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Messages - profdc9

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1
I built a simple peak voltage meter this way.  Sorry, don't have schematic handy right now.

I used a 50 microamp analog DC current meter.  I made a full-wave-bridge of 4 1N4007 diodes into the DC current meter to rectify the AC to DC.   Then I made about a 600 megaohm resistor by putting 33 20 megaohm resistors in series and place this in series with the full wave bridge.  To prevent end-to-end arcing breakdown between the resistors, I laid them out in an undulating pattern and potted them all in epoxy.  This was able to read up to 30 kV peak, but you could add more resistance for a higher range.

2
So how much higher voltage rated MOSFETs could be used? Or have you tested?

The offline (230VAC~325VDC) fed ZVS drivers have always been a widely sought topology but it almost always ends up in flames :)

Yeah, the peak voltage on the transistors is very high.  Perhaps 1200 volt transistors would work for ZVS from mains, but half/full bridge can be run with ZVS easily with an inductive load in series with the primary coil.  For me the high-voltage ZVS is a dead end.  The one advantage of the low voltage ZVS is that it is somewhat safer for induction heaters if no isolation transformer is used to the work coil, but probably isolation is needed for any reasonable safety.


3
Spark gap Tesla coils / Re: SGTC MK1 - An Accomplishment in Progress
« on: November 12, 2019, 08:24:38 PM »
You seem to have solved many problems I had when trying to do this.

One problem I had when trying to use a TV flyback transformer is that the peak voltage can be very high and damage the capacitors.  The open circuit voltage of some flyback transformers can be 30-40 kV!  The other problem is that I destroyed many transformers because when the arc is quenched, it causes a brief burst of high voltage, MHz-frequency RF in the transformer that over the course of a few minutes arced through and destroyed the internal insulation of the flyback transformer.   Then I tried to construct my own beefier  transformer on some huge U-shaped ferrite pieces, and those worked better, but even those were destroyed after a short run. 
I also had problems and could not use a static spark gap, because even with a strong fan blowing on the spark gap it was too hot.  So eventually I had to make a rotary spark gap out of an angle grinder, which is very difficult because it spins very fast and has to be balanced perfectly or will shake itself and everything else to pieces.

Eventually I went to dual MOTs and used a Terry filter which removes the RF spikes, and it was reliable.  This is one reason why DRSSTC can be so much easier, because there is no spark gap to cause voltage spikes, and especially good rotary spark gaps are hard to reconstruct.

Anyways that is a great build and very impressive you got it to work that well.

4
Electronic circuits / Talk on open source hardware in ham radio and KiCAD
« on: October 03, 2019, 03:52:54 PM »
I gave a talk on open source hardware in ham radio, and had a tutorial on using KiCAD to design PCBs as an example of open source hardware design.  You can download the talk from:

https://www.rars.org/documents/Open%20Source%20for%20Amateur%20Radio%20Projects_%202019_09.pdf

Enjoy!

Dan

5
Dual Resonant Solid State Tesla coils / Re: UD2.7 Gate Signals
« on: September 14, 2019, 04:50:10 PM »
You might want to consider the UD2.9 version I posted earlier.  You can see the results here:

https://highvoltageforum.net/index.php?topic=346.0

It is a "skip pulse" version so that, unlike the UD2.7 where the spark stops growing when the overcurrent is tripped, the skip pulse will resume exciting the primary once the current falls below the threshold.  It will keep going on as long as you keep the interrupter pulse on.  It might be one way to grow the spark bigger.

6
Dual Resonant Solid State Tesla coils / Re: UD2.7 Gate Signals
« on: September 08, 2019, 07:20:04 PM »
I don't know if it would help but I made a through-hole version of UD2.7 that might be easier to work on...

https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/ud27c%20thru%20hole

I also made a slightly more featureful one I call UD2.9

https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/ud29

Dan

Hi

yesterday I viewed every thing twice because there has to be an error somewhere. And while grabbing around on the board I feel something warm on my finger but not the 5V V-reg or something like that it was the comparator it selfe  :o
Its not driving any load at all so I can´t imagine that this is its normaly state... It makes sense because the inverted output is doing this hook thing and it seems that the IC is switching, according to the feedback but not at the right time, maybe its because it can not detect the right voltage level any more, dont know.

So to be on the save side, a couple of new TL3116 are on the way- also run out of other ideas  ::)

If the comparator do not thinks right, i´ll ending up having the phase lead induktor´s ferritcore drilled out because it´s doing nothing when turning it  ;D

I also come up with a new GDT drive stage ! There for I also bought some FDD8424H smd drivers which originaly build in, in Loneocean´s UD2.7  Because they contain a pair of good matched P and N fets, the problems about crossconductions should be eliminated.

The new comparator is now the more significant part so the "ringing end of burst" thing has to wait meanwhile.

I´ll give you a update such as the parts arrives ^.^


reguards, Andi

7
Electronic circuits / Re: Version 2 of power supply
« on: September 02, 2019, 12:32:52 AM »
So I built up my power supply board.  So far so good.  I need to get a bigger heatsink, fan, and enclosure.  The next version has a few changes not on this version, including bigger pads for single diodes for the full wave bridge, capacitors, and TO-247 as well as TO-220 transistors.

If there are any other suggestions, let me know.



Dan

8
Electronic circuits / Re: Version 2 of power supply
« on: August 28, 2019, 04:17:21 AM »
Ok, I changed it so there is space for four bigger diodes (P600 type) and bigger capacitors, with bigger holes to solder pads for external capacitors.

I also changed the footprints of the transistors to allow for TO-220 or TO-247 type pass transistors which has a higher power dissipation package.

I thought TO-220 was good up to 50 watts, but I suppose even with a good fan it will still get too hot, perhaps even to do 30 watts per device.  If so, then I had better go with the TIP3055 (TO-247 package).   I don't want to use the 2N3055 as the TO-3 package is expensive and rare, and is relatively hard to mount.


9
Electronic circuits / Re: Version 2 of power supply
« on: August 27, 2019, 08:30:37 PM »
I am aware of the current sharing issue with diodes.  If I could find a TO-220 or some similar case power diode (especially cheap) it would be better.   But I was thinking that I could use some heatsink compound and use the copper layer on top of the board to equalize the temperature, or the same fan used to blow on the transistor heatsinks could also help cool the diodes.  Otherwise I could use one of the "brick" full-wave rectifiers.  I'm just trying to keep the costs down, anticipating that most of the components used to assemble this in practice are cheap fleabay/Shenzhen generic components.

For the capacitors, I was thinking that the large capacitor bank would be connected off-board, and a smaller capacitor on the PCB which a smaller inductance for surge currents.  So I just put locations for three capacitors, thinking that one or two might be used to place capacitors off-board.

The TIP41C goes up to 6A, but mostly the four are there so that if you drop a high voltage to a low one with high current, there are many transistors to share the heat load with.  Also, a TIP3055 can go up to 10 A, but I think the heat load will be a problem before the current is maxxed out.

I haven't put relays in this design but I will consider it for a future design.  However, I am trying to make the simplest, more adaptable design I can.  It's not elegant, given that a lot of power could be dissipated in the transistors, so if a high voltage is used, a large heatsink and fan is likely required.

Thanks for any feedback you can provide,

Dan

I have not looked through it fully, but there are a couple of areas that I'd think about:
- Diodes in parallel - they don't look like they will be heatsunk together, so equal current sharing may be an issue
- Tap switching relays may be useful to limit dissipation; these are common in the linear supplies that you're looking to upgrade (though I do not know what downsides they have, as I haven't designed one myself).

10
Electronic circuits / Version 2 of power supply
« on: August 27, 2019, 04:39:47 AM »
I am working on my version 2 of a linear power supply.  The first one worked fine, but I think I can do better.  The idea of it is to make it so that when you tear down and recycle the bits of old linear power supplies (the transformers and capacitors for example) you can reuse them with this new power supply PCB.  This design is a constant voltage (up to 30 volts) and/or constant current (perhaps up to 20 amps, depending on dissipated power).   This design uses very common op-amps (LM358) and up to four pass transistors in parallel (TO-220 TIP41C or 3055-type).

The new design has a few improvements, including a connection for analog or digital meter voltage and current outputs on the PCB, and provides 5 volts low current (< 50 mA) output for digital panel meters.  Also, a connection for an external analog control of the voltage and current if you want to use an Arduino to control the power supply. 


11
Electronic circuits / Re: ESAB Power TIG 200 Welder Teardown
« on: August 27, 2019, 04:30:12 AM »
It looks like there's a schematic available for the welder.  I was hoping it would be more informative as a guide for future designs, but it seems to be somewhat opaque.




12
It is possible that there is increased residual stress in the bottom of the container which makes it more vulnerable to hydrolysis.  Perhaps by viewing the bottom of the container between crossed polarizers, birefringence due to internal stresses can be visualized as compared to the container walls.

I find it interesting that you see the attack in the middle where the plastic is actually thickest. And I think I know why.

I worked with PET blow moulding machines for breweries and other liquid product manufacturers for 3 years and this was the kind of machines I did service/upgrades on: https://www.krones.com/en/products/machines/krones-contiform-3-pro.php

The PET preform is heated in a oven before entering the blow mold station, but it is the sides of the preform and not the top/bottom that gets the most heat, so the bottom middle is actually pretty brittle and it makes sense when you see the proces of the blow. It is pressurized low first and then bang up to some 25-40 Bar at the end, but you have a very uniform stretch and in the perfect world you have the "tap" of the preform dead centered as the bottom of the bottle.



So my theory is that you have a stronger and more uniform plastic structure in the thin walls than the thicker bottom middle that was transformed at a lower temperature from preform to bottle, as the preform cools off fast from oven to final blow stage, the blow air is not pre-heated.

13
Dual Resonant Solid State Tesla coils / Re: Next Gen DRSSTC
« on: July 16, 2019, 04:05:07 AM »
The through-hole PCB is at

https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/Psoc5-power

You just need to zip the gerber files and send it to a PCB house like JLCPCB or Seeedstudio and they will send you a board.

Dan

That video is awesome and it got so intense at 0:45!

It seems like I am running out of excuses to get a UD3 up and running, didn't someone promise me to write up a guide on which hardware to use etc? Was it Hydron? Futurist? Profdc9? I forgot and unfortunately I do not have the time or mental surplus to take in more new things from scratch right now :)

14
Dual Resonant Solid State Tesla coils / Re: Kaizer half bridge driver
« on: July 12, 2019, 07:16:40 PM »
There's one other thing I realized too about C4 and C7...

C4 and C7 provide both snubber behavior (stabilizing the voltage at the MOSFET/IGBTs).  But because they also split the supply for driving one end of the half-bridge, there is another consideration when driving a tesla coil.  When driving an inductive load like a tesla coil primary,  you have a series resonance with L=tesla coil primary inductance and C=C4+C7.   With the added series capacitance C5, the resonance frequency given by L and Ctotal = 1/(1/(C4+C7)+1/C5).   So that the voltage drop of this LC series circuit is mostly across C5, C4 and C7 must be much greater than C5 so that the LC resonance is dominated by C5.  Otherwise, the voltage drop across C4/C7 approaches the supply voltage and may exceed it, causing catastrophic failure either due to excessive primary current or overvoltage on the transistors.  Of course the voltage on your Tesla primary coil and C5 depends on the Q of the primary, and so the exact capacitance for C4+C7 needed to keep the voltage swing on those capacitors under a certain amount is going to depend on the Q also.   Again because C5 is generally going to scale with coil power, as the frequency of the primary tends to drop with increasing power, so to will C4 and C7 increase as well.

Not to ramble on, but I made a half bridge to drive a hefty ferrite transformer and used about C4+C7=16 uF, but I was driving the transformer at 25 kHz, so a larger capacitance was needed.  In addition, I needed snubbers across the emitter/collectors and load itself as well as the power supply rails, as the inductive kickback of the transformer would blow out the IGBTs as well, because there is a lot of energy stored in the magnetic field of a ferrite with 6 square centimeters of cross-section and a permeability of 1500 as well as the gap in the transformer magnetic circuit.  The kickback occurs when you have a spark gap and the current is cut suddenly by quenching of the spark.  But maybe this given you a rough idea of what you need, because C4+C7 is going to scale inversely with the square root of frequency.

Dan

15
Dual Resonant Solid State Tesla coils / Re: Kaizer half bridge driver
« on: July 12, 2019, 06:33:00 PM »
I will venture an answer...

I think the answer to this is perhaps a little complicated, because it depends on the ESR of the bus capacitors and the inductance of the connection of those capacitors to the half bridge.    Ideally, you would want the impedance of the snubber (also called dc-link) capacitors to be much less than the total impedance of the inductance of the connection and the ESR of the bus capacitors at the frequency of use.  Of course, the snubbers themselves have their own ESR and inductance of the connector to the MOSFET/IGBT sources/emitters and drains/collectors, which adds to the impedance of the snubber, which is why bridge layout is important.  The inductance of the connection from the capacitors (both the bus capacitors and snubbers) could cause voltage spikes under transient changes in current that cause the drain-source/collector-emitter voltage to exceed safe operating area and failure of the device.  This is why short and fat connections between these capacitors and the transistors is necessary, and for example why some snubbers screw right onto the terminals of IGBT bricks.

Another criterion that could be used is to reduce the voltage transients on the MOSFET/IGBTs under a certain amount, which would basically be then the average current supplied to the transistors over a cycle multiplied by the impedance of the capacitor.   The tolerable amount of voltage change is partially going to be determined by how closely you operate your device bus voltage compared to the maximum safe operating area voltage.   If you are operating, for example, with a bus voltage from a doubled single-phase 220VAC supply, you will be operating perilously close to the limits of a 650 V transistor.  Operating with a lower bus voltage, however, can also stress devices because of the increased current for a given power, so you have to consider that when choosing the MOSFET/IGBTs.

So while that is a complicated answer to your question, the bottom line is that if you err on the side of making the capacitors larger and the connections short and fat, you are likely to have fewer problems.  I have an example of a half-bridge PCB I designed (you can get the plans from https://github.com/profdc9/DRSSTC-PCB-Pack/tree/master/half-bridge-transistor if you want to make the PCB).  Like Mads said, usually 2 to 4 uF total snubber capacitance is good enough for most applications, and probably the best estimator on the total snubber capacitance is given by the circulating power (voltage X current) in the primary circuit, as in general the capacitance needed will tend to scale with that. But a combination of good bridge layout, adequate snubber capacitance, and not operating too close to the SOA voltage of the devices is likely to work.

Dan


16
Spark gap Tesla coils / Re: rotory spark gap
« on: July 03, 2019, 06:03:20 AM »
FR4 is the circuit board material with copper on it.  G10 is the material without the copper (and usually the fire retardant).

https://en.wikipedia.org/wiki/G10_(material)

By the way balancing spark gap wheels is very tough.  I used an angle grinder for mine, and I destroyed the bearings on one trying to balance the wheel.   I made a paper template and stuck it on the wheel to get the spark points about in the right place, and then I placed on the arbor of the angle grinder and spun it slowly and used a file to grind the end off into a circle.  Make sure you are wearing protective gloves and face mask for sure.

Dan



17
High voltage transformers for mains frequencies usually are large because they both need many turns and relatively large cores.  You could certainly use a neon sign transformer with a low current mains voltage input for this purpose.  However, modern neon sign power supplies are usually switched-mode power supplies, and so limiting the current to such as a supply would not have the intended effect, the power supply simply wouldn't function.  You would need to find an old neon sign transformer, but you can generally still find those being sold on e-bay, though they are becoming more scarce.

A television flyback transformer is a fairly decent alternative as well as inexpensive.  You wrap four or five turns around the primary of the flyback transformer, and then drive this with a MOSFET (such as a IRF540) turned on and off by a 555 timer oscillator.  This would be powered directly by 12 volts DC.    The flybacks usually have a built in high voltage diode which will produce DC high voltage, which may be needed for your experiment.  You could extra inductance in series with the primary if you wanted to limit current further.  The duty cycle or frequency of the oscillator can also control the output power to a limited extent.  Like the neon sign transformer, the flyback transformer is a source of high voltage and can be driven to produce dangerous amounts of current at high voltages, or can potentially charge capacitors with lethal amount of energy.  So this approach does not completely eliminate the risk, but can be used to generate high voltages with low currents.

Auto or motorcycle ignition coils can also work well too, but generally do not have built-in rectifiers.  Both flybacks and ignition coils can be bought easily on ebay.




18
Electronic circuits / Benchtop power supply PCB
« on: June 09, 2019, 04:28:29 PM »
I design a power supply PCB based on mixing the attributes of several designs floating around on the internet. You can find it at:

https://github.com/profdc9/LinearPS

The range is up to about 30 volts and the current with a single TIP3055 maximum is about 4 A, though if you run it at low voltage output and high voltage input, you probably want to use multiple TIP3055 to dissipate all that power.

It works. It is intended to take the output of a step-down AC transformer, and it provides constant voltage and constant current controls. It also provides sampled outputs of the actual voltage and current output to connect panel meters, and a low current (zener) +5V to supply digital LCD meters. It can be adjusted for different input AC voltages and different ranges of output voltages and currents using trimmers. Also, it can have up to four TO-220 output devices that can be mounted to a common heatsink (for example, TIP41C or TIP3055 devices) to achieve higher output current.

I made this so that old junk and surplus transformers can be turned into useful benchtop power supplies.

DC can also be input into the board, but the minimum limiting output current will be around 500 mA.

Dan


19
I converted the "Game of Thrones" theme to 2 channel MIDI for an event, here it is.

Dan

20
A relay might work, but it is slow and requires a lot of coil current to operate.

Perhaps use an optoisolator such as the 4N28/4N35 to pull the signal to ground if there is undervoltage.

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