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Messages - Mads Barnkob

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1022
Sell / Buy / Trade / WTS [DK]: Ferrite cores, lots of them
« on: April 14, 2017, 08:49:10 PM »
This is all 3C85 or 3F3 material, has a frequency spectrum for use in the range of 200kHz to 1MHz, this is basically for medium power work in a few kW range.

Prices can be discussed according to amounts wanted. Open to offers :)

Shipping, world wide! 8€ for 500g and 16€ for 2000g!

1) 68x E core, 3C85 material, 80x40x20mm, 170g each, (7€/set of 2)


3) 32x Square core, 3C80 material, 25x25x100mm, (10€/set of 4)


4) 46x E core, 3C85/3F3 material, E65/32/27, (6€/set of 2)


1023
I also tried to summarize the differences between 1 and 3 phase, half and full wave rectification with some pictures and charts here: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/rectifiers/

1024
Electronic circuits / Re: Royer induction heater
« on: April 14, 2017, 10:46:10 AM »
You do have a oscilloscope, so you should wind yourself a cascaded current transformer (two ferrite ring cores with each 33 turns, 1 looped into the other and that gives 1:33:33 ~ 1:1000 turns ratio, so 1000 A through the first gives 1A out, then you can adjust shunt resistor for the voltage desired) to measure the primary circuit current, it could be that you actually have 200 Ampere flowing there and that explains your large current draw from the power supply.

It sounds like kamelryttarn has a good point in the large inductance of your filter, I never used a L part of the filter, just 4x 10000 uF in parallel. This circuit is paramount to fail at too low supply voltage and that is the true killer and also why this circuit sucks, you never know what happens at startup and you risk blowing it all up :)

About ferrite markings, there is no standard at all and there are numerous different names for the "same" materials as different manufacturers have copyrighted their own branding names. Micrometals does a two colour identification but mostly I have uncoloured cores that just has a small writing with the material type like "3C85" or "3F3".

I have a lot of ferrite cores for sale, check my thread that I'll make tomorrow :)



1025
Great to see it work and looking forward to the future improvements.

I have to do some more debugging on my own once I get it out again, after rebuilding the TL494 output setup, the waveform on the GDT was strange, maybe there are some more issues not yet found on the final PCB that I made for it.

1026
Hi AndreaF90, welcome to the forum :)

You could try to use a smaller value capacitance, if the leakage current is too high in the capacitor, you actually do have earth fault conditions and your breaker should trip.

Generally it is the scheme by Steve Ward that most people uses: http://stevehv.4hv.org/DR_plexi/general%20wiring%20scheme.pdf

Some of the advices on that and other methods are in this thread: http://4hv.org/e107_plugins/forum/forum_viewtopic.php?163880

1027
Printed Circuit Board / Re: PCB etching, DIY (chemistry mostly)
« on: April 11, 2017, 10:36:57 PM »
I only know your problems from using a too thin, saturated or cold Iron(III) chloride / ferric chloride solution.

They are weak acids for copper etching, but they are also relatively harmless, but will colour your clothes for life :) I have a solution that I have been using for years and with the small amount of boards I etch, its still the most cheap way.

I recently bought some Sodium persulfate, but have not yet tried it out.

I will make a thread on toner transfer method and etching later when I have time

1028
Dual Resonant Solid State Tesla coils / Re: Top Loads
« on: April 10, 2017, 09:02:09 PM »
Welcome to the forums Uwe

In terms of performance, I have not seen much difference from stacking random items on top compared to perfect round surfaces, spark length(performance) pretty much lies with the capacitance alone.

The biggest issue is field shaping and trying to control where the spark channel goes. The larger and more powerful a Tesla coil is, the more you are interested in having the spark travel outwards from the coil before going towards ground. There is not much fun in a Tesla coil that can make 4 meter sparks, but will always shoot straight to ground from its 3 meter in the air break out point :)

Field shaping also help protect the primary circuit/control electronics from strikes.

Skeleton topload, even my own, lack the last inner rings, that a toroid "have" in its smooth surface, I think it is vital to remember to make that last inner ring for shielding the top of the secondary windings even better, but not really something that has been an issue for me yet.

I agree with Uspring that the large diameter tubing you are using, the more it looks like a smooth surface, I have seen some FEMM simulations of toroid vs. rings before, but I can not find them right now.

1029
Solid state Tesla coils / Re: My First SSTC (and exploding IGBT's)
« on: April 09, 2017, 09:25:45 AM »
42 turns is too much. You need to calculate it and make it the right way :)

You could play around with this little spreadsheet calculator that I made for GDTs, it is made in openoffice but I think you can import it to excel if needed, else google drive's spreadsheet editor can read it fine.

1030
Solid state Tesla coils / Re: My First SSTC (and exploding IGBT's)
« on: April 08, 2017, 07:58:56 PM »
Just be aware that a attenuator does not provide isolation from higher voltages, a differential probe is a much better idea, but also costs a lot of money.

I missed that you paralleled them and not in series, but that just makes it 1:1 GDT then, it is a turns ratio voltage product. Around 10-20 turns should make a good GDT for a SSTC, you could also calculate it: http://thedatastream.4hv.org/gdt_index.htm

1031
Looks great, I can imagine that it must have been interesting winding those 38 turns of 6 mm^2 wire, that has to done carefully to get a good looking result like you have there.

What do you have in mind for filtering the DC supply? A huge stack of electrolytic capacitors?

Is the bridge/bridges the next part of the project?

1032
Solid state Tesla coils / Re: My First SSTC (and exploding IGBT's)
« on: April 08, 2017, 07:12:59 PM »
Good that you got a oscilloscope! My own first one was also a analog 15 MHz, two channels though, but it is vital to just be able to see one thing at a time, at the right sample rate and bandwidth. It will do just fine for almost any Tesla coil stuff, getting a expensive DSO is just to make life easier :)

It looks like a filter choke ferrite and bobbin, it will properly be good enough, maybe on the low side speaking of permeability, but good enough frequency wise, which is also indicated by your square waveform. But the cross section is on the low side, you do risk not having enough electromagnetic energy transfer and maybe its suffering from saturation.

It sounds like you do not have galvanic isolation and something is not correct with the windings of that GDT.

Are you sure it was 4 separate coils to start with? If you paralleled two coils, that could only be used for the primary, and then two singles for the MOSFETs, that would make it a 2:1:1 GDT and actually drive your MOSFETs with half the voltage of what your drivers are driving the GDT with.

So maybe that is your only problem, that the GDT is outputting a insufficient voltage to drive the MOSFETs properly under load?

1033
Unless you bought that green ferrite ring core as a high permability core in the range of 4000-6000, it is most likely just a regular iron powder core from a old power supply, those could be made from N3 material which has a permability down in the range of a few hundreds, absolutely not useful for a GDT in hundreds of kHz region.

1034
You are absolutely right, I made a mistake and it is actually driving the GDT inverted, which properly explains why the finalized and boxed version never worked, but then I moved on to another project, as the prototype worked fine.

I am wondering if those pull up resistors were even in the prototype then...


1035
I added 3 different ferrite cores to my ebay selling list:

If sold through forum and paypal is used, its 10% cheaper on both item price and shipping than on ebay.

2x Ferrite E80/38/20 3C85/3F3 4590nH 170g 392mm2 A80mm Ferroxcube/Philips

2x Ferrite U127/96/29-20 3C85/3F3 650g 580mm2 Philips

2x Ferrite U102.2/57.5/26 3C85/3F3 510g 520mm2 Philips

1036
Solid state Tesla coils / Re: My first half bridge SSTC
« on: April 06, 2017, 10:13:42 AM »
If you have questions, then start a thread in the DRSSTC section and you will get some help if you have specific questions :)

I saw on facebook that you tried a new primary coil with better results, but properly also higher primary currents, there is a thread just under yours here in forum where primary current in SSTC is discussed: https://highvoltageforum.net/index.php?topic=40.0

The reason I advocate helical or pancake coils are that they have a geometry that makes them able to be calculated, which can be real hard for a "bunch" of wires

If you have any questions to the DRSSTC design guide, things you do not understand or think could be explained better, you can add them in this thread: https://highvoltageforum.net/index.php?topic=38.0

1037
From the STMicroelectronics newsletter from today, there was a new interesting PFC controller that is well within the power range for use in fairly large Tesla coils, especially easy to make a design with their eDesignSuite (online circuit designer) that gives you a complete schematic after giving it components values for like 10 key parts. It does seem that you need a ST account to use it though!

The new product: http://www.st.com/content/st_com/en/products/power-management/ac-dc-converters/pfc-controllers/stnrgpf01.html?ecmp=tt4938_gl_enews_mar2017

Digikey got it in stock: https://www.digikey.com/products/en?WT.z_cid=sp_497_0928_buynow&Enterprise=44&lang=en&Vendor=497&mpart=STNRGPF01

Quote
The STNRGPF01 is a digital controller designed specifically for interleaved PFC boost topologies and intended for use in high power applications.

The controller is capable of driving up to 3 interleaved channels, generating the proper signals in each condition. Moreover, it implements a flexible phase shedding strategy that enables the correct number of PFC channels based on the actual load condition. With this function, the STNRGPF01 is always able to guarantee the highest power efficiency across a wide range of load current requirements.

The device works in CCM at fixed frequency with average current mode control, and implements mixed signal (analog/digital) control. The inner current loop is performed by hardware, ensuring cycle-by-cycle regulation. The outer voltage loop is performed by a digital PI controller with fast dynamic response.

The controller implements several functions: inrush current control, soft start-up, burst mode cooling management and status indicators.

It also features a full set of embedded protections against overvoltage, overcurrent, and thermal faults.

The STNRGPF01 is configured through a visual dedicated software tool (eDesignSuite) to match a wide range of specific applications. Using eDesignSuite, the user can customize the PFC conversion configuration and all the relevant electrical components. As a result, the tool will automatically generate a full schematic which includes a complete list of material and the final binary object code (FW) to be downloaded to the STNRGPF01.

Key Features

    Interleaved boost PFC
    Up to 3 interleaved channels
    CCM, fixed frequency
    Average current control, cycle-by-cycle
    Inrush current control
    Burst mode support
    Overcurrent and thermal protection
    Soft start-up
    Flexible phase-shedding strategy
        High operating frequency with small PFC inductor, suitable for high power-density applications
        Low ripple current (input/output)
        Simpler integration with other applications
    Flexible design customization to meet specific customer needs
    Firmware
        Turnkey solution for quick design
        eDesign Suite graphical user interface (GUI) for application configuration
    Embedded memory data retention 15 years with ECC
    Communication interfaces
        UART asynchronous protocol for bootloader support
    Operating temperature: -40 °C to 105 °C


1038
I'm sorry to hear about the demise of the project. :(
Quote
I tried tuning the coil at 120 kHz and 130 kHz, way above the estimated loaded secondary Fres of 88 kHz. When I ran the coil and zoomed in on the current waveform, it was oscillating at 175 kHz, I am not even sure what is going on anymore :)
Given enough coupling that is what you'd expect. The problem with running at the upper pole is, that arc loading will move the secondary res frequency away from the operating frequency thus increasing primary current, which will lengthen the arc. That is a positive feedback situation. Running at the lower pole the feedback will be negative, stabilising the primary current.
I don't think the variacs inductance plays a role as long as you have a large enough cap on the DC bus. Large enough means, that the voltage drop on the DC bus cap due to the primary current (i.e. using primary current frequency and amplitude) is much less than the bus voltage.

I am only calling quit on it because of the induced voltage spikes in the mains supply, I was warned about this before moving into testing it, but if you look at the video and see that blue, inverter voltage output has spikes up to around 750V, it is not pretty on the output, I do however not have any measurements from the variac output, but as the voltage meter broke in it, I guess it was bad enough :)

I only had 10 uF of DC bus capacitance, in form of a snubber.

I guess this my first adventures into running a coil at the upper pole, which is normally much closer to the lower pole in a regular DRSSTC, but as you can see, tuning this primary over a span of 60 kHz doesn't really change that much :)

A future for this could be a new 300+ kHz secondary coil, less primary turns and so on

1039
I found my old TL494 project box, I actually rebuilt the bridge to use some much bigger 88N30W MOSFETs and it would no longer oscillate, so it is not in a working condition right now, so bare with me if it takes a little while before I can reply with some measurements :)

1040
From last nights experiments, I think that this idea might work on a small scale as demonstrated by the modified oneTesla coil.

I tried tuning the coil at 120 kHz and 130 kHz, way above the estimated loaded secondary Fres of 88 kHz. When I ran the coil and zoomed in on the current waveform, it was oscillating at 175 kHz, I am not even sure what is going on anymore :)

Nevertheless, it performed better than ever before at 120 kHz tap, which properly makes a little sense compared to the better performance at 65 kHz, so maybe it would go nuts at 175 kHz? It certainly does seem to be a harmonics pattern here. But I do not think I can tap it that far down on the inner side of the primary coil right now.

There was however also much higher current draw, loud clunks from the variac and lights dimming! The voltage spikes on the mains supply are at levels where my voltmeter was damaged in my variac. This is also why I call quit on the project as it is, its future will be rebuilding it to a conventional, properly PWM controlled, QCW.

I had sparks fly out to about 50 cm as it can be seen in the video

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DO NOT REPLICATE THIS PROJECT, HARM TO NEARBY ELECTRONICS IS A HIGH RISK

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