QCW questions

[davekni]

Thank you for the replies David

You are certainly welcome.  Great to see your progress.

[Rafft]

David

before, Ive had smps power for UD and buck control circuitry(Gao), power input from LiPo battery.

I have tried using Linear PS for the UD. IGBT driver ps is from 7824 regulator.

on the ramp buck side, Ive got the IGBT high-side driver in un-regulated 25vdc(17Vac traffo).

can you please check attached. where are those hashes/spikes coming from? previously, same problem with using smps power for UD and buck control.

edit: I was thinking maybe I would get 'cleaner' system with Linear PS for the logics and drivers.


the only smps power left, is the boost (16v8 to 300Vdc for buck power)

[davekni]

can you please check attached. where are those hashes/spikes coming from? previously, same problem with using smps power for UD and buck control. though what Ive noticed is that the Iprim current waveform is cleaner when there are no spikes present(with using linear PS)

the only smps power left, is the boost (16v8 to 300Vdc for buck power)

It appears that the UD2.x driver is getting momentarily confused at times (as before), switching away from zero-current point (hard switching).  Would be a bit easier to tell for sure if either a GDT input or H-bridge output were scoped too.

Why UD2.x is getting confused is harder to determine.  Could be interference from 16-300V converter or from ramp generator buck converter or from some other source.  General techniques to reduce interference include ground planes within circuitry, shielding around circuitry, and common-mode chokes (ferrites) around cables between modules.  Sometimes it is easier and more effective to make such general interference reduction changes than to determine the exact cause.

It still may be useful to find the cause.  Perhaps the 16-300V converter or ramp generator is also misbehaving momentarily, generating large noise spikes that couple into UD2.x driver.  In that case it is helpful to locate and fix the initiating noise source.  You may want to scope a switching node in each converter simultaneously with primary coil current to look for any correlation between current noise spikes and other switching events.

Good luck!

[Rafft]

David

as per your reply, here are some images and scopeshots.
blue=primary current , 1v=100amp
yellow=Full-bridge output, scope x1 , probe x10 with 2pF in series
note=I made a new GDT here. taken from VGA cables, making sure they both look the same. they have the same dimensions as per your posts. 3T and measures 40uH.

judging from my previous Iprim scopeshot, I think these now have better(?) results... same setup, only GDT changed. there are still those noise but are far lesser

**I have opto on the interrupt input (RCA)
***I have direct connections (GND) from arduino (pwm-ramp) to buck, but controller and buck are separately powered though they share the same GND. I wonder if I should opto-isolate this as well(?)
reason Im using opto is that fiber optic parts are hard to come by.

**point0000.png the initial ramping on the bridge output is 450KHz. and when Iprim starts ramping up, its 370KHz. and because of the 'fast rise' of bridge output, spark output branches early on! 

this -stuffs/early branching of arcs- just happened when I increased UD mosfet drivers supply from previous 20v supply(smps) to 24v Linear-regulated. and from the buck gate driver 15v(smps) to  25v Linear-UNregulated.

-or

just my controller settings!
edit: redid test, adjusted the 'wick' control, even to the minimum setting(virtually removing wick voltage) but there is still the 'quick rampup' on bridge output..

edit2 on phone photo. I have adjusted scope brightness to minimum. no its not 'quick rising'.

[davekni]

**point0000.png the initial ramping on the bridge output is 450KHz. and when Iprim starts ramping up, its 370KHz. and because of the 'fast rise' of bridge output, spark output branches early on! 

I think the "fast rise" is when feedback takes over from self-oscillation.  Perhaps self-oscillation frequency needs to be reduced, and/or feedback signal made stronger relative to self-oscillation.  Not sure how far you can go with either change before frequency locks to lower pole instead of upper as desired.

Glitches appear to occur even when bridge output is not switching.  Any chance the other bridge output is switching there?  Shouldn't be given single GDT.  Unless there is some difference between half-bridges, such as a damaged IGBT or damaged diodes/resistors between GDT and gates.  At least on this side of the bridge, it appears that glitches occur first, then the controller gets confused and causes more glitches.

***I have direct connections (GND) from arduino (pwm-ramp) to buck, but controller and buck are separately powered though they share the same GND. I wonder if I should opto-isolate this as well(?)
reason Im using opto is that fiber optic parts are hard to come by.

Not sure if isolating buck control will help or not.  You could try to see.
Hand-wired breadboard circuitry tends to be noise sensitive.  Ground planes are difficult to add.  Best to have as much of a ground grid as possible:  ground nodes connected to each other both horizontally and vertically within the breadboard wiring.  Also, you could add a copper ground plane to the top of the plastic sheet mounting your driver board.  Cover copper where necessary with tape to avoid shorting to board.  Wire board ground nodes to this ground plane where possible, ideally at least one connection on each edge or each corner of the board.  Wire all connector grounds to this plane too.

[Rafft]

thanks for the inputs David.

whole system got 'different' with my 1st mod attempt, mainly switching my 12v6 boost to 20vdc(powering whole UD) --->> Linear PS 24vdc with 7824. so making the igbt drive to 24v.

do remember these are counterfiet(!) IGBTs.. maybe they cant handle higher than 24v gate drive 

my previous hardware UD ps was 20vdc(and 7809,7805). for the buck, 15vdc only for IGBT high- side driver. maybe its better to go back my previous PS voltage. and do the added GND planes for UD. and maybe add an opto for the buck input as well.

btw, about your phase lead input section on the other thread(20R 10uH 6R8), these values good also for 300KHz-450KHz operation?

edit1
I dont think some of the IGBTs are damaged. I always test them in low-power mode(45vdc & in DRSSTC mode only) and check bridge output. this I do especially when changing new GDT(phasing). I get about 100vpk2pk with a freq of around 410KHz. if all works, then proceed with the usual qcw

below images.bridge output.checked from usb 'wave' saves
**1 burst in DR mode, scope x10 probe x10(no cap in series)
** 410KHz on start (self osc IIRC was set to 480KHz)
** then at end of switching, settles to 360KHz (coil resonance)

[davekni]

do remember these are counterfiet(!) IGBTs.. maybe they cant handle higher than 24v gate drive 

I doubt the IGBTs have any specific issue with 24V.  However, switching times will change a little.  Might change dead time slightly.  Also, at 24V any hard-switching may cause larger noise spikes.  If driver never makes such mistakes, then there should be no hard switching and therefore no such issues.

btw, about your phase lead input section on the other thread(20R 10uH 6R8), these values good also for 300KHz-450KHz operation?

Probably best to use OCD version from later posts, with 5R1 followed by 1k and BAT54 clamp diodes.  Older versions are roughly same equivalent bottom resistance, just made with 6.8 ohms paralleled with 20 ohms (10 ohm POT and 10 ohm resistor).
10uH is probably high for this frequency.  I'd go with the final 4.7uH.
20R on top is fine.

[Rafft]

David

regarding OCD, I have my 3rd CT(isolated) with 100Amp/per volt.

What do I have to modify so the existing LM311 have the same output?

I would be using my existing 1:32:31(currently ocd) to be the new fb_ct input.

thanks

[davekni]

regarding OCD, I have my 3rd CT(isolated) with 100Amp/per volt.

What do I have to modify so the existing LM311 have the same output?

I would be using my existing 1:32:31(currently ocd) to be the new fb_ct input.

Since you already have three CTs, do you have any reason to change to my new OCD version?  Only reason I designed it was to avoid an additional CT.

If you do want to use the new OCD version, your circuit looks good.

[Rafft]

 ok no reason at all except for future reference.

I would just have to rewind my  existing 1:9:9 fb to 1:31:31 for the new self-osc circuit (only for fb, will use existing ocd)

pretty excited about the phase lead adjustment. will also house the entire UD board on a aluminum case.

thanks again 

[Rafft]

guys

sanity check please 

qcw is battery powered, nothing is connected to mains. using UD2.1b with David self-osc mod(set to 470KHz)

*SEC + topload standalone on cardboard, same height as when mounted = 315KHz
                                                                                                              266.22KHz lower pole
                                                                                                              406.66KHz upper pole
                                                                                                              k = 0.4

                                                                                                              Equip used:
                                                                                                              Rigol scope , mains powered
                                                                                                              555 Fres finder, 9v powered
                                                                                                              *LEDs light up brighter (resonance) when scope GND is connected to 555ckt

*PRI alone (MMC parallel) on mount, no SEC 8Turns(12.6uH/14n4) = 367KHz

                                                                                                              Equip used:
                                                                                                              Rigol scope , mains powered
                                                                                                              Sig Gen, 4s(12.6v) batt powered + 10k
                                                                                                              *only one strong peak(resonance) reading

*PRI + SEC (grounded-counterpoise)

8Turns (12.6uH 14.4nF)
279KHz
433KHz

9.5Turns (17uH 14.4nF)
259KHz
407KHz

Equip used:
Rigol mains powered / Sig Gen + 10k, shows 2 peaks (lower and upper poles right?) actually seeing this on scope made me HAPPY 

Actual QCW Operation @225VdcBus:
8Turns = 446KHz~415KHz~ 128Apk & triple-transition can be seen
9.5Turns = 463KHz(self-osc) then 403KHz~381KHz 72Apk only
Rigol scope mains powered. bridge output (yellow) is capacitively coupled with 2pF

Am I nearing tuned state?
why is 8T have more streamer length compared to 9.5T(w/c has close upper/lower poles to SEC)?
what to do?

also posted a shot with phase lead tuning. (yellow) Vce,lower sw (cyan)Vge, lower sw (magenta) separate CT for Iprim 100A/div.
 close enough perhaps(?). done on DR mode only and at a low 40Vdc

Im using 8 Igbts for these. 10R/IGBT. who knows what the specs are, but these are sold(cheaply) as replacments for inverter/welders. IIRC these had high gate capacitance.

thank you for the time reading
-Ralph

[davekni]

*SEC + topload standalone on cardboard, same height as when mounted = 315KHz
                                                                                                              266.22KHz lower pole
                                                                                                              406.66KHz upper pole
                                                                                                              k = 0.4

Don't think I understand this.  What does "standalone" mean?  I presume no primary.  But that means no coupling factor (k) and only one resonant frequency.  Unless you are getting the second resonant mode with voltage peaks at top and middle of secondary.  Are you driving the bottom of the secondary relative to earth ground (signal source grounded on one side and fed to secondary bottom on other side)?  I think that is the normal way to measure secondary resonant frequency.  Should be measured with counterpoise in place so that all sources of topload-to-ground capacitance are present.  Might as well leave primary in place too, just not connected to MMC to avoid primary resonance.  Do you have a ground strike rail protecting primary?  If so, that should be in place too.

also posted a shot with phase lead tuning. (yellow) Vce,lower sw (cyan)Vge, lower sw (magenta) separate CT for Iprim 100A/div.
 close enough perhaps(?). done on DR mode only and at a low 40Vdc

Low Vdc scope capture looks to have more phase lead than the higher voltage captures.  Probably all OK.

why is 8T have more streamer length compared to 9.5T(w/c has close upper/lower poles to SEC)?
what to do?

My guess is that your primary impedance is a bit too high.  Detuning increases primary current and therefore energy transfer.  May be a fine solution.  Optimum might be to reduce primary frequency with a higher capacitance MMC rather than with more primary coil turns.

[Rafft]

David

I measure sec+top Fres the 'usual' way. lower sec winding is signal input.using 555ckt for 'peaks' or using signal gen for 'dips'.

I get my coupling coeff by inputing pri(&top) and sec dimensions on  javatc. thats how I get upper/lower pole calculations.

regarding PRI lower/upper, they are measured by sig gen/scope, again seeing 2 'peaks' , lower & upper. measured when tesla coil is assembled(with mmc parallel to pri)

will again TRY tuning. goal is tuning PRI 5% lower than sec. or maybe id make lesser K by halfing PRI height(and remeasure again upper/lower pole).

[davekni]

or maybe id make lesser K by halfing PRI height(and remeasure again upper/lower pole).

Lower coupling is another way to get higher primary current (instead of detuning).  However, for QCW, I think high coupling is generally better.  Allows energy transfer to continue better as arc grows.  My guess is that lower primary impedance would be the ideal solution.  However, I don't have enough experience to be certain.

I get my coupling coeff by inputing pri(&top) and sec dimensions on  javatc. thats how I get upper/lower pole calculations.

OK, so 315kHz is a measured value and 266kHz and 407kHz are calculated values.

[Rafft]

 do you think it would be better measuring Fres of SEC mounted in place with everything & leaving MMC out?

from what ive seen on some qcw, 13~17uH PRI & 12~15nF MMC. maybe there is some *magic* in there(?). qcw operation 300~500KHz.

have some more question

Im using MKP X2 1uF 225VAC rated caps. this is for bridge snubber. 2s4p. 225VAC would equal 500VDC? I series two, just to be on the safe side. max bus sees only 225Vdc(for now)

for my final phase lead, Im using 1R+R47(but total resistance is only around 1R2) and made a variable inductor 0.6uH~1.5uH. 1:10:10 fb . would this be enough for 380KHz~440KHz operation? was it lowering inductance 'adding' phase lead? or the opposite? when I adjust the inductor around 0.6uH, I see triple transitions. when inductance higher, triple transitions go away. BUT when I test it in DR mode only(40vdc) and low bps, the one with triple transitions have a bigger 'bang' sound than when there is no triple transitions. just wondering w/c of the 2 is best at phase lead tuning. is 'have more phase lead' better? 1R2/1.5uH need another value adjustment perhaps?

[davekni]

do you think it would be better measuring Fres of SEC mounted in place with everything & leaving MMC out?

Yes, though it may not make a significant difference.

from what ive seen on some qcw, 13~17uH PRI & 12~15nF MMC. maybe there is some *magic* in there(?). qcw operation 300~500KHz.

I think most QCW coils use higher DC bus voltage than you do.  For your lower DC voltage ramp, a lower primary impedance may be appropriate.

m using MKP X2 1uF 225VAC rated caps. this is for bridge snubber. 2s4p. 225VAC would equal 500VDC? I series two, just to be on the safe side. max bus sees only 225Vdc(for now)

1s8p would reduce parasitic inductance and almost certainly be fine.  225VAC is 318V peak.  X2 caps are designed to handle much higher pulse voltage for line surges.  Very unlikely to have any issue with voltage on your X2 caps even with 1s8p.

for my final phase lead, Im using 1R+R47(but total resistance is only around 1R2) and made a variable inductor 0.6uH~1.5uH. 1:10:10 fb . would this be enough for 380KHz~440KHz operation? was it lowering inductance 'adding' phase lead? or the opposite? when I adjust the inductor around 0.6uH, I see triple transitions. when inductance higher, triple transitions go away. BUT when I test it in DR mode only(40vdc) and low bps, the one with triple transitions have a bigger 'bang' sound than when there is no triple transitions. just wondering w/c of the 2 is best at phase lead tuning. is 'have more phase lead' better? 1R2/1.5uH need another value adjustment perhaps?

Your adjustment range looks good.  Higher inductance is more phase lead.  Yes, the triple-transition point is optimum.  However, any adjustment mistakes are more problematic if too-little phase lead than too-much phase lead.

[Rafft]

I think most QCW coils use higher DC bus voltage than you do.  For your lower DC voltage ramp, a lower primary impedance may be appropriate.

Yes I agree with this. more PRI inductance for higher bus/ramp voltages.

I have been meaning to up my Vbus supply lately, but my IGBTs are just 600v devices. I have also been testing with PRI with K=0.166(L=13uH) 6" diameter but not pancake. even with measured 420KHz upper pole, I get branching streamers. I have also tried really high k=0.57, problem is the upper pole goes too high (~520KHz), they do work, but I don't want to stress the unknown spec IGBT... so I just used k=0.4 (somewhere between too low and too high) and it works quiet well. Iprim somewhere around 150~170Apk(sometimes OCD). maybe  I need to upper this as well. maybe 200Apk.

and actual measurement of PRI upper/lower pole , and comparing it with SEC calculated upper/lower pole gave me a better chance of tuning my qcw. but I do still need 'calculator' for getting the coupling coeff. next best thing to do is fine tune. PRI taps -or- mmc taps -or- PRI height. still wondering how  wide(or narrow) the tuning range is with QCW, though Im pretty sure its -almost- tuned. just need to squeeze a few more 

225VAC is 318V peak.  X2 caps are designed to handle much higher pulse voltage for line surges.

Good to know. actually it was rated 275vac, so will be around 389v peak. still ok with my low voltage qcw  btw, is it ok to mix 100nF 220nF 330nF 1uF for bridge snubbers? maybe as a multi-freq snubber(?)

Your adjustment range looks good.  Higher inductance is more phase lead.  Yes, the triple-transition point is optimum.  However, any adjustment mistakes are more problematic if too-little phase lead than too-much phase lead.

got it. Thank you! I opted for the higher inductance adjustment on mine. as what you have said before, a cleaner Iprim means good phase lead. I have also noticed a triple-transition when Fres/tune is off (like: tuned 410KHz , off-tune: 350KHz or 480KHz, then I see triple-transitions on bridg output.)  so this means(?) phase lead adjustment is freq dependent... if so, does this mean "tune coil first/look for optimal Fres" before doing phase-lead adjustment? or is (my) phase-lead has wide freq range of when it can work optimally?

[davekni]

btw, is it ok to mix 100nF 220nF 330nF 1uF for bridge snubbers? maybe as a multi-freq snubber(?)

Yes, mixing snubber caps is beneficial.  Smaller value caps tend to do better with the high frequency currents.  (For low-voltage bypass capacitors on logic chips etc., many data sheets suggest using two or three different value caps.)

phase lead adjustment is freq dependent...

Yes, the standard phase-lead adjustment is frequency-dependent.  Ideal phase-lead circuit would lead by a fixed time rather than a fixed phase.  The required time is slightly more than the delay through driver and H-bridge.  Delay time is roughly constant over frequency, so ideal phase-lead would also be constant.  In other words, time-lead would be more ideal than phase-lead.  For normal UD2.7 style phase lead, as frequency increases, the lead increases in phase, but decreases in time.  (For example, 60 degrees at low frequency is more time than 60 degrees at high frequency.)
Yes, proper phase (time) lead is most important when primary current is highest.  That is the best frequency to use for adjusting.  However, make sure that phase lead isn't too little at the higher starting frequency.  Some compromise is needed.
BTW, I designed a roughly-constant-time lead circuit for my DRSSTC covering 50-80kHz.  That circuit has down-sides too, so wouldn't recommend copying.

[Rafft]

finally!

99% tuned

 after 9 months of working(from scratch) with my QCW DRSSTC, I have finally acheived  +1 meter(50" or x10 sec length) of arc from a  battery-operated coil. using 4s(16.8v) 2000mAh Lipo boosted to around 295Vdc. bulk cap is 6600uF 350vdc.
and fed to TL494 buck (asynchro) & single switch IRG4PC50FD . modified UD2.x for self-osc(450KHz). using single full-bridge MBQ60T65PES(counterfeit) for inverter. OCD set to 200A limit. 9n8 MMC wima mkp10. secondary coil 3"×4.75".
big-ass topload 4"x12.5".coil resonates at 459~439KHz 124Apk@295Vdc bus.

included are couple shots from buck output. single trace(cyan) is with low voltage test & 1R load. next 2 traces(yellow) is from ramp output +200vdc input. blue(Iprim). done only on low voltage. dont have x100 probe.

tuning IS the key 😉

[davekni]

Congratulations!!!  Your perseverance is impressive, as is the result.