequency. Test may or may not have included crucible, at least I didn't notice that being specified. If crucible was included, implies it's conductivity is too low to block most magnetic field from center. Higher frequency (resulting in higher volts/turn for same magnetic field) will move more heating to crucible and away from iron in center.

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: Secondary Splicing

« on: March 07, 2024, 03:43:25 AM »

I'd guess a splice to be fine in the upper half of secondary away from primary. Peak volts/turn tends to be lower there. Just make a smooth splice and add a few extra layers of epoxy coating over it as extra protection. Smooth coating will spread out field from remaining splice unevenness as well as insulating splice better.

Hope you get other opinions too. Above is just my speculation. Haven't tried such personally. I've seen one large SGTC with a splice in upper part of secondary (from a local friend who got me started with TCs).

Electronic Circuits / Re: CM400 Induction Heater

« on: March 07, 2024, 01:19:03 AM »

Quote

So does this mean I would be better of with a lower capacity, for example half? A quick test shows that I end up around 40kHz with that.
Downside is that my Arms will also be cut in half..

Higher frequency generally requires less current to deliver same power to load being heated. However, that depends on load. And you can easily increase current by supplying higher bus voltage. Especially for experimenting before adding impedance matching, higher frequency will be closer to reasonable impedance.

Quote

edit: I forgot to mention that switching to 15V really improved the temperature of the gate resistors. They still get kinda hot with higher duty cycles, but the larger resistors I ordered will help with that hopefully.

Higher frequency increase gate resistor power proportionately. That is one down-side. But gate power resistors are relatively inexpensive. Or change to a buffered circuit.

Quote

IGBT heatsink started heating up

Expected. Switching losses are low with ZCS and low bus voltage. Vce forward drop is the dominant loss, tracking current, not voltage.

Quote

Btw - is it better to connect one of the supply wires to the other end of the "U" instead for better current sharing between the bus caps? Or is this a bad idea since I will get a huge loop = adding lots of inductance?

Unlikely to make any significant difference. Most AC (ripple) current is between IGBTs and caps. Inductance to supply is not very important.

Quote

Would it be an issue for the PSU if I completely removed the bus caps (since I am using an interrupter)?

Probably would be a problem. Most PSU output capacitors are intended to handle ripple current generated within PSU, not huge ripple current from load.

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: First DRSSTC Build Log

« on: March 07, 2024, 01:06:15 AM »

Quote

I think this is how its supposed to look like with a resistive load or are the voltage spikes too high? I think they should reduce once I reduce the GDT connection lead length.

Looks reasonable. GDT would be better with four parallel primary wires, one twisted with each secondary wire (along with shorter leads).

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: UD2.7C Debugging

« on: March 06, 2024, 02:34:46 AM »

Looks good.
BTW, real GDT is best made with twisted pairs such as from CAT5 cable. Manually twisting wire pairs works too. Parallel one wire of each pair for primary, as in this tutorial:
https://highvoltageforum.net/index.php?topic=1854.msg19355#msg19355

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: UD2.7C Debugging

« on: March 05, 2024, 05:18:28 AM »

Quote

The mosfet Q4 irfp540 keeps dying (2 have died so far).

One likely cause for IRFP540 dying is that the paired IRF9540 is failed shorted. Or that 1k gate pull-up resistor(s) are open (ie. bad solder joint) or 0.1uF coupling capacitor is shorted.

Quote

Even the time in which it is on, the gate drive output waveform doesn't look good and it keeps moving.

Scope traces of the two GDT primary leads (UD2.7 output terminals) would be more useful for debug.

Quote

It still tends to turns off after a few seconds of operation, also the LM7812 voltage regulator gets extremely hot.

Output FETs don't directly connect to +12V, only UCC27423. Since it is still good, implies high load on UCC27423 output(s). Most likely cause is a bad FET with shorted gate. Another reason to suspect an IRF9540 having died (or both).

If still problematic, I'd remove all four FETs and test with UCC27423 chip installed. Scope FET gate waveforms and verify supplies are not loaded excessively.

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: Big Coil Build Log

« on: March 05, 2024, 03:42:57 AM »

Quote

The partition of RF current might depend a lot on the inductance of wires.

Exactly what I was thinking, why I guessed wire size was not an issue.

Quote

Inductance depends on log of (wire spacing / wire diameter), but the empirical formulas are less accurate when the insulation is much thinner than the conductors.

Very rough estimates should be fine here. Physical layout prevents twisting for ~half of wire length anyway.

Just looking at existing wiring, I'd guess between 0.6uH and 1uH for wires. At 40kHz coil, ripple current is 80kHz. 0.6uH is ~0.3 ohms reactance at 80kHz. 560uF capacitor at bridge is ~0.0036 ohms. Thus very little 80kHz current will flow through wires. Interconnect inductance of 560uH capacitor is likely higher than 0.0036 ohms, so may control wire current more than capacitance.

Edit: Forgot about pulse-skipping. That will generate lower frequency ripple current. At 20kHz, current sharing would be closer to 5:1. But I think RMS current component at 20kHz will be lower than 80kHz of full-on operation. Would need to simulate or hand-calculate a bit more to be sure of this.

The biggest risk may be if pulse-skipping frequency happens to hit exactly at LC resonant frequency of 560uF and wire inductance. That's where some form of R+C snubbing might be needed at bridge.

Pages: 1 2 [3] 4 5 ... 139

Show Posts

Messages - davekni

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: 160mm DRSSTC II project | Questions

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: Bleeder resistor for MMC

Beginners / Re: No Corona Discharge with ZVS Driver

General Chat / Re: Welcome new members, come say hello and tell a little about yourself :)

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: Super flat QCW simulation (does this look reasonable?)

Beginners / Re: No Corona Discharge with ZVS Driver

Voltage Multipliers / Re: Bleeder resistor in CW multiplier

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC Questions

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: DRSSTC Questions

Transformer (Ferrite Core) / Re: Frequency

Beginners / Re: Unknown Diode Replacement

Electronic Circuits / Re: CM400 Induction Heater

Transformer (Ferrite Core) / Re: Frequency

Electronic Circuits / Re: CM400 Induction Heater

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: Secondary Splicing

Electronic Circuits / Re: CM400 Induction Heater

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: First DRSSTC Build Log

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: UD2.7C Debugging

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: UD2.7C Debugging

Dual Resonant Solid State Tesla coils (DRSSTC) / Re: Big Coil Build Log

Recent Topics and Posts