Author Topic: QCW questions  (Read 5014 times)

Offline Rafft

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QCW questions
« on: January 26, 2022, 10:49:14 AM »

 hi

I have a bunch of 360uF 470uF 560uF 400v elcaps. if paralleled, will total almost 3000uF. can I use this for the DC BUS?

from the few coils I have seen on the net, all use single huge capacitor.

whats the theory behind that?
SGTC / SSTC / DR-SSTC / QCW

Offline davekni

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Re: QCW questions
« Reply #1 on: January 27, 2022, 03:15:18 AM »
Yes, paralleled smaller caps works fine.  That's what my DRSSTC uses.  In my case, 96 parallel 470uF caps to handle high power pulses.
David Knierim

Offline Rafft

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Re: QCW questions
« Reply #2 on: January 27, 2022, 07:09:29 AM »
thanks David

alright then, will parallel more

currently, this one is on 1800uF/400v using 560uF/370uF. charged by dcdc boost . 4S LiIon batt. bellow is at 250vdc. basically a battery-powered qcw.  ;)

https://youtube.com/shorts/kzEzVNB3zBA?feature=share

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Offline Rafft

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Re: QCW questions
« Reply #3 on: January 30, 2022, 05:06:11 PM »
im in DR mode for phase lead adjustment. here is a scope shot of halfbridge output(yellow) and Iprim(blue). its the BEST ADJUSTMENT I could do (56uH and around 50 - 65R from 500R pot). im using IRG4PF50WD. according to calculation, its rated for max 250KHz.

Iprim has 1.7uS period(588KHz). too high. ive measured my primary inductance(LC meter) and no secondary to be around 8uH. resonant cap is 13.1nF. this should be around 493KHz. my secondary w topload(according to javaTC) is 420KHz.

so
secondary 420KHz
primary 493KHz
BUT this coil is stubborn and loves to oscillate at around 555-588KHz. I have tried messing with some caps for resonance(11nF and 15nF) but I gett smaller sparks.

IGBT is 'low frequency' but still operates

running out of ideas



and is this normal? looks like my coil is not DR'ing? looks like my Iprim is not 'amplitude modulating'?


more ON-time


info on secondary:
3.2" diameter x 4.85" Height
awg #33 684T(javatc)
609KHz javatc and actual Fres measurement seem close

topload (back to using 1)
1.3" x 6.4"

sec & topload = 420KHz (javatc & measurement)

I dont see anything else why this coil loves to oscillate around 588KHz, except like its resonating FROM secondary w/o topload(610KHz)  ::)

« Last Edit: February 01, 2022, 03:58:28 AM by Rafft »
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Offline davekni

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Re: QCW questions
« Reply #4 on: January 31, 2022, 04:33:40 AM »
Quote
and is this normal? looks like my coil is not DR'ing? looks like my Iprim is not 'amplitude modulating'?
QCW coils generally have enough arc loading to lower secondary Q so much that little energy is left to transfer back to the primary.  That's my guess as to what you are seeing, but I am not certain.  Hopefully members with direct QCW experience can contribute more information here.

Quote
I dont see anything else why this coil loves to oscillate around 588KHz, except like its resonating FROM secondary w/o topload(610KHz) 
Primary and secondary are coupled resonators.  There is an upper pole frequency and a lower pole frequency.  You appear to be running at the upper frequency (where most QCW coils run).

Quote
im in DR mode for phase lead adjustment. here is a scope shot of halfbridge output(yellow) and Iprim(blue). its the BEST ADJUSTMENT I could do (56uH and around 50 - 65R from 500R pot). im using IRG4PF50WD. according to calculation, its rated for max 250KHz.
Presuming typical UD2.X driver circuitry (at least phase-lead input part), maximum theoretical phase lead (with infinite inductance) is 90 degrees.  Practical upper limit is ~60 degrees.  At 588kHz, 60 degrees is only 284ns lead.  Driver + IGBT delay is likely more than 284ns.  To get phase lead at that frequency will require significantly faster driver and/or H-bridge, or different phase-lead circuitry such as a PLL.  (One somewhat-simple option is to reverse CT leads and add phase lag instead of lead.  In other words, start with 180 degrees and add lag such that driver/IGBT time and lag is not quite another 180 degrees.  Downside of this option is that phase lead increases as frequency decreases.)

Impressive that you have those IGBTs running at 588kHz and making sparks.
« Last Edit: January 31, 2022, 04:36:53 AM by davekni »
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Offline Uspring

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Re: QCW questions
« Reply #5 on: January 31, 2022, 05:59:50 PM »
I believe the primary and secondary resonance frequencies are too far apart to get visible 'amplitude modulating'. This amplitude modulation is caused by energy sloshing back and forth between the 2 tanks. A large difference in res frequencies impedes that.
Once you have breakout, the arc will add capacitance to your secondary tank, which will lower secondary fres and even increase the difference.

Offline Mads Barnkob

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Re: QCW questions
« Reply #6 on: January 31, 2022, 07:22:28 PM »
Impressive that you have those IGBTs running at 588kHz and making sparks.

Do not underestimate the resonant switching capabilities of IGBTs. You are instantly handed like 4 times the speed and switching peak current (extremely rough estimate)

I believe the primary and secondary resonance frequencies are too far apart to get visible 'amplitude modulating'. This amplitude modulation is caused by energy sloshing back and forth between the 2 tanks. A large difference in res frequencies impedes that.
Once you have breakout, the arc will add capacitance to your secondary tank, which will lower secondary fres and even increase the difference.

This is why Steve Wards added a series of small capacitors inside his secondary coil. His first QCW versions simply needed more "self capacitance" to withstand detuning from the long sparks.
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Offline Rafft

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Re: QCW questions
« Reply #7 on: February 01, 2022, 01:22:56 AM »
hi guys

thanks for the input.

just had the "idea" to RUN the secondary to a MUCH lower Resonant Freq. like 200KHz, If I could achieve it. of course I will adjust the PRI res to be lower as well, 10% closer to sec res. I will try to let it run lower so it can be switched by the IGBTs limit.


currently


will TRY this out (350Khz JTC)
« Last Edit: February 01, 2022, 03:59:35 AM by Rafft »
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Offline Rafft

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Re: QCW questions
« Reply #8 on: February 01, 2022, 01:25:41 AM »
I believe the primary and secondary resonance frequencies are too far apart to get visible 'amplitude modulating'. This amplitude modulation is caused by energy sloshing back and forth between the 2 tanks. A large difference in res frequencies impedes that.
Once you have breakout, the arc will add capacitance to your secondary tank, which will lower secondary fres and even increase the difference.

Thanks Uspring

copy that. will try to keep it closer next time. this is my first proper DR build, please forgive the n00b  ;D
SGTC / SSTC / DR-SSTC / QCW

Offline davekni

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Re: QCW questions
« Reply #9 on: February 01, 2022, 05:00:35 AM »
Quote
just had the "idea" to RUN the secondary to a MUCH lower Resonant Freq. like 200KHz, If I could achieve it. of course I will adjust the PRI res to be lower as well, 10% closer to sec res. I will try to let it run lower so it can be switched by the IGBTs limit.
Quote
will TRY this out (350Khz JTC)
Yes, lowering to 200kHz would be difficult using top load changes only.  Halving frequency requires 4x capacitance.
Standard UD2.7 drivers usually settle on the lower pole, so actual frequency may be a bit under 350kHz.  You may be able to squeeze enough phase lead at 350kHz or a bit under.  Optimizing IGBT gate resistors to get barely-enough dead time can help.  To get ideal switching, the final turn-on transition (after dead-time delay) should be roughly at zero-current.

Quote
Do not underestimate the resonant switching capabilities of IGBTs. You are instantly handed like 4 times the speed and switching peak current (extremely rough estimate)
Yes, these IGBTs can switch at 588kHz as you have shown.  Proper phase lead is difficult (requires PLL or ...), and switching losses will still be on the high side at that frequency.  Turn-off current would be significant in order to achieve turn-on at zero-current time.

Good luck with your 350kHz version!
David Knierim

Offline Rafft

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Re: QCW questions
« Reply #10 on: February 01, 2022, 11:01:44 AM »
guys

did some minor adjustments on my coil

- refit variable inductor (12-50uH) to UD2.x because trimpot(for phaselead) OPENed! good thing there is the 5819 on feedback input. smelled something burnt. good thing comparator did not get damaged.
- reconfigured MMC 22nF/1000VDC MKP10 from 13nF to 27nF (4S4P). lets go for less L more C  :)

my setup. only place where I could connect EARTH GND. its only in DR mode. just wanna check sparks and phase lead. small dc fan is THERE to blow air into the 5V linear regulator(need to attach small heatsink), not the IGBTs  :D


checking long ON-time


and the good(?) thing is its oscillating around 312KHz and I havent touched anything on the coil, except for the MMC. where do you think this is going? south pole? Im really getting more confused  :'( or maybe its time to wind another secondary(?) maybe with Fres 200KHz w/o topload(?)


I do get better waveforms than before, and the variable inductor IS "finally" working(because Fres is lower , I  ASSUME).


--------------------------------------
primary coil TAP measured with LC meter with secondary mounted(unGNDed) = 14.3uH
resonant cap of 27nF & 14.3 primary = 258KHz (Resonance calculator)
Actual Resonating Freq = 312KHz
--------------------------------------

uhhhh why  :o


cheers
Ralph
SGTC / SSTC / DR-SSTC / QCW

Offline davekni

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Re: QCW questions
« Reply #11 on: February 02, 2022, 05:48:43 AM »
Quote
- reconfigured MMC 22nF/1000VDC MKP10 from 13nF to 27nF (4S4P). lets go for less L more C 
22nF at 4S4P would be 22nF, not 27nF.  Is it actually 4S5P?  Or are the MMC capacitors actually 27nF/1000VDC?

Quote
--------------------------------------
primary coil TAP measured with LC meter with secondary mounted(unGNDed) = 14.3uH
resonant cap of 27nF & 14.3 primary = 258KHz (Resonance calculator)
Actual Resonating Freq = 312KHz
--------------------------------------

uhhhh why 
If MMC is 22nF, calculation gets a bit closer to 312kHz.  Also, a previous post listed your primary inductance measurement as 8uH.  If this is at the bottom end of your LRC meter's capability, that 8uH to 14.3uH change may be just measurement error.  What does JaveTC say your primary inductance is?  That may be more accurate than measurement.

Quote
I do get better waveforms than before, and the variable inductor IS "finally" working(because Fres is lower , I  ASSUME).
Does it work to get all the way to bridge switching just before zero current?

Quote
and the good(?) thing is its oscillating around 312KHz and I havent touched anything on the coil, except for the MMC. where do you think this is going? south pole? Im really getting more confused  :'( or maybe its time to wind another secondary(?) maybe with Fres 200KHz w/o topload(?)
Are you getting sparks at 312kHz?  That might be reasonable for the lower pole.  Now that I think about it, I recall some LTSpice simulations suggesting that UD2.7-style driver feedback is likely to start at lower pole if primary frequency is below secondary frequency (as is typical for DRSSTC designs), and start at upper pole if primary frequency is higher.  That would fit your experience here.

200kHz may be too low for this small coil.  Lower frequency requires more voltage to get breakout.  May have secondary arcing problems at higher voltage.
David Knierim

Offline Rafft

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Re: QCW questions
« Reply #12 on: February 02, 2022, 07:20:42 AM »
David

thanks for the reply

Quote
Is it actually 4S5P?
sorry typo. MMC is 4S5P of 22nF 1000Vdc

Primary coil is 4.4" diameter. I removed it from setup and measured the inductance (single coil alone). the most spark length I could get is at 6th tap. it measured 7.16uH on LC meter. JavaTC shows 7.3uH at 6th tap.

Code: [Select]
5T = 5.36uH
6T = 7.16uH
7T = 9.15uH
8T = 11.15uH
8.5T = 11.2uH
9T = 13.4uH

 6th TAP 14.3uH from LC meter/measured WITH SECONDARY coil / 27nF with resonance calculator = 258KHz
6th TAP 7uH (from LC meter/measured PRI w/o SECONDARY)/27nF with resonance calculator = 362KHz,
 javaTC shows 359KHz
 and the actual resonance is 312KHz.

TEXT
Code: [Select]
J A V A T C version 13.6 - CONSOLIDATED OUTPUT
01/02/2022, 21:13:49

Units = Inches
Ambient Temp = 68ºF

----------------------------------------------------
Secondary Coil Inputs:
----------------------------------------------------
Current Profile = G.PROFILE_LOADED
1.6 = Radius 1
1.6 = Radius 2
1 = Height 1
5.85 = Height 2
683.1 = Turns
33 = Wire Awg

----------------------------------------------------
Primary Coil Inputs:
----------------------------------------------------
Round Primary Conductor
2.2 = Radius 1
2.2 = Radius 2
0.7 = Height 1
1.45 = Height 2
6.25 = Turns
0.06 = Wire Diameter
0 = Ribbon Width
0 = Ribbon Thickness
0.027 = Primary Cap (uF)
0 = Total Lead Length
0 = Lead Diameter

----------------------------------------------------
Secondary Coil Outputs:
----------------------------------------------------
417.21 [kHz] = Secondary Resonant Frequency
90 [deg °] = Angle of Secondary
4.85 [inch] = Length of Winding
140.8 [inch] = Turns Per Unit
0.00002 [inch] = Space Between Turns (edge to edge)
572.3 [ft] = Length of Wire
1.52 [:1] = H/D Aspect Ratio
117.4376 [Ohms] = DC Resistance
51585 [Ohms] = Reactance at Resonance
0.09 [ lbs] = Weight of Wire
19.679 [mH] = Les-Effective Series Inductance
19.753 [mH] = Lee-Equivalent Energy Inductance
19.032 [mH] = Ldc-Low Frequency Inductance
7.395 [pF] = Ces-Effective Shunt Capacitance
7.367 [pF] = Cee-Equivalent Energy Capacitance
13.716 [pF] = Cdc-Low Frequency Capacitance
4.28 [mils] = Skin Depth
5.49 [pF] = Topload Effective Capacitance
262.5383 [Ohms] = Effective AC Resistance
196 [Q] = Quality Factor

----------------------------------------------------
Primary Coil Outputs:
----------------------------------------------------
358.72 [kHz] = Primary Resonant Frequency
14.02 [% high] = Percent Detuned
90 [deg °] = Angle of Primary
7.2 [ft] = Length of Wire
20.74 [mOhms] = DC Resistance
0.06 [inch] = Average spacing between turns (edge to edge)
0.566 [ inch] = Proximity between coils
0 [inch] = Recommended minimum proximity between coils
7.29 [µH] = Ldc-Low Frequency Inductance
0.01996 [µF] = Cap size needed with Primary L (reference)
0 [µH] = Lead Length Inductance
107.959 [µH] = Lm-Mutual Inductance
0.29 [k] = Coupling Coefficient
0.127 [k] = Recommended Coupling Coefficient
3.45 [half cycles] = Number of half cycles for energy transfer at K
4.55 [µs] = Time for total energy transfer

----------------------------------------------------
Top Load Inputs:
----------------------------------------------------
Toroid #1: minor=1.3, major=6.4, height=6.75, topload

JTC
Code: [Select]
units=0,
ambient=0,
s_ws=0,
s_Al=0,
p_ws=1,
p_Al=0,
p_ribbon=0,
temp=68,
g_radius=0,
w_radius=0,
ceil_height=0,
s_radius1=1.6,
s_radius2=1.6,
s_height1=1,
s_height2=5.85,
s_turn=683.1,
s_wd=33,
p_radius1=2.2,
p_radius2=2.2,
p_height1=0.7,
p_height2=1.45,
p_turn=6.25,
p_wd=0.06,
p_vwidth=0,
p_rthick=0,
Cp_uF=0.027,
Lead_Length=0,
Lead_Diameter=0,
desired_k=0,
t.inner=1.3,
t.outer=6.4,
t.height=6.75,
TT=true,
TG=false,
x_Vin=0,
x_Vout=0,
x_Iout=0,
x_Hz=0,
x_Vadjust=0,
x_ballast=0,
rsg_ELS=0,
rsg_ELR=0,
rsg_rpm=0,
rsg_disc_D=0,
rsg_ELR_D=0,
rsg_ELS_D=0,
stat_EL=0,
stat_EL_D=0,
stat_gap=0,
SPE=true,
RGE=false

Quote
Does it work to get all the way to bridge switching just before zero current?
it auto 'phase leads' with higher interrupter ON-time. with low on-time, there is no phase leading.

Quote
Are you getting sparks at 312kHz?
yes. and the longest, starting from 5th tap to 9th tap.

Quote
Now that I think about it, I recall some LTSpice simulations suggesting that UD2.7-style driver feedback is likely to start at lower pole if primary frequency is below secondary frequency (as is typical for DRSSTC designs), and start at upper pole if primary frequency is higher.  That would fit your experience here.
Im not sure what to answer here, but its my best spark output and "cleanest" Iprim I have scoped, from all the testing I have done with 100Vdc. im guessing its around L=20uH'ish and 50R for the phase lead.

« Last Edit: February 02, 2022, 09:45:12 AM by Rafft »
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Offline davekni

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Re: QCW questions
« Reply #13 on: February 03, 2022, 04:59:04 AM »
Quote
6th TAP 14.3uH from LC meter/measured WITH SECONDARY coil / 27nF with resonance calculator = 258KHz
6th TAP 7uH (from LC meter/measured PRI w/o SECONDARY)/27nF with resonance calculator = 362KHz,
What frequency is your LC meter using to measure?  Most LC meters measure at 100kHz or below, well below your secondary resonant frequency.  At low frequency, adding the secondary should have insignificant effect on primary inductance.  (If the secondary is shorted, primary inductance should go down a little.  If readings are precise enough, coupling factor can be measured this way.)  My inclination is to believe the w/o secondary reading, especially since that roughly matches JavaTC result.

Quote
it auto 'phase leads' with higher interrupter ON-time. with low on-time, there is no phase leading.
Sounds like phase lead is marginally sufficient.  Long ON-time matters most for IGBT power dissipation since that is where most time is spent.

Quote
Im not sure what to answer here, but its my best spark output and "cleanest" Iprim I have scoped, from all the testing I have done with 100Vdc. im guessing its around L=20uH'ish and 50R for the phase lead.
I wasn't looking for an answer.  I was just suggesting that perhaps the frequency reduction you achieved with more MMC capacitance seems reasonable.  Capacitance scaling alone would be only a factor of sqrt(13nF/27nF) = 0.69.  Since your actual frequency reduction was 312kHz/588kHz = 0.53 (If I'm understanding your post details correctly).  The additional frequency reduction is likely due to a change from upper-pole to lower-pole operation.

Overall, it seems like your 312kHz operation is a reasonable place to run.
David Knierim

Offline Rafft

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Re: QCW questions
« Reply #14 on: February 03, 2022, 02:54:15 PM »

David

Quote
What frequency is your LC meter using to measure?
according to the circuit, 550KHz. this is the one I have built years ago. yes that JTC has close results with the LC meter readings (w/o secondary)
https://pic-microcontroller.com/very-accurate-lc-meter-based-on-pic16f628a-using-pic-microcontroller/

Quote
Sounds like phase lead is marginally sufficient.  Long ON-time matters most for IGBT power dissipation since that is where most time is spent.
does this mean phase leading worked because IGBT speed (250KHz)  got closer to the operating resonant freq? or its just the way UD2.x works?

Quote
The additional frequency reduction is likely due to a change from upper-pole to lower-pole operation
Its time for a better tuning then

btw here are a couple scope shots with it in QCW, indoors only. DC ramp(yellow) and Iprim(blue). this is the maximum amplitude setting(clean ramp up/down) before it flats out at the top(much thicker sparks) . ramp time is more or less around 8-10mS. any longer and the sparks go hissy and thick. Im using synchronous buck. switching freq of 20KHz. IRG4PC50FD IGBT for the switches. 

DC BUS its at 130Vdc.


and at 240ish Vdc


just scared sh*t If I crank up the DC bus more (Im too close to the coil)  ;D I even forgot to check phase lead and measure Resonant freq. oh well, will do it next time... plus a short vid outdoors


actually , GOAL ACHIEVED = unTUNED QCW DRSSTC   ;D
SGTC / SSTC / DR-SSTC / QCW

Offline Uspring

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Re: QCW questions
« Reply #15 on: February 03, 2022, 05:33:18 PM »
I don't think your coil is untuned. The flattening of primary current while input voltage is rising is an indication of the secondary drawing power from the primary.
This is not really unexpected, since you are now running at the lower pole, i.e. a frequency below secondary resonance frequency. The arc capacitance will decrease the secondary fres and move it closer to the operating frequency. Power transfer to the secondary will increase.
That is different from upper pole operation, which you had previously. In that case the lowering of the secondary fres due to the arc will move secondary fres away from the operating frequency and move the coil out of tune.

Offline Duane B

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Re: QCW questions
« Reply #16 on: February 04, 2022, 03:55:10 AM »
Deleted. I will start a different thread.
« Last Edit: February 04, 2022, 04:41:18 AM by Duane B »
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Offline davekni

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Re: QCW questions
« Reply #17 on: February 04, 2022, 06:34:03 AM »
Quote
    What frequency is your LC meter using to measure?

according to the circuit, 550KHz. this is the one I have built years ago. yes that JTC has close results with the LC meter readings (w/o secondary)
https://pic-microcontroller.com/very-accurate-lc-meter-based-on-pic16f628a-using-pic-microcontroller/
That explains the change in reading with secondary in place.  Inductance reading is no longer valid at resonance.  Ignore that with-secondary reading.

Quote
    Sounds like phase lead is marginally sufficient.  Long ON-time matters most for IGBT power dissipation since that is where most time is spent.

does this mean phase leading worked because IGBT speed (250KHz)  got closer to the operating resonant freq? or its just the way UD2.x works?
250kHz is not directly relevant.  It worked because frequency was lower, so ~60 degrees of phase lead represents a longer time period, enough to almost compensate for total driver+IGBT delay.

Quote
    The additional frequency reduction is likely due to a change from upper-pole to lower-pole operation

Its time for a better tuning then
No, tuning is fine.  Lower pole is generally preferred for DRSSTC operation.  Both upper and lower pole frequencies exist when primary and secondary frequencies are identical.  The coupled system does not resonate at their center frequency.  Coupling splits the resonance into two frequencies, called the upper and lower poles.
« Last Edit: February 04, 2022, 06:38:11 PM by davekni »
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Offline Rafft

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Re: QCW questions
« Reply #18 on: February 04, 2022, 04:52:17 PM »
guys

just a small update: using upper pole again. added 5"dia x 5.8" H cylinder for topload. made another Primary coil also. 3 taps only. 6T(9.13uH) 7T(11.84uH) 8T(14.2uH) Cres = 14.66nF.   <=== measured with my LC meter and primary coil alone

Secondary Resonant freq with 2 topload is 343.6KHz (JTC) ....... freq drop from 420KHz to 343KHz

Primary resonant 8T(343KHz) 7T(385.3KHz) 6T(435KHz) (res calc)

I get biggest spark at 6T(435KHz)

I have also cleaned the wiring , UD is under the coil. buck and boost is outside. RAMP DC connected thru deans(T-plug) connector.


mey boost(4S input) and buck. this is a battery-powered QCW


checking the resonant freq and phase lead . Half-bridge output(yellow) Iprim (blue). 2.3us is 434.78KHz. wow. so close to the primary Fres (435KHz)  :o . measurement taken at peak of ramp output. resonant freq varies from start of ramp(438.6KHz), ramp peak(434.78KHz), ramp end(431KHz)




ramp out vs Iprim


half-bridge vs Iprim. Iprim still rising, need MORE juice perhaps  ;D  I have only 3100uF bulk cap.


video below. started with 130Vdc bus and 250Vdc........


=================================
so in summary:
Secondary Fres = 343.6KHz
Primary Fres = 435KHz
91KHz difference. IS this a BIG or small difference? is this NORMAL ? ;D I mean the freq difference. I was thinking maybe a 10-20KHz would do, but I guess it needs bigger difference cuz its higher freq compared to DRs in the 50-150KHz (?)

though Im still not sure what the 'best' freq is YET. I aim to use the 8Th tap(or more) and re-adjust the MMC. high-impedance(more L less C) for primary.  still need to save up for BIG elcaps . and possibly make this into full-bridge driver.

cheers
Ralph

SGTC / SSTC / DR-SSTC / QCW

Offline Duane B

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Re: QCW questions
« Reply #19 on: February 04, 2022, 06:15:26 PM »
so in summary:
Secondary Fres = 343.6KHz
Primary Fres = 435KHz
91KHz difference. IS this a BIG or small difference? is this NORMAL ? ;D I mean the freq difference. I was thinking maybe a 10-20KHz would do, but I guess it needs bigger difference cuz its higher freq compared to DRs in the 50-150KHz (?)

Are you measuring these frequencies or just using javatc and calculations? I think your primary and secondary are too far off frequency from each other. It does not look like you have reached critical coupling yet between primary and secondary. Your waveforms look more like a single resonant system to me. Scan the primary resonant circuit and see if you get two resonant frequency peaks.
Duane Bylund

High Voltage Forum

Re: QCW questions
« Reply #19 on: February 04, 2022, 06:15:26 PM »

 


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