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Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
I was contacted by a 4hv member wanting a supply good for about 20kv and 500w of power. So I built him this beast
It is based off of the standard mazzilli driver (gate resistors upped to 900ohms to prevent unwanted oscillations that seem to be present in very low inductance designs) that feeds a home wound flyback transformer that was made exactly like my previous thread and (second post) that feeds a voltage doubler made out of a 5nf 'plastic' oil/film cap (you know the red glass encased ones) and a string of about 40 uf4007 diodes to form a voltage doubler like is found in a microwave oven. I also added a little smps out of a power brick for an external dvd-burner to run the gate drive, and stuffed it all in an ATX power supply case. To get the hv out I made a custom connector that was basically a banana jack surrounded by a piece of 1/2" PVC pipe, that is plenty long to keep the arcs away from fingers and the like. I enlarged the fan hole in the supply and added a piece of smokey polycarbonate (painted black on the back) to make everything look nice and pretty.
The flyback driver (built using one of my PCBs that are for sale it anyone needs them) and the beginnings of the flyback transformer
Overall view of the guts (I used insulators made out of 1/8" poly to keep sparks from forming where they shouldn't) and the finished supply
Output without flash and with a flash (that is a hot arc!) the wires on that jacobs ladder are just over 6" long as measured from the point where the arc initiates to the tip.
I am working on a video, and a more detailed build description. But its midnight and I have my last day of work for the summer tomorrow...
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
He is planning mostly to draw arcs off of of (for production of NOx among other things_, which will work best with this type of supply. And it runs off of 0-50v @ 15a (at full power it can do 750w) fed into the banana jaks on the back. I am still working on a main powered supply, which will be really sweet if I ever get it working (no external power supply needed).
BTW, it came out at 49.7oz, so its a tad bit lighter than a resonant mot supply
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
The primary (6+6 turns wound out of some roughly 14awg litz wire I extracted out of a slr cap charger), secondary (34awg wire, about 750 turns in 8 layers), and core (about .2in^2 crossectional area) do not heat more than a few degrees than ambient. I have a small (probably about 5-10 mill) gap in the flyback, and am using a powdered iron dc choke (wound with about 80 turns of 16awg magnet wire, it heats about 10-20degrees above ambient in jacobs laddar duty)
Your core is probably saturating. I found this core is good for about 25v/turn at 25khz (which is where it is running in those pictures), but that was right on the edge. To find that I put a ferrite donut (one of the goldmine cores) on one of the primary leads, wound a 10 turn sense winding, put it into a 1r/10w low film resistor soldered to a heatsink, and noted when the primary current shifted from a sine wave to a triangle wave, and backed things off a few volts. When running in saturation the core did heat appreciably.
What does get hot is the bottom of the case. I am not sure if it is heat from the heatsinks on the tranformers (extended runs at >500w gets them to about 130f) or if I made a induction heater, but it will often be the hottest part of the supply
One thing I will point out is that the mazzilli drive does not like capacitor charging in any way shape or form. If works fine with doubler arrangements, etc, but trying to charge a large capacitor throws off the resonance somehow and just causes all sorts of problems.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
I've charged big capacitors fine with a Mazzilli. I used a full-wave doubler with grossly undersized capacitors to feed the main cap. The small capacitors act as a ballast to limit the charging current and stop it from messing with the resonance too badly.
Registered Member #1232
Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881
> I am not sure if it is heat from the heatsinks on the tranformers... or if I made a induction heater...
If there is a gap in the ferrite core and it is run at high flux density, then it is possible that fringing flux from the core will heat surrounding metal. Copper windings in "high-power" flyback transformers are often kept away from the immediate vicinity of the air gap to prevent them overheating due to fringing flux.
20'c temperature rise for the iron powder core sounds reasonable, but if it gets too hot it could start to deteriorate with thermal ageing. Something to keep in mind if the supply will operate continuously in a high ambient temperature environment.
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20kv 500w SMPS Supply
