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Struggling with my coil having very low impedance on the primary side...

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Wolfram

Tue Dec 27 2011, 09:24PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

teravolt wrote ...

if you had a poly cap in parallel with your primary it would reduce the impedance that your bridge sees at resonance and increase your circulating current in the primary. have you built a ZVS before? You could put a group of ferrite U cores around your coil to concentrate your magnetic field. another option would to replace your coil with a custom fly-back and put it in the oil. If you had a big fly-back you could use your bridge or ZVS with a resonant primary.

Don't do this! A capacitor in parallel with the output of a voltage fed bridge is a recipe for disaster.

teravolt

Wed Dec 28 2011, 02:36AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

Hi Anders M. if you look at the picture closely he already has some amount of capacitance on the output as described on the first part of the thread. I'm saying put some capacitance in parallel with the primary to be resonant at the secondary frequency.
With a poly type cap in parallel with the primary the circulating will be higher and the impedance if the parallel primary tank will be higher. It was my understanding that his circuit draws to much from his bridge. With a parallel primary tank the the bridge won't have to conduct all 180 deg on each cycle. The ZVS works similarly in that if its done right the primary has a high circulating current at the resonant frequency of the fly back secondary. Any how thats my idea, obviously some amount if tinkering will have to be done to any experimental circuit to make it work right.

Electra

Wed Dec 28 2011, 02:10PM

Registered Member #816 Joined: Sun Jun 03 2007, 07:29PM
Location:
Posts: 156

I think Anders.M has a point if the drive is a square wave, as it would be almost a short circuit to all the hf harmonics.

But making the primary resonant like teravolt says probably would make it more efficient, though the ZVS in the normal centre tap arrangement has an inductor feeding the transformer.

So perhaps itâ€™s how it driven needs a little thought, perhaps a filter/matching network or a current fed type bridge. To keep it on frequency ultimately it would need feedback, or to be of the self oscillating power oscillator type.

Wolfram

Wed Dec 28 2011, 04:15PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

teravolt wrote ...

Hi Anders M. if you look at the picture closely he already has some amount of capacitance on the output as described on the first part of the thread. I'm saying put some capacitance in parallel with the primary to be resonant at the secondary frequency.
With a poly type cap in parallel with the primary the circulating will be higher and the impedance if the parallel primary tank will be higher. It was my understanding that his circuit draws to much from his bridge. With a parallel primary tank the the bridge won't have to conduct all 180 deg on each cycle. The ZVS works similarly in that if its done right the primary has a high circulating current at the resonant frequency of the fly back secondary. Any how thats my idea, obviously some amount if tinkering will have to be done to any experimental circuit to make it work right.

I don't see any capacitance on the output of the bridge in the first post. If there is a cap across the primary in your design, please remove it.

Yes, there is a cap across the primary in the standard Mazzilli ZVS driver. This is just fine because the Mazzilli driver is current-fed. This project is, as far as I know, a voltage fed bridge, and capacitance across its output will lead to enormous current spikes during switching.

teravolt

Wed Dec 28 2011, 05:56PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

Hi si2030, how come you want to use a 100kv resonant transformer VS a voltage multiplier circuit thats what I used and it wourked fine for a cuple of my marxes?

Electra

Wed Dec 28 2011, 06:52PM

Registered Member #816 Joined: Sun Jun 03 2007, 07:29PM
Location:
Posts: 156

With the number of stages in that multiplier looks like he was aiming for the Megavolt range.
Donâ€™t know how practical itâ€™s going to be, but interesting to wait to find out.

(edit thought of this)

Does anybody agree with this? That he should make the coil form larger like a short tesla coil say 500Lx100d mm the secondary might fit as a single layer.

And make more primaries for example say 5 shorter coils 100mm long stacked along its length end to end but with greater turns say 50. Then connect these all in parallel, yes this will lower the inductance again but as each coil has more turns not as much.
Think of it is as number of transformers connected with the secondaries in series

Possibly will still need a lot of amps of reactive current flowing through it in order to generate any significant voltage across it, as any air cored coil at low frequency will have a low impedance with low turns, but following on with the idea of making primary resonant like a tesla coil. Then decide upon the best topology to drive it.

Adding the multiplier might throw it all off though.

(Edit 2)

Just realised I now messed up the turns ratio, so youâ€™d need an even larger voltage across the primary which wouldnâ€™t work as itâ€™d need too much current same as previous situation.
Fail by the laws of physics again.

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