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Messages - Mads Barnkob

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1
Dual Resonant Solid State Tesla coils / Re: Next Gen DRSSTC
« on: Today at 02:51:26 PM »
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
Since it in practise works to detune the primary 10-15%, why is it your model only suggest that 3% should be enough, or that detuning is actually worse?

Detuning does make a Tesla coil produce longer sparks, but it also takes a almost full input power before any break-out is produced, but then it will suddenly lash out huge sparks, there seems to be some non-linear growth here that is missing in your model?

3
General chatting / Re: A problem solved with hand tools
« on: Today at 01:48:08 PM »
Nice to see a old unit, where you can actually repair it, gets repaired and put back in service :)

My father always had some of those in his garage, those were oil filter changing wrenches.

https://www.bahco.com/en/p/chain-oil-filter-wrench/ca-a5-b5-25-fa-c2-a1-5d-30-b5-60-9c-c3-85-d1-73/


4
This question about the voltage splitter / DC blocking capacitors, led me to find an unfinished article I started long ago, so I finished it up and hopefully that answers a few questions and I would like to get feedback on it: http://kaizerpowerelectronics.dk/tesla-coils/sstc-design-guide/

5
Solid state Tesla coils / Re: tesla coil varnish is dumb
« on: July 14, 2019, 08:20:52 PM »
I tried something similar once, where I tried to fix it with a different type of varnish and that was just another mistake on a mistake. I used a oil based furniture varnish first and when that failed I tried to add spray on polyurethane and that just cracked up everywhere!

Since it cracks its either reacting with the electrical tape or you had huge temperature differences?

Fixing it.... hmm, try to fill out the cracks with another varnish type and just live with the fact that it will never be pretty :)

You have a sad doggo in the varnish.


6
Dual Resonant Solid State Tesla coils / Re: Drsstc 3
« on: July 14, 2019, 02:06:26 PM »
You could properly need a slightly higher gate resistance to damp the overshoot, but generally that is a near perfect driving waveform for a IGBT gate. 10% overshoot would be perfect, 20% is borderline to too much, but okay!

7
Dual Resonant Solid State Tesla coils / Re: DRSSTC in brust mode
« on: July 14, 2019, 02:04:22 PM »
Burst mode is when you have longer on-times, but lower BPS, so you get this long roaring burst of sparks for maybe 500-1000us but only a 10-20 times a second.

You have to look at the average on-time to compare it to f.ex. 200us and 200 BPS, what kind of heat dissipation that gives you in the IGBT die or MMC capacitors, a too long burst can easily rise the temperature of the die by 50-100 degrees if its too long and that is asking for trouble if you have a too high BPS.

8
Dual Resonant Solid State Tesla coils / Re: Drsstc 3
« on: July 12, 2019, 09:56:38 AM »
It looks very nice! Now that you went for the hexagon base, did you see the covering plates in the thread with the twin system? Where they sit into slots in the supports.

You should place your CTs at either output from the bridge, never between the primary coil and MMC, as you have a high voltage ringing between L and C.

Small progress is better than no progress! I am currently in a period of no progress, mostly due to starting on a new job and that takes all my mental capacity :)

9
Capacitor banks / Re: Completed my pulsed power generator
« on: July 11, 2019, 02:58:13 PM »
Very nice machine you have put together here!

Do you have any links to Bert Hickmanns design for the spark gap?

What is the black cable with a clamp lying on the ground for? Grounded negative rail of the capacitor?

The Discharge voltage meter, is that to get an indication of the voltage reversal? I seem to recall that a way to avoid this is using a thin enough wire for the work coil that it goes open loop before voltage reversal happens.

I only ever tried firing 4 kJ indoor and that was scary, 6kJ is in the same ball park, but at 10+ kJ even the mechanical stiffness of your current path wants to rip itself apart and what is it with that white piece of plastic pipe on the laminated copper bars?

Got any video of it firing?


10
Dual Resonant Solid State Tesla coils / Re: Kaizer half bridge driver
« on: July 11, 2019, 02:45:24 PM »
You need something in the range of 1-10 uF, low ESR and low dissipation factor, so that pretty much says MKP (polypropylene) capacitors, derate the voltage 50% as the mid-point voltage can vary according to load changes. MKP capacitors also have the required frequency and current ratings you need here.

The higher sudden load changes and the higher overall power consumption of your inverter, you need more capacitance to avoid sagging.

If you look at different MOSFET/IGBT manufacturers application notes for inverters/converters using half-bridges, they usually use something in the range of 1-20 uF.

The voltage splitter capacitors is however not necessary, they are perfect if you want to add a voltage-doubler, but you can also just remove them both and tie midpoint end of the primary coil to ground instead.

I can not give you any math to calculate it, maybe someone else can chime in on that :)

11
X-ray / Re: Siemens Polyphos 30 xray machine
« on: July 09, 2019, 03:53:37 PM »
Teardown of the Siemens Polyphos 30 X-ray systems control panel including computer, safety functions, HMI and high voltage inverter circuit.


12
Pushing the limits with a small work coil for annealing brass cartridges.  For this video, I make and use the smallest diameter work coil yet for the 1000 watt ZVS induction heater.   Although I focus on annealing a brass cartridge casing very quickly, this video is really a next step in my ongoing series about work coil design and  work coil frequency limits for reliable circuit operation.

Pete, I love your videos, you really get deep into the topics, do a lot of experiments and share your results. Kudos to you Sir.

You video editing was also really good in this video, keep up the good work, it had a nice flow and I enjoyed it from start to end!

13
Dual Resonant Solid State Tesla coils / Re: Twin System Build
« on: July 07, 2019, 08:03:59 PM »
That is a couple of really good looking coils, I especially like your hexagon base and the way the lids are mounted in a slot in the supports, I would like to steal that idea for a future coil :)

What did you have as "bad grounding"?

Usually when I have interference issues, it has more to do with my interrupter/computer being too close to the coil, I mean if you just have a wire shorter than 5-10 meters to a metal construction, something in the ground, that would not be my first place to look for issues. But for sure, use thin ribbon or multiwire cables with a good large gauge for ground connection to a solid grounding rod in moist soil.


14
Spark gap Tesla coils / Re: rotory spark gap
« on: July 03, 2019, 03:03:44 PM »
Whatever material you end up using, spend a few minutes to calculate the speed at which the circumference of your RTG has, this should give you a good idea about how important sturdy materials and mountings are important for your own safety, as well as adding a blast shield around it to catch flying objects in the case of a failure.

15
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC
« on: July 02, 2019, 07:52:14 PM »
Nice looking coil, I can see the resemblances to my DRSSTC1 :) Which is also what makes it easy for you to use the MMC calculator, it has both the same capacitor and my coil data in its drop down boxes: http://kaizerpowerelectronics.dk/calculators/mmc-calculator/

I have upgraded my own coil to a SKM200 bridge and it it ripping MIDI at 800Apeak, the MMC has survived that so far, but it is properly suffering from shortened life time. So you MMC will do fine at 600A, maybe just add a fan for forced air cooling. I would also connect the MMC cables in each their end of the copper busbar, so the current path through each string is equal, here you have a minuscule difference between the two middle pair of capacitors and the two outer pairs, this has an impact of the current sharing, it might make a difference if you push things too hard.

Those red caps for the ground rail, is that custom 3D print or something you can buy off the shelf?

16
Capacitor banks / Re: Grounding of pulse capacitor case
« on: July 02, 2019, 07:42:06 PM »
I would run it with high voltage floating and dangerous, because that is what it is, dangerous, it can never be assumed to be any kind of safer just because its grounded in one end.

I would ground the case so that any metallic non-conducting parts is at all times at same potential, ground potential.

I would not rely on any kind of high resistance path to earth either. Either it is dangerous and assumed to be charged or all terminals of the capacitor is crowbarred to ground.

17
X-ray / Re: Siemens Polyphos 30 xray machine
« on: June 30, 2019, 07:07:32 PM »
Teardown of the Siemens Polyphos 30 collimator and image plate. Collimator had an interesting moving blinds design with a lot of gears, pulleys and strings. Image plate has a lead grid and some kind of sensor.


18
Maybe we should split the topic, so that this stays for electronic discussion of the heater and the heating of metals, but the melting, casting and crucible discussion has its own thread?

19
X-ray / Re: X-ray with tesla coil
« on: June 28, 2019, 10:49:25 AM »
One of the best and most thorough guides on the dangers of Tesla coils is the list on pupman: https://www.pupman.com/safety.htm

Quote
5.0) Ultraviolet Light and X-ray Production

Ultraviolet light may be produced by the spark gap during operation of a tesla coil. The human eye has no pain sensors within it, so the bioeffects are felt later, when it is too late. (Ever look at the sun for a while, or watch a welder at work?) The light produced in a spark gap is essentially identical to that produced by an arc welder, containing substantial amounts of hard ultraviolet light. As any professional arc welder will tell you "Don't Look At The Arc!" Spark gaps produce a large amount of UV and visible light. The visible light is extremely bright, and the ultraviolet light will damage your eyes, and can cause skin cancer. The arc is so bright that you couldn't make out any detail anyway, so why bother? If you must study your spark gap, use welder's glasses. Generally, it is not too difficult to rig up a piece of plastic, cardboard, etc. that will shield yourself and others.

X-rays

X-rays can be produced whenever there is a high voltage present. Although a number of coilers have tested their coils for x-ray radiation and found none present that is not to say that x-rays cannot be produced, especially if vacuum tubes, light bulbs, and other evacuated vessels are placed near a coil. Here is a little information about X-rays.

X-ray Production

A number of vacuum tubes work pretty well as X-ray tubes, and several articles have appeared in Scientific American magazine in the distant past. X-rays are typically produced by slamming electrons into either the nuclei or inner shell electrons of atoms. The source electrons are usually boiled off a heated filament (cathode), and accelerated toward an anode via some large potential difference, typically 25-150 kV in the medical world. Basically, any time the voltage gets above 10 kV, there is a significant risk of X-ray production, and the risk increases with increasing voltages. You can also get some X-ray production via field emission, whereby electrons escape a cold metal due to very high local electric fields (the Schottky effect). This was probably the type of emission obtained by an amateur described recently on the list. For the remainder of this discussion I will limit my comments to conventional X-ray tubes, using a filament and anode, although most of it applies to both forms. The target or anode is normally a high atomic number material like tungsten. X-ray production is relatively inefficient, so most of the energy is wasted as heat (typically about 99% with good X-ray tubes). Tungsten works well because of its high melting point (to absorb all that wasted heat energy). If the potential difference between the anode and cathode is +100 kV D.C., a spectrum of X-rays will be produced with energies from zero to 100 keV. The graph of the number of X-rays produced (y-axis) versus X-ray energy (x-axis) has a negative slope with a Y=0 point at x = 100 keV. Hence, many more low energy X-rays are produced than high energy X-rays. Some of these low energy photons are absorbed by the tube housing. In a clinical X-ray machine, the tube is placed in a leaded shield with a window (hole) in it for the X-rays to escape through. This window has a piece of aluminum over it to further attenuate the low energy X-rays. In conventional equipment, the tube, housing and aluminum filter accounts for about 2.5 - 3.5 mm of aluminum equivalent material in the exit port. This effectively knocks out most of the low energy (<10 keV) radiation, which would be absorbed in the patient and could not contribute to producing an image anyway.

X-ray Absorption

High atomic number materials readily absorb x-ray radiation. There is an energy dependence here, as high energy X-rays are more penetrating than low energy x-rays. For example, the percentage of radiation which will pass through 10 cm (about 4 inches) of water is 0.04% at 20 keV, 10% at 50 keV and 18% at 100 keV. Compare this with 1 mm of lead (about 0.04 inches), which transmits 0.02% at 50 keV and 0.14% at 100 keV. The human body absorbs X-rays pretty readily (similar to water), but becomes more transparent as the energy of the X-ray increases. That is why we use 50-150 keV for many clinical procedures. The low energy X-rays are filtered out of the spectrum before they enter the patient, usually through the use of an aluminum filter, which lets the high energy X-rays pass through with little attenuation (except possibly to give you enough contrast to see what you want). Most of the x-rays are absorbed in the patient, with 1-5% exiting the patient typically. Low energy X-rays (0-15 keV) are totally absorbed in human skin near the skin surface, and would contribute substantially to patient dose if allowed to reach the patient. This is to be avoided in general!

Shielding

The best material is lead. Concrete and steel also work pretty well. Aluminum is a poor absorber of radiation, unless the radiation is very low in energy. Most plastics are similar to water in attenuating properties (quite poor).

Hazards

X-rays are capable of producing ionizations, which means that the electrons can be stripped off of atoms when an x-ray is absorbed in a material. This results in the production of chemically reactive free radicals, and the direct disruption of chemical bonds. This is generally bad in humans, causing cancer, leukemia cataracts, etc. However, due to natural background radiation levels, humans have built in radiation repair mechanisms and can handle low doses of radiation quite well. Bio-effects are not generally observed for doses of less than 25 rem. Skin reddening occurs with doses of around 300 rem or so. Natural background radiation levels typically contribute 0.2 - 0.5 rem per year. Most regulatory agencies recommend no more than 0.5 rem per year above background radiation levels for the general public. Occupational radiation workers can get 5 rem per year above background. The radiation from a well designed X-ray tube can be as high as 10-50 rem per minute of exposure, at a distance of 1/2 meter. The radiation source acts like a light bulb, decreasing in intensity via the square law with distance. Hence, don't stand close to a possible radiation source, use adequate shielding and minimize the exposure time. Incidentally produced radiation from metal objects other than X-ray tubes will generally be at much lower production levels, but should be avoided, nonetheless.

Regulations

In the U.S. the individual states regulate X-ray machines. They generally keep close tabs on clinical and industrial X-ray machines and aren't too impressed to see them in the hands of people without the appropriate licenses. If you happen across an old X-ray tube, you might consider releasing the high vacuum inside (very carefully, please) so that it is inoperable, and a little safer to handle for show and tell (and much more acceptable to the regulators). This can be done by making a small hole in the glass envelope with a file, keeping the tube wrapped in a large quantity of towels for implosion protection during the process. (It goes without saying that you should always have your favorite towel handy anyway [for you Doug Adams fans]).

Monitoring

At this point I presume you are wondering how to tell if that great apparatus in your basement or garage is producing X-rays. There are several ways to tell. First, go look for a surplus Geiger-Mueller counter at your local hamfest or make friends with someone in your local fire department, since many fire departments have radiation survey meters at their stations (in case we have a nearby nuclear explosion, etc.). (Don't bother with the fire department if your apparatus is likely to upset them!) In addition, nearly every hospital has a radiation safety officer who is likely to be more than willing to take a look at your toys, and will bring a radiation survey meter along. The standard method for monitoring radiation dose is via film badge and/or thermoluminescent dosimetry monitors, but these are not all that useful to the experimenter since they must be mailed back to the dosimetry lab for reading. In general, film is quite insensitive to radiation, and is of limited value in the experimenters setting unless you can leave the equipment on for a long time to get adequate exposure. Cloud chambers are great fun and can detect a variety of radiation particles, but get easily overwhelmed by devices that put out even low radiation levels. If you don't expect any radiation but still want to check, a cloud chamber can be used. Buy a thorium doped lantern mantle at your local camping store to use as a radiation check source to make sure your chamber is working okay before you power up your equipment. Another possibility is to construct an electroscope and place it near your apparatus. An electroscope measures the amount of charge using two thin metal foils which are charged up to a high potential, causing them to swing apart due to repulsion of like charges. Radiation ionizes the air in the electroscope chamber, causing a loss of charge on the foils. Naturally, this type of equipment has limited utility in the direct vicinity of high voltage equipment if electric fields are significant.

X-rays and Tesla Coils

I have monitored my various tesla coils using a number of different radiation instruments and have not seen measurable radiation levels. My coils produce 3 to 5 foot sparks in magnifier and conventional forms using up to 15 kV input, with power levels of no more than 1.5 kVA. Obviously, you don't want to get a survey meter too close to an operating tesla coil.

Finally, always keep safety in mind with all of this equipment. Humans are not able to sense X-ray and ultraviolet radiation. If you think you are producing some, use an appropriate instrument to find out for sure.

 

20
With 6 gates in parallel, for a full-bridge, you would need atleast 10Apeak driving power and 0,144A average driving power, you risk having sagging 24V from that heavy load, so beef the 24V rail up with larger lytics, but I also think you need something larger than a 24V 1A linear regulator.

All datasheet parameters are given for hardswitching in a regular inverter type of application, like a motor drive.

A DRSSTC utilizes softswitching/resonant switching to handle the much higher peak currents we need for spark generation in a very short time.

You need to calculate the Fmax2 value and you can follow my guide here on how to do it: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/igbts/

Just remember there is a lot of assumptions and it is worst case scenarios, so you can tweak some of the values of derate them even  further, it all just comes at the cost of lessened life time of your components :)

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