Borislav,
I done it again, I will have to start proof reading better. I get in a hurry
and hit the send button way to fast. OK, I said;
"Then the primary current is the secondary current plus the losses".
That should have said power and not current or;
Then the primary power is the secondary power plus the losses.
Sorry about that. In other words, wattage in equals wattage out plus the losses.
Best,
Will
>
> Borislav,
>
> The current drawn by the circuit shouldn't be any more than maybe
> 5% higher on the transformer side than what's on the supply side at
> the filter capacitor. Transformers are figured by power needed
> (wattage or volt amperes VA). Then the primary current is the
> secondary current plus the losses. One loss is called watts per
> pound loss and are the iron loss in the performance curves. You add
> the I^2 X R losses for the wire to it to determine the primary
> wattage and current. This is also its efficiency which will
> probably be about 80-85% at a worse case. So the power difference
> will be about 15-20% between the primary and secondary. I wouldn't
> doubt if the maker didn't wind the MOT with mybe 500 circular mils
> per ampere which some appliances have. These run hot especially
> when a shunt is used. In your case though the shunt is gone and the
> core acts normally but 500 cir mils per amp is cutting it close.
> It's according to what the original primary and secondary wire size
> is. Another
> thing that might be screwing you up is just using two inductors
> for a transformer in the simulator. That then wouldn't have any
> iron in it and throw the baby out with the bath water. To roughly
> determine the core area(A), you can use A = 0.16 X sqrt of P (in
> watts) for 60 Hz. For 50 hz it raises by X 1.2 or 0.192 X sqrt of
> P. That would get you in the ballpark of where you need to be.
>
> Best,
>
> Will
>
>
>
> >
> > 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
> > _______________________________________________
> > Amps mailing list
> > Amps@contesting.com
> > http://lists.contesting.com/mailman/listinfo/amps
>
>
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