Thunderdrome 2

When we left last time, the sputtering power supply was halfway done. It was missing a current limiting resistor, an HV voltage divisor and proper cable management to the outside.
Finally, received the parts and got to it.

There is no point in having a power resistor without a heatsink, right? XD

Everything is held down with M6 nylon screws, wich also make good standoffs for the voltage divisor, comprised of 10*1MΩ and 1*100KΩ for a 1/10 reduction. (I didn’t had at hand a 100k, so I used 2*220K in parallel, wich is not exact, but aht I really need is a percentage to avoid multimeter breakdown, not a precision measurement.

A slot was cut in each screw so the resistor lead would get trapped with a nut, simple but effective.

I also had to deal with the M25 gland and a hole made by the previous owner for a SMEMA connector (SMT line interconexion standard). For the first, I would have preferred to have it at the bottom of the box for the 220V input line, but well, it was free, so I can’t complain much, so I just routed the cable away from everything to the bottom of the box. The other hole kinda messed up with my head. I could not realistically leave it there and/or solder something into it to make it disappear, so…

…I got wild and 3D printed a holder plate and two custom glands:

Since the HV lines also run inside silicone tube, I didn’t worry much about PLA dielectric constant and/or conductivity.


Looks neat enough.

For the internal connections I used faston connectors in the capacitor and screw-on terminals for the resistor. The divisor extremes where soldered to silicone cable.

Closeup of the setup:

Everything sits nicely and away from everything else, ensuring proper isolation up to the 2Kv+ the system is capable of. Note that the silicone cable was sleeved over the faston connectors, just in case the cable got yanked out, it doesn’t hang live on the inside of the case.

Final setup:

 

This will only require for current and voltage monitors, but I still haven’t received them yet, and they get installed on top as a “separate” unit.

Till next time!

3 responses to “Thunderdrome 2

  1. Nice project! I have had a similar project sitting for awhile…

    Can you please explain why you use a current limiting resistor in series with the sputter? This means lowering the voltage between anode and cathode which is what you need to keep high for the process to work..? If you want a lower voltage, why not set the variac at a lower setting?

    • It’s to prevent current spikes when an arc is formed through the plasma.
      Whenever that happens, the resistor will increase the drop in voltage quickly and extinguish the arc, preventing damage to the high voltage diodes on the rectifier bridge (rated only for 2A)

      • Ahh, I see. I have been fine so far but I will probably include it now that I know more :) Thank you for your reply.

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