Maybe the other Jim VE7RF can give us some actual numbers on the peak current
from his calculator. I am too lazy to figure it out at the moment.
73
Gary K4FMX
## This is a new PC I'm using and I can't run psud.. just yet.. on this
machine.
## However, I have ran hundreds of PSUD simulations in the past 12 months at
work.
## PSUD requires an input for pri dc resistance of plate xfmr.. and also sec
dc resistance, plus input pri ac voltage,
+ sec no load, output ac voltage, incoming line freq, type of rectifier, fwB ,
etc, and also what kind of filter,
simple C filter, choke, choke value etc. Also what's required is the dc load
drawn, [800ma 2 A, etc]
## also required is value of C filter.
## Psud will spit out the Z of the xfmr in use, and also depict the exact
waveform shape, every 8.3 msecs,
and will also show what this high current pulse looks like, both in duration,
and level [ peak current. ]
## here's where I think a limitation of psud is.... and that I believe psud
doesn't factor in the Z of the 240 vac
line from xfmr pri.... back to the street / pole pig in street.
## the only way I could simulate the Z between pri of xfmr... and pole pig in
the street was to calculate the total loop resistance,
and then add it to the PSUD's plate xfmr PRI dc resistance. Once u add
that resistance in.... everything changes !!
## typ, IF the dc resistance is discarded for a moment, [ what psud wants]
and just the pri dc resistance of my plate xfmr
is inputted .. [ .008 ohm]... and sec dc resistance of same plate xfmr [ 6.0
ohms across the highest tap]
and with 80 uf filter cap [ simple C filter].... it spits out that peak
current through the diodes is aprx a whopping
15 amps.. [ with a 3A load]. Next up was to go to an extreme.. and
increase C by 10 x ...to 800 uf. Peak current rises
only a TINY bit... to 15.8 Amps. However, P-P ripple is reduced by a
factor of 10 ! Loaded B+ is also higher.
## IE: peak current is aprx 5 x what the dc load is.
## what PSUD will NOT simulate is a dynamic load... like SSB. And here is
where more C in the filter makes a big difference,
better dynamic regulation, and more pep out [as much as 8-10%] .
## Now here is where everything goes to hell. Toss in the dc loop
resistance, between pri of xfmr, looking back through all contactor's
contact resistance, plus all 240 wiring back to main panel, and then the drop
wire into the house... and add all of that to the PSUD
'plate xfmr pri dc resistance'... and everything changes. Peak current
through the diodes is way down. [30-40%]
I don't know if this is valid or not [ adding drop line loop resistance to
pri dc resistance]
## of course, with diode current being typ 4-5 x the dc load current...
this also is reflected right back through the xfmr itself !
IE: peak current on the 240 vac line.. back to street is also 4-5 x
steady state reading [ clamp on ac ammeter] . Now with
peak currents being 4-5 times average current.... you end up with one
helluva big PEAK V drop on the 240 line.
## To simulate the 25 ohm resistor in question [ this may not be valid
either]. I added 25 ohms to the plate xfmr's
6 ohm dc sec resistance. As soon as that's done, now it really goes to
hell. Peak current are way down. It's like the
power supply is gagging on itself. Massive v drops. Again, toggling C
values from X... to 10X.... u still get an improvement
in steady state vdc, [static] regulation, but only a miniscule amount.
## try sucking 4-5 times the dc load current.. through that 25 ohm
resistor, and the Huge vdrop across it is nothing to
sneeze at. That's a 125 v drop.. with a typ ham amp [drawing 1A dc plate
current] What it really does... is impede
current to the caps ! The caps only get ..'topped up' 120 times per
second as is. the conduction angle is really low ,
like 1.4 msecs at the bottom of the base line... and narrowing down to just
.4 msec at the top of the graph.
## Ok, now forget the simulations, either with PSUD, or trying to
extrapolate from a 30 vdc condx. I inserted
a 25 ohm, 225 watt WW... between FWB... and B+ filter. Regulation goes
straight to hell, really bad.
Try it yourself. The more plate current u draw, the worse it gets. [ this was
a 3100 vdc supply]
Or if you have a 10-25 ohm resistor already installed, put a temp short across
it.
## BTW.. to make that 30 vdc test valid... you would have to drop the load R
in proportion, other wise you are not
simulating anything. Install a 22 ohm resistor for the load on the output..
then re-run your test.. you will get an eye opener!!
Putting a 2200 ohm res [= 1.3 ma load.] on the end of a 30 vdc supply isn't
even simulating zsac. U need a 167 ohm load,
just to simulate ZSAC [ 180ma @ 3 kv]
## another thought here. The power factor is really bad with a typ C filter.
That diode conduction curve on psud looks like
a square wave ! [ and ditto back to the street, it passes through both
the pri and sec of any xfmr]
Use a HP current probe and SA... and the 3-5-7-9 th harmonics will amaze
you. esp the 3-5th. All this harmonics generates dirty
power back to the street. It also increase the pri VA power on the xfmr. A
typ 2.5 kw dc input b+ supply, will draw 20-30% more VA
power on pri vs dc input. Harmonic current's gets added to the pri current...
but only partially in phase.. otherwise pri VA power
would be a lot worse.
sri for the diatribe
Jim VE7RF
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