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HVHF Bobbins

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Thomas W

Tue Sept 16 2014, 05:45AM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
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Posts: 1276

the core is +22kv - 0 - -22kV with each tap at 2000v.

From what i can see, the circuit seems fine with the only worry being that it may jump to core to other terminal. however i don't think it shall due to the distance it would have to jump, however its somthing to keep an eye on i suppose. If it runs fine up to half the operating voltage in air, then it should be even better under oil i guess.

The distance between those taps are about 120mm i think.

Patrick

Tue Sept 16 2014, 06:18AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

With 17 graduations that leaves 2.6kv.

so if you can fight off surface tracking and arcing to core, you should be fine in air by 2 times I think.

But be ready if it molotovs' on you.

and watch out for the PVC softening with frequency.

Thomas W

Tue Sept 16 2014, 06:45PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
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Im going to be using Polypropylene not PVC, i think it will be fine, after all, its a material used in capacitors as it is.
going to go with this version in the end:

I am a tad worried however as the college im going to machine it as may not have the needed tooling :/

klugesmith

Tue Sept 16 2014, 07:20PM

Registered Member #2099 Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716

Looking good, Thomas.

If your intent is to rectify the HVHF output without further multiplication,
it will behave better if you separately rectify each section of the secondary winding,
then stack the DC outputs in series.
Less stress on insulating materials, less effective capacitance to the core,
less exotic fast diodes, etc.

In fact you can even distribute a voltage doubling function, as seen in this thread here:

Ash Small

Tue Sept 16 2014, 07:39PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Thomas W wrote ...

Proud Mary wrote ...

Big nylon washers can be handy for splitting HF chokes into sections, though I'm not sure how you could apply it here. You can alternate small and large nylon washers to make a really good split bobbin.

Thats a rather interesting idea... but i think machining it would be better however as there are no gaps that the electricity can track through.

If it is under oil and vacuum pulled the electricity won't track through any gaps, the oil will insulate it.

I'm considering a composite bobbin for mine, built up from washers, etc., but I've not completely finalized the design yet. I want gaps that the oil can flow through for cooling. Core losses are the limiting factor with these big cores, especially when pushing them hard.

I'm planning on using 'Oil Directed Air Forced' cooling for mine.

EDIT: Here's a link:

Thomas W

Tue Sept 16 2014, 08:15PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
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Hmm i see... thats some interesting stuff there.

Im thinking that maybe i will just buy the tool or 2 i need for working on this, then when i get my lathe, i can use them myself maybe.

Hmm, anyone else got input on these bobbins?

Patrick

Tue Sept 16 2014, 09:09PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

i think youve seen and prepared enough, time for fabrication and testing.

Ash Small

Tue Sept 16 2014, 10:38PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Patrick wrote ...

i think youve seen and prepared enough, time for fabrication and testing.

I disagree on this occasion. I'd design the bobbin to serve the dual purpose of isolation plus cooling of ferrite.

Core losses are the limiting factor here, see the link posted by Patrick a few posts above

EDIT: Actually in another thread:

Patrick

Thu Sept 18 2014, 07:04AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Sooner or later he's gotta stop the planning, and have a first device. If necessary redesign and rebuild after a failure.

But yes, the core in air handles much less power than in oil, due to heating.

And in my thread, you see why I went for planar, instead of traditional shapes.

Thomas W

Thu Sept 18 2014, 08:00AM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

Patrick wrote ...

Sooner or later he's gotta stop the planning, and have a first device. If necessary redesign and rebuild after a failure.

But yes, the core in air handles much less power than in oil, due to heating.

And in my thread, you see why I went for planar, instead of traditional shapes.

Hmm, yes, i think i shall move on and make it, my main issue is i need to actually make the coilforms, im just thinking about how to go about that (due to lack of tools at college, yet they have the machines)

The good thing about this core is its not square. its 28mm x 20mm, that does add a bit more surface area :)

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