Message-ID: <15c5fe5fd93.marcocadeddu@tin.it>
Date: Wed, 31 May 2017 21:05:27 +0200 (CEST)
From: "marcocadeddu@tin.it" <marcocadeddu@tin.it>
To:  <rsgb_lf_group@blacksheep.org>
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Subject: R: Re: Re: LF: Re: I: Fw: For today the FETs survived...
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Status: RO

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: andy.g4jnt@gmail.com
Data: 31-mag-2017 20.39
A: <rsgb_lf_group@blacksheep.org>
Cc: <dead.fets@gmail.com>
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, marcocadeddu@tin.it <marcocadeddu@tin.it> 
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: andy.g4jnt@gmail.com
> Data: 30-mag-2017 23.50
> A: <rsgb_lf_group@blacksheep.org>
> Cc: <dead.fets@gmail.com>
> 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 <andy.g4jnt@gmail.com> 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, marcocadeddu@tin.it <marcocadeddu@tin.it>
> 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: andy.g4jnt@gmail.com
> >> Data: 28-mag-2017 21.18
> >> A: "marcocadeddu@tin.it"<marcocadeddu@tin.it>,
> >> <rsgb_lf_group@blacksheep.org>
> >> Cc: <dead.fets@gmail.com>
> >> 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, marcocadeddu@tin.it <marcocadeddu@tin.it>
> >> 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: "marcocadeddu@tin.it" marcocadeddu@tin.it
> >> > Date: Sun, 28 May 2017 17:01:33 +0200
> >> > To: rsgb_lf_group@blacksheep.org
> >> > 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: "marcocadeddu@tin.it" <marcocadeddu@tin.it>
> >> > To: <rsgb_lf_group@blacksheep.org>
> >> > 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.
> >> >
> >> >
> >> >
> >> >
> >>
> >>
> >>
> >>
> >>
> >
>
>
>