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Messages - Twospoons

Pages: [1] 2 3 ... 11
1
General Chat / Re: Can I Trust This Super Cheap Site?
« on: March 18, 2024, 08:57:06 PM »
At those prices you'd be lucky to find any silicon in them at all. Got to be a scam.

2
And 30kV/cm is for perfectly uniform conductors on either side of a gap. 

And thats for dry air at sea level. When the humidity or altitude get up a bit then you could be as low as 10kV/cm.

3
I had one, and it blew the IGBT and main diode bridge. So don't go hoping to salvage those parts, thats probably why the microwaves are dead.

4
Transformer (Ferrite Core) / Re: Simple oscillator instead a ZVS
« on: March 12, 2024, 11:55:37 PM »
There are lots of design notes out on the internet. eg https://ez.analog.com/cfs-file/__key/telligent-evolution-components-attachments/00-330-01-00-00-06-34-74/FlybackSnubberDesign.pdf
Start there.

You can also go a long way with SPICE simulation for these things. Characterizing your transformer will be the most difficult, but so long as you stay away from saturation, a linear model will do OK.

5
General Chat / Re: Electric insulator. Paraffin wax?
« on: March 12, 2024, 01:16:48 AM »
Paraffin wax will shrink as it cools and may crack.  You can make it tougher and slightly flexible by dissolving hot-glue sticks in the wax.

6
Transformer (Ferrite Core) / Re: Simple oscillator instead a ZVS
« on: March 12, 2024, 01:14:35 AM »
Its lacking a clamp or snubber  on the drain.  This means that any energy not coupled out the secondary gets dumped in the MOSFET, in the most nasty way possible: by overvolting the drain.
Example of a flyback clamp:
https://www.ti.com/ods/images/SSZTCV1/GUID-5300FB37-4574-4023-BC85-9BCA1E7D92CF-low.jpg
Note: these things need to be designed, not just hacked together.

Have a look at flyback circuits based on the old favorite UC3845.  This is a current-mode PWM controller - useful as you get direct control over the primary current.

7
Transformer (Ferrite Core) / Re: Simple oscillator instead a ZVS
« on: March 10, 2024, 12:05:09 AM »
Nothing wrong with using a 555. As you have found you can get better control over the output than the usual self-oscillating 2 switch converter. The only real advantage of the 2 switch ZVS is simplicity.

8
How about two lengths of copper pipe mounted in a block of insulator (wood? plastic?) so that they form an 'X', but spaced apart so a spark gap is formed at the middle of the 'X'. Viewed from the front, one arm of the 'X' would be behind the other. 
The long arms of the copper pipe 'X' should act as a heatsink.  If you can seal the bottom of the pipes too, then you could fill them with water, which would also remove heat by boiling.

Best I can come up with using minimal materials and time.

9
Is there a reason you don't want to use a triggered spark gap? Or maybe a hydrogen thyratron?

10
  I found an IEEE paper(https://ieeexplore.ieee.org/document/4181239) that estimates the resistance of a low voltage arc (anything up 600V or so) as 40/I0.85

11
Electronic Circuits / Re: Need help with DC biasing an AC voltage source
« on: November 12, 2023, 10:48:53 PM »
I have been trying to use ChatGPT to understand how ...

ChatGPT is not a reliable source of information.

12
General Chat / HV pulse capacitor source?
« on: November 07, 2023, 01:24:15 AM »
I'm looking for a source for a 20uF 5kV pulse capacitor for use in an electrical surge tester. Does anyone have a lead on a reputable manufacturer? (not interested in used parts)

13
If you read the text you linked to you will see the final voltage across the gap consists of that due to the plasma channel resistance plus the anode and cathode fall.  This is the reason for needing more than 5V to sustain the arc.
So even with your HV ignitor, you will still see more than 5V potential across the gap and no current will flow from your 5V supply.

14
Perhaps your chosen triode connection is not the best. Maybe try Screen (g2) to anode, and supressor (g3)  to cathode. As suggested here https://www.audiodesignguide.com/New2A3/ETF06TS.pdf
The fact that you know you have shipping damage does not inspire confidence. If the tube got whacked hard enough to short a grid to the plate then lots of other things may be bent out of shape and affect tube performance.

15
It is a tradeoff though. If you try and reduce the frequency too much, the flyback core can saturate. Mine operates at 28K Hz.

Could you not increase the core gap to compensate? That would both reduce the saturation risk and lower the primary (and secondary) inductance, raising the resonant frequency again.

16
Capacitor Banks / Re: What Cable Thickness for Capacitor Discharges?
« on: September 16, 2023, 11:33:56 AM »
Inductance will be your limiting factor.  A mere 1uH would limit your current to around 30,000 A peak. 
If you ever did achieve 1.5million amps the force pushing your cables apart would be on the order of 50 million newtons per metre.

17
Voltage Multipliers / Re: Super High Voltage Capacitor
« on: September 11, 2023, 05:13:19 AM »
Doing a string of 10 x 30kV caps isn't a great way to build a 300kV cap, unless you add balancing resistors. Typical cap tolerance is 10%, which means the voltage across any individual cap in the string is going to vary. So for 300kV overall, you probably want 12 or 13 x 30kV caps minimum (without balancing resistors).
You will also find that 1nF 30kV ceramic caps, while measuring 1nF at low volts, are a lot less than 1nF at 30kV.

18
Voltage Multipliers / Re: Super High Voltage Capacitor
« on: September 11, 2023, 04:31:32 AM »
If you do 'roll-your-own' (in both senses of the phrase) then using multiple thin dielectric sheets is better than using a single thick sheet. The rationale for this is that all plastic sheet will have defects, but with multiple thin sheets these defects are unlikely to line up, and so the multi-sheet stack has better performance.

Then again, you'd need ~0.06" (1.5mm)  total thickness in Mylar, so that will be quite a few layers.

Alternate would be something like 100mm foil discs with 3mm PMMA,PET or PC sheet - that would net you ~80pf, so thats only 5 metal layers to hit ~300pf. You could hot-press the stack to seal the edges and get rid of air.
A 200mm dia foil would get you 300pf in one layer. Then you can take your lead out from the middle of the disc, on each side.
I think I've seen PET sheet thats thinner than 3mm, so that would also be a option.
If it must be cylindrical you could use PMMA tube, foil on the outside, and either metal tube on the inside, or possibly salt water?

19
Voltage Multipliers / Re: Super High Voltage Capacitor
« on: September 11, 2023, 12:01:03 AM »
So how much capacitance do you actually need? A few 100pF at more than 300kV is going to be big no matter how you do it.

20
Electronic Circuits / Active EMI Filters
« on: August 28, 2023, 06:49:43 AM »
I really did not know this was a thing. But it seems TI have chips which can improve common mode performance of EMI filters, by actively driving the "Y" capacitor so that smaller CM chokes can be used.
(No, I'm not a shill for TI.)
https://www.ti.com/power-management/power-supply-filter/overview.html

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