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4hv.org :: Forums :: High Voltage
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Need advices before buying an expensive Variable Vacuum Capacitor

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PhilGood
Wed Jun 19 2013, 10:10PM Print
PhilGood Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259
Hi all,

I need an advice ... I would like to buy a Variable Vacuum Capacitor

I plan to use it for various small/mid size VTTCs (572B, GK71, GU81M) powered with a 2480V MOT (with eventually voltage doubler, full wave rectification, smoothing)

With full wave rectification my power supply is around 2480 x 1.414 = 3500V
With voltage doubler it goes up to 7000V peak

But I wonder how high the voltage at tank capacitor can climb due to oscillation and resonance

There are two "ranges" of operating voltage for these VVCs:

- 10kV nominal / 15kV peak / 20kV peak test
- 25kV nominal / 35kV peak / 50kV peak test

Basically my question is: is a 10kV nominal enough for my needs or shall I get the 25kv nominal one ?

Thanks for your advices :)
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MR-ZAPPY
Wed Jun 19 2013, 10:14PM
MR-ZAPPY Registered Member #16018 Joined: Fri May 03 2013, 07:19PM
Location:
Posts: 53
Just to be safe I would get the 25 kv one
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PhilGood
Wed Jun 19 2013, 10:49PM
PhilGood Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259
Mr.Plasma-CRAZY wrote ...

Just to be safe I would get the 25 kv one
Agreed with that

My dilemna is the max value I found @25kV is 200pF, while there are 500pF and 1000pF models @10kV
And of course I would prefer the max capacitance

That's why I'd like a precise answer...
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MR-ZAPPY
Wed Jun 19 2013, 10:59PM
MR-ZAPPY Registered Member #16018 Joined: Fri May 03 2013, 07:19PM
Location:
Posts: 53
If they do not cost much you can put 2 in series in parallel with 2 in series
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PhilGood
Wed Jun 19 2013, 11:06PM
PhilGood Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259
They do cost a lot ! (around $200)


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MR-ZAPPY
Wed Jun 19 2013, 11:06PM
MR-ZAPPY Registered Member #16018 Joined: Fri May 03 2013, 07:19PM
Location:
Posts: 53
Each?
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Antonio
Wed Jun 19 2013, 11:32PM
Antonio Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
If you don't need the full range of adjustment you can just place a fixed capacitor in parallel to have greater capacitance.
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PhilGood
Thu Jun 20 2013, 12:08AM
PhilGood Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259
Mr.Plasma-CRAZY wrote ...

Each?
Yes

Antonio wrote ...

If you don't need the full range of adjustment...
I need it. That's why I wanna invest into a VVC
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Myke
Thu Jun 20 2013, 02:06AM
Myke Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969
You can swap in different fixed capacitors with the single variable capacitor to get a large range of capacitances... unless you need to have it smoothly adjustable while it's on (you could even swap out the caps with high voltage relays if needed).
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PhilGood
Thu Jun 20 2013, 04:09AM
PhilGood Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259
Myke wrote ...

unless you need to have it smoothly adjustable while it's on ...
Well yes this is my goal

And the larger the VVC capacitance, the better. Hence my initial question

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