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Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
Patrick wrote ...
i worry about claims of 120 watts and above based on some few mA at the short circuit voltage. I really wonder if the "real" voltage sags more than 10kv. I suppose im the one in a position to confirm or reject my suspicions.
I have the high voltage probe. a similar flyback, and would just need a load resistor and mA meter that wouldnt be killed easily.
Indeed, accidently used Watts instead of apparent power in the last sentence. I was looking at it from a perspective similar to an NST: a 15kV 60mA unit will draw ~900VA on the primary side with the secondary shorted, but the secondary certainly isn't dissipating 900W of real power. W vs VA vs VAR can get very annoying, especially if someone changes units mid-paragraph without reason, sorry :)
Registered Member #580
Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410
GrantX wrote ...
These transformers should easily handle 120W at 10kV for hours, and Kizmo stuffed several kilowatts into his. What circuit do you intend to use as a driver? Do you have any specific frequency range in mind?
mostly single mosfet drive (20Khz) but i do have a zvs board too (but i dont like it, its pretty hopeless for high voltage output with 12v input, mostly only good for high current output)
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
Avi wrote ...
GrantX wrote ...
These transformers should easily handle 120W at 10kV for hours, and Kizmo stuffed several kilowatts into his. What circuit do you intend to use as a driver? Do you have any specific frequency range in mind?
mostly single mosfet drive (20Khz) but i do have a zvs board too (but i dont like it, its pretty hopeless for high voltage output with 12v input, mostly only good for high current output)
Well, the last batch of customers seemed pleased with their transformers (hence why I'm buying some) and I think I saw a couple of videos of them driven in flyback mode. It would be a challenge to overheat the secondary with a 20kHz single-switch driver, but you would have to make sure the voltage spikes don't exceed ~20kV or so. A fixed safety gap is the easiest solution. The insulation between the core and secondary, as well as the HV leads, appears to be the limiting factor. I'm wondering if oil immersion could be used to increase the safe maximum voltage up towards 35-40kV.
Registered Member #54608
Joined: Mon Mar 09 2015, 10:15AM
Location:
Posts: 3
I've done somethink like that but I think using FBT coil is bad idea. From one hand you have a coil with no work :) but on the other hand the FBT coil is very pure... low current, half wave rectifier and you must use low voltage at primary or many many turns on primary.
I would like to supply any projects from 230V stright from wall :) so I've made somethink like that:
1. Put of a core from FBT
2. Wire 50 turns at 8 sections on some pipe
3. make a input and output pin from screws
4. Sink in epidian
This transformer is driving by full bridge or half bridge and have very good parameters. I use this with voltage multiplier to have 80kV 10mA with no problems like overheating or breakdown voltage.
I am the person Erlend mentioned before,and we are the manufactures of AC,DC,HV transformers,if you are interesting in bulding,we can discuss together
The only criticism I have of Fiddy's flybacks is that there is not much room to fit a primary UNDER the secondary. There is some room there and I'll see if I can fit a foil primary in there.
I think there is a market for AC flybacks with sufficient room for the primary UNDER the secondary. I'd buy some myself if they were available.
This SHOULD improve the characteristics of these flybacks considerably.
(Maybe there is sufficient insulation in Fiddy's flybacks to open up the hole in the secondary? Maybe ream it out a bit, but I've not tried this yet. Has anyone sawn one of Fiddy's secondaries in half yet?)
How baout built an AC 5-6KV 300W HV transformer? This is some pictures of our company manufacturing details
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
lets not get to far off fiddy's topic, as Ash said, a foil primary may be the way to go. Al or Cu with a ultrathin plastic might get closer to the gap, but that raises local heating concerns with flux lines terminating on the nearest current path, not the whole width of the foil conductor. that gap can cuase this and other problems.
For those who were worried about >100W extended runs:
I used mine to power a soft-failure HeNe Brewster tube that I repurposed as a decorative lamp. I ran it in parallel-tank-ZVS with I think about 5 turns at 14V 20A input. Tank measured something like 34Vpk @ ~270Apk circulating current. It ran for more than ten days continuous before the frit seals on the HeNe failed and the tube ruptured. Flyback and driver were unharmed.
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Modern AC Flyback Transformers
