Chris,
I guess there is a little misstyping in the calculation performed from
Clemens on the DJ5IL tool....
he entered 2.5 instead of 25 in the impedance box: the primary
winding after the combiner should work on 25 ohms. If you enter 25 ohm
the flux rise a lot beyond the saturation of the 3 stacked cores and
therefore they have all the rights to warmup!
On the other hand if you apply the Bmax formula given from Andy, the 3
stacked cores have A of 471mm²
and with 2kW of power on 25 ohms the minimum number of turns on the
primary should be 8 not 5.
So one more turn to keep B below 0,1T and you should run more
confortable with N1/N2=9/13
73 de Marco, IK1HSS
----Messaggio originale----
Da: [email protected]
Data: 15-mag-2017 14.42
A: <[email protected]>
Ogg: Re: LF: RE: Combining LF amps revisited
For transformers the core is not terribly critical provided you use a
grade
of ferrite designed for the frequency of interest. And at LF that
means
SMPSU cores
If I see a certain size core being used in a 500W SMPSU then there's a
pretty good chance a core of the same size is going to work OK in an LF
Tx
of the similar rating. No data sheets or trying to work out
temperature
rises.
I just use whatever feels right and apply the V < 4.44F.N.A.B
absolutely
rigorously, keeping B to less than 0.1 usually
As for impedances: well they're just Z1/Z2 = SQRT(N1/N2)
Use V = 4.44.F.N.A.B to give you turns min, then calculate N1 and N2
while
meeting that criteria
Andy G4JNT
On 15 May 2017 at 11:59, Chris Wilson <[email protected]> wrote:
> Hello Clemens,
>
>
> Thanks for the reply, the 3 stacked cores will rise to 70 degrees
C
> plus even with a small computer processor fan blowing through them.
I
> am investigating ways of reducing this, the cores are shown as
77
> material in jay's schematic, but he and I are using the newer
78
> material for the PA output transformer cores. I may try using this
76
> material in the combiner transformer. Someone else suggested
making
> the PA output transformers work at 100 ohms and using
a
> transformer less zero degree hybrid coupler. I'd try Andy's
twin
> primary, one secondary transformer instead of the coupler if i
knew
> what winding ratio and what core to start off with. Thanks again.
>
> > Hi Chris,
>
> > I have a tool by DJ5IL here which predicts around 60°C for the
cores
> > (excluding heat caused by the winding)
> > and ca. 480 Gauss flux density.
>
> > 73
> > Clemens
> > DL4RAJ
>
>
>
> --
> Best regards,
> Chris mailto:[email protected]
>
>
>
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