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Messages - Mads Barnkob

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981
You can approximate the primary sinusoidal current from the DC bus voltage and reactance of the primary coil. To get a "RMS" value you need to find a time sum from frequency and on-time to get a duty cycle factor to multiply it with.

X(L) = 2 * pi * f * L

Primary peak current = DC bus voltage / X(L)

982
My ebay items for sale: http://www.ebay.co.uk/sch/madskaizer/m.html?item=232279971579

It is a mix of electronics and high voltage related components. I will update this topic when I put up new interesting items :)

983


The 450 VDC capacitors has a surge rating at 495VDC for some 1000 non repetitive pulses, so a balance between that and not burning too much power in the balancing resistors themselves, I chose 82K resistors. The discharge curve can also be seen in the attachment. The 100 Watt burned from the load balancing and discharge resistors does that discharge after charging has to happen fast, but at 400 VDC across each capacitor, it will be at its 4kJ charge. The high losses is the price to pay for the increased safety margin on a safe level of maximum voltage across each capacitor.

For each capacitor I will add a red LED in series with a 120K to 220K resistor, this corresponds to approximately 4 to 2 mA through it at 450VDC, ~2 to 1 watt. This is only for charged indication on each individual capacitor.

I will have a analogue meter across the entire bank to measure voltage, a long string of resistors for the voltage dividers adequate voltage rating is necessary.

984
Hello all

This is my attempt to write a long guide about practical DRSSTC design. I try to cover the most critical design issues in a way that most electronics interested should be able to understand. I have tried to hand pick the necessary theory and calculations to our specific purposes of building a DRSSTC.

It is a work in progress and I would like to invite you all to help me make it better, correct and add more topics.

Topics of the DRSSTC design guide
01. Rectifiers (done)
02. Busbar and primary circuit (done)
03. IGBTs (done)
04. DC bus capacitor (done)
05. PFC (20% done)
06. Snubber capacitor (done)
07. MMC / tank capacitors (95% done)
08. GDT / driver (5% done)
09. Secondary coil (done)
10. Topload (done)
11. Grounding and EMI (done)
12. Tuning and testing (25% done)
13. Featured Tesla coils (40% done)
14. DRSSTC FAQ
15. Online design tools

I hope this guide can help others to understand why and how components are chosen for a DRSSTC.

This thread will serve as a status for the complete guide, when I add new data it will be posted here.

985
Solid state Tesla coils / Re: My First SSTC (and exploding IGBT's)
« on: March 20, 2017, 10:37:05 AM »
Reversing the phasing of the primary coil is one of the first things to try out when starting up a new coil, but that would normally never lead to switch failure/explosions, just very small output.

986
Solid state Tesla coils / Re: My First SSTC (and exploding IGBT's)
« on: March 17, 2017, 01:35:47 PM »
I do not have any experience with PLL driven SSTC's, all my SSTC's used a circuit based on the SSTC schematics from Steve Ward.

One thing that strikes me is however the very loose coupling between primary and secondary coil, the setup you have right now is much more suitable for a SGTC/DRSSTC, which is also where you had it from. If you take a look at the SSTC's at my website, you can see that I use a very tight coupling where the primary coil is wound directly onto the secondary coil with only 4 layers of plastic sheet in between.

As to why the switches explode...

Wrong phasing of the GDT, so that both switches are turned on at the same time or off at the same time, but just a little energy is let through, enough for small sparks.

Antenna feedback is not stable, raise the antenna further up the secondary coil.

Have you tried using MOSFETs instead of IGBT?

987
I reinforced the UD2.1 driver with solid copper wire rails for the output stage, a 3300uF capacitor underneath each MOSFET pair, heat sinks on the MOSFETs and the 200 Watt 26VDC power supply for it. It is properly able to drive a bridge directly by now :)

I was forced to use a low resonant frequency, as I was using brick IGBTs, that is the only reason. But yes, I do expect a lot of branching.

The small capacitance for start up, is that DC bus capacitance? So that a snubber capacitor across the DC bus would be sufficient for that?

I will wind a new 1:50 CT for the feedback and adjust resistor accordingly, that sounds like a easy and good first step to take before taking much more apart for single component checks.

988
You have really set sails for a large induction heater here!

How many bridges have you planned to use in parallel? I know that RogerInOhio on 4hv made one with 4 or 8 bridges in parallel, that would draw around 4 kW.

To experiment with the power supply design, where to place choke, capacitors etc, if you want a CLC or LC filtering, check out the Duncan amplifiers PSU designer: http://www.duncanamps.com/psud2/

From the part list for the welding machine, I can see that there is a shunt resistors and a digital Ampere meter in the front, you could use those for measuring the DC current drawn from the power supply.

I look forward to see the rest of this monster build and how it performs melting stuff :)


989
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990
Electronic circuits / Re: Mazilli ZVS Induction Heater (With IGBT's)
« on: March 15, 2017, 12:20:48 PM »
Unfortunately no. I was planning to take a video this past weekend and ended up using the IGBT's in my sstc after I rebuilt it and added some modifications to the GDT. Unfortunately, the GDT was not the issue and I ended up destroying the IGBT's (after a successful 40v run, I switched to 110 to tune it further. After that it only made 3cm arcs.) I promptly decided I should reduce primary turns by tapping it off. I slowly decreased turns, still only 3cm arcs, untill I switched it on and a loud pop indicated that an IGBT  died.  Still no decent output and I am mildly disappointed in it XD.

You should write a thread about the SSTC, let us see if we can troubleshoot it and get it working properly :)

991
General chatting / Re: Hello everyone
« on: March 15, 2017, 12:19:49 PM »
Hi all, I'm a long time 4hv member but I came here from Reddit so it was interesting seeing so many familiar usernames.

It's a shame about the 4hv software, I remember when it migrated to the software that it is running now back in 2005 - and that was a clean start from whatever it was running before that. I've been a lurker for the last few years, nothing much on at the moment.

Hi Avalanche, welcome.

4hv is still undergoing investigations to bring it into the future, I am also a part of a group that took up this work long ago, but things does not always move as fast as we wish for :)

992
Capacitor banks / Re: Best way to discharge capacitors ?
« on: March 13, 2017, 10:13:37 PM »
Install bleeding resistors! Safety first!

Also have a two factor voltage indication, like both a analog meter, but also neon lamps/LEDs around the circuit to indicate voltage at a certain level, it is always a good idea to have more indicators or fail safe circuits.

I wrote about bleeding resistors here: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/dc-bus-capacitor/ and with the link there is to the capacitor discharge calculator you can check if the curve is falling too fast, if voltage sharing is a greater design issue etc.

993
Radio frequency / Re: Ice Bridge Ground
« on: March 13, 2017, 10:09:31 PM »
Modern antenna towers are not floating, isolated from ground, as old ones are.

It properly just is cable protection from falling ice from the tower itself and the grounding on it is just a result of the rules for machine building and grounding all metal objects. A galvanized iron cable tray / walkway does not make any fantastic ground anyway, so that would not primarily be used for that.


994
Electronic circuits / Re: Mazilli ZVS Induction Heater (With IGBT's)
« on: March 12, 2017, 10:20:50 PM »
That is a great guide on testing and trouble shooting, thank you for taking the time to share that.

Not the most low inductance design, but I must also say that I am amazed of the discoloured alligator clips, you have without a doubt pushed around 50-100 Ampere through them!
You need some much better connection to the MMC than that, since you have the capacitors mounted in a ring, use at least 4 wires from the large wire, spread out evenly on the ring, to distribute current sharing on the capacitors as even as possible. Scroll down to current sharing between parallel capacitors on this part of my DRSSTC guide: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/dc-bus-capacitor/

Do you have any video of heating/melting some metal?

995
Nice work so far.

Can you run the system off the signal generator to check the IGBTs out?  Just keep the voltage low, and keep the drive frequency above resonance so you never have body diode recovery.

What turns ratio did you use for the current feedback?  Perhaps it would help to reduce the turns ratio so you have a higher loop gain, it should make it easier to start oscillating.

It looks like you get some ringing current on the primary (which is a good sign), but is the amplitude significant?  And is the frequency right?

I will try to run the bridge directly from a signal generator and see what I can get from primary current/inverter voltage.

CTs are regular 1:33:33, I could try to wind a new one, something like 1:20:20 maybe? Or do you suggest even higher gain?

I did not note down how much it was, but I am pretty sure that the primary current measured on the scope shots are only in the 10's of Ampere range.

996
Radio frequency / Re: Ice Bridge Ground
« on: March 11, 2017, 08:27:32 PM »
Cell and microwave towers often have an "ice bridge ground." Does that simply protect the coax/wave guides from falling ice while serving as a ground or is there some other theory behind it?

It is there for electrical safety alone. From the US electrical code we have:

Quote from: NEC article 100
Grounding of electrical equipment. Conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials [Sec. 250-2(b)].

There is however slight differences to EU electrical code on machines, EN60204-1:

Currently the NEC in Article 100 defines the terms "ground" or "grounded" as "connected to the earth or to some conducting body that serves in place of the earth." Yet, the NEC often uses the term "ground" when it really means "bond" (connected to an effective ground-fault path to clear a fault) [250.2 and 250.4(A)(5)]. The two concepts have quite different meaning.

Grounding - Grounding metal parts to the earth in premises wiring is only useful to provide a path for lightning, shunting high-frequency noise, or reducing static discharge.

Bonding - Bonding all metal parts together and then to the system winding is done to provide a low-impedance path to the source (system) to facilitate the opening of the circuit-protection device to remove dangerous voltage on metal parts. In addition, bonding the system to metal parts (typically to the X0 terminal of a transformer) stabilizes the system voltage to the metal parts and it provides a zero system reference (to the metal parts).

So far it is all clear, those are the definitions. The question is now is what to connect to Ground and what pieces of equipment should be bonded together.
The approach of the Noth American Techical norms (mainly NEC and NFPA 79) is unfortunately a bit different from the IEC (IEC EN 60204-1) and that makes the subject more complex since at the end the risk of electric shock is the same for a worker in UK or in USA.
So why two different approaches? That probably goes back to the cultural difference between the two people: the Anglosaxon Pragmatism vs the Greek and Roman Dialectics.... but we are going too far now...

Both approaches recognise the need for a ground fault path, and that is the main reason for bonding. The real difference is the concept of Class II electrical devices or apparatus that is in the EN 60204-1 but that cannot be found the National Electrical code or in the NFPA 79.

997
Laboratories / Kaizer Power Electronics, the basement lab
« on: March 11, 2017, 09:55:56 AM »
Here is my current "lab", approximately 10 square meters of unheated basement, good enough for dump tools and parts, but not for measurement equipment.

So I have to keep all my expensive and sensitive equipment in my apartment at the 2nd floor, while all the dirty work can be done here, as well as a huge collection of parts, which is pushing me out of the lab, there is hardly room for two humans in there by now :)

I even lend a neighbouring room for 3 additional file cabinets for parts in a separate room just to reclaim some space where the work bench is located.

998
Thanks for the addition. The website of Tony VanRoon seems incredible broken, so I left it out of the list.

999
General chatting / Re: Hello everyone
« on: March 10, 2017, 09:23:32 PM »
Edit: Just encountered a strange bug in the reply editor (WYSIWYG mode). When the cursor is at the beginning of the line and I press backspace, the line doesn't only move to the end of the previous one as it should, but is also shrinked. And, possibly anoter bug, in the preview the [size] BBCode (generated due to the shrinking) is not considered. Oh, and I just wanted to attach some pics to show what I mean but somehow I'm to stupid for that. I select the file, it shows up below the select file field and then? If I hit the "(Insert Attachment1)" link, it adds "[ Attachment=1 ]" to my text but in the preview I see only  " [ Invalid attachment ] ". Maybe useful: I'm working with Chrome on Windows 8.1 x64.

I could not replicate the backspace/size tag error, in firefox

The attachment mod error, I did notice that there isn't a insert link for any, but the first attachment, you can however just write 2, 3 or 4 etc as it corresponds to the attachments, but this is not the intended functionality.

I contacted the mod developer about the error: http://www.simplemachines.org/community/index.php?topic=525705.600

1000


I got 35 of these BHC 1500 uF / 450 V electrolytic capacitors that all comes from the 3x 30 kVA UPS that I took apart a while ago, as these come from a continues duty equipment they are properly to worn out that a little fun could be had with them.

I want to try all 35 capacitors in series for a 42.8 uF / 14000 V bank, when fully charged that would store 4194 joule and a charge of 0.5 coulomb, if we compare it to all them in parallel, that would be 21 coulomb instead, so the higher voltage might actually be good on the capacitors when discharging them, assuming there will be a much lower short circuit current alone from the "high" ESR.

A single capacitor has a ESR of 7.1 mOhm, so all 35 in series would have a ESR of 2.485 Ohm, short-circuited at 14000 V that would result in just under 6 kA short-circuit current, which is about 1/10th of what my other 4000 joule single capacitor can deliver in short-circuit current.

Do anyone of you have experience with making a extreme series connected capacitor bank like this?

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