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General Chat / Re: New EE student asks about Cutting-Edge fields
« on: May 16, 2024, 05:45:08 AM »
Well actually its exactly the same question - verbatim.
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General Chat / Re: New EE student asks about Cutting-Edge fields« on: May 16, 2024, 05:45:08 AM »
Well actually its exactly the same question - verbatim.
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General Chat / Re: designing and building electron gun help!« on: May 11, 2024, 12:10:44 AM »
I think you might find this to be a useful resource https://reprap.org/wiki/MetalicaRap .
Its a project to create a metal sintering 3d-printer using electron beam melting. There's a lot of detail on the electron gun and its focusing system. 3
Beginners / Re: Aluminum electrolytic capacitor ripple current issue« on: May 10, 2024, 03:02:13 AM »
Yeah, its a "gotcha" that traps fresh graduate EEs all the time.
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Beginners / Re: Aluminum electrolytic capacitor ripple current issue« on: May 10, 2024, 12:06:50 AM »
I meant the relative phase between the switching of your MOS rectifiers and the signal you are rectifying. For example, slow turn off would result in current flowing back to the pick-up coil, and therefore higher ripple in your caps. As I said - try it with schottky diodes and see what happens. Also your 25V MLCC caps running at 15V will be at about 40% of rated value. Murata have a useful tool for this stuff https://ds.murata.co.jp/simsurfing/index.html?lcid=en-us 5
Beginners / Re: Aluminum electrolytic capacitor ripple current issue« on: May 08, 2024, 06:41:48 AM »
One more thing to check is the switching of your pmos ideal diode - if the phasing is wrong then you would see higher than expected ripple current. As a test, you could replace it with a schottky diode, then recheck your ripple current.
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General Chat / Re: X-ray generation from nixie bulbs?« on: May 01, 2024, 12:43:46 AM »
Generating xrays requires accelerating electrons to high speeds then slamming them into a metal target. The neon gas fill in a nixie would likely stop the electrons ever reaching speeds where significant xray generation would occur.
But thats just my opinion. 7
Transformer (Ferrite Core) / Re: High Voltage from LG Microwave Inverter« on: April 29, 2024, 03:33:58 AM »
There's no reason to assume the LG control signals resemble the Panasonic ones, in fact you could pretty much guarantee they will be different.
Without a schematic you are flying blind. Google search on the PCB number turned up nothing. So unless you want to reverse engineer the thing yourself, you may be better off just using it for parts. 8
General Chat / Re: Tesla coil UV eye protection?« on: April 25, 2024, 11:40:08 AM »
N2 emission at 337nm and 357nm is classed as UVA, so what you really need is sunscreen. Or long sleeves. UVA causes skin damage.
Its worth noting that the UV in the arc is a lot brighter than it appears as your eye sensitivity drops off rapidly below 400nm. The 337nm and 357nm peaks are 3-4 times brighter than the 400nm you can see, and your eye is roughly 1/10th as sensitive to 400nm as it is to green light around 550nm. Anyone own a light meter than covers the UV end of the spectrum? 9
General Chat / Re: Tesla coil UV eye protection?« on: April 25, 2024, 04:33:57 AM »
Any hard plastic sheeting rated for use outside will have a UV blocker added that absorbs anything shorter than about 400nm. Without that sunlight will rapidly degrade hard plastics like PC, PMMA and PVC.
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Capacitor Banks / Re: Ignitron trigger drive ideas?« on: April 15, 2024, 11:02:05 PM »
What a beautiful thing! I was puzzled by the oval electrode at the bottom, then I realised its a puddle of mercury
Looking at the plasma might not be too healthy for your eyes, depending on what kind of glass was used. The wikipedia article on ignitrons would suggest a reasonably high current ignition pulse is required - probably similar to driving a big thyristor. Oh look - a nice datasheet! https://frank.pocnet.net/sheets/119/n/NL1001.pdf So the trigger appears to need 200 volts, and a peak current to at least 30A. To me this looks like cap charged to about 300V with a series inductor to control peak current and a thyristor switch. And a diode across the ignitron trigger to prevent reverse volts. Doesn't handle as much current as I thought it would for something that big. 11
General Chat / Re: Upper and Lower Explosive Limits on Confined Flammable Vapors at -79 C.« on: April 01, 2024, 11:40:52 PM »
Well, if you are using ethanol then to get 3% vapor you'd need it to be at about 10C. Super-cooling is going to drop the ethanol vapor pressure well below the LEL, even though it will be over saturated. Lower temperatures will also raise the LEL.
Liquid ethanol has a flashpoint of 12.8C. Realistically you don't need to worry. If you do still want to inert your chamber, I wouldn't bother calculating gas ratios. Just do a CO2 or N2 flood, then add your alcohol. 12
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.
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Spark Gap Tesla Coils (SGTC) / Re: Where's all this voltage coming from?« on: March 18, 2024, 02:36:11 AM »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. 14
General Chat / Re: 2x Panasonic Inverter Microwaves - what to salvage, dangers?« on: March 17, 2024, 04:45:17 AM »
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.
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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. 16
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.
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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. 18
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.
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Spark Gap Tesla Coils (SGTC) / Re: Any quick way of makeing a spark gap that can sustain long runs with high temps?« on: December 23, 2023, 10:26:11 PM »
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. 20
Voltage Multipliers / Re: Has anyone tried using series IGBT to control Marx gen firing rate?« on: December 06, 2023, 10:45:55 PM »
Is there a reason you don't want to use a triggered spark gap? Or maybe a hydrogen thyratron?
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