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Registered Member #95
Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308
That's just due to the limitations of the core, and there's nothing you can do about it other than lower the drive frequency. Running high flux densities (too few primary turns) will heat up the core too. Not bad getting 15kV from a single layer transformer like that! If you're using your bridge then tuning for mains won't be an issue. Just increase the number of primary turns by the same factor that the voltage increases. The leakage inductance, which is like an internal ballast, should increase at the same rate thus preventing failure. Of course throwing in a little air core inductor for good measure wouldn't be a bad idea.
Registered Member #1132
Joined: Mon Nov 19 2007, 06:15PM
Location: Slovenia
Posts: 84
An i toght i was simply putting too much in to the core to make it heat so much.Too bad i don't have any bigger cores around here.
Well im being careful cause i already blew bridges on mains and i don't want to do it again.
I hope the transformer keeps working this well, since its nice not to use oil.I guess im quite happy with 15kV so the insulation is not a problem anymore. Now i just need to crank the current up. I plan to do it by increasing the primary turns and the input voltage.
Also its fun to make a shorted turn on it with a pice of wire, good induction heating.As for induction heating i did try a 10 thurn coil insted of the transformer and it made a big nail turn red hot in a few seconds.( The last time i tryed induction heating the pin of the capacitor turned in to a lightbulb and melted, using lots of smaller caps in parallel solved this)
Registered Member #1829
Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74
BWAH HAHA
Ha... ha?
Well it's a start I guess. scope + HV probe says it's about 1.5 KV or so.
Pri. is two coils of 8 turns each 22 AWG. Sec. is 90 turns of 30 AWG. Again driven with a sawtooth generator powered 3055. It still gets hot but not as much as before. Supply voltage was about 8-10 volts. Frequency was about 108 KHz The output current is enough to stick the ends of the 30 AWG wires together if they accidentally touch. I wonder how much more power I'll get with the Mazilli driver. I hate waiting for parts in the mail.
Registered Member #1829
Joined: Sun Nov 30 2008, 01:06AM
Location: Raleigh N.C.
Posts: 74
I started with a couple wraps of kraft paper. Then layered kraft and polyethylene so there's about 2.5-3 mm between the core and windings. Then it's just 30 AWG magnet wire covered in masking tape. For my final design I think I'll replace the PE with PP and vacuum soak the former in varnish and cut notches in it so it'll be nice and secure on the core.
Registered Member #1132
Joined: Mon Nov 19 2007, 06:15PM
Location: Slovenia
Posts: 84
A little update from me. I increased the supply to 150V and more current available. It sure improved things by a lot.The arcs seam to start at 3cm now so im guessing thats 30kV, but they sure are hot as hell. Also the transformer still seams to be handling it happily.
Although the overcurrent protection is not very happy about it and keeps shutting down the inverter.It may be that my protection is too sensitive.
Registered Member #2008
Joined: Tue Mar 03 2009, 05:11AM
Location: USA, Frederick, MD
Posts: 118
Berni wrote ...
When i was looking at Steve's page and saw his HV power supply.I toght i might try a smaller version of it with a flyback ferrite core i had laying around.
So i sawed some small plastic pipe to size and wound some relatively thin wire on it, thrown it on the core and some litz wire for the primary. Add in some IGBTs and the testing started. First thing i figured out is that the series capacitor needs to be beefed up a bit since it got hot.It was noting special at 50V it needed like 3-5mm to start a arc and it could be drawn to about 2cm (It was nicely fat and hot tho) So i decided i replace the 50V transformer with a 1:1 transformer making it 300V input.
After the power boost the arcs became big flaming MOT like arcs.Then the dangeling output wire of the secundry comes close to the winding arcing over and melting the wire in a flash, but i got it working again by unwinding the coil until the burned part since its arced over near the end of it.
I want to add some protection to my half bridge since i don't want to blow it too esaly.Can anyone tell me how effective is a current transformer on the output and some kind of comparator circuitry that makes it shut down.
This transformer is just something i quickly sloped together to try the concept( I know its made like crap) The secondary is varnished tho.
So from what i saw til now it might be a good idea to continue trying this. Anyone has any advice?
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
I made a high voltage transformer, before this thread but i never bothered taking a video as i never thought there was any interest.
It was made for fun in about 30 minutes or less. It uses one leg of a flyback core for the secondary and one for the primary. I did no calculations. I used about 6 or so layers of around 28 gauge, which used about half of the spool (a salvaged microwave oven fan). The voltage is around 6-8kvac, but i will just go with 6kv ;).
I use a beefy ZVS driver to drive it, with .68uf capacitor, and 10 center tapped turns. The arcs are much brighter than a MOT, and i push about 700 watts through it while arcing.
I have done jacobs ladder, and made a small tesla coil with it. The sparks where about 6 inches with a too small tank cap, and WAY too slow diodes that are a bit slower than 2 times slower than the 1n4007 . I was basically getting AC out at that point.
The arcs are about 6 or more inches long, and they are thicker than my little finger (which is really saying something, considering i have a severe case of sausage fingers ) I melt nails, and even the screwdriver bit i was using. I shall post an arc and jacobs ladder montage when i get my movie maker software working..
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Homemade HV transformer.
. I was basically getting AC out at that point.
) I melt nails, and even the screwdriver bit i was using. I shall post an arc and jacobs ladder montage when i get my movie maker software working.. 