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Messages - profdc9

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1
Dual Resonant Solid State Tesla coils / Re: Next Gen DRSSTC
« on: July 16, 2019, 04:05:07 AM »
The through-hole PCB is at

https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/Psoc5-power

You just need to zip the gerber files and send it to a PCB house like JLCPCB or Seeedstudio and they will send you a board.

Dan

That video is awesome and it got so intense at 0:45!

It seems like I am running out of excuses to get a UD3 up and running, didn't someone promise me to write up a guide on which hardware to use etc? Was it Hydron? Futurist? Profdc9? I forgot and unfortunately I do not have the time or mental surplus to take in more new things from scratch right now :)

2
Dual Resonant Solid State Tesla coils / Re: Kaizer half bridge driver
« on: July 12, 2019, 07:16:40 PM »
There's one other thing I realized too about C4 and C7...

C4 and C7 provide both snubber behavior (stabilizing the voltage at the MOSFET/IGBTs).  But because they also split the supply for driving one end of the half-bridge, there is another consideration when driving a tesla coil.  When driving an inductive load like a tesla coil primary,  you have a series resonance with L=tesla coil primary inductance and C=C4+C7.   With the added series capacitance C5, the resonance frequency given by L and Ctotal = 1/(1/(C4+C7)+1/C5).   So that the voltage drop of this LC series circuit is mostly across C5, C4 and C7 must be much greater than C5 so that the LC resonance is dominated by C5.  Otherwise, the voltage drop across C4/C7 approaches the supply voltage and may exceed it, causing catastrophic failure either due to excessive primary current or overvoltage on the transistors.  Of course the voltage on your Tesla primary coil and C5 depends on the Q of the primary, and so the exact capacitance for C4+C7 needed to keep the voltage swing on those capacitors under a certain amount is going to depend on the Q also.   Again because C5 is generally going to scale with coil power, as the frequency of the primary tends to drop with increasing power, so to will C4 and C7 increase as well.

Not to ramble on, but I made a half bridge to drive a hefty ferrite transformer and used about C4+C7=16 uF, but I was driving the transformer at 25 kHz, so a larger capacitance was needed.  In addition, I needed snubbers across the emitter/collectors and load itself as well as the power supply rails, as the inductive kickback of the transformer would blow out the IGBTs as well, because there is a lot of energy stored in the magnetic field of a ferrite with 6 square centimeters of cross-section and a permeability of 1500 as well as the gap in the transformer magnetic circuit.  The kickback occurs when you have a spark gap and the current is cut suddenly by quenching of the spark.  But maybe this given you a rough idea of what you need, because C4+C7 is going to scale inversely with the square root of frequency.

Dan

3
Dual Resonant Solid State Tesla coils / Re: Kaizer half bridge driver
« on: July 12, 2019, 06:33:00 PM »
I will venture an answer...

I think the answer to this is perhaps a little complicated, because it depends on the ESR of the bus capacitors and the inductance of the connection of those capacitors to the half bridge.    Ideally, you would want the impedance of the snubber (also called dc-link) capacitors to be much less than the total impedance of the inductance of the connection and the ESR of the bus capacitors at the frequency of use.  Of course, the snubbers themselves have their own ESR and inductance of the connector to the MOSFET/IGBT sources/emitters and drains/collectors, which adds to the impedance of the snubber, which is why bridge layout is important.  The inductance of the connection from the capacitors (both the bus capacitors and snubbers) could cause voltage spikes under transient changes in current that cause the drain-source/collector-emitter voltage to exceed safe operating area and failure of the device.  This is why short and fat connections between these capacitors and the transistors is necessary, and for example why some snubbers screw right onto the terminals of IGBT bricks.

Another criterion that could be used is to reduce the voltage transients on the MOSFET/IGBTs under a certain amount, which would basically be then the average current supplied to the transistors over a cycle multiplied by the impedance of the capacitor.   The tolerable amount of voltage change is partially going to be determined by how closely you operate your device bus voltage compared to the maximum safe operating area voltage.   If you are operating, for example, with a bus voltage from a doubled single-phase 220VAC supply, you will be operating perilously close to the limits of a 650 V transistor.  Operating with a lower bus voltage, however, can also stress devices because of the increased current for a given power, so you have to consider that when choosing the MOSFET/IGBTs.

So while that is a complicated answer to your question, the bottom line is that if you err on the side of making the capacitors larger and the connections short and fat, you are likely to have fewer problems.  I have an example of a half-bridge PCB I designed (you can get the plans from https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/half-bridge-transistor if you want to make the PCB).  Like Mads said, usually 2 to 4 uF total snubber capacitance is good enough for most applications, and probably the best estimator on the total snubber capacitance is given by the circulating power (voltage X current) in the primary circuit, as in general the capacitance needed will tend to scale with that. But a combination of good bridge layout, adequate snubber capacitance, and not operating too close to the SOA voltage of the devices is likely to work.

Dan


4
Spark gap Tesla coils / Re: rotory spark gap
« on: July 03, 2019, 06:03:20 AM »
FR4 is the circuit board material with copper on it.  G10 is the material without the copper (and usually the fire retardant).

https://en.wikipedia.org/wiki/G10_(material)

By the way balancing spark gap wheels is very tough.  I used an angle grinder for mine, and I destroyed the bearings on one trying to balance the wheel.   I made a paper template and stuck it on the wheel to get the spark points about in the right place, and then I placed on the arbor of the angle grinder and spun it slowly and used a file to grind the end off into a circle.  Make sure you are wearing protective gloves and face mask for sure.

Dan



5
High voltage transformers for mains frequencies usually are large because they both need many turns and relatively large cores.  You could certainly use a neon sign transformer with a low current mains voltage input for this purpose.  However, modern neon sign power supplies are usually switched-mode power supplies, and so limiting the current to such as a supply would not have the intended effect, the power supply simply wouldn't function.  You would need to find an old neon sign transformer, but you can generally still find those being sold on e-bay, though they are becoming more scarce.

A television flyback transformer is a fairly decent alternative as well as inexpensive.  You wrap four or five turns around the primary of the flyback transformer, and then drive this with a MOSFET (such as a IRF540) turned on and off by a 555 timer oscillator.  This would be powered directly by 12 volts DC.    The flybacks usually have a built in high voltage diode which will produce DC high voltage, which may be needed for your experiment.  You could extra inductance in series with the primary if you wanted to limit current further.  The duty cycle or frequency of the oscillator can also control the output power to a limited extent.  Like the neon sign transformer, the flyback transformer is a source of high voltage and can be driven to produce dangerous amounts of current at high voltages, or can potentially charge capacitors with lethal amount of energy.  So this approach does not completely eliminate the risk, but can be used to generate high voltages with low currents.

Auto or motorcycle ignition coils can also work well too, but generally do not have built-in rectifiers.  Both flybacks and ignition coils can be bought easily on ebay.




6
Electronic circuits / Benchtop power supply PCB
« on: June 09, 2019, 04:28:29 PM »
I design a power supply PCB based on mixing the attributes of several designs floating around on the internet. You can find it at:

https://github.com/profdc9/LinearPS

The range is up to about 30 volts and the current with a single TIP3055 maximum is about 4 A, though if you run it at low voltage output and high voltage input, you probably want to use multiple TIP3055 to dissipate all that power.

It works. It is intended to take the output of a step-down AC transformer, and it provides constant voltage and constant current controls. It also provides sampled outputs of the actual voltage and current output to connect panel meters, and a low current (zener) +5V to supply digital LCD meters. It can be adjusted for different input AC voltages and different ranges of output voltages and currents using trimmers. Also, it can have up to four TO-220 output devices that can be mounted to a common heatsink (for example, TIP41C or TIP3055 devices) to achieve higher output current.

I made this so that old junk and surplus transformers can be turned into useful benchtop power supplies.

DC can also be input into the board, but the minimum limiting output current will be around 500 mA.

Dan


7
I converted the "Game of Thrones" theme to 2 channel MIDI for an event, here it is.

Dan

8
A relay might work, but it is slow and requires a lot of coil current to operate.

Perhaps use an optoisolator such as the 4N28/4N35 to pull the signal to ground if there is undervoltage.

9
Does your controller have undervoltage protection and is it set up correctly?

If the gate drivers on the controller are nor forced off as the voltage falls when power is removed then you may get shoot through blowing the IGBTs.

Dan

Hi I’m new here,

I want to build a DRSSTC for my state-certified technician final project.
I have from now on roundabout 38 weeks.
I’ve already started.

In the past I've already tried to build a DRSSTC. I got about 10cm arc from this coil:

Primary: 5 Turns 6mm²
Secondary:
110mm Diameter
370mm length
0,1mm enameled copper wire diameter (I think this is far to low)
100x280mm topload
72kHz resonant secondary resonant frequency
fixed coupling

I think it's better when I make a complete new coil.
Is this coil good?
* final.txt


I already built:
H-Bridge
Interrupter (Steve Ward)
Control circuit
Gate driver (I don’t use GDT)
Galvanic isolated power supplies for the gate driver

I’ve tested all and it works as it should. (At least I think so)
I don't have tested the feedbackfunktion I just used my funtiongenerator.

I made some H-Bridge tests with a 75W Alight bulb.

Voltage at bulb:


When the interrupter stops the H-Bridge the last falling edge is not straight, it’s more like an e-function.
I don't have a picture of this because I killed yesterday one of my IGBTs....
I Switched the 5V off while the H-Bridge was oscillating.
Both IGBT switched on I think, because of a wrong signal and the short-circuit current killed them -.-
So I made this highly professional paint picture:


Is this curve ok?? or really bad??? Idk...

Which ferrite core is good for the feedback is this one here ok (I have some of them here from my first coil):
https://www.reichelt.de/ferritring-59770027-ft-140-77-p7921.html?

I've added the circuit diagram
I uploaded some pics as a zip file to my dropbox (can't attach them here cause they are to big):
https://www.dropbox.com/s/jcgcy6su8wmc3cz/Tesla.zip?dl=0

Greatings from Germany

Vaclav

10
Electronic circuits / Re: Offgrid 48V solar to 24V battery setup
« on: May 20, 2019, 11:30:34 PM »
Are those monocrystalline or polycrystalline solar cells?

One thing I was wondering about such a setup is the feasibility of setting up a wireless repeater that would charge a battery.  What kind of average power over 24 hrs over the year do you think you could get?  Problem is in the winter at 55.6 N the amount and number of hours of daylight are relatively low.  But perhaps an average of 40 watts is feasible?

Dan

First test with all 3 panels on a sunny day

/>

11
I'm working on a mmc bank for my dual mot tesla coil, is it absolutely necessary to add bleeder resistors if I can easily discharge the capacitor? The terminals are close enough together that I can easily put a metal rod across them with the help of a well insulated pole. And wouldn't they discharge across the secondary coil of the transformer anyway? Can I simply short out the ends of the capacitor bank or must I discharge each capacitor individually? Thanks in advance for any information.

I made a dual mot tesla coil, and I discharged my capacitors with a rod across the safety spark gap.  However, if you forget to do this, and don't have bleeder resistors, the charge could easily kill someone.  Also, discharging the capacitors this way is hard on the capacitors, and occasionally even high quality Cornell-Dubilier capacitors have been known to explode if accidentally shorted.  I included twelve 33 megaohm resistors in series across each metal-oxide varistor as a bleeder.   I also had to include about 1000 pF of capacitance @ 20 kV for RF protection as well.

I have to say having built both a rotary spark gap MOT tesla coil and a DRSSTC, the DRSSTC is much more fun, and in some ways, easier to build.  Getting the rotary spark gap to work reliably was very hard.  The spark gap wheel is very hard to balance.  But I am happy to share details of how I put it together.  The schematic of my dual MOT tesla coil is attached.

Dan

12
If you look at the transformer with an equivalent "T" network, there is a shunt arm that is in parallel with the secondary and therefore isn't in series with the gate, and a series arm that is.  I would think the leakage inductance from the series arm is something like A_L N^2 K where A_L is the inductance of a single turn, N is the number of secondary turns, and K is the flux coupling constant (0 to 1).  I would think that a bifilar winding on a high permeability core has a K pretty close to 1, but it could be an issue I suppose.

Dan

Quote
The purpose of the gate resistor is to suppress oscillations of the series LC circuit formed by the IGBT gate capacitor about 3000 pF for the IGBT you have chosen) and the inductance of the connection to the gate.
Wouldn't you have to add the GDT leakage inductance to this?

13
I will venture an answer to this...

The purpose of the gate resistor is to suppress oscillations of the series LC circuit formed by the IGBT gate capacitor about 3000 pF for the IGBT you have chosen) and the inductance of the connection to the gate.  This is one reason why the connection to the gate should be kept as short as possible, and the signal is carried to the gate using a transmission line of some sort, for example, a twisted pair of a cat 5 cable which has a characteristic impedance of about 100 ohms.  Many gate drive transformers already use cat 5 twisted pairs so this is convenient.  The gate is a load on this transmission line that is very much like a short circuit being a large value capacitor, and the capacitor formed by the two conductors of the transmission line adds only a little extra capacitance to this.   If the gate resistor resistance is too large, the RC circuit formed by the gate resistor and the gate itself has a rise time that is lengthened and therefore slows down the transition of the gate.  If it is too small, you get the oscillations.  So for example, lets say you have 3 cm of trace which has a inductance of perhaps 20 nH.  The impedance of the LC circuit formed by the trace and the gate is sqrt[20 nH/3000 pF]=3 ohms.  To critically damp this LC circuit, you would use a 3 ohm resistor.  This would result in a RC time constant of (3 ohms)(3000 pF)=9 ns.  This does not increase the transition time of the gate that much.  Typically you err a little on the side of a higher resistance, so that 5 ohms is a typical series resistor value.  The value of the resistor is not that critical because in practice it is difficult to measure some of these quantities in-circuit.

Dan

Hi all I am new to the forum. I have built quite a few Spark gap style coils throughout the years and am now trying my hand at my first DRSSTC. I am going to use loneoceans UD2.7 c for the driver and his 80mm Full bridge board for the bridge. I will be using FGA60N65SMD for the igbt's. I am having trouble wrapping my head around calculating the gate resistors values. Could someone point me in the right direction to a good place to read up on this ? I tried using the calculator but I am at a loss as to how to figure out the maximum gate drive current the driver is capable of. Better stated what do I calculated it off of? My assumption is the current of the mosfets that drive the bridge and if so is it x1 since there is a gate resistor per igbt or total current x4?

Any help would be greatly appreciated. Thank you

14
The UD2.9 changes the way that the UD2.7C works.  I modeled it in Qucs (Quite Universal Circuit Simulation) and I attached the schematic below and show the screenshot.

The way it works is a little different than the UD2.7C.  In the UD2.7C (see schematic below), the overcurrent condition clears the second D-latch U7B unconditionally.  This latch output Q is ANDed at U5D, goes through a double NOT gates U8D/U8E and clears U7A, and then is ANDed with the TL3116 outputs at U5B/U5C to turn off the drivers.  The latch U7B can only be reset by another interrupter edge, so once the overcurrent condition happens during a pulse, the driver stays shut off until the interrupter edge reoccurs.

The UD2.9C on the other hand works like this:  When an interrupter pulse comes in at U8C, the diode/capacitor network causes a brief low edge signal.  This sets BOTH U7A/U7B and allows pulses to start.  If J16 is open for not skip pulse operation, when the overcurrent condition occurs, U7A is cleared.  This in turn takes a path through U5B, U8D, U8E, and then resets U7B, similar to what happens in the UD2.7C.  U7A and U7B can only be set again by the rising edge of another interrupter pulse, and so the behavior is the same as the non skip pulse, even though it is arranged a little different.

If J16 is closed, then while the current in the primary is ringing down, once the overcurrent condition clears, the signal from U4 Q is conducted through J16 and allows U7A to be set.  This turns on U7A Q and then if the interrupter pulse is still continuing, the output of U5B is high and so the signal is also clocked in on U7B, reenabling both D-latches and so the driver turns back on until either the overcurrent occurs and U7A/U7B are shut off again, or the interrupter pulse terminates and the output of U5B is low and shuts off U7B.    One other feature is the presence of the transistor Q5.  This transistor prevents another interrupter pulse edge from turning the driver back on if there if at that moment there is an overcurrent condition, so one can not force the driver on excessively and risk damaging the transistors with excessive current.

Typically I don't get a problem with dead time because I use a gate driver transformer to drive the upper and lower transistors with opposite polarity windings.

You can take a look at the simulation below where I verified I could turn the skip pulse on or off depending the connection of the jumper.

Dan



Hello guys, I want to use a skip pulse driver for my Tesla but I'm lazy to design and programming a CPLD driver :p . So I decided to create a skip pulse driver for full bridge drsstc without any programmable devices.
I found peoples who already worked on a logic skip pulse driver ( https://4hv.org/e107_plugins/forum/forum_viewtopic.php?p=1&id=178230#post-178230 and https://highvoltageforum.net/index.php?topic=346.20 ) but I don't understand how they work.

First I begin with the logic of the UD2.7 driver and I added 2 D flip flop. It seems to work on simulation  :D : http://tinyurl.com/yyan2agj


But i have a question about the switching of IGBT : How the driver generate the dead time to not short-circuit the half bridge module ? I didn't find any information on the UD2.7 drive about dead-time generation but I'm using it and it works so I believe it have dead time...


And if you have some advices to improve the skip pulse logic of my driver It will be usefull  :) thank you !

15
Solid state Tesla coils / Re: Flat Secondary Coil on PCB?
« on: May 02, 2019, 02:06:27 AM »
The only thing I can offer here is another reference. This coil is still early days but it is a drsstc.
https://hackaday.io/project/165112-pcbtc-gan-edition

Thanks for the link.  That looks like an awesome project.

Thanks to you both for the info.  It gives food for thought.  I didn't think I was the only one who thought of this, but obviously there's been some movement here. :)

I was thinking of keeping the primary and secondary on separate PCBs so I could stack several secondaries to get more turns, and also I put the sense coil on the other side of the secondary board so that it there is less of a chance of having a coil strike damage the circuity (if it is possible to have a streamer that long).

dan

16
Solid state Tesla coils / Re: Flat Secondary Coil on PCB?
« on: May 01, 2019, 07:34:33 PM »
You wouldn't happen to know of a video of it in use?  I am curious to see how they work.  I was thinking of adding a buck converter before the half/full bridge so that I could modulate the power with an audio signal.

Dan

Hello

I know that such tesla coils work, because they are sold commercially: https://highvoltageshop.com/epages/b73088c0-9f9a-4230-9ffc-4fd5c619abc4.sf/de_DE/?ObjectPath=/Shops/b73088c0-9f9a-4230-9ffc-4fd5c619abc4/Products/TESLA_MINI_v1.2_

In the description you can see the technical data of the coil, it has 120 turns: https://highvoltageshop.com/epages/b73088c0-9f9a-4230-9ffc-4fd5c619abc4.sf/de_DE/?ObjectPath=/Shops/b73088c0-9f9a-4230-9ffc-4fd5c619abc4/Products/TC12_flach

Greetings
Phoenix

17
Solid state Tesla coils / Flat Secondary Coil on PCB?
« on: May 01, 2019, 05:54:26 PM »
I was thinking about designing a small kit-based Tesla coil where rather than the seconary coil being a solenoid, it is a flat spiral.  Of course the secondary inductance goes down, but is there any reason this shouldn't work?  Flat spirals are already used for resonant power transfer applications (e.g. wireless charging and induction cookers).

The board I designed has (I calculate) about 1 mH of inductance.  It is about 150 turns of 0.13 mm wide traces separated by 0.15 mm.  This is the thinnest I could fit in the design rules of the process.

Anyways I was up late last night and drew up a PCB.  The hole in the middle is for a post to put the topload on sticking up from the PCB.  The hole on the edge is to connect the ground.  There is a six turn coil on the back that is used to sense the current in the secondary for feedback purposes.

I was thinking too that I could stack the boards to get more turns and place a thick HDPE insulator between them.    The center of each coil would be connected to the ground of the next in series, and these would be stacked as to be placed over the primary coil  so that the board would intersect  the magnetic field lines of the primary coil.

Here is what I drew up last night:



Any comments about this design?  I want to call it the "Conversation Piece" which would be a little tabletop SSTC coil.  It would be powered by 12-30 VAC.

Dan

18
I made a bobbin using a sheet of high density polyethylene a while back.  I should take a picture of it, but I would have to clean the oil off of it. :)

The sheet was about 6 mm thick.  I cut four 80 mm wide, 150 mm long pieces and made a rectangular long tube with the edges of the pieces glued to each other.  To adhere the polyethylene to itself, I used a butane torch to flame treat the polyethylene so that I could join the four sides together with epoxy.  Then I field off the corners of the rectangle to smooth them somewhat.  I was able to wind 500 turns of 0.25 mm magnet wire around it.  I had some large U-shaped ferrites which then were inserted into the bobbin.

It was one of the first things I did when getting started in high voltage and it was very difficult to get working figuring it out by myself.  After I was done I wrote a document on it.

https://drive.google.com/file/d/0BwFicJLV0O4jYlQ0ejJ6NE9XVE0/view

Dan

19
Solid state Tesla coils / Re: GDT Experiments
« on: March 31, 2019, 05:47:08 AM »
I moved the OC LED backwards so the potentiometers may be better separated, there should be plenty of space now.

Dan

20
Solid state Tesla coils / Re: GDT Experiments
« on: March 30, 2019, 07:13:05 AM »
I have to confess I had an ulterior motive for designing the SSTC circuit this way.  I hope to try to use to make an induction heater using the SSTC board.

Basically, use a feedback coil rather than antenna near the workpiece to drive it into resonance.  So I designed it with some stuff that may not have been necessary.  I did not really worry about the dead time but I thought I should look into it after you brought it up.

If you need even less dead time, you can swap R5 and R11 for 4.7k resistors.  The limit is that the overcurrent circuit can only sink 6 mA and so if the resistors are too low resistance, the overcurrent protection does not work.

Dan

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post Re: Twin System Build
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
August 17, 2019, 08:06:42 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
Lane
August 17, 2019, 10:45:26 AM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
Lane
August 17, 2019, 06:21:45 AM
post Re: My second DRSSTC
[Dual Resonant Solid State Tesla coils]
Hydron
August 17, 2019, 12:59:20 AM
post Re: Twin System Build
[Dual Resonant Solid State Tesla coils]
fnordest
August 17, 2019, 12:18:48 AM
post Re: Drsstc 3
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
August 16, 2019, 10:34:46 PM
post Re: Teardown of Danfoss VLT6000 4kW Variable Frequency Drive
[Electronic circuits]
Mads Barnkob
August 16, 2019, 10:26:19 PM
post Re: My second DRSSTC
[Dual Resonant Solid State Tesla coils]
Mads Barnkob
August 16, 2019, 10:19:18 PM
post Re: [Development] Project of an SSTC driver.
[Solid state Tesla coils]
Mads Barnkob
August 16, 2019, 10:07:31 PM
post Re: Suitable capacitors and switches? 10kV
[Capacitor banks]
T3sl4co1l
August 16, 2019, 09:28:35 PM
post Re: Suitable capacitors and switches? 10kV
[Capacitor banks]
ElectroXa
August 16, 2019, 09:17:04 PM
post Re: ESAB Power TIG 200 Welder Teardown
[Electronic circuits]
T3sl4co1l
August 16, 2019, 09:14:36 PM
post ESAB Power TIG 200 Welder Teardown
[Electronic circuits]
Mads Barnkob
August 16, 2019, 08:03:18 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
petespaco
August 16, 2019, 01:49:53 PM
post Suitable capacitors and switches? 10kV
[Capacitor banks]
MrFox
August 16, 2019, 12:21:36 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
Lane
August 16, 2019, 11:22:45 AM