Author Topic: Ok now I'm stuck ¯\_(ツ)_/¯  (Read 475 times)

Offline dj.cosmo.esq

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Ok now I'm stuck ¯\_(ツ)_/¯
« on: January 05, 2020, 05:31:14 AM »
Ok here is my first technical post so please be gentle. Ok I jumped into the drsstc thing from spark gaps. Although a lot of things are similar there's still a hell of a learning curve but if I can figure out these little quirks i know I'll be ok. So im running the cloud leopard driver from China which was on a whim from banggood for like 30 bucks with the interrupter. The GDT is humming along switching a half bridge of 1MBI600PX-140 igbts both have 2kvdc 2.5uF fabmika caps sitting on the bricks. Two 350v 4200mfd electrolytic caps in series run voltage doubled.  Of course TVS to block any surge. My MMC is 9 series 2 parallel of Cornell Dubilier UPP10W3P3K 3.3mfd 1050vdc caps. So 9450v at .7333uF and I have 9 more if needed to do 3 strings but they have never even gotten warm when just running 1 string of 6. Here's now my dilemma, I can't get this coil to go be past 2 foot arcs. I have tapped and tuned to the best of my (limited) knowledge and it's maxed out. I'm assuming with this setup I should be able to get some good arcs? I used a scope and got my fres of about 58khz and the adjusting it to about 49khz I get 2 foot arcs. Now here are the noob questions(sorry ahead of time). For the life of me I can't get feedback to drive the damn coil. So I'm using a signal generator to run it but even with as much as I'm pushing into this coil 2 feet seems really small... Any input or silly oversights on my part are highly appreciated.
Thanks, Courtney

Offline Mads Barnkob

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Re: Ok now I'm stuck ¯\_(ツ)_/¯
« Reply #1 on: January 05, 2020, 01:59:29 PM »
Running a DRSSTC from a signal generator = hard switching = dead IGBTs

You need to fix the feedback before trying to make bigger sparks.

I always recommend people to use a Steve Ward 1.3b or 2.1 Universal Driver for their first DRSSTC. It works, it is simple and many people knows how it works. The Chinese drivers are hit and miss on documentation due to loss in translation, if there is a translation.

Here I kill a bridge with a signal generator

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Offline dj.cosmo.esq

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Re: Ok now I'm stuck ¯\_(ツ)_/¯
« Reply #2 on: January 05, 2020, 09:56:42 PM »
Thanks for the reply Mads. I feared that was  going to be the answer. So this is what I know the input for the feedback and ocd do work because I can trigger them artificially. Is there a size limit to the core or the feedback? Like if the core is too big it won't pickup the current? I have some small ft-140-75 and some larger ft-240-77. I've tried cascading but nothing I've only observed feedback once but somehow the wire melted going through the toroid.  I'd there a easier way to get feedback like maybe 2 or 3 turned of primary? Or is it possible it's my startup procedure? I start the driver , then Interrupter, then the bridge with a variac set to zero and slowly ramp up. In order for the feedback to work it has to get started from somewhere and once the power is up enough on the bridge if it hasn't switched the gate at all how does start? Do I have to then turn the driver on and off to Kickstart maybe?  Is it the whole cascading the trick because I've seen the switch to the three toroid recently where the larger wraps 1 turn around the two smaller cores? More turns or less turns? I'm so close yet this feedback seems like a unicorn I'm trying to catch.
Thanks again,
Courtney

Offline davekni

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Re: Ok now I'm stuck ¯\_(ツ)_/¯
« Reply #3 on: January 05, 2020, 10:35:21 PM »
To repeat one of Mad's suggestions from other posts, do you have bleed resistors across the H-Bridge output?  Most drivers are not self-oscillating without feedback.  The first half-cycle after enabling needs to create enough feedback signal to trigger the next half-cycle.  Depending on the remaining charge on the MMC, the first half-cycle may be driving it to the same state it's already in, so create no feedback signal at all.  Bleed resistors across the H-Bridge output forces the MMC to neutral (no charge) state between drive bursts.
David Knierim

Offline dj.cosmo.esq

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Re: Ok now I'm stuck ¯\_(ツ)_/¯
« Reply #4 on: January 06, 2020, 10:04:41 AM »
Thanks davekni and Mads. Ok ok ok I see what you mean about the voltage ramping up.and the bleed resistor immediately draining the output to start say a swing or oscillation of sorts? In that case, Nope, no bleed resistor! I swear I've read every post on this forum but I must have misunderstood the context. I apologize about that RTFM moment. Now my question would be what rating on the resistor!?! Cause that's a nice chunk of power!

Offline Mads Barnkob

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Re: Ok now I'm stuck ¯\_(ツ)_/¯
« Reply #5 on: January 06, 2020, 10:40:52 AM »
Thanks davekni and Mads. Ok ok ok I see what you mean about the voltage ramping up.and the bleed resistor immediately draining the output to start say a swing or oscillation of sorts? In that case, Nope, no bleed resistor! I swear I've read every post on this forum but I must have misunderstood the context. I apologize about that RTFM moment. Now my question would be what rating on the resistor!?! Cause that's a nice chunk of power!

Luckily it is not the full charge of the MMC you need to drain, but a low voltage residual charge. I have used 10-15 kOhm 50 Watt power resistor, but you can just calculate it from the inverter output voltage and resistor resistance to get the power rating needed. It is even also a very low duty cycles (2-5% for a DRSSTC).
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline dj.cosmo.esq

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Re: Ok now I'm stuck ¯\_(ツ)_/¯
« Reply #6 on: January 06, 2020, 11:11:31 AM »
Thanks Mads! And just to double check I would be putting the resistor from the collector to emitter, parallel with the output of the MMC and NOT from the output of the MMC to the other side say bypassing the primary in essence shorting the MMC bank with the resistor? Correct?
Thanks, Courtney

Offline Mads Barnkob

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Re: Ok now I'm stuck ¯\_(ツ)_/¯
« Reply #7 on: January 06, 2020, 03:08:54 PM »
Thanks Mads! And just to double check I would be putting the resistor from the collector to emitter, parallel with the output of the MMC and NOT from the output of the MMC to the other side say bypassing the primary in essence shorting the MMC bank with the resistor? Correct?
Thanks, Courtney

Yes, it goes directly on the inverter output and across the LC primary circuit. This is mostly for convenience, it could go across the MMC and do the same job, but you just suddenly need a 10-20 kV voltage rating instead of 1 kV.

If your MMC have individual bleed resistors, that will properly work as well, but that it not seen so often anymore, when we use large snubber capacitors
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Offline davekni

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Re: Ok now I'm stuck ¯\_(ツ)_/¯
« Reply #8 on: January 06, 2020, 09:38:46 PM »
Since this is a half-bridge, you'll need to try the bleed resistor across one transistor's C-E, then across the other.  It needs to be across the transistor that is in the OFF state for the first half-cycle of oscillation.  Not knowing the controller or phasing of your GDT, can't say which transistor needs the bleed resistor.  If you have a scope, you could capture which IGBT is on first at the start of a burst, rather than guessing.  Put the resistor on the other IGBT (the one that's not on first).
David Knierim

Offline wuschel

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Re: Ok now I'm stuck ¯\_(ツ)_/¯
« Reply #9 on: January 11, 2020, 12:40:23 AM »
Hi,
im looking over your JavaTC Calculation. Im thinking there is something wrong with the Toroid calculation.
The Toroid from this calculating must be an Monster.
The resulting Frequency must be higher.
You can test it with the "Helicat calculator" from mad Barnkobs Homepage.
PS 2 Feet Arcs are not so Bad for an first try.


Have Fun

Offline dj.cosmo.esq

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Re: Ok now I'm stuck ¯\_(ツ)_/¯
« Reply #10 on: January 13, 2020, 09:21:59 AM »
I'm pretty sure it's right or very very close I'm still smoothing the darn thing out but  I must admit it was a ton of work but it's slowly coming out to a nice finish. I saw a tutorial of sorts on good ol YouTube
and they guy was saying how to get a (close to) spun aluminum toroid look. So I decided to go with his idea but tweak it just a tad. I went by Mads suggestions on his site (or tried) by going with the diameter of the coil for the minor of the toroid and the length of the coil for the major. Definitely correct me if I misunderstood because I'm here to learn as much as possible. Anyways 5 cans of spray foam later. I usually never take pics but I attached a couple. As you can see my work space has been overrun by the BMW :-\

Offline Mads Barnkob

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Re: Ok now I'm stuck ¯\_(ツ)_/¯
« Reply #11 on: January 13, 2020, 08:22:20 PM »
Your JavaTC calculation is correct, I am not sure what wunchel is refering to by my helical coil calculator, since its for coils, maybe that I got a example of a toroid capacity in it: http://kaizerpowerelectronics.dk/calculators/helical-coil-calculator/ but that is 26 pF, close to yours.

Secondary coil diameter = toroid minor diameter and secondary winding length = toroid major diameter gives you a secondary system that has proportions optimized for electromagnetic field shaping, charge storage, getting distance to the primary coil out from the primary coil and it easily goes along with hitting the magic 50k impedance.

It is a very nice toroid you made, the one I made for my DRSSTC1 with epoxy was way too much work and I should have gone with foam :) But aluminum tape is hard to get all flat and shiny, he must have polished it up in his video, the one you embedded.
http://www.kaizerpowerelectronics.dk - Tesla coils, high voltage, pulse power, audio and general electronics

Offline dj.cosmo.esq

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Re: Ok now I'm stuck ¯\_(ツ)_/¯
« Reply #12 on: January 13, 2020, 11:42:07 PM »
Yes Mads it looks to be that way. I figured out a trick to actually getting the wrinkles and imperfections out.  :D Since it's only aluminum foil and adhesive I basically take multi oscillating tool and 3m 2000 grit wet dry sandpaper and run over all the lines which makes the lines smooth relative to the overlapping piece, then I use 3000 grit and erase it completely. The result after a light polish is like a mirror. Initial test have shown no corona discharge from anywhere except the breakout point. So much so I had to polish the breakout point because it ended up being the most jagged surface and it was to the naked eye perfectly smooth! Now it is only discharges from the very tip of the tungsten rod resulting in larger and cleaner streamers. It's a ton of work but I'm pretty sure that the roughly $35-40 in materials is way less than getting a spun aluminum toroid in the size I needed for this project.

High Voltage Forum

Re: Ok now I'm stuck ¯\_(ツ)_/¯
« Reply #12 on: January 13, 2020, 11:42:07 PM »

 


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