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Registered Member #2893
Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242
So my friend and I are thinking of starting a company in the future selling stuff nobody else makes. For some of the stuff we'd need to charge big HV caps (~35kv) from batteries. The only method I can think of doing this would be voltage multipliers, and thus we need AC flybacks (~6kvrms); a steady supply of them. Does anyone even make those things anymore? And if so, are they at a reasonable price (<$20 each). I know glassman uses them in their HV supplies...
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
Why not just use a DC flyback? Modern ones are normally rated to supply 25-32kV DC, so I don't think 35kV would be pushing them too far.
Or if you want to go with a multiplier, I don't think you need as high voltage as you think you need. If you're settling for 35kV, and a 6-stage multiplier is acceptable, then each stage needs to provide 35kV/6, around 6 kilovolts, this means that the peak to peak input voltage needs to be 6kV, which is 3kV peak or just over 2kV RMS. Of course the input voltage needs to be a bit higher than this, to account for the voltage losses, but I still think you could get away with 3kV RMS or so. Finding a 3kV transformer is going to be a lot easier than finding a 6kV RMS one, or maybe winding some yourself is an alternative.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
As an alternative flyback transformer, what about an auto ignition coil - readily available or what? High-rel, and at a reasonable price. They also come in a range of sizes, down to diddy ones for small motorbikes. From browsing the racks at my local auto shop a few years ago looking for a ready-built HV transformer, I noticed that a few were built more like real transformers on a closed ferrite core than the traditional lower primary inductance iron-core oil-filled tube, I didn't buy one of those to investigate.
There are various ways to drive them, from copying the old 12v contact break principle with a transistor (500v withstanding to survive the spike), through 100s of volts capacitor discharge, to resonant H bridge drive at a few 10s of volts at a few kHz (lowest stress, largest step-up, but frequency dependant on the specific model). They'd get to 30kV in one go if your rectifiers could take it, or allow you to get away with a doubler rather than a hexupler (more efficient).
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141
HR Diemen still manufacture and sell lopt, e.g. I have 10 new HR6549 rated 35.5 kV dc which is not exceptionally high.
Since crt TVs/Monitors are going out of manufacture, there will be no reliable source of eht lopt !
In any case commercial 35+ kV lopt are not designed for 12 Vdc etc supplies so you'd have to hand-wind primaries ....... in which case you'd be better off with a lower voltage transformer and multipier as above, I'd expect any of the manufacturers that make/sell smps transformers would be ok.
Registered Member #1408
Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679
I agree. I believe that in general, the move to low voltage, energy conservation items has begun in earnest. At this period there are still monitors available but it's a "self-tear-out" agenda. I had a source for NST's and they dried up since the overwhelming majority are going to solid state supplies commercially. The "handwriting is one the wall" for a substantial tightening of the supplies for HV hobbyists. Look at the price of tubes! Notice how HV passives have become much rarer & extremely expensive.. Realistically, now would be the time to gather what you may need in the future because the availability (& cost) will simply be tightened to a greater point.
What's more many things like CRT monitors are shipped to low-wage countries to be dissembled; if sources exist, they should be sought out. I am very glad I gathered what I did; even though it cost me time and hassle.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
There are alot of good suggestions here, and i have one that nobody ever suggests. Take a DC flyback, and bypass the diodes . It's possible, and then, you have the stuff to take an X-ray to find the diodes.
Registered Member #33
Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971
quicksilver wrote ...
I agree. I believe that in general, the move to low voltage, energy conservation items has begun in earnest. At this period there are still monitors available but it's a "self-tear-out" agenda. I had a source for NST's and they dried up since the overwhelming majority are going to solid state supplies commercially. The "handwriting is one the wall" for a substantial tightening of the supplies for HV hobbyists. Look at the price of tubes! Notice how HV passives have become much rarer & extremely expensive.. Realistically, now would be the time to gather what you may need in the future because the availability (& cost) will simply be tightened to a greater point.
What's more many things like CRT monitors are shipped to low-wage countries to be dissembled; if sources exist, they should be sought out. I am very glad I gathered what I did; even though it cost me time and hassle.
I don't really agree with you on these points.
Flybacks are going to be available for a long time, billons have been made of them. Right now there is a buy-it-now auction on eBay where I can buy modern DC flybacks for 5 dollars a piece, or put in a best offer, and the seller has listed over two thousand of them. Flybacks can also be bought from Electronics Goldmine for 4 dollars each, and I don't really see the world stock running out any time in the near future.
Also, electronic components have never been as cheap as they are now, and specifications are improving constantly. On eBay, I can find HV diodes and capacitors for quite cheap, how much did HV diodes and caps cost 20 years ago? How about 40 years ago, compared to the average income then? And they were also significantly slower than the sub-100ns Trr diodes of today. Improvements in semiconductor technology have made amazingly powerful MOSFETs and IGBTs available to the hobbyist for pocket change, and opened up a lot of possibilities.
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
If you want 35kV easily, pick up a flyback intended for a CRT projection TV. These can be had for free if you're willing to haul away the whole TV and save someone paying to dispose of the beast. You also get some cool optics in the deal including a gigantic Fresnel lens that will burn aluminum cans and crack concrete with focused sunlight. I have one that effortlessly produces 50kV and I've measured over 80kV out of it before it started arcing all over the place. Needs more silicone or an oil bath to be pushed harder.
MAT Electronics has loads of replacement flybacks, mostly under $20 each. The PTV types will usually have an anode wire with a special HV connector meant to attach to a splitter block rather than the "suction cup" type anode connector used on direct view sets.
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Steady supply of AC flybacks
. It's possible, and then, you have the stuff to take an X-ray to find the diodes.