Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Topics - davekni

Pages: [1] 2
1
Purchased a TA-40CS ultrasonic plastic spot welding transducer with aluminum horn.  Input is via what looks like a deep BNC connector.  Turns out to be SHV connector, generally rated to 5kV.  So far I've been using no more than +-1kV peak.

Anyone have specs for these?  There isn't even a brand listed on transducer, only model and serial numbers.  Model number hints at 40kHz.  Lowest resonant frequency is 12.6kHz with overtones to at least 130kHz.  40.2kHz resonance is narrow-band (high Q), appearing to be intended operating frequency.  Drops towards 40.0kHz as transducer warms up.  One reason for so many overtones and low minimum frequency is that the horn with this transducer is a full wavelength long rather than the usual half wavelength.  (BTW, recently purchased another transducer/horn shown in video below.  It is normal half-wavelength.  Haven't measured resonant frequencies yet, other than to know that it works well at 40kHz.)

Big question is how hard to drive the transducer without damage.  I've found a bit of general information about ultrasonic welding converters.  One table listed typical transducer output amplitude as 8um P-P for 40kHz transducers.  Used a microscope with strobed LED illumination to measure displacement.  I'm running 6-7um for a bit of margin.  Displacement at horn tip is ~20um.  This is called horn "gain" by industry terms, about 3x here.  Really just coupled mechanical resonators increasing amplitude by 3x and reducing force by 3x.

Measuring impedance vs frequency of transducer around 40kHz, I made an electrical model covering only this one resonant frequency.  Standard topology for crystal resonators (high-Q series resonant circuit paralleled by capacitor).  Resonant series resistance changes with mechanical load, increasing ~10x as plastic melts and becomes viscus.  Frequency changes a bit too.  Displacement is proportional to voltage across small series-resonant capacitance.  For fixed frequency, current tracks voltage.  I made a 3-winding current transformer.  Main 1-turn primary monitors transducer current.  Second 20-turn primary is driven by a capacitor roughly 1/20th of transducer parallel capacitance to cancel that part of transducer current.  CT secondary tracks transducer resonant current which tracks displacement.



Added a parallel L and C to CT burden resistor to reject harmonic frequencies.  Third harmonic of 40kHz is close enough to an overtone that my control circuit would occasionally lock to that instead of fundamental.  Occured when fundamental was heavily damped due to mechanical load.

Built this from the H-bridge laying around from this thread:
    https://highvoltageforum.net/index.php?topic=1324.msg9886#msg9886
Wound a new GDT for lower frequency.  Added common-mode chokes to GDT output; unlikely to be needed here, but perhaps for some future use.  Output feeds a 19:47T gapped ferrite transformer.  Gapped because some parallel inductance helps with H-bridge ZCS at max load.  Transformer output drives transducer through an inductor.



Finally, a video showing the setup and use:
   
/>
I've had best success with welding polyethylene and polypropylene, even mixed PP to PE.  Those two melts don't mix.  Mechanical interlock of melted bits makes a reasonable strength joint.

2
Voltage Multipliers / 440kV Marx Generator with 120Hz repetition rate
« on: November 14, 2023, 06:02:58 AM »
Retrospective post of my 440kV Marx generator built in 2017.
    12 stages
    2.7nF per stage, made from 8 series-connected 22nF 6kV WIMA FKP1 caps.
    2 * 68meg 10kV resistors across each 22nF cap
    170mH inductors instead of resistors.  Each made from series connection of 119 x 1mH inductors.  Magnetic proximity of cores increases total inductance from 119mH to 170mH.
    Spark gaps made from 3/4" copper pipe end caps.  Ends made spherical by cold forming, pounding bearing ball inside copper end cap into hollow recess carved into wood outside end cap, repeated for each cap.
    Gaps adjusted for 42kV breakdown.  Line-of-sight between gaps allows UV light to help synchronize triggering.
    Air flow directed at each gap.  Could achieve only ~40Hz repetition rate without forced air.
    Charged by +-21kV supply.  4-stage voltage multiplier (+- 2 stages) from +-11kV 30kHz ferrite transformer output.
    Resonant H-bridge drive to transformer primary.
    Charging supply shuts off for 1-2ms after each firing.  Allows time for arcs to extinguish.  This off time varies (increases) to control repeat rate.  No explicit triggering of spark gaps.  Charges to ~42kV breakdown voltage in ~7ms.  Each firing occurs ~7ms after charging starts.
    About 6kW average power.

Schematic:


Inductor/capacitor side:


Spark gap side:


Video of initial build with max repetition rate of 100Hz.  Updated PFC unit with higher power allowed 120Hz for 2018.
   
/>
Initial version used hand-wound inductors, made like tapped TC secondaries on pipes up each side.  Too much corona and arcs between windings (racing sparks).  Second version used commercial automotive spark coils (secondaries only) rated for 50kV.  Fast rise times (much faster than normal engine spark generation) made internal voltage distribution uneven.  Worked for a few short demos (with replacing a few spark coils after every few minutes of operation).  Final version is as shown, using 24 170mH inductors each containing 119 small inductors.  Physical layout makes capacitive voltage division roughly even across each inductor.  No more inductor failures with this version.

3
Documenting the isolated 310Vdc bulk cap supply feeding buck converter of my QCW coil.  Requirements (features) of this circuit:
1) Charge bulk caps (54000uF) from 0V to 310V.
2) 120VAC 15A input.
3) High power factor to get 1.8kW without significantly overloading 15A circuit.
4) Output isolated from line voltage.  Allows grounding Vbus- for convenient QCW scoping at full power.

Used a ZVS oscillator for this design (higher voltage version of typical cheap induction heater circuits).  ZVS oscillators are very simple, but have many potential problems.  I'm still intrigued with these even with bits of added complexity needed to avoid problems.  ZVS oscillator drives a ferrite transformer with coupling ~0.84.  Coupling is low enough to avoid oscillation dropping out independent of load impedance.  Circuit diagram shows actual measured inductances and coupling factors for transformer after construction:



Two primary ZVS power transistors are STP60H65DRF IGBTs.  FETs M2 and M3 (AOD4S60) provide cross-coupling (instead of diodes).  Gate supply voltage is "p19v_sw".  It is switched between 0V and 19V to enable and disable oscillation.  I'd previously avoided gate drive switching in ZVS oscillators due to the need to dump energy from the main series inductor(s) on power input (L3+L4 in this circuit).  However, energy is not all that high.  And clamping voltage across inductor(s) is more efficient than clamping to ground.  D12+D13 provide this clamping.  Some clamping across IGBTs is still necessary to handle wiring and leakage inductance energy.

As has been discussed in several ZVS oscillator threads, ZVS oscillators have trouble starting if main power is applied before gate power.  That makes a problem for gate power control.  Main power is always present.  I found through simulation that splitting the power feed inductor into two and adding a resonant capacitor C7 makes startup possible with gate supply after main power.  This C7/L3 resonance is adjusted to work with main ZVS oscillation frequency range.  Functions in both simulation and now in practice.  Worked fine for two days of local science festival last month (starting 10 times/second during regulation).  However, there is no protection in this circuit in case oscillation fails to start.  Even one failed start will cause current to ramp up until something burns out.  See farther below for my next idea to improve starting.

Edit:  Or perhaps a failed start would become a delayed start when the conducting IGBT desaturates, with Vce increasing enough to turn on opposite IGBT.  If current has not ramped too high, perhaps everything survives.  This would be a good reason to keep Vge around 15V.  There are no high peak currents in normal ZVS oscillator operation (as there are in DRSSTC H-bridges).  Vge above 15V provides only marginal reduction in Vce at normal operating current.

Control circuit is bang-bang (on/off) regulation at 310Vdc.  Minimum off time limits cycling to 10Hz to avoid excess power in clamp diode D13.  During initial bulk cap charging and after each QCW arc, output power is at its maximum 1.8kW and input power factor is reasonably high.  (Haven't measured exactly, probably around 0.9.)  Of course, bang-bang control makes for low power factor during regulation.  Total power is low during regulation, so power factor isn't as important.

No one will want to copy my discrete transistor control implementation.  Posted here anyway for completeness:



My next idea (that works in simulation) is to make a delay timer for each IGBT gate.  If either gate stays high (on) for too long (as when oscillation fails to start), it is forced off by this delay timer.  As with above control circuit, no one is likely to copy my discrete transistor delay.  Below is my simulated but untested circuit:



This one increases input capability to 240VAC at 40A using 1350V IGBTs.  I'm initially building a version of this circuit as higher power drive for my SSTC (changing to DRSSTC).  (Existing drive is 3kW.)  Power board with IGBTs is built now, but not control nor most of MMC.  Control will be times with line voltage zero-crossings, further reducing energy and power in clamp diodes.  (Should have done that in the initial 120VAC supply too.)

Note that this new circuit uses diodes for cross-coupling as with standard low voltage ZVS oscillator circuits.  (Few reasonable FET options at 1350Vds.)  Diodes feed emitter follower gate buffer.  4.1V shift is added between buffer and IGBT gate.  This DC shift keeps Vge low enough even when Vce forward drop gets high.  Plan to increase gate supply voltage a bit to keep Vge high enough when on, to at least 20V or perhaps 24V.  Schematic still labels gate supply as 19V.

4
Made a test circuit to measure IGBT turn-off characteristics at relatively high current as is needed for phase-shift QCW use.  Made with copper foil on both sides of 1mm plastic (polycarbonate) to minimize interconnect inductance.  IGBT leads are held against copper with a spring clamp and rubber pad to allow for replacing parts.  Thermocouple taped and clamped to IGBT top, also clamping IGBT to a small piece of aluminum sheet metal to simulate heat sink.  Having that heat sink metal adjacent and parallel to circuit board helps reduce inductance.  IGBT body is against edge of circuit board (foil/plastic) for almost zero (<1mm) external lead length.  Still some lead length inside package epoxy.  This testing is at 320Vbus, switching from 140A to 0A.

Schematic:



Picture with spring clamp holding IGBT leads.  Only connection between left emitter lead carrying 140A and right emitter lead for gate drive is inside IGBT package.  Isolated on board.  Gate drive is from GDT through buffer, so circuitry is isolated too.



Spring clamp removed for visibility:



Even with all the measures to minimize parasitic inductance, voltage spikes are high.  These are fast IGBTs, chosen intentionally for phase-shift QCW, to minimize turn-off energy.  First scope plot (left image) shows Vge with ~12ns fall time and Vee (voltage from one emitter lead to the other).  Emitter spike is ~55V and around 12ns wide, indicating roughly 12ns current fall time.  Shows value of Kelvin connection (of not adding that 55V signal to internal gate voltage).  Also shows how spike exists just across internal-package lead inductance.  Right plot shows Vce, measured on board foil and again on IGBT package back-side (on heat sink aluminum).  About 50V difference.  Combined emitter and collector spikes add 105V to internal IGBT Vce due to just inductance of leads inside package.
Red is Vge and blue is Vee on left plot.  Green is measuring current.  Ignore that one for turn-off.  Inductance in current-sense resistors causes large spike compared to the 28V drop at 140A.  Right plot, red is Vce measured on IGBT package back (heat sink).  Blue is Vce measured on board foil.



Next scope plot shows Vge with ~12ns fall time, and again at ~30ns fall time in the hopes that current fall time might increase a bit.  Delays Vce spike (measured on foil), but doesn't reduce amplitude significantly:



Tried 50ns Vge fall time.  Still no reduction in spikes.  Current fall is enough delayed from Vge fall that Vge timing doesn't seem to matter.



Tried even slower, 120ns Vge fall time.  Still same spike amplitude.  (Horizontal scale is now 25ns/div, so spike looks narrower.  Really about the same.)  Blue is Vge.  Red is Vce measured on board foil.



Fast switching is good for low Eoff.  Was hoping to slow it slightly.  Looks like I'll need some R+C snubbers instead to keep Vce below 650V specification.  BTW, I fried first test part testing at 200A before realizing how high spikes were.  Even at 140A, considering combined emitter and collector spikes, peak voltage is about 700V, so slightly above spec limit.  LTSpice simulations appear to show R+C snubbing will be effective.  Adds significant power dissipation.  However, at least that power is in resistors, so not adding to thermal stress of IGBT die.

5
A friend mentioned a fascinating thought:  He is contemplating a future project of a high-voltage squirt gun to make water-guided arcs.  That got me thinking about options for squirting water from the top of a Tesla coil and ways to avoid getting the base wet.  Also thinking in general about water streams and conductivity.  Surface tension of water usually makes thin streams (ie. from squirt gun) break up into drops.  Series of drops would be more conductive than plain air, but require rather high voltage to bridge all the gaps.  Adding a little surfactant to the water reduces surface tension, so should help make a more continuous stream.  High molecular weight water soluble polymers (tiny amount) would further help keep stream connected.  That combination of surfactant and trace of polymer are the key ingredients of soap bubble solution.  Many surfactants are sodium salts, so would color the arc yellow.  Down side is that any additives to the water make protecting the coil base more important, as mist or splashes would be more conductive and leave residue rather than evaporating completely.

Another variation would be to have a water stream arch spaced away from a Tesla coil to form a strike target.  Might be safer for the coil.   But I could also imagine arc causing water splatter when it hits stream.

Has anyone tried arcs guided by water streams?  It is a new item for my list of some-day projects.


6
Dual Resonant Solid State Tesla coils (DRSSTC) / Oversized QCW
« on: March 26, 2023, 01:10:00 AM »
After experimenting with a low-frequency (100kHz) QCW coil earlier:
    https://highvoltageforum.net/index.php?topic=1268.0
Decided to try a somewhat-more-normal QCW coil.  Larger than typical.  No arc length to secondary height records here.
    5.6uH primary, 4 turns of copper foil tape.  Two interleaved 4-turn windings, in parallel except for separate halves of MMC.
    11.8mH secondary, 170mm diameter, 210mm high on 300mm high core.  255 turns + 4 spiral from 210mm to 300mm.
    0.71 coupling factor.  Ferrite floor and center post.  No potting.  Top of post is NiZn ferrite for low conductivity.
    545mm OD top load.  Ring of 19mm OD copper tube with foil/plastic center.  ~32pF total including coil capacitance.
    64.8nF MMC, 3s72p MMC of 2.7nF 1600Vdc PP caps, split into two 32.4nF halves for the two primary windings.
    H-bridge using pairs of FGH75T65SHDTLN4 IGBTs for each switch, 8 total.  Buffered GDT outputs per this thread:
    https://highvoltageforum.net/index.php?topic=2389.msg17547#msg17547
    485kHz upper pole unloaded.  440kHz at end of normal arc.  413kHz at end of ground strike arc.

H-bridge in its milk-crate home:



With MMCs added.  One folded back for this picture:



With lid and ferrites:



With coils and top load.  Control electronics live outside and aren't shown here.  Plan is to experiment with different control methods.  Initial tests are with ramped Vbus to H-bridge using one side of buck converter from my earlier low-frequency experiments.  Didn't need both interleaved halves of buck since 350A is plenty for this coil.



I'll add more pictures and scope plots in a second post to this thread.  One image to get started:



Vbus ramps to 240V for above image.  Average primary current ramps to 220A, so 345A peak of sine wave.
Peak power to H-bridge is 53kW at end of ramp.  Primary is quite low Q, so around 40% of this power is consumed in losses, mostly in primary foil winding.  That is based on matching LTSpice model to measured parameters.  Foil provided high coupling but also high losses.

Video of some arcs:
   
/>All arcs in this video are with same ramp parameters.  Amazingly varied arcs.  Anyone with QCW experience:  With more refinement of ramp parameters, is there likely a setting where arcs behave more similarly from one pulse to the next?

7
Dual Resonant Solid State Tesla coils (DRSSTC) / GDT output buffer
« on: March 20, 2023, 04:32:07 AM »
For years I've pondered the trade-offs between GDTs (simple) and isolated gate driver chips (more complex, including isolated supplies for each gate).  For my new QCW experiment platform, decided on a compromise: GDT with simple output buffer.  Rising edge behavior is standard GDT output through damping resistor.  Falling edge is a local PFET shorting Vge.

This is intended for IGBTs with no internal gate resistors (all TO247 devices I've seen and some smaller bricks).  For these IGBTs, there is no need for negative Vge as long as gate drive impedance is low.  In normal GDT drive, Vge falling edge speed is limited by GDT leakage inductance.  With buffer, GDT has light load on falling edges, so is fast.  For high frequency CW applications where gate power is a significant concern, avoiding negative Vge reduces power by ideally 4x.  Reality here is about 3x.

Posting this under "DRSSTC" category, though it could be useful for induction heating or other applications.

Buffer schematic.  One needed for each IGBT (or parallel set of IGBTs):



R1 is the normal rising-edge damping resistor for GDT output, 9.4 ohms in this example.  R1 has a series diode D1 to prevent conduction when GDT output is negative (when Vge is zero).  PFET M1 (IRFZ24) provides low-impedance shorting of Vge when GDT output is negative.  D2 limits PFET Vgs to spec +-20V.  Would likely work fine without D2.  R2 provides damping for PFET Vgs and limits current through D2 during any GDT undershoot.  I use this circuit with +-19V into GDT.  D3 clamps Vge under any anomalous conditions, especially ESD during construction and handling.

Here's my first H-Bridge using four of above buffer circuits and two GDTs (one per half-bridge).  Circuit is simple enough to construct on raw double-sided copper-clad board and dremel-tool cuts.  IRFZ24's are surface-mounted on one side and remaining parts on other side.  R1 is an array of 1206 SMD resistors here to handle power of continuous 500kHz operation.  Power is significant even though much less than it would be with +-19Vge drive.  IGBTs here are parallel pairs of FGH75T65SHDTLN4, which are in 4-lead TO247 packages (Kelvin emitter lead).  Power ECB is per my low-parasitic-inductance tutorial with bypass caps on back side.



Only issue so far with actual use is that these IGBTs have roughly the same turn-on and turn-off times, at least in my testing.  With this buffer's very fast turn-off (~20ns from UD output to Vge falling), turn-on delay (dead time) can't be set low enough.  Reducing R1 below 9.4 ohms causes more overshoot on Vge.  That would be OK for low duty cycles, but increases gate drive power dissipation for CW cases.  If excess dead-time becomes too problematic, I'll need to make new GDTs with even lower leakage inductance to allow lower R1 values.

Below are a bunch of scope captures.  Including all these for a second purpose, as an explanation of H-bridge output triple-transitions.  Ideally, I'd get rid of triple-transitions by reducing dead-time.  Only other option is to increase phase lead.  However, at ~480kHz, additional phase lead causes IGBT turn-off at high current, since current slew rate is so high.

For all below scope captures:
Ch1 (black) is H-Bridge output, differential between two outputs, 20V/div.
Ch2 (green) is H-Bridge (primary) current at 50A/div.
Ch3 (red) is Vge at 5V/div.
Ch4 (cyan) is one output from UD-like driver.

Near end of a small burst at +-190A:









Notice the triple-transitions in H-bridge output.  Initial transition is at IGBT turn-off, while that IGBT pair had been conducting current.  A bit later current reverses polarity, pulling H-bridge output voltage back in the opposite direction.  As voltage gets about half-way back, opposite IGBT pair turns on, pulling H-bridge output voltage to desired new state.


Start of burst where current is low:









Notice that above low-current captures have no triple-transition.  H-bridge output transitions only after opposite IGBT pair turns on.  That's because there is insufficient current to cause a voltage transition at turn-off.  Below is a capture at mid-current, enough current for output transition at IGBT turn-off, but barely enough to cause a hint of triple-transition:




Finally, here's a capture at the end of a burst where residual primary current is causing H-bridge output transitions.  GDT input is at 0V (both GDT inputs high in my case rather than more normal both-low).  IGBT Crss (collector-to-gate capacitance) causes small swings in Vge.  Positive swing is limited by PFET threshold voltage.  PFET must be selected to have threshold voltage well below IGBT's threshold voltage.





8
Retiring my SRSGTC which was never fully packaged.  Looking for a home for an old Bodine Electric Company synchronous motor I'd originally purchased on EBay.  It is rated 1/20HP, 1.1A, 40C temperature rise, 5uF run capacitor.  (Works with 4.3uF.)  1.95kg.  If useful, I'll leave on the 8mm to 10mm shaft coupler.  I do not know what its internal synchronization method may be.  It does lock to the same mechanical phasing every time I've used it.

I'm in Oregon, USA.  To anywhere else in USA, a $17.10 flat rate box would work.  I have no idea what international shipping might be.




9
Electronic Circuits / Analysis of cheap 1080-LED colored light string
« on: December 11, 2022, 05:56:28 AM »
Purchased a cheap string of 1080 LEDs:
https://www.amazon.com/dp/B0B8JSQFMB?ref=ppx_pop_dt_b_product_details&th=1
(BTW, amazing how prices bounce around.  Was $24.99 a couple weeks ago.  Now $55.99.  When searching earlier, many strings were ~$50.  Purchased this one because it was cheap.)

String runs on +-30V provided by a small supply/controller, drawing +-200mA.  String is wired 9S120P, with 60 of each 120 connected reverse polarity.  Allows effects such as fading from one half to the other.  Down-side is that "steady-on" mode is slightly under 50% duty cycle, not as bright as when one half or the other are lit.  255Hz chop frequency, 100us dead time one direction, 140us the other direction.

LEDs are all blue.  Phosphor converts blue to red, yellow, and green.  Less saturated color than with normal LEDs.  Advantage is that identical forward voltage allows direct paralleling.  Appears to have no per-LED series ballast resistors.  Ballast is provided by thin copper interconnect, total around 27 ohms for the string.  Wiring keeps all LED voltages matched:


I plan to make a higher-power supply, steady-on mode only.  About +-38V increases current from 200mA to 400mA.  Efficiency of red and blue drops as current increases.  Unfortunate that DC powers only half the LEDs.  200mA DC would be better than 50% duty cycle of 400mA.  However, green slightly increases efficiency as current increases.  Not sure if phosphor is non-linear, or if the change in blue wavelength with current matches phosphor better.  Yellow efficiency is roughly linear with current.

10
Has anyone tried (or even considered) NP0/C0G ceramic capacitors for higher-frequency (ie. QCW) MMC use?  Or for induction heating?

I'm finding more app notes about using such capacitors for wireless charging and other resonant circuits.  Some ceramic caps are getting AC voltage and current ratings too.  Voltage rule-of-thumb appears to be AC Vpp < cap's DC rating.  At higher frequency, AC current becomes limiting factor due to ESR and self-heating.  A few links:
https://www.kemet.com/en/us/technical-resources/using-mlccs-in-wireless-power-transfer-resonant-circuits.html
https://product.tdk.com/en/techlibrary/solutionguide/mlcc04.html
https://product.tdk.com/en/techlibrary/solutionguide/mlcc05.html
https://product.tdk.com/en/search/capacitor/ceramic/mlcc/info?part_no=CGA9Q1C0G3A333J280KC
Last link is a specific part specification that includes an AC current vs frequency graph.  First link includes a calculator tool for AC current limits.

I recently purchased some Epcos/TDK film capacitors that looked good for high-frequency MMC use, B32671L1272J.  Rated 2.7nF, 1600Vdc, 630Vac.  Derating curves at 450kHz show 250Vrms and 2Arms.  Distributor Arrow had a good price.  However, I wonder if they are genuine, or if TDK has quality control issues in their Chinese factory making these parts.  Measured several at this rated condition of 250Vrms 450kHz.  Outside case temperature rise varied from 21C to 54C among different parts, measured at hottest point at center between leads.  Leads provide heatsinking to copper foil in my test.  Most MKP caps specify RMS current for 10C rise, though that 10C value isn't listed in TDK's spec.  Unlike these, other MKP capacitors I've tested for temperature rise have been quite consistent part-to-part and generally meet specifications.  On the good side, even the part with 54C rise survived fine for ~50 hours.

Update:  For comparison, I purchased 10 each of B32671L1272J (same part as above), B32671L1272J289 (same part except longer leads on tape), and B32671L1412J (4.1nF), all from Digikey.  Didn't take time to measure temperature rise, but did compare dissipation factor at 2MHz (high enough frequency to get enough loss to measure).  Digikey parts' measured dissipation factors were all close to that of the better Arrow parts.  So I suspect it was a bad batch (or counterfeit, or perhaps someone stole a reject batch and sold them as good).  Even so, 20-25C rise at spec current is higher than other parts at spec current.

Decided to test some NP0/C0G 1206 SMD caps I have around, Samsung CL31C222JHHNNNE, 2.2nF 630Vdc, no AC rating.  Two parts have very similar temperature rise, and lower than the best of above MKP caps in spite of being much smaller size.  At 250Vrms 450kHz: 8-10C rise.  At 340Vrms: 18-20C rise.  Survive fine for 50 hours at 340Vrms.  So these tiny 1206 (3.2mm x 1.6mm x 1.6mm) capacitors handle more voltage and current (slightly over 2A at 340Vrms even though capacitance is a bit lower at 2.2nF) than the larger 13mm x 5mm x 11mm MKP capacitors.  And this is for a ceramic capacitor rated only 630Vdc compared to an MKP rated 1600Vdc.

Update:  Decided to push this 1206 SMD cap farther.  Running at 450kHz 467Vrms (+-660V) 2.9Arms now.  Peak voltage is slightly above rated 630Vdc.  Temperature rise has been creeping up over 4 weeks (675 hours so far).  Started at 36C rise.  Now up to 127C rise!  (20C ambient, 147C case.)  Still hasn't failed.  I really want to see what the failure mechanism is, but am getting impatient.  So far the dissipation factor is increasing (Q falling), but no measurable change in capacitance (as would occur with a film capacitor as it degraded).

I think the biggest down-side of ceramic caps is their higher probability of failing shorted.  Film capacitors are more likely to burn to carbon and become resistors.  Anyone have experience with H-bridge survival when MMC shorts?  Without resonant current, I'd guess that UD2.7 may not detect over-current.

Ceramic capacitors don't appear to have a cost advantage in general (unless they can be over-driven as with my above test).  Primarily a size advantage.  Size/weight is important for many commercial applications, but presumably less important to coilers.

11
Light, Lasers and Optics / LED arrays for use with Tesla coils
« on: October 29, 2022, 10:53:04 PM »
Made LED strings specifically for use in AC electric fields such as near Tesla coils.  Idea is to replace more fragile fluorescent tubes.

/>
Standard LED replacements for fluorescent tubes work OK, but are lower voltage and higher current than is ideal for Tesla coil use.  Most emit light on only one side.  So I made LED strings as an alternative, with different colors on the two sides.  They are visible under HV power transmission lines, and of course brighter in the higher-frequency field of Tesla coils.

One option is to connect pairs of LEDs anti-parallel.  Made a couple small ones that way previously.  However, each LED gets only half the total current (either positive or negative half-cycle).  To improve current efficiency, these strings use signal diodes in a bridge rectifier connection for every 20 or 24 series-connected LEDs.  That way full current passes through each LED.  Pitch is one LED per 5mm (one per 10mm on each side), for 100 and 120mm long sections.

One feature didn't work very well:  A goal of sectioning the strings was to mimic behavior of fluorescent tubes where sliding one hand up the tube prevents the section between hands from glowing significantly.  My issue appears to be insufficient capacitance from LED strings to outside of plastic tube (hand), especially for my SMD version.  LED ECBs are only 7mm x 120mm inside a 16mm OD tube.  Next version needs to have some metal closer to tube walls (and perhaps larger-diameter tube) to increase capacitance.  Not sure how to best accomplish this while minimize light blocking.  The three commercial LED tubes connected in series worked well in this regard, but in large steps of their ~300mm tube length.  I think their opaque back side appears to have metal just under plastic outer layer, so plenty of capacitance.

If there's any interest, I'll post ECB files.  SMD version uses 2835 LEDs and SOT23 series-pair diodes (MMBD1203).  Includes anti-parallel diodes across every 3 LEDs to avoid any reverse-current in case capacitance from hand introduces AC to middle of the string.  Not at all sure such is necessary.  One could populate just the two diode packages, one at each end, that form the rectifier bridge.  (BTW, this is how direct-replacement LED tubes work.  One diode pair at each end of tube rectify incoming AC from ballast.)  Through-hole version is for 5mm LEDs.  Diodes are same, still SMD.  I plan to make an updated SMD version with multiple test-pad holes for the internal DC rails for adding external wires to increase capacitance.

I'd be happy to send MMBD1203 diodes to anyone who needs them.  Saw a good EBay deal for left-over Fairchild parts originally purchased from Mouser.  I now have ~6k parts and no need for that many. :)

12
Decided it was worth a post on a project I'm finally abandoning.  Haven't kept exact track, but I've spent well over 1000 hours intermittently over past 3 years.  Goal is to add MMC capacitance to primary as arc adds capacitance to secondary, making frequencies track.  Used 432 TRIACs across six boards.  Here's a spread-out image of the project.  The six boards were to be stacked for any actual use.



Four of the pure capacitor array boards aren't included.  Full MMC capacitance was to be six of these capacitor-only boards.  Smaller switched MMC sections are in series with each, keeping switching at a little lower voltage (reduced GDT insulation stress).

The pile of failed TRIACs is from the second board.  Had gotten the first one working after a similar number of failed parts.  I'd thought initial failures were a result of stress caused by my debug mistakes.  Didn't save those dead TRIACs.  After getting the first board working, built the other five.  Made one testing mistake on second board, frying the TRIACs shown.  Tested the third board without making any mistakes AFAIK.  Still had failures (not repaired).  What I've learned is that in this stress-case use, TRIACs tend to fail with A2 to gate breakdown.  This failure sends a large spike backwards through GDT and into other GDTs, triggering all the TRIACs at the wrong time (not at zero-crossing).  Newly damaged TRIACs then failm damaging yet more.

At the start of this project I ran many tests on individual TRIACs at the current/voltage/frequency/timing of this use.  I'm over rated dI/dT by about 2x.  With high gate-drive current, this was working in my initial testing, including margin.  I think the problem is statistics.  If any one part in the array of 72 on one board can't handle that stress, most of the board's TRIACs fail.  It's tricky to figure out which parts failed.  Usually failure is not a solid short, limiting options for determining which part(s) failed within each directly-paralleled set of six.

This was planned to go with my DRSSTC:
https://highvoltageforum.net/index.php?topic=798.msg5285#msg5285
Bottom schematic of that initial post shows sketches of this TRIAC switched-MMC project.  I'd already started planning for it as I built my DRSSTC.  If there's any interest, I can post schematics of boards I built for the final (failed) version.  I've also learned a lot about potting GDTs for high-voltage isolation etc.  (72 GDTs in total, one for each set of six directly-paralleled TRIACs.)  Used the best ones at the higher-voltage end, and the ones with more air bubbles at the lower-voltage end.

I've thought about other switch options.  Triggered spark gaps come to mind.  However, I suspect spark gaps are hard to trigger near zero-crossing.  Triggering at higher voltage will dump a bunch of MMC energy into spark gap (and be hard on MMC capacitors with the sudden voltage step).  I'd love to hear other options.  Not planning to try any other ideas at all soon.  Time for other pending projects.  Brainstorming thoughts would still be of interest, however.

13
I've been looking through TO247 IGBTs available through normal electronics distribution, focusing on fast parts suitable for phase-shift QCW.  Also looking for large internal diode to handle pulse-skip.  Ended up purchasing FGH75T65SHDTLN4 ($3.88 each, a bit less in quantity):
https://www.arrow.com/en/products/fgh75t65shdtln4/on-semiconductor
Cheap because Arrow is closing out this discontinued part.  83 parts left there and 450 at Rochester Electronics (a bit more expensive) last I checked.

650V, 75A at 100C case (both IGBT and diode), 300A pulse, 4-pin TO247 (kelvin emitter connection).

FGH75T65SHDTLN4 has only a preliminary data sheet from 2018.  Short time in production.  I can't find any difference between this and the same part without 'N' character, FGH75T65SHDTL4 (from 2015 and still active).

A very similar part FGH75T65SHD-F155 appears to have the same IGBT die paired with a faster diode die, but diode is rated only 50A at 100C case.  It's available from Mouser for $6.55 each.  Would be better if any hard turn-on switching is needed.  This part is in the more-typical 3-pin TO247 package.

No personal experience yet.  Just posting what I purchased after some data-sheet searching.

Other fast IGBT suggestions?  Even though I've already purchased these parts, it would be interesting to see other recommendations.

14
Electronic Circuits / Failure analysis of a 120VAC LED light bulb
« on: October 14, 2022, 09:42:44 PM »
Cut apart a failed LED bulb, rated 17.5W 1600 lumen (designed to replace 100W incandescent):





Looks like initial failure was mechanical.  One-sided ECB with electrolytic capacitor supported by leads only.  Radial leaded cap laid flat against ECB.  Not in contact with housing nor glued down.  ECB traces at cap leads had torn lose.  I re-soldered cap leads to adjacent parts in a repair attempt before taking above pictures.  LED array works fine, but appears the open-circuit capacitor caused another supply circuit failure.  Didn't continue diagnosis beyond this.

I'd used the bulb in a clamp-lamp fixture in garage, so it experienced random motions during its relatively-short life.  Bulb is rated for moist environments.  Housing was well sealed with glue.  Surprised that a dab of glue wasn't used for the cap too.

LED packages are 2835 SMD (2.8mm x 3.5mm) mounted to a one-layer aluminum board.  Aluminum board attached to another aluminum disk with two small screws and standard-looking white thermal grease.  That aluminum disk was glued to base cone, which is aluminum (likely stamped sheet metal) covered in plastic.  46 LED packages wired as 23S2P.  Paralleling at every LED pair.  Within each 2835 package are 3 LED die.  LED die are thus 69S2P.  Forward voltage is above peak of 120VAC.

Circuit appears to be a boost converter, similar to PFC input stages of larger power supplies.  Lamp base line and neutral each connect through 20R resistors to ECB.  Given the bulb's 165mA rated current, ~1W is dissipated in those two resistors.  I presume the resistors are there to limit inrush current and improve line surge survival.  ECB starts with small bridge rectifier then boost converter.  Inductor is wound on a tiny E-core, so likely gapped ferrite.

I'm guessing the 69S2P configuration is changed to 138S1P for 230V bulbs.

15
Looking for ways to measure surface tension of surfactant/water mixtures, I ran across capillary waves as a measurement technique.  Read a paper about a smart-phone app for that using phone's vibrator, flash, and camera.  It has a few drawbacks, however.  Key one for me is that I don't own a smart phone :)

Since I had some small 25mm diameter off-axis parabolic mirrors, decided to make a small telecentric Schlieren setup to view capillary waves in plastic petri dishes.  A stepper motor driver generates sine wave current feeding a small E-core coil.  Coil field vibrates a permanent magnet taped to petri dish, generating capillary waves in water inside dish.  LED pulses synchronously with sine wave, imaging capillary waves at the same phase each cycle.  (Red LED to match gold-plated mirrors.)  A 2mm pitch scale below the dish provides a measurement reference.  Due to telecentric optics, scale is viewed at the same magnification as waves.  Frequency is manually adjusted to make 2mm wavelength.  Measured frequency is used to calculate surface tension using formula (edited from Wikipedia):
        surface_tension = density * frequency^2 * wavelength^3 / (2 * PI)

The entire setup, measuring water at 242Hz:


Side view to show optical path.  LED reflects down to lower mirror, forming parallel beam up towards upper mirror.  Upper mirror images parallel beam to small rectangular aperture (hole in black paper) above LED.  Lens just past aperture (behind wood frame) images the object space (parallel beam) onto a finite-distance screen.  (Would otherwise image at infinity.)  The aperture is reverse-imaged at infinity by the upper mirror, which makes the setup telecentric.


With pure water (low viscosity), the image is quite clear as shown above.  With detergent-water, viscosity is higher, which damps waves.  It still works, but is a bit harder to view and adjust accurately to 2mm wavelength.

Even though the result is fairly simple, this project took much longer than I'd expected - especially trying different ways to vibrate the petri dish or vibrate an object within the dish.  Advantage of vibrating the dish is avoiding another surface that needs cleaning between testing different surfactant solutions.  Final goal is to optimize surfactant solutions for making bubbles.  Perhaps became more of a project than this goal warrants.  Measuring bubble film strength may be more relevant than surface tension.

16
Thought it would be appropriate to start a new thread to discuss top-load scope results.  This is a continuation of the thread on optical-fiber-isolated scope probe under the Lab Equipment category:
https://highvoltageforum.net/index.php?topic=1263.msg14493#msg14493
Decided to post this in the DRSSTC category.  Initial measurements are on my bottom-fed uninterupted SSTC, but the goal is to continue with my DRSSTC eventually.

This is a repeat of measurements linked above, with improved accuracy.  Better transmit shielding reduced error of charge-sum (which should add to 0) from ~7% to ~3.5%.  Other improvement is that the scope inputs are DC-coupled.  Removed final probe DC offset after data-capture by averaging DC voltage of flat pre-trigger signal.  So the only high-pass function is the 61ms time constant of 2.0uF charge accumulation capacitors and 30.7k probe input resistance.

Plot images of four captures, followed by ZIP file of CSV files of corresponding four data sets.  First two are with the wire breakout (sharp).  Second two are with the stubby rounded breakout point.









Noticed one more interesting feature of the first two wire breakout captures.  First one peaks at higher charge (higher top-load voltage) before breakout compared to the second.  I hadn't touched the setup between those two captures.  Only cause that seems reasonable is that the power relays closed slightly earlier on the second capture, towards the end of the previous half-line-cycle.  Perhaps that generated a bit of corona that reduced breakout voltage for the first full half-line-cycle.

Edit:  Looked more closely.  In the first capture, the relay closed a bit after line zero-crossing.  That caused secondary voltage to rise more rapidly, more like it would if this were an interrupted coil.  That's likely the real reason for higher peak voltage before breakout.

* scope_data_csv.zip

17
Beginners / GDT (Gate Drive Transformer) tutorial
« on: November 28, 2021, 11:40:56 PM »
Hopefully this isn't wasted redundant work.  I've seen many builds with good GDT construction, using both halves of each twisted pair.  However, all the GDT construction guides I've found use a single primary wire.  Below is construction of a half-bridge GDT using two twisted pairs from CAT5 cable.  This is easier to see in pictures.  Extension to full-bridge isn't difficult.  Use four pairs, with four paralleled windings for primary, one wire from each pair.  (BTW, CAT5 isn't necessary.  If starting with single wires, twist pairs together, and use those pairs exactly as you would with pairs extracted from CAT5 cable.)

Start with a suitable high-permeability ferrite core.  (Some options listed at the end.)  The core I'm using here works, although the shape is not typical.  Pay attention to winding technique, not so much to core shape.

Wind two (for half-bridge) twisted pairs around the core.  More discussion about the number of turns to follow.  See subsequent post on this thread:
    https://highvoltageforum.net/index.php?topic=1854.msg19355#msg19355
I'm using 4 turns here.  Mark the starting end of all four wires for later identification.  Here I've "marked" starting ends by length (short), with the tail ends left longer.  Other (preferred) options are to add bits of tape to the starting ends or strip insulation from the starting ends only.





Untwist the pairs almost to the core:



Twist each wire (each winding) with itself all the way back to where the pair twisting starts.  Don't leave any significant loop area of untwisted wire:



Pair one winding of each pair together for the primary.  I've chosen the lighter-color wire of each pair for simplicity, white and light-blue.  Most important: connect the two starting ends (short ends or stripped ends or however you marked them) together, then the two tail ends together.  If pairing is swapped, driver can be damaged by the shorted load.  (Test at very-low duty cycle initially just in case of error.)  The remaining winding of each pair is for an IGBT.  Starting end of one IGBT winding is gate.  Starting end of other IGBT winding is emitter of other IGBT.



Since I hadn't used tape to identify starting ends at the beginning, I added tape now.  Then cut the tail ends to length and strip.  Connect the two primary tail ends together:



The reason for the twisting is to minimize leakage inductance.  Leakage inductance slows down gate waveforms and causes overshoot and undershoot and generally-sloppy gate drive.  Twisting forces the wires to remain close together with little loop area between wires for magnetic field to slip through.  Best to maintain this pairing all the way to the driver for primary and all the way to gate and emitter terminals of IGBTs (or FETs) for the secondaries.  Avoid excess loop area when adding gate series resistors.  Keep the emitter wire adjacent the resistor to minimize loop area.

Now for a bit about cores and turns.  I'll add a second post on measuring cores and finished GDTs, a bit more advanced topic.
Toroid shape is generally preferred, but E-cores work if ungapped (no air gap or spacer between the two halves).
Most important two parameters are:
     Core material (reasonably-high permeability and saturation flux density).
     Core cross-sectional area.  Picture the area of a core slice inside one turn of the GDT winding.
Iron and other compressed-powder cores never work well.  Most (but not all) ferrite materials are OK.
Low-frequency EMI suppression cores are reasonable.  That is what I used above.  Most larger EMI cores are low-frequency, so workable.  This includes common-mode chokes found in power supplies.  (Remove existing windings.)  Such EMI materials include:
3C11, 3E6, 3E12, 3E10, 3E15, 3E25, 3E26, 3E27, 3E65
More ideal ferrite materials are generally designed for switching power supply transformers etc.  These include:
PC40, PC200
N27, N30, N35, N41, N49, N51, N72, N87, N88, N92, N95, N96, N97
T35, T37, T37, T38, T46, T57, T65, T66
3C90 through 3C97

Concerning cross-sectional area, more is better, within constraints of fitting the GDT mechanically into the build.  The core I used above is 28mm long, 14mm ID, 28mm OD.  The ring is 7mm thick (0.5 * (OD - ID)).  So cross-sectional area is 7mm thick * 28mm long = 196mm^2.  If using a more-typical ring toroid, the formula includes a factor of PI/4:  Area = length * 0.5 * (OD - ID) * PI / 4.

In general, look for cross-sectional area to be at 50mm^2 or more.  A bit smaller is fine for high-frequency Tesla coils.  Larger for low-frequency coils.  10 turns is usually plenty.  Excess turns increases wire length and therefore leakage inductance.  The above example is 4 turns.

(All my GDTs have either 2 turns or 3 turns.  That works with large area cores and careful measurement to make sure its enough.  A few more turns is generally safer.  Too many turns causes subtle issues due to leakage inductance.  Too few turns is more catastrophic, possibly damaging the driver and/or IGBTs when the core saturates.)

Here's a great picture from Mads of a full H-Bridge GDT constructed this way:
https://highvoltageforum.net/index.php?topic=1856.msg13969#msg13969

A couple other posts with images that aren't quite as obvious.  For this first, look at the upper GDT wound with CAT5 cable including jacket:
https://highvoltageforum.net/index.php?topic=588.msg3779#msg3779
And this 3-turn GDT from my bridge tutorial:
https://highvoltageforum.net/index.php?topic=1324.msg9886#msg9886

18
Capacitor Banks / 3kJ coin shrinking
« on: October 21, 2021, 05:48:49 AM »
My 2002 coin-shrinker is built into a corner of my garage semi-permanently.  Wired into my house through 1meg array of power resistors, avoiding exposure to lethal current when charging and triggering.  Cap is an ancient oil/paper pulse unit, 14uF at 20kV, which I run at ~20.5kV for ~3kJ energy.  Over 1500 coins shrank in its 19 year life, with a few repairs along the way.

Optimization is different depending on capacitance.  At 14uF, two layer coils are better than the more common 1-layer coils.  Magnet wire is terrible, immediately arcing between layers.  Even with wraps of tape between layers isn't enough.  Enamel cracks as wire stretches, and arc paths develop.  Thin stretchy insulation over stranded wire works best for me (radiation-crosslinked PVC).  Broken strands overlap, so conduct better as wire stretches.  Coil shrinks axially and expands radially as it explodes.  My optimum ended up as 2x9 (2 layers of 9 turns each) of 18AWG.  Started with 4x6. but 2x9 passes through optimum shape (wire close to quarter rim) as it explodes.

A few pictures for comparison.  I haven't made a video.

Original wood containment box, lasted about 15 shots before 2x6 boards split.



After 3 rebuilds, changed to 1/4" thick aluminum cylinder.









Coil voltage at 5kV/div.  Pulse lasts about 17us.  This short pulse time maximizes shrinking, but does leave the outer rim thicker than the center.  Skin effect prevents coin current from penetrating to the coin center.  See above image.







Edit:  Thought I should add one more image showing the aluminum cylinder (160mm OD, 6mm wall) 20 years and ~1500 shots later:



Not certain of the alloy, but this is hard aluminum, used in a solid-ink printer that required minimum deflection during ~6000N load from an adjacent rubber-coated transfix roller.  Forming is all from impact of broken strand bits from 18AWG wire.  Shows clearly that coil explodes radially.  (And contracts axially as mentioned above.)

19
Electronic Circuits / Micro-power continuity checker.
« on: July 20, 2021, 05:37:36 AM »
About 15 years ago I built a couple simple continuity checkers, one for home and one for work.  They apply low voltage to avoid forward diode junction conduction and light an LED when resistance is below about 10 ohms.  Power is from a single 18650 LiIon cell.  I find them very convenient - probing an ECB to see which side of a bypass capacitor is ground, checking for hidden solder bridges under parts, etc.  However, these draw enough quiescent current that an on/off switch is necessary.

Last weekend I made two new continuity checkers drawing only 10uA quiescent.  Also reduced threshold resistance to between 1 and 2 ohms.  No on/off switch to forget to switch and battery life of 5-10 years between charges. :)

Normal people would use a micro-power opamp for such a circuit.  Being abnormal and fond of discrete circuity, mine uses three transistors instead:



Dremel-tool cut circuit board:



Finished continuity checker.  Most of the volume is the 18650 LiIon cell.  Board and probe tip are taped to the cell.





The circuit can easily be made in reverse, using PNP transistors and an NFET.  (Actually, one of the two I made is reversed.)  Power supply is reversed too.  I prefer the version shown here, as one probe is the negative supply which is battery case.  Makes accidental shorts of the battery less likely.

20
DSLR / Global shutter synchronized to arcs?
« on: July 19, 2021, 06:32:35 AM »
Just a thought at this point.  Does anyone have a global-shutter camera?  It would be interesting to sync the camera exposure with DRSSTC sparks.  With a properly timed and short exposure it should be possible to get good arc images in brighter background situations.  Synchronized global-shutter video could allow daytime DRSSTC testing while still monitoring for errant sparks.

Two possibilities for synchronizing.  The likely-easier option would be to use a camera output intended for strobe-light triggering to trigger single DRSSTC enable pulses.  The down-side of this option is longer exposure times (unless the camera has an option to generate a trigger slightly prior to shutter opening.)

The other possibility is to trigger camera exposure from the DRSSTC enable pulse, perhaps with some controlled added delay.  Then the exposure could be short, covering just the active arc portion of the DRSSTC pulse.

I've built similar systems at work for strobed microscope viewing of ink drops.  Unfortunately, I don't think there's any equipment available to borrow.  I see cheap (~$70) global-shutter webcams from China.  Can't find any information about options for trigger input or strobe output.  The cheapest global-shutter camera I've found that lists trigger capability is $200+shipping.  Perhaps someday when my project list gets short ;) I'll buy a camera and experiment.  That is if no one else has tried it first.

Pages: [1] 2

* Recent Topics and Posts

post Re: Turning SSTC into DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Simranjit
Today at 02:14:17 AM
post Re: Turning SSTC into DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
June 12, 2024, 11:04:57 PM
post Turning SSTC into DRSSTC
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Simranjit
June 12, 2024, 10:23:08 PM
post Re: UD2.7C constantly in OCP despite having signal
[Dual Resonant Solid State Tesla coils (DRSSTC)]
verliebt_in_neukölln17
June 12, 2024, 08:41:06 PM
post Re: UD2.7C constantly in OCP despite having signal
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
June 12, 2024, 07:53:31 PM
post Re: Van de Graaf Voltage measurement with voltage sensor and voltage divider
[Static Electricity]
haversin
June 12, 2024, 06:57:13 PM
post UD2.7C constantly in OCP despite having signal
[Dual Resonant Solid State Tesla coils (DRSSTC)]
verliebt_in_neukölln17
June 12, 2024, 06:54:49 PM
post Re: Van de Graaf Voltage measurement with voltage sensor and voltage divider
[Static Electricity]
Mads Barnkob
June 12, 2024, 03:47:28 PM
post Van de Graaf Voltage measurement with voltage sensor and voltage divider
[Static Electricity]
vK
June 12, 2024, 03:42:18 AM
post Re: Bigger sparks?...
[Vacuum Tube Tesla Coils (VTTC)]
davekni
June 12, 2024, 03:32:22 AM
post Re: Bigger sparks?...
[Vacuum Tube Tesla Coils (VTTC)]
Teslaventje
June 11, 2024, 11:05:49 PM
post Re: Bigger sparks?...
[Vacuum Tube Tesla Coils (VTTC)]
MRMILSTAR
June 11, 2024, 05:36:46 AM
post Re: Sling Psychrometer
[Laboratories, Equipment and Tools]
Twospoons
June 11, 2024, 12:29:31 AM
post Bigger sparks?...
[Vacuum Tube Tesla Coils (VTTC)]
Teslaventje
June 10, 2024, 11:05:55 PM
post Re: Syntherrupter - A Feature-rich, Polyphonic Interrupter
[Computers, Microcontrollers, Programmable Logic, Interfaces and Displays]
Max
June 10, 2024, 10:57:51 PM
post Re: Benjamin's DRSSTC3
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
June 10, 2024, 08:08:04 PM
post Re: Plasma Torid - Class E Self Resonant Dual/Stereo - Plasma Torid Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Hi-Deff
June 10, 2024, 06:04:09 PM
post Sling Psychrometer
[Laboratories, Equipment and Tools]
klugesmith
June 10, 2024, 04:43:59 PM
post Re: Benjamin's DRSSTC3
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
June 10, 2024, 03:35:28 PM
post Re: Benjamin's DRSSTC3
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Jj
June 10, 2024, 01:36:41 PM
post Re: Is a 60UF 800VDC Dawncap good for an induction heater?
[General Chat]
Anders Mikkelsen
June 09, 2024, 05:44:29 PM
post Is a 60UF 800VDC Dawncap good for an induction heater?
[General Chat]
yourboi
June 09, 2024, 03:31:30 PM
post Re: Steve Ward's DRSSTC Interrupter stops working when adjusting pulse width
[Electronic Circuits]
NyaaX_X
June 09, 2024, 01:34:49 PM
post Steve Ward's DRSSTC Interrupter stops working when adjusting pulse width
[Electronic Circuits]
verliebt_in_neukölln17
June 09, 2024, 01:56:51 AM
post Re: Return of Electronics Flea Market in "Silicon Valley"
[Sell / Buy / Trade]
klugesmith
June 08, 2024, 06:06:25 AM
post Re: Coulometric hourmeters
[Laboratories, Equipment and Tools]
klugesmith
June 08, 2024, 05:38:14 AM
post Interrupter for SSTC
[Beginners]
Simranjit
June 08, 2024, 12:47:47 AM
post Re: Adding capacitor to primary in SSTC
[Solid State Tesla Coils (SSTC)]
Michelle_
June 07, 2024, 03:59:57 PM
post Re: Adding capacitor to primary in SSTC
[Solid State Tesla Coils (SSTC)]
davekni
June 07, 2024, 06:42:26 AM
post Re: Space-X Starship test this week
[Science, Research and News In Other Fields Than Electronics]
MRMILSTAR
June 07, 2024, 05:08:00 AM
post Re: Half bridge sstc different waveform on two mosfets
[Solid State Tesla Coils (SSTC)]
davekni
June 07, 2024, 03:16:31 AM
post Re: Space-X Starship test this week
[Science, Research and News In Other Fields Than Electronics]
klugesmith
June 06, 2024, 11:37:20 PM
post Adding capacitor to primary in SSTC
[Solid State Tesla Coils (SSTC)]
Simranjit
June 06, 2024, 11:20:23 PM
post Re: Plasma Torid - Class E Self Resonant Dual/Stereo - Plasma Torid Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
alan sailer
June 06, 2024, 10:54:48 PM
post Re: Half bridge sstc different waveform on two mosfets
[Solid State Tesla Coils (SSTC)]
ZakW
June 06, 2024, 05:17:02 AM
post Re: Half bridge sstc different waveform on two mosfets
[Solid State Tesla Coils (SSTC)]
Simranjit
June 06, 2024, 04:50:00 AM
post Re: Half bridge sstc different waveform on two mosfets
[Solid State Tesla Coils (SSTC)]
davekni
June 06, 2024, 04:00:52 AM
post Re: Half bridge sstc different waveform on two mosfets
[Solid State Tesla Coils (SSTC)]
ZakW
June 06, 2024, 01:43:41 AM
post Re: Half bridge sstc different waveform on two mosfets
[Solid State Tesla Coils (SSTC)]
Simranjit
June 05, 2024, 11:11:17 PM
post Re: Half bridge sstc different waveform on two mosfets
[Solid State Tesla Coils (SSTC)]
Michelle_
June 05, 2024, 10:18:57 PM
post Re: Half bridge sstc different waveform on two mosfets
[Solid State Tesla Coils (SSTC)]
Simranjit
June 05, 2024, 10:13:03 PM
post Re: Half bridge sstc different waveform on two mosfets
[Solid State Tesla Coils (SSTC)]
ZakW
June 05, 2024, 09:29:18 PM
post Half bridge sstc different waveform on two mosfets
[Solid State Tesla Coils (SSTC)]
Simranjit
June 05, 2024, 08:46:53 PM
post Re: Want to build HV HF oscilloscope probe.
[Electronic Circuits]
Twospoons
June 05, 2024, 07:04:45 AM
post Re: Want to build HV HF oscilloscope probe.
[Electronic Circuits]
Domo
June 05, 2024, 04:58:35 AM
post Re: Pearson current monitor model 1330 teardown (100kA)
[Laboratories, Equipment and Tools]
klugesmith
June 05, 2024, 01:42:04 AM
post Re: Coulometric hourmeters
[Laboratories, Equipment and Tools]
klugesmith
June 04, 2024, 10:31:58 PM
post Re: My completed 14-stage Cockroft-Walton voltage multiplier
[Voltage Multipliers]
pete_dl
June 04, 2024, 08:08:28 PM
post Re: Want to build HV HF oscilloscope probe.
[Electronic Circuits]
Twospoons
June 03, 2024, 11:13:26 PM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
June 03, 2024, 10:35:57 PM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Hi-Deff
June 03, 2024, 05:51:05 PM
post Re: Want to build HV HF oscilloscope probe.
[Electronic Circuits]
Domo
June 03, 2024, 07:41:41 AM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
June 03, 2024, 05:28:44 AM
post Re: RDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
June 03, 2024, 05:02:19 AM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
June 03, 2024, 03:47:33 AM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
June 03, 2024, 02:23:58 AM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Hi-Deff
June 03, 2024, 01:25:24 AM
post Re: RDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ZakW
June 03, 2024, 01:08:47 AM
post Re: RDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
June 02, 2024, 10:29:02 PM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
June 02, 2024, 10:02:45 PM
post Re: Racing sparks
[Spark Gap Tesla Coils (SGTC)]
davekni
June 02, 2024, 08:25:37 PM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
June 02, 2024, 04:51:58 PM
post Re: RDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Michelle_
June 02, 2024, 04:44:30 PM
post Re: My completed 14-stage Cockroft-Walton voltage multiplier
[Voltage Multipliers]
MRMILSTAR
June 02, 2024, 03:25:11 PM
post APC Smart-UPS 1500VA Teardown
[Electronic Circuits]
Mads Barnkob
June 02, 2024, 01:36:11 PM
post Re: My completed 14-stage Cockroft-Walton voltage multiplier
[Voltage Multipliers]
pete_dl
June 02, 2024, 11:43:40 AM
post Re: RDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ZakW
June 02, 2024, 08:49:11 AM
post Re: RDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
June 02, 2024, 08:36:07 AM
post Re: RDRSSTC - Project Build
[Dual Resonant Solid State Tesla coils (DRSSTC)]
ZakW
June 02, 2024, 12:41:50 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Benjamin Lockhart
June 01, 2024, 08:24:35 PM
post Pearson current monitor model 1330 teardown (100kA)
[Laboratories, Equipment and Tools]
Mads Barnkob
June 01, 2024, 08:22:28 PM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
June 01, 2024, 03:56:53 AM
post Re: Racing sparks
[Spark Gap Tesla Coils (SGTC)]
Terry
June 01, 2024, 12:03:50 AM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Hi-Deff
May 31, 2024, 11:46:20 PM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
May 31, 2024, 06:13:59 PM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
May 31, 2024, 01:55:22 AM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
flyingperson23
May 30, 2024, 11:57:49 PM
post Re: First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
May 30, 2024, 11:50:06 PM
post First DRSSTC questions
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Hi-Deff
May 30, 2024, 11:23:35 PM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
davekni
May 30, 2024, 10:43:06 PM
post Re: Benjamin's DRSSTC3
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
May 30, 2024, 10:24:35 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
NyaaX_X
May 30, 2024, 06:10:04 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
Simranjit
May 30, 2024, 04:56:11 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
Michelle_
May 30, 2024, 04:48:05 PM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
May 30, 2024, 04:37:22 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
klugesmith
May 30, 2024, 04:16:31 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
NyaaX_X
May 30, 2024, 03:34:10 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
Simranjit
May 30, 2024, 02:53:50 PM
post Re: SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
NyaaX_X
May 30, 2024, 12:44:47 PM
post SSTC tripping circuit breaker
[Solid State Tesla Coils (SSTC)]
Simranjit
May 30, 2024, 07:52:56 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
NyaaX_X
May 30, 2024, 07:07:53 AM
post Re: Benjamin's DRSSTC3
[Dual Resonant Solid State Tesla coils (DRSSTC)]
Benjamin Lockhart
May 30, 2024, 07:04:40 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
May 30, 2024, 05:16:50 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
May 30, 2024, 05:08:17 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
davekni
May 30, 2024, 04:29:30 AM
post Re: Benjamin's DRSSTC3
[Dual Resonant Solid State Tesla coils (DRSSTC)]
davekni
May 30, 2024, 03:52:36 AM
post Re: Racing sparks
[Spark Gap Tesla Coils (SGTC)]
davekni
May 30, 2024, 03:47:12 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Benjamin Lockhart
May 30, 2024, 03:41:34 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
May 30, 2024, 03:27:28 AM
post Re: Steve Ward SSTC5 build
[Solid State Tesla Coils (SSTC)]
Michelle_
May 29, 2024, 03:55:16 PM

SimplePortal 2.3.6 © 2008-2014, SimplePortal