Andy.. you are almost better than online help desks :-D
yes the guard circuit is on place but no current is flowing toward the
PA, testing disconnetting it needs just to warm up the iron ;-)
the PS should
provide enough juice for 1200W input and the IRF460A are rated for 20A
@ 25°C (13A @ 100°C) so.. I admit it would like to give a try ;-)
I don't guess the core is saturating specially at this power level
where rms is only 22V, the core is 50mm OD and has 195,7 mm²Ae: if I am
not totally wrong B should be < 0,03T @50V with 7 turns on the primary
Will tru to disconnect the guard circuit just in case the squirrel is
running in its cage ;-)
Thanks again for assistence
Marco IK1HSS
----Messaggio originale----
Da: [email protected]
Data: 31-mag-2017 20.39
A: <[email protected]>
Cc: <[email protected]>
Ogg: Re: Re: LF: Re: I: Fw: For today the FETs survived...
7:19 turns (assuming 50R output) means you have a load resistance of
6.8
ohms which for 180V DC (81 V RSM fund sine) is nearly 1kW I don't
think
you really mean to go that extreme do you? 13 ohms is more
realistic.
As for the tank resonance changing as power increases, that is very
wrong.
I wonder if the transformer is saturating. Not sure of your core Ae,
but
lets assume 200mm square, a core of about 16mm diameter.
V = 4.44.F.N.A.B Plugging in 137kHz 7 turns, 200 mm^2 and a Bmax of
0.1
that suggests 85V RMS.
Which is exactlyly what you have. I suggest more primary turns .
Before
a transformer ratio of 1:2 was suggested, for Rload = 13 ohms
Is the guard circuit in place ? Don't forget, it has to be customised
to
you exact currents and coil Q. Get teh PA operating to its proper
settings
foirst - that you can do at low voltage power, it scales perfectly.
Only
when it it working properly can you add and set up the guard circuit.
When I did teh 700W PA, I had a complete workign (albeit unreliable)
unit
before even thinking of teh guard circuitry.
Andy
On 31 May 2017 at 18:50, [email protected] <[email protected]>
wrote:
> Hi Andy... me again...
>
> I was so curious to see what could happen thatI had a very quick
> dinner and connected all, but...
>
> now the output xfmr has 7T/19T here my
> readings/calculations:
> (see attached picture)
> again the power increase from 10 to 30Vcc then from 30 to 50Vcc after
> an initial burst it start to fall down..
> I checked also the resonance of the LC: till 30Vcc is tuned on 137
kHz
> with a 3dB bandwidth of 20 kHz, when I move to 40 and 50Vcc the
> "maximum" output shifts to 165 kHz...
>
> mumble mumble
>
> I tempted to have roasted FETs for dessert and see what happens at
> 180V!
>
> Marco, IK1HSS
>
>
> ----Messaggio originale----
> Da: [email protected]
> Data: 30-mag-2017 23.50
> A: <[email protected]>
> Cc: <[email protected]>
> Ogg: Re: LF: Re: I: Fw: For today the FETs survived...
>
> I've just looked again at the circuit diagram you sent - on there the
> values are different from your statement in the email. It shows
> primary 5
> turns, secondary 12 turns so a load resistance in the order of 9 ohms
> which
> is rather low if you are intending a Vdd of 180V - but closer to the
> ideal
> Rl
>
> The tank components have a reactance of 130 ohms which is too high a
Q
> is
> used with that 9 ohms Rload, You should be aiming for a Q in the
region
> of
> 6.
>
> Even with the optimum load R of 13 ohms described last time for 500
> Watts
> from 180V rail the resulting Q of 10 is a bit too high - you will end
> up
> with high voltage and critical tuning
>
> Andy G4JNT
>
> On 29 May 2017 at 19:07, Andy Talbot <[email protected]> wrote:
>
> > Yes.
> > As you'll see in my original write up, I originally forgot that the
> peak
> > of the fundamental sine component of a square wave is GREATER than
> the peak
> > by a factor of 4 / pi and initially my PA delivered a lot more
power
> (1.6
> > times) than it was supposed to.
> >
> > So if the square wave has a peak value of 1, its fundamental sine
> > component has a peak value of 4/pi or around 1.27. The RMS of the
> > resulting sine is SQRT(2) less than this giving a Peak square to
RMS-
> sine
> > ratio of 0.9.. If you specifye peak-peak of the square wave, a
> further
> > factor of 2 applies, leading to the 0.45 ratio described before.
> >
> > Incidentally, this same ratio appears in that equation for flux in
a
> > magnetic code, V = 4.44.F.N.A.B
> > The magic number 4.44 is actually SQRT(2) * pi and comes about
> from
> > the same sort of sine to square transform.
> >
> > Andy
> >
> > On 29 May 2017 at 18:48, [email protected] <[email protected]>
> wrote:
> >
> >>
> >> uhuh... a slightly silly misleading assumption... Vdc are the same
> of
> >> Vrms before FETs make their work!
> >>
> >> Thank you Andy for pointing out it!!
> >> With this approach calculation changes a bit and probably with the
> >> right Xfmr the PA can give higher satisfaction :-)
> >>
> >> Hopefully the FETs will survive and this time I'm ready to burnout
> the
> >> antenna hi
> >>
> >> Will keep you both updated, thank you once more Andy
> >>
> >> 73 Marco, IK1HSS
> >> ----Messaggio originale----
> >> Da: [email protected]
> >> Data: 28-mag-2017 21.18
> >> A: "[email protected]"<[email protected]>,
> >> <[email protected]>
> >> Cc: <[email protected]>
> >> Ogg: LF: Re: I: Fw: For today the FETs survived...
> >>
> >> First thing I noticed is that your turns ratio on the output
> >> transformer
> >> doesn't look right.
> >> You quote "* ... with primary winding of 15 turns and secondary of
> 12
> >> turns...*"
> >>
> >> 180V DC in a half bridge is 180V peak-peak square wave.
> >> The fundamental sine part of that is 4/pi * 180 = 229V pk-pk
> >> so is 229V /[2.SQRT(2)] = 81V RMS
> >>
> >> To a good approximation RMS(fund) from a half bridge is Vrms(fund)
=
> >> 0.45VDC
> >>
> >> For 500 Watts out, Rload = 81 ^ 2 / 500 = 13 ohms
> >>
> >> So to match to 50 ohms you need a turns ratio of SQRT(50/13) =
1.9:
> >> 1 so
> >> call it 2:1 Keeping 12 turns on the secondary means you need 6
> turns
> >> on
> >> the primary
> >>
> >> When operating at reduced voltage, the power out will vary exactly
> as
> >> the
> >> square of the voltage.
> >> Recalculating from first principles for a 12V supply:
> >>
> >> 12V DC = 12V pk-pk = 12 / [2.SQRT(2)] * 4/pi = 5.4V RMS
> (fundamental)
> >> in 13 ohms should give 5.4^2/13 = 2.2 Watts
> >>
> >> check using ratio of voltages, squared :
> >>
> >> (12V/180V) ^ 2 * 500W = 2.2 Watts which is the same as above.
> >> QED
> >>
> >> Your 15:12 ratio result sin a load impedance of (15/12)^2 * 50 =
78
> >> ohms
> >>
> >> At 40V DC == 18V RMS(fund) that will give 18^2/78 = 4.1 watts
which
> is
> >> actually LESS that you are seeing - the 2* discrepancy is odd, but
> the
> >> low
> >> power is in the area of what you measured..
> >>
> >> Andy G4JNT
> >>
> >>
> >>
> >> On 28 May 2017 at 19:34, [email protected] <[email protected]>
> >> wrote:
> >>
> >> > Hi Chris,
> >> >
> >> > I tried to post this message on the reflector but apparently I
had
> no
> >> > success..
> >> > As promised I keep you updated but as you can read in the
> >> > attachment the first trials were not enocouraging...
> >> > Andy, may I ask you to read my report? your interpretation and
> >> > suggestion are welcome!
> >> >
> >> > 73, Marco IK1HSS
> >> >
> >> >
> >> > -----Original message-----
> >> >
> >> > From: "[email protected]" [email protected]
> >> > Date: Sun, 28 May 2017 17:01:33 +0200
> >> > To: [email protected]
> >> > Subject: For today the FETs survived...
> >> >
> >> > Hi LF,
> >> >
> >> > hope that also the toroids of Chris survived!
> >> > My FETs survived, but they are not working as expected :-(
> >> > Attached the report on my attempt to duplicate the half bridge
of
> >> > Andy..
> >> > Has anyone suggestions before I try to cook all connecting to
the
> >> > 180Vdc supply?
> >> >
> >> > Thank you
> >> > 73 Marco IK1HSS
> >> >
> >> >
> >> > --
> >> > This message has been scanned by E.F.A. Project and is believed
to
> be
> >> > clean.
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> >
> >> > ---------- Forwarded message ----------
> >> > From: "[email protected]" <[email protected]>
> >> > To: <[email protected]>
> >> > Cc:
> >> > Bcc:
> >> > Date: Sun, 28 May 2017 17:01:33 +0200 (CEST)
> >> > Subject: For today the FETs survived...
> >> > Hi LF,
> >> >
> >> > hope that also the toroids of Chris survived!
> >> > My FETs survived, but they are not working as expected :-(
> >> > Attached the report on my attempt to duplicate the half bridge
of
> >> > Andy..
> >> > Has anyone suggestions before I try to cook all connecting to
the
> >> > 180Vdc supply?
> >> >
> >> > Thank you
> >> > 73 Marco IK1HSS
> >> >
> >> >
> >> > --
> >> > This message has been scanned by E.F.A. Project and is believed
to
> be
> >> > clean.
> >> >
> >> >
> >> >
> >> >
> >>
> >>
> >>
> >>
> >>
> >
>
>
>
|
