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Messages - davekni

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1
Voltage Multipliers / Re: HV resistor in oil
« on: Today at 05:21:07 AM »
Steve,

You could use well less resistance if you want to make sharper sparks.  The 30mA diodes are likely rated well higher for peak current, probably over 100mA.  Any sudden discharge event will draw current for only a short pulse.  Even that short pulse sends only half of the discharge current through diodes.  Half will go through each capacitor chain.  The one chain connected to ground and your resistor string will not contribute to diode current during a discharge event.

For limiting average diode current, the capability of the ZVS/flyback is likely sufficient.  To reach 30mA average into even a shorted load, the flyback needs to output +-60mA, with each diode conducting for half-cycles.  That would be +-6A flyback input current if the turns-ratio is 100:1 (not including the resonant current).  With a 2meg output resistor string, the current would share some among the first several diodes, so could handle more than +-60mA.  It would require simulation for a more precise analysis, but I suspect 2meg total would be enough.

Of course, 15meg would be more conservative if that's your bent.  It would also lower the dV/dt of the caps during discharges - don't know what your caps can handle.

For mounting, how about making the single long string without covering, then wind it around a smaller internal piece of PVC pipe, perhaps an extension of something used to mount the caps and diodes?  Or make a zigzag up one side of the internal PVC.  Either way, there are many options for keeping the string in place.  Drill holes in the pipe and have excess lead stubs from the resistors stick into the holes.  Or, make small saw-cuts along one side of the pipe and wrap string or fishing line around the pipe and resistors,  with the string in the saw cuts.  The string could wrap up and back down and tie together.  Or, use epoxy on the resistor leads or on string instead of saw cuts.  Or, cut small scraps of PVC (say semicircles of pipe) and use PVC glue to attach them between turns of resistors...

2
Voltage Multipliers / Re: HV resistor in oil
« on: December 04, 2019, 04:31:16 AM »
Steve,

Thank you for the EBay link!  At the picture looks to be in very nice shape.

Is there a list of AC flyback part numbers?  I haven't found anything showing that F0239 is AC-output, nor any way to search EBay (or other places) for AC flyback transformers in general.

This question isn't critical.  At the moment I have only one HV AC transformer plan (DIY plasma globe), which I have by frying diodes in an old DC flyback.

3
Beginners / Re: Full bridge showing half the voltage
« on: December 04, 2019, 04:26:38 AM »
If your new schematic is accurate, the bridge rectifier you are using to measure voltage is connected to the gate-drive on the right side rather than to the right-side H-Bridge output.

4
Voltage Multipliers / Re: HV resistor in oil
« on: December 03, 2019, 04:34:46 AM »
Steve,

For more specific electronic parts such as VR68 resistors, I purchase from electronic distributors.  There's a wonderful web site:
    http://www.oemstrade.com
Enter a part number, or the initial string, and it searches most distributors, displaying price@quantity (and quantity in stock). with links to the distributor's page for that specific part.  It's wonderful for finding the best price.  (For work, it's also helpful to see if a part is widely available.)

Arrow (arrow.com) often has one of the best prices, and has free shipping for >=$50 orders.  For a couple years they had free overnight shipping on all orders of any size.

DigiKey often has the highest price, but not always, occasionally the lowest.  They have the widest range of parts in stock and the best search tools (IMHO).  So, I often start at DigiKey, search for the parameters I want (ie. >=10kV 10meg resistor), look for the lowest price options on DigiKey, then enter those part numbers into Oemstrade.  (Sometimes I need to order a larger variety of parts or more unusual ones, so end up ordering from DigiKey or Newark or Mouser.)

Also, if exact value isn't critical, look on Oemstrade for several similar parts.  Sometimes one of the discount distributors such as chip1stop or Verical will have excess stock and dramatically-lower prices on specific parts.

I looked through the videos from backwoodsBrophil that you linked, and commented there with a question about source of his AC-output flyback transformers.  He's using old Sanyo FO241 transformers from Ebay.  I don't see any source for those at the moment.  Do you have AC-out HV transformer(s) for this project?  If so, where did you find them?  Or, are you frying the diodes in a DC-output flyback?

Saw your comment on backwoodsBrophil's video about more diodes than necessary.  My experience suggests this is necessary.  Series diode strings have a problem at the turn-off point.  Some diodes in a series string will have shorter Trr, so turn off first.  The first diode turning off now sees the entire reverse voltage.  It goes into avalanche breakdown, and must handle the remaining reverse recovery charge from the other diodes w/o frying.  My larger Marx generator is fed from a +-11kV home-made transformer and two-state multiplier to get 44kV.  Each diode needs to handle 22kV reverse and ~0.5A forward current.  Made strings of 1.5A 1kV 75ns Trr diodes.  (Also tried some 120ns diodes separately.)  Had frying issues until using 40+ diodes per string.  The diodes died slowly, increasing leakage current and lowering breakdown voltage from the avalanche current.  (They were avalanche-energy-rated diodes.  Initial try with diodes not rated for avalanche failed almost instantly.)  For my initial 30-diode strings, I kept testing each diode and replacing the failing ones.  When I didn't test often enough, the failures cascaded throughout the strings.  With enough diodes, the few fastest ones fry and there's still enough good diodes left.

BTW, my low-current CW multiplier uses pairs of 20kV 5mA diodes, even though the input voltage is ~20kVpp.

You may get as much or more voltage than backwoodsBrophil even with fewer stages.  If I heard his video correctly, he has 500pF caps.  With 20 stages, he's getting quite a bit of loss from stray capacitance.

5
Spark gap Tesla coils / Re: SGTC MK1 - An Accomplishment in Progress
« on: December 02, 2019, 04:09:37 AM »
When measuring pin 2 to 6 Vpp, there's no need to derate the 90 Vpp rating.  The diode reverse voltage is the output peak-to-peak voltage.  (The output peak voltage will be lower because of sine-wave drive, with as much reverse voltage as forward voltage.)

The inductance for a flyback I wound with 10 turns is ~60uH.  It's probably physically a bit larger than your small ones.

Can you provide any more details about your comment: "I found it interesting that the voltage across the caps was quite low when tied to ground"?  The peak voltage across each cap should be the same grounded or drain-to-drain.  Peak-to-peak will be half, because each cap sees a one-sided waveform, not going more than a diode-drop below ground.

Having some of the resonant capacitance to ground could have an advantage when using IGBT parts for a ZVS oscillator.  It will make the IGBT current negative just before switching off.  I haven't explored the effects yet, but it might be useful for IGBTs with slow turn-off.

Looking forward to your new update!  Hopefully it's a successful day of experimenting.

6
Voltage Multipliers / Re: HV resistor in oil
« on: December 02, 2019, 03:42:16 AM »
I use Vishay's VR68 series, such as VR68000004703JAC00 for 470K, or VR68000001005JAC00 for 10meg.  They are rated for 1W, 10kV, and much smaller than many HV parts.  Being interested in low current for human touch (standing hair on end etc.), I used a string of 32 10-meg parts on the output of my CW multiplier.  I use the 68meg ones for bleed/balancing resistors on my larger Marx generator.

7
Phasing isn't too critical for initial operation unless it's way off.  It requires +-60 degrees to get down to 50% output (cosine function).  The more sensitive use for phasing is to improve IGBT efficiency by having them switch off just before current reaches 0.  If your IGBTs aren't getting too hot, precise phasing can wait.  Yes, R2 could be used for phase adjustment.

Does your scope have a separate trigger input?  If not, measuring phase with a single channel will be difficult.  If it does have a trigger input, connect that to a fixed place, ideally the enable input.  Trigger on the lead edge of enable.  Then use the single channel to measure points around the loop:  CT output, 4069 input, 4069 output, gate drive transformer inputs (each side separately), and H-Bridge outputs (if your probe can handle 200V).  Set the scope for say 5us/division to see the startup phasing.  This exercise should show phasing and hopefully give clues on the surprisingly-rapid HV output start-up.  Scope your antenna pick-up as well with the same trigger and horizontal scale.  Images of all those should be enough information to figure out the puzzles.

Of course, your call on whether it's worth all that measurement and analysis.  I have fun figuring out puzzles, so tend to ask for lots of information.

I'm still hoping someone else can comment on the fast rise and slow fall of your antenna waveform.

8
Spark gap Tesla coils / Re: SGTC MK1 - An Accomplishment in Progress
« on: December 01, 2019, 02:56:39 AM »
Bifilar winding shouldn't matter much.  For the ZVS, the leakage inductance just adds to the inductance from positive DC input, so is a slight advantage.

I'd missed your original note about the two 0.33uF caps being from drain-to-ground.  Most ZVS circuits I've seen have a capacitor between the two drains, but not to ground.  Having capacitors to ground causes the FETs to carry the resonant current in addition to the DC input current, so increases their power dissipation.  Having capacitors to ground as you do may have advantages, though.  I was thinking it might help keep the oscillation to the lower resonant frequency of the two for the case of coupled resonant circuits.  Attempted simulation of that topology a few days ago, but LTSpice didn't converge well, and I didn't take time to play with the algorithm parameters (charge tolerance, ...).

That's likely why you're measuring 70kHz instead of 80kHz - the HV winding capacitance scales by turns^2 and adds to the primary capacitance in the lower-frequency mode.  (The flybacks I've been playing with drop even more due to secondary capacitance.)

BTW, due to my not reading carefully about caps to ground, I'd been presuming 0.66uF primary rather than 0.167uF.  So, that may have messed up some of my previous-post calculations.  However, with 0.33uF from each drain to ground, the effective resonant capacitance is actually 0.33uF, not 0.167uF.  That's because at any given point in time, one of the two 0.33uF caps is shorted by a FET.  Which cap toggles, but only one is active at a time.  The higher FET current is due to that cap shorting, carrying the resonant current from the other cap.  You can see this easily in simulation - measuring frequencies and FET currents in both topologies.

How did you determine 22uH?  Was that something I calculated (from bogus assumptions)?  The best way I know is to measure frequency with a much larger capacitor (ie 3-30uF) so the secondary capacitance is less significant.  (For best accuracy, measure with two different large capacitors and do the algebra to calculate inductance and parasitic capacitance - two measurements and two variables.  That's what I just did for a flyback last week - one I intentionally fried the internal diodes to get AC output.)  Ring-down is the best method with large capacitors.  Running the ZVS will result in low frequency and high current and therefore core saturation, which lowers inductance.

A larger flyback is likely to have a bit more inductance (for 10-turns), but probably not enough to explain 70kHz to 40kHz (about 3x inductance).  Inductance could actually be 3x higher, or perhaps the resonant mode is different.

The HV return pin definitely needs to remain grounded, along with pin 7.  Otherwise the HV return current passes through the high-value resistors of the pin 7 internal network.

150W seems reasonable, 5-6mA at 24-30kV.   With ZVS sine-wave input, the current can probably be a bit higher, and the voltage a bit lower.  (Lower voltage because sine-waves are symmetric, while flyback waveforms have much less reverse voltage.  Higher current because the diode forward-conduction will have higher duty cycle with sine-wave drive, so lower peak current.)

For measuring turns ratio, the signal generator doesn't need to make more than 1-2V peak.  The secondary turn count is likely at least 1000, so at least 100x your 10-turn primary.  However, it needs to get 1-2V peak into a fairly low impedance, which it may not be capable of doing.

For your new flyback for which you attached a schematic, pins 2 to 6 is shown as 90Vpp.  That would be a great place to measure with your scope.  Ground pin 2 and measure pin 6 or visa-versa.  With no HV load, measure pin 2-6 Vpp relative to ZVS input voltage.  That will determine what input DC voltage is safe to run.

Fun project!  Thank you for the detailed information.

9
Voltage Multipliers / Re: Suggestions for CW HV feed-through
« on: November 30, 2019, 05:22:19 AM »
Interesting full-wave schematic.  Requires two AC inputs, presumably 180 degrees out of phase.  When reduced to a voltage-doubler, that does not match the normal circuit called a "full wave voltage doubler", which uses a single AC input:


Of course, what circuit is called what doesn't matter.  The voltage multiplier you are building is the one that makes sense for your project (and for mine and likely most others).

10
Voltage Multipliers / Re: Suggestions for CW HV feed-through
« on: November 29, 2019, 09:12:32 PM »
Steve,

I'd thought that "full-wave" applied to only voltage-doubling.   Is there a circuit for higher multiplication factors that's called "full-wave"?

At 1.7nF and 14 stages, parasitic capacitance will have some effect, but probably not excessive.  (I have 16 stages starting with only ~550pF.)

Another thought for your interconnect at the bottom:  How about using a pair of battery-contact springs on the bottom of the multiplier and two pieces of nickle or nickel-plated sheet metal at the bottom of the housing?  Alignment could have very loose tolerances that way.  I expect the weight of your multiplier is well more than twice the contact force of a typical AA battery holder.

11
Voltage Multipliers / Re: Suggestions for CW HV feed-through
« on: November 29, 2019, 07:23:28 PM »
Banana plugs/jacks sounds like a good solution as long as you have the alignment issue solved.  The stamped metal "banana-peel" part typically produces sharp edges of contact, which likely have enough pressure to break through the oil film.  You could bend the banana-peel tabs a bit to create even more pronounced edge contact rather than contact along the surface of the stamped metal.  I'd suggest having the male plug parts on the multiplier in case you need to tweak the tab bending and/or find a part with stronger (higher insertion force) tabs.

BTW, have you ran any simulations on the multiplier including parasitic capacitance between the two capacitor columns?  I was surprised how much voltage loss came from capacitive coupling between columns.  (If you are making a high-power unit with relatively large column capacitors, stray capacitance may not be significant.  I was purposely using as small capacitors as possible for safety - using it as a Van de Graaff alternative.  Also added a string of 30 x 10meg 10kV resistors in series with the output.)

12
My guess for the higher-power instability is power supply capability.  The pulsing load can be difficult for power supplies to handle.  Scoping the supply output will show if the voltage is dropping during each pulse when the noise starts.

The goal is to have roughly 0 degrees phase shift for the entire circuit.  Positive H-Bridge output voltage when the current is positive and negative voltage when current is negative.  Since there are some delays (HC14, gate driver, FETs), a bit of phase lead in the current feedback would be optimum, perhaps 20-30 degrees.  That's for optimum output power.  If using IGBTs where there's more value (efficiency) to switching just before their zero-current point, the optimum phase shift may be slightly different.  Depends on inductance of Tesla primary coil.

With this controller circuit, phase will change as the power increases at the start of each burst.  At the beginning of a burst, the current feedback will have almost 90 degrees phase lead.  That's because the CT output voltage will be under 5Vpp, so the diodes won't conduct, so infinite load impedance.  Current into an inductor creates the 90 degree lead.  As the power builds, the CT output increases and the diodes conduct more of the time, so the effective load resistance on the CT drops towards 1k.  12.6mH at 220kHz is 17.4k reactance, so phase shift is arctan(1k/17.4k) = 3.3 degrees.  That's the limit at infinite power.  So, the phase lead is dropping from almost 90 towards 3.3 at the start of each burst.

R1 in my schematic is just further isolation of the HC14 input from CT feedback voltages below 0 or above 5V.  The 1N4148 diodes clamp the voltage to one diode drop below 0 and above 5V.  That's the same as the HC14 input, so the input and the 1N4148 diodes share the current.  R1 forces most of the current to stay in the 1N4148 clamp diodes.  Modern HC14 inputs can handle input current fairly well without disrupting operation, so R1 isn't all that important.  Old parts were more sensitive.  (The original schematic had a note about changing the clamp diodes to schottky parts, which is another way to accomplish the same goal, as they have lower forward voltage drop than the HC14 input  The suggested 1N5818 part is rather high capacitance, however, so I'd not recommend that particular schottky diode.)

I'm a bit puzzled as to why the scope signal amplitude ramps up at the start of the burst so much faster than it ramps down at the end.  Is this normal for SSTCs?  If so, will someone please explain why?

Passing the Tesla secondary ground lead once through the CT core as you pictured is effectively 1 turn.  The "turn" is just quite large, counting the path to the ground/counterpoise and back through the air to the top-load.  2 turns would be one more loop of wire, so the ground wire goes through the core twice.  As long as one turn produces a signal large enough for reliable starting, more just adds to heating in the 1k resistor.

13
Induction launchers, coil guns and rails guns / Re: Sense coil fabrication?
« on: November 28, 2019, 06:46:53 AM »
There's no need for a second coil if the test frequency is high enough (if minimal magnetic field penetrates the disk).  Just measure the primary coil inductance as a function of disk height above the coil.  Call the no-disk inductance "Linf" (for disk-at-infinity).
    Coupling factor K = sqrt(1 - L / Linf).
Here "L" is the measured drive coil inductance with the disk above the coil.

The assumption about the disk blocking most of the field is probably valid for the relatively large disks and high frequency that klugesmith has been discussing.  It was for my old experiments with 50mm disks on a 14uF 20kV cap.  It isn't a valid assumption for my penny launcher - smaller disks and lower frequency.  That's why the zinc-filled pennies go about half as high as the older mostly-copper pennies.  (Still 5% zinc for pre-1982 pennies, a brass alloy.)  Dimes go even higher, as they are "pure" copper inside, so block more of the field.

14
Spark gap Tesla coils / Re: SGTC MK1 - An Accomplishment in Progress
« on: November 28, 2019, 06:20:37 AM »
Your small flyback transformers may be designed for a bit lower voltage and higher current.  As Steve suggests, it's probably OK to run the ZVS input voltage a bit higher.  The biggest issue may be the unconnected focus pin, if it decides to arc inside the potted windings.  Those small flybacks look new enough that they are likely from a color TV or monitor, which suggests they'd be good for at least 20kV output.

Measuring the turns ratio would help decide what input voltage is safe.  One way is to feed your signal generator sine wave to the flyback input through a resistor, and measure the flyback HV output with your meter.  Hopefully your signal generator can product enough power to get at least 100-200V on the HV output with only the meter load.  Set the signal generator for something in the 20-50kHz range, lower if you can get enough output voltage.  Measure the voltage across the flyback primary with the scope, to see what actual voltage is achieved from the signal generator and resistor.  Adjust the generator and/or resistor to get 100Vdc on the meter.  Record the flyback primary peak voltage from the scope (or P-P and divide by 2).  Adjust the resistor or generator for 200V, and record that input voltage.  The turns ratio is then (200V - 100V) / (peak_input_for_200V - peak_input_for_100V).  The output diode forward drop cancels in the calculation by using deltas (changes in voltages).  (This presumes a 1.0 coupling factor.  The real turns-ratio will be higher by 1/K.)

An alternative method:  Charge a capacitor (0.1 to 5uF) to 100V.  Then connect the capacitor to the flyback secondary, negative to the HV output wire and positive to the HV return pin.  Measure the flyback primary waveform with your scope.  Repeat with the capacitor charged to 200V.  For the primary peak voltage, use the initial fast edge voltage, not the following ring-down.  Calculation is the same as above, except that the actual turns-ratio will be lower by a factor of K.  (It's worth repeating each capacitor discharge multiple times, taking the scope reading from the trace with the cleanest waveform - initial fast step followed by ring-down without subsequent fast steps.  Mechanical touching of wires often makes mechanical bounce.  The good traces will avoid that noise, or at least have it well past the initial step.  Or, use a TRIAC, such as BTA8 or BTA16 or BTB16 or ... as the switch.)

K (coupling factor) is probably between 0.8 and 0.85 based on the couple flybacks I've measured.  If you want to measure K, perhaps the easiest is to run your ZVS at as low a voltage as it can handle.  Measure the frequency with the flyback secondary open (not arcing), then again with the secondary shorted.  If it's like what I see, the frequency change will be ~2.5:1.

Your new flyback has focus taken from an intermediate stage instead of the HV output.  My larger flybacks are that way too.  I'd still suggest grounding that pin (pin 7) to be safe.  Does the specification list anything about output voltage or current?  How about the design input Vcc voltage?

For comparing the flyback arc characteristics, measuring HV return current would be informative.  A series resistor, perhaps 100 ohms to ground.  Measure the voltage with your scope, or add a parallel capacitor and measure DC value with your meter.

Based on how well you are understanding all the information, it's hard to picture that you are just starting.  Impressive progress!

15
Presuming the units of Al are nH, then 800nH * 32T^2 = 819uH for the CT secondary, which is low.  At 220kHz (1.38meg radians/sec), the impedance is 819uH * 1.38meg = 1.13k ohms.  That will produce about 45 degrees of phase lead at high-power when the 1k resistor is the dominant load, and more at low power.  If you can get more wire, and it fits, you could compensate for the low Al core by winding 100 turn secondary and 2 turn primary.

Thinking about Al more, startup is the more stringent condition than full-power.  Until the CT output voltage is high enough for the clamp diodes to conduct, the CT secondary is mostly unloaded, so 90 degree phase lead.  The higher Al range that Mads suggests (Al around 5uH/T^2, or or 100/2 turns on a lower Al core) will help the CT output get to higher voltage sooner.

16
Agreed, great simulation.  Are you going to expand to dynamic field with the disk present?  Or is that beyond hobby work?  Somewhere years ago I had a time-only simulation based on measured drive coil inductance-reduction vs. position.  No actual geometry.

For fields below saturation, iron is quite helpful.  At least it is on my little penny launchers.  On my higher-power version, I have 10mm x 11mm stack of transformer I laminations for launching 19mm diameter disks (pennies).  Did have trouble with the rebound force.  Initially just clamped the laminations together, backed by a thin rubber pad opposite the coil end for damped support.  The rebound force against the pad slowly worked the center laminations upwards, so the penny no longer fit in its place.

17
Solid state Tesla coils / Re: Feedback current transformer doesn't work
« on: November 27, 2019, 06:16:11 AM »
I'd suggest removing the second blocking cap - it's the perfect place for a second 1k resistor.  BTW, the second resistor should not affect performance, just reduce HC14 input current in high-power situations, improving reliability.  (As it stands, the HC14 pin 1 is not at a defined DC level because of the second cap.  The HC14's internal input clamp diodes conduct once oscillation starts, making that second coupling cap voltage go to roughly zero.)

The startup issue is this:  When the enable pulse comes, the gate drive transformer is driven to one state or the other (one pair of H-Bridge FETs turned on).  Depending on what charge is left on the H-Bridge output DC blocking capacitor, that initial state may or may not generate much current (or voltage, so this applies to antenna feedback too).  Mads suggests adding a ~5-10k power resistor across the H-Bridge output, at least for DRSSTCs.  (For SSTCs, across the DC blocking capacitor works too.)  This makes the initial H-Bridge output state centered, so the initial enable edge generates a half-voltage edge.  That single half-voltage edge must generate enough current signal to change the HC14 state, which then makes another H-Bridge output transition, making another current half-cycle, etc.  (Oscillation starts.)

R2 in the second circuit Mads shared does two things.  It defines the DC level of the HC14 input between enable pulses.  It then changes the level on the HC14 input after the enable edge.  That makes a full-voltage H-Bridge output transition to initiate oscillation.  If R2 were placed across the HC14 (pins 1 to 2), then the HC14 will oscillate even without enable, so will create H-Bridge edges after enable goes true, until oscillation takes over.

18
Spark gap Tesla coils / Re: SGTC MK1 - An Accomplishment in Progress
« on: November 27, 2019, 05:58:09 AM »
My guess about insufficient voltage is that the MMC is charging to barely the spark-firing voltage.  When the voltage is marginal, a spark gap can fire or not depending on just how a corona streamer forms - what dust particles happen to be in the air, UV photons that happen to ionize some air, etc.  If the issue was limited current, the MMC would reach spark-gap firing voltage, just more slowly.

Another possibility occurred to me:  The flyback secondary winding has enough internal capacitance to resonate, and that is coupled to your primary ZVS resonant circuit.  That makes two resonant frequencies, one where the two winding voltages are in-phase and one where they are 180 degrees out-of-phase.  (The two resonant frequencies are discussed in some of the Tesla coil discussions, as the Tesla coil primary and secondary are two coupled resonant circuits.)  Perhaps the ZVS is occasionally locking into the higher-frequency out-of-phase mode.  I saw that occasionally a couple days ago in a ZVS-driven flyback experiment of my own - when the output was loaded more heavily.  The flyback is inefficient in that mode.

Concerning the nature of arcs, I'm just learning with my recent Jacob's ladder project.  My only previous experience was with spark-gap sudden discharges, not with continuous arcs.  Perhaps others here can assist.  If I had to guess, I'd say the fire-y arcs are higher current.  I doubt frequency matters as long as it's in the 10+kHz range.  The ionized air path definitely decays significantly in 1-2ms, but I don't think it decays much in <100us.

Many meter resistance ranges top-out at 20meg, so a 264meg resistor may have shown up as open.  An easy way to look for high resistances is with a DC voltage source and a volt meter.  Meters often have 10meg or 1meg input resistance on voltage ranges.  Apply a DC voltage to the HV output wire, then measure voltage on the pins.  If the DC voltage is negative and above ~30V, then the HV return pin can be found that way.  The internal HV diodes often have 20-30V forward drop, so at least that much voltage is required to see continuity from HV wire (positive output, which is the diode cathode) to the HV return pin.

If you want to head down the analytical path, I'd suggest measuring the flyback output turns.   There are a few ways to do so depending on what tools you have around.  Scope?  Probes good for a few hundred volts?  AC signal generator (some source of low voltage in the kHz range)?

19
Spark gap Tesla coils / Re: SGTC MK1 - An Accomplishment in Progress
« on: November 26, 2019, 05:54:16 AM »
If it's not firing consistently, then it sounds like insufficient voltage rather than insufficient current.  The latter would cause it to be slow (low repeat frequency), but not inconsistency.  At risk of frying the little flybacks, a bit higher ZVS input voltage would help.

The pin arcing may be caused by a feedback resistor within the flyback.  Several of my flyback transformers include a high-value resistor from the positive HV output lead back to a pin adjacent the negative HV return pin.  For example, the one I've been experimenting with recently has 264meg ohms from output lead to pin 7.  Pin 6 is the HV return.  I don't know if the 264meg resistor was for feedback to regulate voltage, or part of a voltage-divider to generate focus voltage (~2kV).  Either way, if your flyback has such an internal resistor, it's better to tie the associated pin to HV return.  (I have 20meg from pin 7 to pin 6 to monitor HV voltage.)

If that HV feedback pin is left floating, it may arc to the HV return or not.  The problem is that it might arc inside the flyback rather than at the pin.  Internal arcing will damage insulation and perhaps start a more extensive internal failure.  That's why I'd suggest tying it to the HV return, directly or through a resistor.

20
Solid state Tesla coils / Re: Feedback current transformer doesn't work
« on: November 26, 2019, 04:30:23 AM »
That's a good question.  Transformer windings (and inductors in general) have zero DC voltage across them (ideally - ignoring wire resistance).  In other words, the average voltage is zero.  That's because the current through an inductor is the integral of the voltage across it (scaled by 1/inductance).  If the average voltage is positive, current will ramp up until it pulls the average back to zero.

With the diodes clamping the CT output directly, the negative voltage is clamped to ~-0.7V (one diode forward drop).  The positive voltage is clamped to +5.7V.  This ramps CT current up until the duty cycle is lopsided enough to make the negative clamp time ~8 times as long as the positive part to get zero average.

BTW, here's the attachment that failed previously, basically the same as what Mads posted, except the cap and resistor are reversed, which makes no difference.  Hopefully it shows up this time.


Note R2 in the second schematic Mads posted.  That helps kick-start oscillation.  Putting the resistor (R2) between pins 1 and 2 of the HC14 should work instead.  That has the advantage of repeated kick-starting if the first one fails.

I'd also suggest an additional resistor between HC14 pin 1 and the clamp diodes D1/D2, ~1k ohms.  That further reduces current to the HC14 input, forcing the clamp diodes to handle most of the current when voltage exceeds 0-5V.

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post Re: HV resistor in oil
[Voltage Multipliers]
MRMILSTAR
December 04, 2019, 06:05:11 PM
post Re: Full bridge showing half the voltage
[Beginners]
shrad
December 04, 2019, 02:57:02 PM
post Re: Sense coil fabrication?
[Induction launchers, coil guns and rails guns]
Uspring
December 04, 2019, 12:40:51 PM
post Re: Full bridge showing half the voltage
[Beginners]
plasma
December 04, 2019, 11:20:25 AM
post Re: Sense coil fabrication?
[Induction launchers, coil guns and rails guns]
klugesmith
December 04, 2019, 08:28:15 AM
post Re: Full bridge showing half the voltage
[Beginners]
klugesmith
December 04, 2019, 07:41:21 AM
post Re: Sense coil fabrication?
[Induction launchers, coil guns and rails guns]
MRMILSTAR
December 04, 2019, 05:15:49 AM
post Re: HV resistor in oil
[Voltage Multipliers]
MRMILSTAR
December 04, 2019, 05:06:39 AM
post Re: HV resistor in oil
[Voltage Multipliers]
davekni
December 04, 2019, 04:31:16 AM
post Re: Full bridge showing half the voltage
[Beginners]
davekni
December 04, 2019, 04:26:38 AM
post Re: Sense coil fabrication?
[Induction launchers, coil guns and rails guns]
klugesmith
December 04, 2019, 04:10:16 AM
post Re: Sense coil fabrication?
[Induction launchers, coil guns and rails guns]
klugesmith
December 04, 2019, 12:28:15 AM
post Re: Full bridge showing half the voltage
[Beginners]
plasma
December 04, 2019, 12:11:32 AM
post Re: HV resistor in oil
[Voltage Multipliers]
johnf
December 03, 2019, 07:58:41 PM
post Re: Driving Nixie-tubes with arduino
[Electronic circuits]
johnf
December 03, 2019, 07:54:08 PM
post Re: Full bridge showing half the voltage
[Beginners]
klugesmith
December 03, 2019, 07:41:00 PM
post Re: Driving Nixie-tubes with arduino
[Electronic circuits]
kamelryttarn
December 03, 2019, 02:14:00 PM
post Re: Driving Nixie-tubes with arduino
[Electronic circuits]
Mads Barnkob
December 03, 2019, 01:24:00 PM
post Re: Driving Nixie-tubes with arduino
[Electronic circuits]
klugesmith
December 03, 2019, 10:45:58 AM
post Driving Nixie-tubes with arduino
[Electronic circuits]
kamelryttarn
December 03, 2019, 09:04:42 AM
post Re: Full bridge showing half the voltage
[Beginners]
plasma
December 03, 2019, 07:29:48 AM
post Re: HV resistor in oil
[Voltage Multipliers]
MRMILSTAR
December 03, 2019, 05:07:28 AM
post Re: HV resistor in oil
[Voltage Multipliers]
davekni
December 03, 2019, 04:34:46 AM
post Re: HV resistor in oil
[Voltage Multipliers]
MRMILSTAR
December 02, 2019, 09:06:07 PM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
T3sl4co1l
December 02, 2019, 10:51:33 AM
post Re: SGTC MK1 - An Accomplishment in Progress
[Spark gap Tesla coils]
jturnerkc
December 02, 2019, 05:49:05 AM
post Re: Help for people buying the "12-48 Volt 1800/2500 Watt ZVS induction Heater"
[Electronic circuits]
petespaco
December 02, 2019, 04:10:14 AM
post Re: SGTC MK1 - An Accomplishment in Progress
[Spark gap Tesla coils]
davekni
December 02, 2019, 04:09:37 AM
post Re: HV resistor in oil
[Voltage Multipliers]
davekni
December 02, 2019, 03:42:16 AM
post Re: HV resistor in oil
[Voltage Multipliers]
MRMILSTAR
December 01, 2019, 10:47:18 PM
post Re: HV resistor in oil
[Voltage Multipliers]
Mads Barnkob
December 01, 2019, 09:17:38 PM
post HV resistor in oil
[Voltage Multipliers]
MRMILSTAR
December 01, 2019, 08:51:31 PM
post Re: SGTC MK1 - An Accomplishment in Progress
[Spark gap Tesla coils]
jturnerkc
December 01, 2019, 07:32:44 PM
post Re: Corona on the.... GDT??
[Solid state Tesla coils]
Weston
December 01, 2019, 12:14:57 PM
post Re: SSTC low voltage at gate transformer and heating drivers
[Solid state Tesla coils]
davekni
December 01, 2019, 04:30:10 AM
post Re: SGTC MK1 - An Accomplishment in Progress
[Spark gap Tesla coils]
davekni
December 01, 2019, 02:56:39 AM
post Re: New to tesla coils, some questions before I start building a SSTC
[Solid state Tesla coils]
Blin
November 30, 2019, 10:28:56 PM
post Re: SGTC MK1 - An Accomplishment in Progress
[Spark gap Tesla coils]
jturnerkc
November 30, 2019, 09:41:17 PM
post Re: QCW ramp generator
[Dual Resonant Solid State Tesla coils]
shrad
November 30, 2019, 06:12:28 PM
post Re: QCW ramp generator
[Dual Resonant Solid State Tesla coils]
hammertone
November 30, 2019, 04:28:34 PM
post Re: QCW ramp generator
[Dual Resonant Solid State Tesla coils]
shrad
November 30, 2019, 02:26:53 PM
post Re: QCW ramp generator
[Dual Resonant Solid State Tesla coils]
hammertone
November 30, 2019, 12:45:22 PM
post Re: Suggestions for CW HV feed-through
[Voltage Multipliers]
klugesmith
November 30, 2019, 06:45:09 AM
post Full bridge showing half the voltage
[Beginners]
plasma
November 30, 2019, 06:42:20 AM
post Re: Suggestions for CW HV feed-through
[Voltage Multipliers]
MRMILSTAR
November 30, 2019, 05:24:50 AM
post Re: Suggestions for CW HV feed-through
[Voltage Multipliers]
davekni
November 30, 2019, 05:22:19 AM