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Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
jpsmith123 wrote ...
. Ash, I think getting 50 kv off the secondary is going to be very difficult. It may be possible, but it will be a real challenge, IMO. Can I ask why so high? Is it intended to feed a CW multiplier?
That's just the target I'm aiming for. I was originally contemplating a supply that would power a fusor at 50kV and 50mA, but I'm also planning on having interchangable secondaries, etc, like some of your ideas seem to involve.
Others have said 50kV is reasonable, but 100kV is probably too high. I plan on using multipliers as well (my dream would be to reach 650kV but you appreciate the obstacles involved probably better than I do (there has been talk on other sites about putting multipliers inside vacuum chambers)).
I understood that 50kV was quite 'do-able', but if I really need >150 turn primary to push 2.5kW through one of those cores (I have two sets, which should push 2.5kW each @25kHz, according to EPCOS) I'm going to need ~25,000 windings on the secondary. I'm hoping I've made a mistake somewhere.
BTW, Are you familiar with the original Cockcroft-Walton experiment of 1932, and why they had to invent the multiplier?
(Other threads of mine on here are related to RF/magnetron ion sources/plasma generation for feeding particle accelerators,etc)
My next project is the rectifier for feeding the rectified 240V mains, which I will also use for DC welding (the rectifier, not 240V mains), I'm still doing the research for the HV transformer, .
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
jpsmith123 wrote ...
. Ash, I think getting 50 kv off the secondary is going to be very difficult. It may be possible, but it will be a real challenge, IMO. Can I ask why so high? Is it intended to feed a CW multiplier?
That's just the target I'm aiming for. I was originally contemplating a supply that would power a fusor at 50kV and 50mA, but I'm also planning on having interchangable secondaries, etc, like some of your ideas seem to involve.
Others have said 50kV is reasonable, but 100kV is probably too high. I plan on using multipliers as well (my dream would be to reach 650kV but you appreciate the obstacles involved probably better than I do (there has been talk on other sites about putting multipliers inside vacuum chambers)).
I understood that 50kV was quite 'do-able', but if I really need >150 turn primary to push 2.5kW through one of those cores (I have two sets, which should push 2.5kW each @25kHz, according to EPCOS) I'm going to need ~25,000 windings on the secondary. I'm hoping I've made a mistake somewhere.
You might want to think about a scaled-down version of this proven push-pull C&W oscillator-driver, which outputs 12kV @ 120kHz, 50kW.
BW1121* is a water-cooled industrial triode with a 6.6V/230A filament - so with the design as it is, you have 460A of filament current to find before you can move your first pawn! (As well as a second mortgage to buy the valves in the first place! They are costly enough to get re-manufactured.)
But you could scale it down to your modest power requirements with the circuit arrangement just as it is.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ash Small wrote ...
Any help would be appreciated. (Should this be in a new thread?)
Yes, lets not highajck JP's thread, start a new one Ash, and ill help you with the usuall math, physics and common screw ups, (im still learning though on the secondary power and relational math for H value, Klugesmith has been helpful too).
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Proud Mary wrote ...
. You might want to think about a scaled-down version of this proven push-pull C&W oscillator-driver, which outputs 12kV @ 120kHz, 50kW.
BW1121* is a water-cooled industrial triode with a 6.6V/230A filament - so with the design as it is, you have 460A of filament current to find before you can move your first pawn! (As well as a second mortgage to buy the valves in the first place! They are costly enough to get re-manufactured.)
But you could scale it down to your modest power requirements with the circuit arrangement just as it is.
Well, the 460 amp filament current could probably be obtained from either rewound welding transformers or even rewound MOT's. The valves themselves I could construct myself (depending on the coatings required on the cathode, etc) They possibly wouldn't even need to be under a permanent vacuum if I pump them down before each use, but a scaled down version probably wouldn't require this.
What advantage would a scaled down version, which, to me, looks pretty much like a 'run of the mill' centre-tapped push-pull transformer with triodes, have over a full bridge?
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Well thanks for the thought but that's ok Patrick; it's all related enough that I don't think it dilutes the thread very much, in fact maybe it's more infomative/useful to expand it a little bit.
Patrick wrote ...
Ash Small wrote ...
Any help would be appreciated. (Should this be in a new thread?)
Yes, lets not highajck JP's thread, start a new one Ash, and ill help you with the usuall math, physics and common screw ups, (im still learning though on the secondary power and relational math for H value, Klugesmith has been helpful too).
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Ash Small wrote ...
Proud Mary wrote ...
. You might want to think about a scaled-down version of this proven push-pull C&W oscillator-driver, which outputs 12kV @ 120kHz, 50kW.
BW1121* is a water-cooled industrial triode with a 6.6V/230A filament - so with the design as it is, you have 460A of filament current to find before you can move your first pawn! (As well as a second mortgage to buy the valves in the first place! They are costly enough to get re-manufactured.)
But you could scale it down to your modest power requirements with the circuit arrangement just as it is.
Well, the 460 amp filament current could probably be obtained from either rewound welding transformers or even rewound MOT's. The valves themselves I could construct myself (depending on the coatings required on the cathode, etc) They possibly wouldn't even need to be under a permanent vacuum if I pump them down before each use, but a scaled down version probably wouldn't require this.
What advantage would a scaled down version, which, to me, looks pretty much like a 'run of the mill' centre-tapped push-pull transformer with triodes, have over a full bridge?
Oh, that's the whole point of showing you the circuit, Ash - to show that it could hardly be simpler, and calls for neither design innovation nor developmental time.
Re-winding large transformers is outside my frame of reference, but no doubt good results could be obtained by a skilful person with the right equipment. I'd be tempted to use 2V 400 AH industrial lead acid cells if I was to have a go at it, as I can't see the need for powering up the filaments for many minutes at a time, and it doesn't need much in the way of initiative or experiment to implement. But it's not something I have the time, space, money or interest to get involved with, intriguing though it most certainly is.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
I should rephrase what I said: I think it's possible, but with the constraints you've mentioned previously (using the N27 core, and no potting, IIRC), it would be a hardship.
Having two sets of cores, to make two transformers, would seem to offer some possibilities.
I think it could be done using my "bud box idea", with teflon wire, using say two 500 to 600 turn coils (one on each leg) and potting it with RTV. I think using two "tall and skinny" coils in series will give you low capacitance, and the volume of the box will give you room (to keep the field strength reasonable) and the RTV will make it robust and reliable.
Of course with 1000 to 1200 turns or so you'll have to run at somewhere around 50kHz @ 200mT, or something like that, which, if using a "3C90" or "50ALL" core, means 30 to 40 watts of core loss and 100 watts or so with the N27 material (unless I made a mistake).
Ash Small wrote ...
jpsmith123 wrote ...
. Ash, I think getting 50 kv off the secondary is going to be very difficult. It may be possible, but it will be a real challenge, IMO. Can I ask why so high? Is it intended to feed a CW multiplier?
That's just the target I'm aiming for. I was originally contemplating a supply that would power a fusor at 50kV and 50mA, but I'm also planning on having interchangable secondaries, etc, like some of your ideas seem to involve.
Others have said 50kV is reasonable, but 100kV is probably too high. I plan on using multipliers as well (my dream would be to reach 650kV but you appreciate the obstacles involved probably better than I do (there has been talk on other sites about putting multipliers inside vacuum chambers)).
I understood that 50kV was quite 'do-able', but if I really need >150 turn primary to push 2.5kW through one of those cores (I have two sets, which should push 2.5kW each @25kHz, according to EPCOS) I'm going to need ~25,000 windings on the secondary. I'm hoping I've made a mistake somewhere.
BTW, Are you familiar with the original Cockcroft-Walton experiment of 1932, and why they had to invent the multiplier?
(Other threads of mine on here are related to RF/magnetron ion sources/plasma generation for feeding particle accelerators,etc)
My next project is the rectifier for feeding the rectified 240V mains, which I will also use for DC welding (the rectifier, not 240V mains), I'm still doing the research for the HV transformer, .
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Ok, I just potted one coil. I potted a segmented coil with 600+ turns of 28 gauge magnet wire. It's sitting in the vacuum chamber curing right now as I type this.
I went to Harbor Freight and bought a 500 gram scale that was on sale for $11.99. Then I stopped at a dollar store on the way home and bought a cheap plastic measuring cup.
Then I used the scale on the cup to get the approximate amount I needed, then I weighed it, then I added 10% by weight of hardener. (Thankfully, as it turns out, the epoxy is much more manageable after you add the hardener to the resin).
The new scale and the measuring cup were the right tools. And it really helps having the right tools.
Anyway, I then mixed the epoxy for about 5 minutes with a spoon and then poured it into the coil assembly. This is where the first difficulty came in. Even with the pour spout on the measuring cup, it's a sloppy process and it makes a little mess.
In retrospect, I should've designed the coil former a little differently. As it was, I had to fill the coil assembly right to the very brim with epoxy, to make sure I had enough insulation between the end of the wire and the end of the housing. The problem is that when you pump it down, it foams up a little bit and wants to overflow the housing. I was able to pump it down a little bit, but not as thoroughly as I wanted to.
Another thing I thought of after the fact was that I should've filled it maybe 2/3 of the way, then pumped it down, then filled it the rest of the way and pumped it down again.
Luckily however, I don't think this particular coil assembly really needed to be vacuum encapsulated, because at most it'll be maybe 14 kv spread out over 2 inches.
I'll see what it's like tomorrow morning and post a picture if possible.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
Yep that's a pencil line. That outer case is made from a slightly turned down 2.5" CPVC pipe. I was going to use that piece in a different way - I was going to bring the HV output leads out radially - thus the pencil line. But then I decided to just machine another piece to do that, because I decided that the piece you see in the picture was too thin.
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Grooved Bobbins For Segmented Windings
