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Just discovered this site. I have been winding HV AC transformers for over a year and wish to purchase two of these when next batch becomes available. Let me know when you want payment. (these are going to US). I am retired EE and if you can provide me with core demensions and material I can give you back max primary voltage vs turns before sat and some air gap data. Your pic of core leads me to belive I have run mumbers on it if it is ASM7070 material. The reason I did not choose to use it is that was marginal for the power I needed so I have been usinbg larger cores. I have never had the patience to get much above 1000 turns, ( 7 ours work), so 3000 turns looks enticing. I will just have air gap it to keep it out of sat.
Registered Member #8817
Joined: Mon Dec 17 2012, 05:16AM
Location: Australia
Posts: 110
LouisHV wrote ...
Fiddy,
I'm in for airmail :)
I'll send you a PM for exchange of required details.
Thanks! Louis.
Too easy, I put you on the list.
Green Hornet wrote ...
Just discovered this site. I have been winding HV AC transformers for over a year and wish to purchase two of these when next batch becomes available. Let me know when you want payment. (these are going to US). I am retired EE and if you can provide me with core demensions and material I can give you back max primary voltage vs turns before sat and some air gap data. Your pic of core leads me to belive I have run mumbers on it if it is ASM7070 material. The reason I did not choose to use it is that was marginal for the power I needed so I have been usinbg larger cores. I have never had the patience to get much above 1000 turns, ( 7 ours work), so 3000 turns looks enticing. I will just have air gap it to keep it out of sat.
Put you down for 2.
I dont know the ferite material but the core dimensions are in the attached photo.
Registered Member #55086
Joined: Sun May 24 2015, 03:18PM
Location: Ukraine, Kyiv
Posts: 7
Experimented with DIY flybacks a few years ago, just bought a pair of П-type ferrites and made my own windings. Results are below.
It outputs only about 3 kV, but because of huge currents the output is almost MOT-like. Also, no need in oil insulation. The circuit is simple ZVS, but powered with 75V.
This is a industry standasrd core size and I strongly suspect the materisal is ASTMP7070 which is the normasl for potted flybacks which would be normal for your supplier. The industry standard specs for this 7070 material can be found at So here is a sample calculation using this xfrmr with the standard Mazilli ZVS with a .68uf tank capacitor. The AL of this core is 2.3uh per Turn square. Choosing a primary of 10 Turns results in a primary inductance of 230uh and in the resonant Mazila Tank of .68uf results in a operating frequency of 13khz. BUT this is at 25 deg C. As core losses cause core temp to rise your AL will drop as will your max B sat. THis is why you want to run at 50kHz or less.
So using your cores cross section area, 10 turns, freq of 13khz, and a 50% margined Bsat of .25 Tesla x the 4.44 constant, yields a max VRMS across the primary of 461 VRMS. So an air gap should not be necessary to keep the core out of saturation with a DC supply up to 60V DC (remember this is a tank with a choke so VRMS accross ther tank will be approx 3- 4x the supply). If the core starts to heat up so it is "very warm" (50 deg c) to the touch,core losses will cause inductance will fall, frequency will rise, and Bsat will have fallen, which is why I used 50% of the mx Bsat of 7070 material in the formula.
The nnumbers say this should be a fine Xfrmer for use with a ZVS. You will want to use more than a 50-60 volt supply becasue the IRF260N FETs are rated at 200V and that is PK-Pk which is 1.4 x RMS which 3-4X your supply. I have made measurements with a scope accross the Mazilli tank and with a 30v supply the Pk-Pk at 50Khz is 180V, which results in each FET seeing 90V, or 50% of its max rating. DO NOT CONFUSE Pk-PK VOLTAGES WITH RMS and be aware of your instruments limitaions in measuring AC voltages over 20Khz.
Fiddy, Looks like you have 25 Xfrms for next buy. When would you like $$$ frtom me? I am happy to pay early to helkp fund supplier if theuy want upfront
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Modern AC Flyback Transformers
