More induction heating

[romy]

Yes I connect first the secondary and later the primary to the 220 AC.  Maybe that was the problem

Unless there was contact-bounce in the switch, turn-on shouldn't be an issue.  Only turn-off on the 220VAC primary side is problematic.  Whatever the cause, sounds like switching supply is safer.  (Or enough filter capacitance after rectifier to absorb any transient energy, say >=5000uF.)  So far my AC line powered ZVS oscillator hasn't died.  However, it runs directly on rectified 120VAC.  No transformer except utility transformer feeding my neighborhood.

do you have this documented somewhere? i found this, but there is no follow up:

https://highvoltageforum.net/index.php?topic=1658.0

[davekni]

do you have this documented somewhere? i found this, but there is no follow up:

https://highvoltageforum.net/index.php?topic=1658.0

No, that is still a project idea/design on my list for building some day   Only simulations completed.  No actual construction.  Was based on a smaller 1kW version I have built, used to feed an HV transformer for Jacob's ladder arcs rather than induction heating:
https://highvoltageforum.net/index.php?topic=831.msg5491#msg5491
Schematic is below pictures in that first post.  Should work for induction heating too.  Induction heating is an easier load to drive compared to arcs since arcs can start and stop more suddenly.

So with the piece of ferrite you can concentrate the induction effect. I have no idea.

I used ferrite cores for a low-power (~60W) induction heating fixture at work.  Haven't seen ferrites used for high power applications.  Perhaps because brute force power is easier and/or it would be too difficult to keep ferrites cool enough.  For your getter flashing project, seems that ferrites might be useful.  Depends on geometry of your getter and how close external ferrites could get, ideally from both sides of getter.

[romy]

i was actually referring to this: "So far my AC line powered ZVS oscillator hasn't died." i couldnt find anything on that.

[Alberto]

Thank you for ypur answers.

romy Yes, I gave the gates with a 19V latptop power supply and the rest of the circuit I used a variable swiching power supply that work great. Later to give the heater its own power supply I tried with a rewound MOT only with bridge rectifier, and one of the mosfet died in 2 seconds.

davekni Thank you. Any idea about how cut ferrite core? It seems very fragile. And if for exame I have to pieces (very flat) and I put togueder, will it work like one piece?

[petespaco]

Any idea about how cut ferrite core?

How would you get a gapped  ferrite core around your titanium getter if the getter is somewhere within a vacuum tube?

[davekni]

davekni Thank you. Any idea about how cut ferrite core? It seems very fragile. And if for exame I have to pieces (very flat) and I put togueder, will it work like one piece?

Perhaps brittle is a better description than fragile.  Ferrites are ceramic.  Reasonable strength but very hard, so not great impact resistance.  Only way I've found for cutting is with a diamond wheel and patience.  I have some diamond wheels for my Dremel tool.  They work well, though slowly.  For this application, constructing a core from multiple pieces is fine.  The tiny gaps due to rough surfaces are small compared to large gap for getter.  I often build large cores from multiple smaller ones.

How would you get a gapped  ferrite core around your titanium getter if the getter is somewhere within a vacuum tube?

I'm picturing a very large ferrite core, something like a U100/57/25-3C90, perhaps with a couple large I-cores attached, or another cut U-core.  Not a small gap, but probably still more efficient than no ferrite to complete magnetic path.

[romy]

how about molding it youself? what would be more appropriate here, iron powder or iron oxide (hämatite)? some aluminum, maybe?

i read that this cirquit will not drive such a concentrator. if a reason was given, i dont remember it. what might be the problem?

→ https://www.ebay.com/itm/164879009641?

[Alberto]

Thank you for all your help!