I just want to let you guys know you've helped out a lot with the
various suggestions, even though I'm not in radio, so I'm very grateful.
OK, say I was to start from my requirements and fitting a transformer to
the application, instead of the other way around. Now, my load is DC
plasma modulated at audio frequencies (above 500 Hz). I think I
mentioned this on this list under another topic.
Here's a simulation of my current power supply with the expected load
(represented by the current sink): http://www.cs.ubc.ca/~trifonov/hv.png
The transformer is just the two coupled inductors, as simulation is too
slow with more complex transformer models. I've simulated the lowest
frequency I expect to draw, 500 Hz. Total (for both channels) is 380 mA
sine peak (not peak to peak as LTSpice uses peak), over a 400 mA DC
offset. I need at least 2 kV after the filter, with a bit of leeway for
inserting a regulator. The rectifiers I have drop about 15 V each. The
choke in the diagram is 4 H (estimated by calculation, as I wound it by
hand on a large core).
So my first question is about something I don't understand at all. When
I ask the simulator for the RMS through the current source, it says
478.43 mA. However, when I ask for the RMS through the secondary
(represented by the second inductor), I get 783.31 mA. Sorry if this is
a stupid question, but why is that? Should I assume that the second
number is the actual rating I should be looking for in a transformer, or
is LTSPice giving me erroneous numbers here?
I'm waiting for a 2 kW industrial control transformer to come in the
mail. If the secondary 120 V windings are not on top of the 600 V
primary, I could rip off the 600 V winding, rewind for 2 kV and drive it
backwards. But before I do this, I'm wondering if the smaller MOT I'm
using right now is big enough to be rewound in the above application.
When I multiplied the secondary current waveform by the voltage across
it, LTSpice says an average of 939.97 W, so I figure the MOT core should
handle it. But again, I don't know if I can trust those numbers to be
even approximately close.
The MOT is 16 lbs. Core (center beam) crossection is 41x54 mm^2, or
3.43 in^2. Using 12000 G in the formula, I'm calculating 189 primary
turns. Currently primary is 14 AWG and secondary is 18 AWG, with space
left from the removed shunts. Assuming the RMS current LTSpice is
giving me on the primary, 13 A, is correct, then I should be using AWG 9
which would fill up the whole MOT core space...what the... I hope I'm
mistaken in these calculations, or the 13 A is wrong (though it probably
isn't much smaller given MOTs have bad power factors).
Will Matney wrote:
> Borislav,
>
> 19 kilogauss is too high for M-6 or Hipersil material for about 28 or 29
> gauge. It's max is about 17 kg., and it's recommended to be ran at 15 kg.
> because after 15 kg., the magnetizing current raises sharply and doesn't gain
> that much for it. After about 18-19 kg, it goes into saturation where the
> permeability drops off sharply, you get a distorted waveform, and it starts
> to act like a short. Then it will finally burn out. Also, did you see the
> correction for the formula from using 4.44 and use 1.11? I messed up there
> when I was in a hurry and didn't proof read it. If your using the 1.11, it's
> correct.
>
> I'm afraid there's no other fix but to rewind it to make it work correctly.
> Even potting it will still leave it saturating, plus running hot. Eventually
> under load, it will finally burn out. If this will be ran ICAS as most
> amateur amps really are, you can get by with using about 700 to 800 circular
> mils per ampere for sizing the wire. If you want CCS, then it needs to be ran
> over 1000. The problem with 1000 is you may not be able to fit all the wire
> on the core. If you have the availability of extra wire, I'd cut the whole
> coil off and start from scratch making a new bobbin too. For layer insulation
> use 7-10 mil paper, and between the different windings use 15-20 mil. Use
> about 40 mil for the bobbin. There's several places on ebay carrying fish and
> kraft paper pretty cheap. That's the only solution and the correct cure I
> know. Maybe others on here may know of something else to do with it.
>
> Best,
>
> Will
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