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Messages - Laci

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1
After waiting a week for the components and another few days of work, I could finally make some better tests.It looks like with longer pulses at lower peak currents I get good results,just like with short pulses at higher currents.I tested midi notes up to 300A peak and transient up to 500 and the midi notes can already destroy 4A fuses.I'm a bit worried about huge sparks,because I blew up my SSTC2 bridge yesterday. I was running it from mains ground and cranked up the power to maximum.A secondary - primary flashover killed it...Stupid!...RIP 2pcs HGTG30N60A4D...

The MMC is the same that I planned, 0.2uF 6400V KEMET R76 series, around 80A IRMS. They are working,but didn't make any measurements yet.
I painted the metal enclosure blue,just like the MMC and added plenty of screw terminals.

For higher power running I want to make sure that it won't kill the bridge. I don't have strike rail and bus negative to earth capacitor.Adding these should hopefully save the bridge from flashovers. Another thing that might result in a fail is the IGBT losses.I have to calculate this...

The sparks already scary to me, I have to get used to them. :)
One bigger spark from the video, spark length is as much as secondary + topload length:













2
Dual Resonant Solid State Tesla coils / Re: QCW music with Midi
« on: May 08, 2019, 05:30:54 PM »
I THINK Steve Ward did something similar with his QCW:
https://www.youtube.com/watch?v=QpKNbvonSic

I didn't make anything similar to this,but I'm interested,so keep up the good work!

3
I did some more calculations and choose the KEMET R76TR31004030J. 4 in series, 8 in parallel gives 0.2uF at 6400V,so around 850A peak. They are cheap and common so I can update the MMC in the future if needed.Their RMS current rating is just under 10A around 100kHz.This gives around IRMS=80A for 8 in parallel.



I calculated a maximum of 100 bps at 800us for the 80A IRMS. What do you think about this choice?

4
Electronic circuits / Re: Attempt to repair a welder
« on: May 04, 2019, 05:31:10 PM »
Thank you for the answer and searching, petespaco!
The manufacture is Awelco,made in Italy.I only found some informations and troubleshoot on a russian website.The welder is nice and compact for the first look,but it has many disadvantages for the person who wants to repair it.Not only the SMD parts make the repair hard,but the shunt based current sensing kills many components in case of a failure.

While probing on the working module I accidentally shorted the UC3845's pin 7 to pin 6.This made the chip to act the same as on the not working module: low duty cycle driving signal.I think these ICs can partly die.
I'll order some replacements and try again...

5
I found this ebay listing with 0.1uF 2.5kV paper in oil capacitors:
https://www.ebay.com/itm/K41-1a-Paper-PIO-pulse-capacitor-0-1uF-10-2-5kV-Lot-of-2/251259264733?_trkparms=aid%3D888007%26algo%3DDISC.MBE%26ao%3D1%26asc%3D20131227121020%26meid%3Dc3967893df3249af835219ad5cd172cc%26pid%3D100009%26rk%3D1%26rkt%3D1%26mehot%3Dag%26sd%3D162844731444%26itm%3D251259264733&_trksid=p2047675.c100009.m1982

Does anybody have experience with this kind of capacitors?Are they any good for a MMC?

Another thing: in series connection the overall pulse resistance(dVdT) of the MMC gets multiplied by the amount of series capacitors? In this case the voltage gets shared by the series capacitors and they see a smaller voltage rise across them,so 1.8kV/us capacitors would already be good with 4 in series at 6kV across the MMC?
I just saw Futurist's DRSSTC1 and he used C4BS capacitors,which have around 1kV/us rating if I remember right and they worked fine for him...

6
Please upload some gate waveforms to see how the UCCs perform.

7
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« on: April 30, 2019, 12:09:19 AM »
Thanks for the useful informations,Phoenix!

I did my calculations until the limitations of the MMC,but you are right about resonance.

The current rise time is not critical for me as I want to run with long pulses,up to 800us with freewheeling.

I used Mads MMC calculator hundread times for now. :)

Many thanks for your calculations and for the webshop.The capacitors are really cheap indeed,although the 10 euro shipping is a bit painful compared to the them.I have to do my calculations about these.
At first I thought 0.2uF is too much and will require only a couple of turns.After running a JavaTC simulation it showed that one less turn,so 5 will be at 113kHz which is good!

What about the number of series and parallel capacitors?The datasheet doesn't mention the current rating,but in theory the more capacitors in parallel,the less the ESR is or in these applications it makes not much sense?For example at 110kHz,800A which one should I choose, 0.2uF 6kV(more in parallel) or 0.15 8kV(more in series)? (in theory more in parallel)

8
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« on: April 29, 2019, 09:42:07 PM »
After spending hours on choosing the greatest and cheapest capacitors to upgrade the MMC,I realised they all have small dVdT rating.With heavy spark loading the frequency should drop to around 110kHz which is 9us period.In this period are two cycles so the rise and fall times of the primary current are 2.25us.At a high voltage,like 8kV,they should be rated over 4kV/us if we are lazy and assume the primary current rises linearly.

The WIMA FKP1 series have the best dVdT rating I could find.I planned to buy 20pcs 0.047uF 2kVDC of these,the same as the current ones,just with 5% tolerance(the current ones have 2.5%).If I combine all of them,I get a 4 in series,7 in parallel MMC,rated 0.0822uF and 8kVDC.

The interesting thing starts here.With the heavy spark loading I mentioned at 110kHz, the MMC's reactance is 17.6 ohm.The highest MMC voltage I would allow is 8125V with the 325V bus.From these,according to ohms law the maximum current is 8125/17.6 = 461A. This was a bit disappointing after making the calculations and the only way I can think of to increase the maximum current is increasing the MMC capacitance.
Am I right in the calculations and should I really increase the MMC's capacitance for higher peak currents?Perhaps knows somebody about affordable capacitors for MMC I can buy?

9
Dual Resonant Solid State Tesla coils / Re: Phoenix's Large DRSSTC II
« on: April 29, 2019, 08:42:52 PM »
...and I thought my SKM400s are huge...
I wonder how big your heatsink will be too. :D

Good luck for the building and looking forward to steal some techniques.  ;)

10
Electronic circuits / Re: Attempt to repair a welder
« on: April 29, 2019, 07:22:32 PM »
After a painful explosion and fail on this project,I thought of trying the repair of this welder again,because it only takes up space in my lab otherwise.

Since many components blew up last time,I replaced those,the UC3845 current mode IC,the L6386 bootstrap driver,the BJT output transistors and some infinite ohm resistors on the current sensing part.

Right now it turns on and nothing blews up,but compared to the other module(the welder is made out of two same inverters in parallel)I get a lower,1.6V at the compensation pin 1 of the UC3845,while the other has 2.7V.It's weird because this pin is the output of the error amlifier,which has an internally referenced input and another is the voltage feedback pin 2,which is 2.5V on both modules!If you take a look at the schematic you can see that pin 1 only connects to higher or equal potentials(VFB=2.5V, VREF=5V) and a connector.Probably this wrong voltage results in a low pulsewidth driving signal,so the inverter's energy transfer is limited.

Does anybody have an idea what causes this?Maybe replace the UC3845?




11
Beginners / Re: SSTC wıth a balast
« on: April 28, 2019, 07:22:43 PM »
The closer the primary to the secondary,the higher the coupling is ,which is essential for SSTCs.As long as you can't see sparks from secondary to primary you can move it closer.

The number of turns is really experimental.If you look at other SSTCs it moves around 10,usually less.

Many things depends on design,so try these instead of making questions that we can't answer...

12
Beginners / Re: SSTC wıth a balast
« on: April 28, 2019, 03:01:53 PM »
If you're in a rush,then make a small compact circuit,as it doesn't require much components.Mount the MOSFET on a solid heatsink,bend the gate and source out a bit for more space and solder the zener diodes directly on these pins,just like the gate resistor,according to Fumeaux's schematic!Make sure nothing connects to the heatsink expect the MOSFET.Solder short,but enough wires to the potentiometer's legs and solder these to the right points.If you have long enough wire from the base of the secondary coil,solder that directly to the base too,make sure it doesn't touch other metal parts.Use the thickest wire you have as primary for a good magnetic field coupling.

The best way to try out this circuit without blowing up the MOSFET is to use a low voltage source,like a transformer rectified for DC.Add a fluorescent light bulb close to the upper end of the secondary.The first thing to do is rotating the potentiometer and see if the light bulb lights up.If it doesn't,then change the direction of the primary.If it does,find the position where the light bulb is the brightest.After you found the best point you can increase the input voltage.

If the MOSFET blows up you can either have gate overvoltage mainly due to bad zener diodes or wrong connection,or too much drain current.To decrease the drain current you can add a few more turns to the primary coil,but too much turns will decrease the length of the arcs,so use more turns while testing.

For a better design and longer arcs you should read other people's projects here and of course the websites which has most of the knowledge required to build a great Tesla coil,for example:
http://kaizerpowerelectronics.dk/tesla-coils/

https://www.loneoceans.com/labs/


13
Beginners / Re: SSTC wıth a balast
« on: April 27, 2019, 10:04:21 PM »
The ballast doesnt specify on it. It is a magnetic ballast. (https://www.3faz.com/yildiz-250w-metal-halide-balast-yildiz-250w-balast?gclid=CjwKCAjw-4_mBRBuEiwA5xnFILMfN0Ybm14MaD_8JeIiclpmyEi0KltvBJWAxysTV4xkCt2L8NNqBBoCgw8QAvD_BwE this is it)

Sorry for the stupid question,I saw the crossed NAME of the diode and thought that it's omited,but if not,then it doesn't matter if the supply is AC or DC.

14
Beginners / Re: SSTC wıth a balast
« on: April 27, 2019, 09:49:09 PM »
Just to avoid confusion: MOSFETs have source,not emitter.

The zener diodes should have their anodes connected together and the other two ends to MOSFET gate and supply negative,to protect the MOSFET gate from over/undervoltage.

Try turning the potentiometer to find the best offset voltage for your MOSFET.

Your ballast outputs DC or AC?

15
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« on: April 27, 2019, 09:41:30 PM »
Thanks,Mads!

A larger topload with less sharp edges is in the plans.

The ground wire is relatively thick;thicker than the primary and around 6-7m long.The ground rod is made out of aluminium,about 1m long with many holes in it.All in all I think this grounding is pretty low impedance and something else causes the problem,but if it's good floating then I don't care. :)

The external buttons are great idea,I never thought of this!Since processing MIDI files in app inventor looks not really possible,I plan to switch to something more professional like android studio,that might take some time.

16
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« on: April 27, 2019, 08:21:51 PM »
First light...on video!
I'd say about maximum 40-50cm sparks under 100us ontime at 250A limit!This 1:1 spark to secondary size is already promising I think. :)
Still many things to do,like thermal protection,RMS current measurement and a WIFI or ethernet interface for better control.For now the app works great,but the BLE distance decreased significantly after the metal enclosure to around 5m,which is still enough in a room.

The largest improvement that can be done is a better MMC.My dream was to find some screw terminal high pulse duty capacitors at affordable price.These are quite rare,for cheap even rarer.If the current WIMA FKP-1 caps can keep up the stress,then I'll probably buy plenty of these in the future to get some 8kV and current up to like 800A.Is this too much for a 12.5cm dia. and 50cm tall coil?! ::)

The grounding is still questionable.Now the secondary base and the heatsink is connected to the ground rod,but the driver enclosure is floating.The general DRSSTC grounding diagram suggests to connect the driver enclosure to the same ground,but I get a lot of noise in the gate drive with that...Also I don't have strike rail and the bus negative to ground capacitor placed.


A pretty spark from the video:


Video: https://mega.nz/#!AKgCGSaD!bLG60IWPkzon7V5Krxq0VxgPT3-mpxzL3VsgE7QD4Fc


(Sorry for the bad quality,the photographer job is the next.  :P)


17
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« on: April 26, 2019, 04:05:09 PM »
I think the 5V noise got lowered to an acceptable level after soldering the 5V regulator close to the input,adding some ceramic capacitors and some thicker wires.

Quickly put everything together and now I get noise from the secondary.Its base is connected to mains ground for testing.If I connect the enclosure to mains ground the waveforms gets worse,but if I only connect the heatsink to mains ground I see some improvements like longer arcs and more current flowing.Should the ground rod connected to the enclosure and heatsink solve this issue?I'll get the rest of the components next week,then hopefully make this ready for a mains test,unless you say that the ground rod would solve the noise,then I test it before. :D

18
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« on: April 26, 2019, 10:19:06 AM »
The + of the PSU goes to the buttom + bus of the output stage(4xNMOS,4xPMOS + capacitors)and the black goes to the upper - bus.The multiple wires from the 4xdriver ICs goes to the gates.The wires which have the ferrite bead are feedback and the other white wires are the PSU wires too.

There's plenty of noise on the +5V!

19
Dual Resonant Solid State Tesla coils / Re: My first DRSSTC on bricks
« on: April 26, 2019, 09:39:32 AM »
I put the driver into a metal enclosure.After trying it out,signal noise appeared again.It looks like there's too much noise if the enclosure is floating and even worse if I ground it to mains earth,because the PSU for the driver is on the same ground.Any ideas about this?




20
Sell / Buy / Trade / WTS [EU]: EPCOS 4600uF 385V Capacitors
« on: April 24, 2019, 11:43:33 PM »
I have some EPCOS 4600uF 385V aluminium electrolytic capacitors from a while ago,bought them in used condition for using in my tesla coils.I tested two,one in my SSTC2 and the other in my current DRSSTC on bricks,they are working fine.
They have a maximum of 70A ripple current capability!
The exact part number is: B43586-S3468-Q1
Datasheet: http://www.platan.ru/pdf/datasheets/epcos/B43566_B43586.pdf

If anyone is interested in these capacitors,feel free to send me a message.




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