Mercury Power Supply Design - Checking for Efficacy

Paully · 11978

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ALEXZ

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Reply #30 on: May 18, 2012, 04:44:30 AM
here we go ...2x475v AC



Offline Grainger49

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Reply #31 on: May 18, 2012, 05:15:36 AM
Beautiful!  It never reaches 500V, the rating for the inductor's insulation.  Looking at the RMS for R1 it is up at 379V.  Interesting, the graph shows different voltage than the RMS value in the chart next to it.  

This is part of my confusion about PSUD II.  The RMS voltage should be the steady state supply voltage.  That is why I'm so befuddled with PSUD.



Offline Grainger49

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Reply #32 on: May 18, 2012, 09:54:50 AM
Ok, I tried with all the same components you have and I got much different results.

WOW  That is tiny.  Click and it will open in a window.  As you can see I have ripple across R1.  I don't think any of the voltage and current values are the same as you have.


This is why I get frustrated with this program.
« Last Edit: May 18, 2012, 09:58:31 AM by Grainger49 »



Offline Paul Joppa

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Reply #33 on: May 18, 2012, 01:20:53 PM
Grainger, your first capacitor is 50 farads, not microfarads. That will make a difference!

Paul Joppa


Offline Grainger49

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Reply #34 on: May 18, 2012, 01:31:34 PM
I'll look at it again, Thanks!

We are still wondering, looking at Alexz's example above, how do you start with a transformer that puts out 750V and R1, the load has a calculated RMS voltage of 379V?  The graph of Vc1 shows DC of 480-490V.

What am I missing?



Offline Grainger49

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Reply #35 on: May 18, 2012, 01:38:45 PM
Second try got almost the same numbers as Alex.



Offline Paul Joppa

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Reply #36 on: May 18, 2012, 03:22:03 PM
Oh yeah - I forgot to post this one. It's bit me in the backside more than a few times!

The average, rms, max, min, etc. cover the entire reported interval. If you don't use a delay, then it includes the initial start transient. A ramp from 0 to 500 volts is an average  of 250 volts. You have to use the "after an initial delay of..." if you want to know where the voltages etc. end up.

By the way, there's another hidden time bomb. If you use a constant current load instead of a resistor, it offers the option of changing the current after a delay time. Very good for approximating tube warmup - but in my experience this gets introduced without your asking for it, at seemingly random times. If it looks weird, re-check the current load specs!

Oh yeah, here's another one. The transformer is described by its UNLOADED voltage plus its DC resistance. Transformers are rated by their LOADED voltage, after the resistance has dropped the voltage due to the entire rated current. The difference is usually at least 5% - so if you use a generously over-rated transformer the voltage will be at least 5% higher than the rated voltage. Plus, most transformers today are still rated for 115 volts input, and most houses have 120 to 125 volts. There's another 5% to 10%. So a transformer rated 375v may have an unloaded voltage of as much as 430 volts. And by the way, the resistance is the secondary resistance PLUS the primary resistance multiplied by the turns ratio squared. There's a calculator hidden in PSUD, but a lot of people aren't aware they need to find it and use it. Bottom line, you need to buy the transformer, measure the heck out of it, and do some calculations before you can actually put it in PSUD and expect realistic results. You can't just use the specs in the catalog. Serious pain in the aforementioned backside.

It's a really cool simulator and very useful, but it does have a lot of traps for the unwary! You know how, in house painting, the surface preparation takes more time than the actual painting? Same thing with PSUD - getting all the numbers and getting them into the program without triggering any hidden "features" takes more time than using it to get useful results.

Paul Joppa


Offline Grainger49

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Reply #37 on: May 18, 2012, 04:18:31 PM
Paul, Thanks!  I am beginning to see the light at the end of the tunnel.  I added the delay and the voltage plot is a sine wave.  But the ripple goes from 476.58V to 476.56V, 20mV.  Additional resistance should bring that down, right?  Or is 20mV good?

PSUD is a free program and so is EAC.  Neither seem well documented.  But I got what I paid for.

If we need to shed voltage do you suggest a resistor before the tube Anodes, after rectified or in series with the inductor.  I am thinking in the AC legs will soften the blow on everything.
« Last Edit: May 20, 2012, 12:46:42 PM by Grainger49 »