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Volts per turn question.

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Ash Small

Wed Dec 07 2011, 12:06AM

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

jpsmith123 wrote ...

Well I tried to simulate a SLR type half-bridge using "CircuitMaker 2000", and under certain conditions I seem to be getting waveforms similar to what I see other people getting, but it seems to be rather "touchy" and load dependent and the power throughput isn't very good.

I'm going to try it using pspice and see what happens, as I don't always trust circuitmaker.

I'll be very interested in seeing the results.

Ash Small

Tue Feb 14 2012, 01:18PM

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

I apologise for bumping an old thread, but it just occurred to me that if I 'double up' on the core, ie, have 18cm^2 CSA instead of 9cm^2 CSA, I can double the volts per turn.

Am I correct in assuming that this will simplify things greatly, or will it lead to any other problems, apart from the associated cooling problems?

EDIT:JPSmith posted this in another thread, but I I'll acknowledge it here, as it relates to this thread:

jpsmith123 wrote ...

@Ash Small: As a side note, with regard to the thread you referenced, I've decided that SLR is the way to go (for a ferrite transformer driven multiplier) based on the simulations I did. I plan on using only the leakage inductance inherent in my transformer and a relatively small value but relatively high current rated series capacitor like a CDE 942C type capacitor.

Thanks for the advice, JP. That's pretty much what I was hoping to do. One question, though. I seem to remember reading somewhere that the resonant frequency of these circuits is load dependant. I've seen ways of controling them using active snubbers on the secondary, but they all use IGBTs, which isn't really feasible at 50kV. Is this something I need to be concerned about?

Patrick

Tue Feb 14 2012, 05:01PM

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

Ash Small wrote ...

I apologise for bumping an old thread, but it just occurred to me that if I 'double up' on the core, ie, have 18cm^2 CSA instead of 9cm^2 CSA, I can double the volts per turn.

Am I correct in assuming that this will simplify things greatly, or will it lead to any other problems, apart from the associated cooling problems?

yes, thats why i use planar cores, the cross sectional area is what we HV'ers need!

Ash Small

Tue Feb 14 2012, 07:31PM

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

Patrick wrote ...

yes, thats why i use planar cores, the cross sectional area is what we HV'ers need!

I think I'm starting to get a grip on the whole thing now.

jpsmith123

Fri Feb 17 2012, 10:41PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

wrote ...
I apologise for bumping an old thread, but it just occurred to me that if I 'double up' on the core, ie, have 18cm^2 CSA instead of 9cm^2 CSA, I can double the volts per turn.

Am I correct in assuming that this will simplify things greatly, or will it lead to any other problems, apart from the associated cooling problems?

The more rectangular you make the core, the more empty space you'll have inside your bobbin. If you're considering doubling the core area, you might rather want to quadruple it, as this would be the most efficient use of copper and plastic.

<snip>

wrote ...

I seem to remember reading somewhere that the resonant frequency of these circuits is load dependant. I've seen ways of controling them using active snubbers on the secondary, but they all use IGBTs, which isn't really feasible at 50kV. Is this something I need to be concerned about?

I simulated a "SLR" half-bridge driving a ferrite transformer driving a multiplier (using "CircuitMaker2000"), subject to a widely varying load, and I didn't see any unexpected problems. I wanted to simulate a full bridge but Circuitmaker 2000 wouldn't let me. I may try to do the full bridge again (either that or'I'll be forced to try to use Pspice, which I don't like).

Later on when I get a chance, I'll post the schematic of the circuit I simulated and the results so you can see how it behaves.

Ash Small

Sat Feb 18 2012, 12:01PM

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

jpsmith123 wrote ...

The more rectangular you make the core, the more empty space you'll have inside your bobbin. If you're considering doubling the core area, you might rather want to quadruple it, as this would be the most efficient use of copper and plastic.

If I understand correctly what you are implying here, I'm assuming you're assuming I'll be using a bobbin with circular cross section.

I remember we didcussed in another thread why circular bobbins are best, but I was assuming that in this case, with a rectangular core, I'd be better off using a bobbin with an oval (ovoid?) cross section.

I can see, though, that four cores, with series secondaries on each one, would have some advantages, but if the secondaries were also wound around the same CSA as the primary, I could have a much higher volts to turn ratio, with (presumably) less inductance and capacitance losses?

(I'll try and add some diagrams later, if this will help to explain what I'm trying to get at.)

jpsmith123

Sat Feb 18 2012, 11:47PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
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Posts: 843

Any bobbin with a cross section which is not circular will be a PITA to wind, IMO, as the tension on the wire will not be constant. In any case, I don't know where you'd buy or how you'd construct such a bobbin in the first place.

As far as the core arrangement is concerned, I'm thinking you have two choices: (1) four cores configured as four separate transformers, with primaries connected in parallel, and secondaries connected in series; or (2) four cores configured as one transformer (in a "cross" arrangement), with primary windings in parallel and one secondary winding.

Ash Small

Sun Feb 19 2012, 12:03PM

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

jpsmith123 wrote ...

Any bobbin with a cross section which is not circular will be a PITA to wind, IMO, as the tension on the wire will not be constant. In any case, I don't know where you'd buy or how you'd construct such a bobbin in the first place.

I'm confident I can manufacture any shape bobbin myself. I also have experience in maintaining coil winding machines and I'm sure I can 'rig something up', as long as it winds reasonably slowly. (you just have to maintain sufficient tension on the wire).

I'm just wondering if there are any other reasons for not wanting to use rectangular shaped cores, as the main advantage, as I see it, is the increased volts per turn on both the primary and secondaries?

jpsmith123

Sun Feb 19 2012, 09:57PM

Registered Member #1321 Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843

I think a non-circular bobbin will have some electric field enhancement (compared to a circular cylinder), although that may not be much of an issue depending on your construction.

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