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1
Dual Resonant Solid State Tesla coils / Re: Futurist's DRSSTC1
« Last post by Mads Barnkob on Today at 12:23:57 PM »
By my experience so far I have a feeling that most people overexaggerate their streamer length
I never got continuous 2m streamers, just caught a few, and more frequent ones were 1.5-1.7m long

Note that my coil is just over 130cm tall which makes 1.5m streamers look incredible

Maximum spark length is usually those once in a while extra long sparks that can you find by scrolling through the frames of your video recordings, while the continuous streamer length is shorter.

I never recorded sparks longer than 1.5 meter on my DRSSTC1, but I think it can do better from tuning and more power, I was limited by 10A fuse back then, on 250VAC single phase.

Great work so far, looking forward to hear more about how you get the best performance from the UD+
2
The application I intend to use the induction heater for requires my to have the work piece already in the coil when I start it up so I must make sure it can start to oscillate, which, as it turns out, it really can. Even at startup current of 50A! The heater I am using now is this one: http://www.ebay.com/itm/322519608639

And yes, I am fully aware that I am running it at least 100% over it's rated specs (that are probably optimistic to start with). At this stage I am not interested in seeing if it runs and oscillates. I know it does. I am trying to figure out it's weak points and how to address them. My goal is to get my own induction heater up to about 2kW, preferably using only one pair of mosfets and to have enough cooling for it to run continuously.

Another potential problem I might run into is that the work piece won't couple enough energy (not sure how to explain it). I now know that a solid piece of iron will mean a fairly large transfer of energy, but I will use a thin walled pipe and I have absolutely no idea if that will work or be enough. I will try and find a regular steel pipe to try with and see what happens, but for my finished application I will have to get hold of some martensitic stainless steel pipe which has turned out to be almost impossible.
3
All potentiometers, switches and push buttons have been mounted in the lid with front plate on. I had the front plate mounted on the lid with the 6 screws when I did all the holes through both front plate and lid at the same time, to ensure perfect alignment, but I fooled myself. As the lid was not mounted on the box, the 6 lid screws was not in center and I will properly break a few of the corners when mounting the lid, since the screws come in off center :(

If anyone else ever build one of these, be sure to notice that the connection points for PW, Frequency and SW are mirrored (channel 1/2), but the optical output connections are not mirrored, so it is easy to mix up the turn direction of the potentiometers and that midi/fixed switch works opposite.

Next job to be done is making a small PCB for the 4 optical transmitters, a small front plate and drill the holes for those and the MIDI connector in the case.
4
Which "unmodified Ebay induction heater" are you using?  If you are using one of the "1000 watt" models, why would you allow 50 amperes to flow?
50 Amps X 40 Volts = 2000 watts.
  When testing the limits of one of these devices, I would not place  any work in the work coil before turning the power on unless I was already confident that the current flow would be acceptable .  I would turn the power on, confirm that the circuit was oscillating, and THEN slowly insert the work, watching the current, making sure not to exceed a practical limit.

In your pictures of the burned traces:
Those components appear to be gate components, not power handling components.  I think those traces are okay to handle several watts.  I think the components overheated when when the Mosfet failed.  I don't think my gate zeners have ever survived a failed Mosfet.

Pete Stanaitis
---------------
5
Dual Resonant Solid State Tesla coils / Re: Secondary Coil Design Decisions
« Last post by Mads Barnkob on August 21, 2017, 03:39:14 PM »
Welcome to HVF :)

A medium sized coil, like the first I built too, is a good start, its not too big and too small and certainly not too expensive either :)

There is not much difference from 2200 to 2100 turns, but it is seen as a common mistake to make the overall coil length too short, also along with base and topload, so that spark length actually gets hindered from a too low sitting break out point.

I prefer the 50k impedance / longer secondary coils as described in my guide, with even dimensions between coil and topload: http://kaizerpowerelectronics.dk/tesla-coils/drsstc-design-guide/

A large topload can store a bigger charge, so it will represent a bigger load to the inverter feeding the secondary circuit. A big topload discharging a large spark will also kick the secondary circuit far more out of tune or result in whiplash like effects with a voltage gradient travelling very fast on the secondary winding, perhabs resulting in flashovers on the secondary coil.

A too wide topload can also result in loss of electromagnetic field control and you can get problems with sparks going downwards for the primary circuit.

That being said, you have to actually go to extremes to get this far, larger topload can give longer sparks as they store more charge, but they also demand more of the inverter.

Building a DRSSTC is one big impedance matching of 3 circuits, inverter, secondary and spark and none of them are really steady and constantly dynamic, its easy ain't it? :)
6
Dual Resonant Solid State Tesla coils / Secondary Coil Design Decisions
« Last post by sparkydownunder on August 21, 2017, 12:58:30 PM »
Hi Guys

New poster here, just starting out on the DRSSTC journey.
I've been in the research phase for about 2 months now and am finally ready to be locking down some final designs.
Im shooting for around a 70khz resonance and (from looking at Mads' DRSSTC1 and build guides) id be looking at around 2200 turns at 60cm or 2100 turns at 55cm.
Does anyone have any preference with a longer coil with slightly thicker wire or a shorter, denser coil?
If the coil is well below the inductance I need expanding the topload will help bring down the freqency. Is there any issues with an oversized topload?   

Cheers

SDU     
7
Long ago I bought one of Gao/Loneoceans' midi2 controllers: http://loneoceans.com/labs/sales/midi2/

I finally dug it out from the pile of kits-to-build-when-I-get-time(tm) and found a suitable aluminium box to house it in.

It has two outputs for optical transmitters, so I wanted to put one of each kind in for each channel, so it will have both a blue IF plastic fiber transmitter (IF-E97) as well as the ST Fiber transmitters (OPF1414T). I will make a separate PCB for these 4 to be mounted in the side of the box.

For the front I wanted to make a simple etched PCB for text, markings etc. It was easy and fast to make in ExpressPCB.

So far I got to etch the front and prepare all the potentiometers and switches with wires



8
Electronic circuits / Re: Royer induction heater and high current power supply
« Last post by kamelryttarn on August 20, 2017, 08:06:42 PM »
Yes the mosfet blowing up was louder than I expected. It's very nice to have a power supply that won't sag under heavy loads. I realized afterwards that I should have set my oscilloscope on a negative slope trigger to catch all values when it blew up but perhaps I will do that later on when I get it running again which shouldn't take too long.

I haven't inspected the pcb thoroughly yet but I noticed a very thin connection that blew up and it makes me wonder why they would make such a thin via if it was supposed to handle large currents. I will see if I can figure out what it was supposed to connect. The other, similar board I have does have the exact same configuration so I can not use that as a reference.
9
Electronic circuits / Re: Royer induction heater and high current power supply
« Last post by Mads Barnkob on August 20, 2017, 07:50:59 PM »
I got 5 of these for a good price: http://www.kemet.com/Lists/ProductCatalog/Attachments/123/F3303_C4DE.pdf

They are rated 100 Amps (10kHz 25C), will they tolerate more or less at 300Hz?

In high frequency applications where these typically are used, it is the power dissipation that is the limiting factor, since losses are higher at higher frequencies. At lower frequencies it is the allowed ripple voltage that is the dominating factor, but since you are using MKP capacitors, this is not a problem, but watch their temperature rise as there is a large current de-rating factor for temperature.

Yesterday I connected everything and it is working great!

I made some triggered measurements with my Hantek 1008 oscilloscope and it looks ok but I am a bit puzzled about the gate waveform. Despite around 40V power supply voltage it does not look very "square-y" but I'm beginning to think that my oscilloscope knowledge or the actual oscilloscope itself may be at least part of the reason. Could it be that the bandwidth is a bit too low for what I am trying to do? Despite that it was very interesting an educational.

At first I did a few runs with nothing inside the coil. There was a large current spike at the beginning but it dropped quickly. Startup current at around 40V was roughly 20A.

Then I decided to see what happens when you put something inside the coil and try to fire it up. I found a piece if solid iron about 3cm in diameter and placed inside of the coil. Now things were starting to get exciting! Startup current was over 50A and it didn't drop as much as before. The iron piece got quite hot in the few seconds the induction heater worked before one of the mosfets blew up (as expected). Since the induction heater started to oscillate and worked well for a little while before blowing up I am assuming the heat losses is the most likely reason for failure. I will try my IRFP4568 next since they have MUCH lower RDSon the the IRFP250N. So far I am using un-modified ebay induction heaters to learn a bit more about them.

Congratulations on having it all working, at least for how long/short it lasted :)

You are right about your Hantek 1008 oscilloscope having a too low band width and sample rate. 2.4MSa/s is very low for a oscilloscope, which is why this is advertised for diagnostics on engines, not high frequency inverters. 2.4MSa/s is most likely also only if you used a single channel, so using all four it is even smaller, like my Rigol DS1054Z is a 1GSa/s if using one channel, but using all 4 its down to 250MSa/s.

Was it a loud boom when the MOSFET went? Did you get it on video?

Certainly looking forward to the repaired inverter updates! 
10
Electronic circuits / Re: Royer induction heater and high current power supply
« Last post by kamelryttarn on August 20, 2017, 09:07:33 AM »
Yesterday I connected everything and it is working great!

I made some triggered measurements with my Hantek 1008 oscilloscope and it looks ok but I am a bit puzzled about the gate waveform. Despite around 40V power supply voltage it does not look very "square-y" but I'm beginning to think that my oscilloscope knowledge or the actual oscilloscope itself may be at least part of the reason. Could it be that the bandwidth is a bit too low for what I am trying to do? Despite that it was very interesting an educational.

At first I did a few runs with nothing inside the coil. There was a large current spike at the beginning but it dropped quickly. Startup current at around 40V was roughly 20A.

Then I decided to see what happens when you put something inside the coil and try to fire it up. I found a piece if solid iron about 3cm in diameter and placed inside of the coil. Now things were starting to get exciting! Startup current was over 50A and it didn't drop as much as before. The iron piece got quite hot in the few seconds the induction heater worked before one of the mosfets blew up (as expected). Since the induction heater started to oscillate and worked well for a little while before blowing up I am assuming the heat losses is the most likely reason for failure. I will try my IRFP4568 next since they have MUCH lower RDSon the the IRFP250N. So far I am using un-modified ebay induction heaters to learn a bit more about them.

In the scope pictures below I have the current clamp hooked up to channel 1, mosfet gates are connected to channel 2 and 3, and finally channel 4 is the supply voltage connected through a 20:1 attenuator.
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