Interesting comments, Jim. That's pretty cool software you're using. Thanks.
## PSUD is available, free. Link to it on GM3SEK's site. Beware, you have
toadd more diodes, stock, it's only good for 1 kv piv. Called duncan's
powersupply modeler. Pse see my detailed responses below. Basically, I get
the same results from
my 30V test that you do, re peak currents and voltages. In my 30V test, I
used a transformer that was stiff enough that I could ignore the primary and
secondary resistance, as well as all the effects of the AC line and the pole
pig, etc. I understand that you believe that for my 30V test I should
dropped the load resistance from 2200 ohms to 22 ohms. I respectfully
disagree, and would be most interested in hearing your reasons. My reason
for keeping the 2200 ohms and merely scaling up the voltages and currents is
that all the circuit components (resistors and capacitors) in the power
supply are linear (setting aside issues of core saturation in transformers).
If you double the current through a resistor, you get double the voltage. If
you double the AC current through a capacitor, you get double the AC
voltage, but the same phase shift and frequency response. Everything scales
exactly with voltage. If the power supply has ten percent voltage regulation
at 3000V, it will also have ten percent regulation at 30V. So long as all
the circuit components are linear, all the voltages, currents, and waveform
shapes scale exactly. Of course, once non-linear elements are introduced
(transformer core saturation being the biggie) then the scaling breaks down.
### Point well taken. Had I reduced my load Ro to 22 ohms as you suggest, the
characteristics of
the power supply would have changed enormously. The discharge time for the
load (RoC), which is the rate at which the load drains stored charge from
the capacitor would drop by a factor of a hundred. This would change
everything and render the results of the experiments invalid. Now a few
detailed comments:
## Now with peak currents being 4-5 times average current.... you end
up with one helluva big PEAK V drop on the 240 line.
This is a valid point, but I think it overestimates the problem. In my 30V
test, the xfmr could easily handle the peak current. In a real-life HV power
supply, the inductance in the transformer secondary will help maintain the
voltage over the msec or so that the peak currents are being supplied.
### when one see's a 4-8 vac drop in the 240 vac line, back to main
panel,rest assured, that the peak V drop will be 3-5 X that much.
You are also right that with the 25 ohm resistor the transformer
and diodes can't "top up" the charge in the capacitor as quickly, because
the resistor limits the peak current. However, you've not allowed for the
fact that the conduction angle increases in order to compensate for the
reduced peak current. In essence the diodes conduct a longer time during
each cycle.### That's what I thought too! However PSUD does NOT show
increasedconduction angle though. Dunno why, but it doesn't. End result, V
regulation goes to hell. Try it with an actual 3 kv supply. If u alreadyhave
a 22 ohm resistor installed.. then wire a spst vac relay across it.then you can
toggle ..'resistor IN /OUT ' and do a real deal test. The reason the
conduction angle increases is because the voltage
on the capacitor is proportional to the charge stored on it. (The definition
of capacitance is C=Q/V, where Q is the stored charge. As the Q drops, the
voltage drops proportionately). Thus if charge isn't being replenished
adequately, then V will drop, thus turning on the diodes for a longer time.
When one works out the details, the net effect of the reduced peak current
and the larger conduction angle is exactly what one would expect from
considering only the DC voltage drop across the 25 ohms, which is only 25
volts.
### PSUD does not show any increased conduction angle.
## 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!!
Here, as I said earlier, we disagree. I'm keeping an open mind
on this point, but will need to hear your reasons why I should install a 22
ohm resistor, and also why my justification for keeping it at 2200 ohms is
wrong.
### If you want to keep the plate load Z the SAME... yes, you are correct!
### Plate load Z is 1222 ohms scaled up to 3kv... and also 1222 ohms,when
scaled back down to 30 vdc [ and using the same 2200 ohm load] I stand
corrected on that one. I'm sure this whole discussion must seem pretty
boring to many list members.
However, it's important that we come to agreement, since the outcome
potentially affects every power supply that an amp builder puts together.
73, Jim W8ZR
### agreed. Now install a 20-25 ohm resistor [50-200w WW]between FWB and a
B+ filter, and short it out with a vac relaythen tell us what u get ? I
have 6 x HV supplies here, and V regulationis terrible.... IF a 25 ohm
resistor is installed b4 caps on any of them.The sign at Nasa say's..... 'one
test is worth a 1000 opinion's . PSUDmay or may not be out to lunch.... but it
jives with my tests, with theresistor installed.. and again with it removed.
At this point, I'd sayPsud is dead on. later... Jim VE7RF
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