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Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
So I was playing with this fancy flyback (the white one) when the secondaries started arcing. Upon closer inspection I realized the HV secondary could be removed, so I proceeded to remove it and remove all the windings.
I was left with an empty core, so I figured it'd be neat for this FBT to have a center tapped primary, so I made one.
I then spent a half hour cutting and wrapping freezer paper around it so the secondary would fit in place.
I then hooked it up to a 24V zvs and the arcs were long and hot, about 4.5" long and 15mm wide. Since there are no evil secondaries I think this fbt could be pushed up to even 40kV before bad things happen. One primary side has a 2.3uH inductance while the other has a 1.7uH inductance, yet that didn't seem to have any adverse effects on performance. My biggest concern is that the wire I used for the primary may be a bit too thin, but too late now.
I noticed something interesting. With an external primary the ZVS would tend to go into parasitic oscillations and squeal, but with an internal primary this was not the case. This leads me to believe that the zvs circuit itself is not the problem, but the flybacks that we drive are...
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
I try to use the internal primary windings whenever I can. Adding new windings on the other side of the core increases leakage inductance which is generally undesirable. As you mention, the existing primary windings can sometimes arc when overdriving the thing. Biggest problem I've had is arcing from the secondary to the core. Grounding the core and the inner end of the secondary does help to prevent this.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
James wrote ...
I try to use the internal primary windings whenever I can. Adding new windings on the other side of the core increases leakage inductance which is generally undesirable....
Im not sure what you mean here? I think the leakage is the same for a any same primary any where along the length of the core? What Grenadier maybe seeing is the capacitive effects, which may be better one way or the other.
EDIT: Grenadier, that white one is a beauty, but that gap in the last pic may be abit excessive? maybe? Have you experimentally determined that it needs to be that big?
Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
Patrick wrote ...
EDIT: Grenadier, that white one is a beauty, but that gap in the last pic may be abit excessive? maybe? Have you experimentally determined that it needs to be that big?
I didn't clamp down the core yet, and I forgot to subscribe to this thread.
I plan to combine that FBT with this dual capacitor to make a 60-70 kV or so power supply (voltage doubler). Should be pretty neat when I get around to it, and since the FBT is plastic insulated it should have no problem pushing 35kV.
Edit: Look what I just found
Two Ig3gt HV recitifers. Now I have all I need to make the voltage doubler. (of course the rectifiers will need a lead sheath to block the 30kV xrays)
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Experiments with internal flyback primaries
