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PSUD2 Gurus, I need help...
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Old 16th May 2017, 07:00 PM   #1
Ryssen is offline Ryssen  Sweden
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Default PSUD2 Gurus, I need help...

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I am making a PSU that is going to leave 490v.and its working except that I dont know how many ohms the trafo should be at right now it is at 35,633ohm.
But I think I get more accurate result if I set it to 1 ohm...
I would be glad to know wich is right before I order a custom made toroid.

If I calculate 379v X 1.41 =I get 534v witch don make sence..
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Old 16th May 2017, 07:37 PM   #2
DF96 is offline DF96  England
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To get the most accurate result set the transformer resistance to what the transformer resistance will be. This is secondary resistance plus transformed primary resistance. I think PSUD2 will do the calculation for you if you input the two DC resistances.

What is it that doesn't make sense to you?
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Old 17th May 2017, 04:49 AM   #3
PRR is offline PRR  United States
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1 Ohm suggests a 1,000VA transformer. Since you only have a 50 Watt load, a 1,000VA lump is a lot to pay for, ship, and lift.

Transformers I have used and abused say that you are probably facing 20 to 30 Ohms transformer resistance. 1 Ohm is awful optimistic and you will be disappointed by reality.

IF you know rated V and I and Regulation, PSUD has that calculator hidden under a small arrow on the transformer dialog box. If you do not know the rated reg, for a PT this general size I would pencil 12%.
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Old 17th May 2017, 09:58 AM   #4
AndrewT is offline AndrewT  Scotland
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Ryssen. Add in a delay before it calculates results.
that way you see what is happening during the operational state.

Have a look at the ripple current in the first capacitor.
Now swap the capacitor values and look again at the ripple current.

You need to specify capacitors that can handle that ripple current in the longer term. It is this that heats up the capacitor and brings on a shortened lifetime.
A small bank of much smaller capacitors may be a cheaper way to obtain adequate ripple capacity in that first C.
4off 100uF @ 630Vdc might be a lot cheaper than 470uF 630Vdc and buy you additional ripple capacity.

Did you mean to type 47mF into PSUD2?
that means 47milli-Farad = 47000 micro-Farad.
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Last edited by AndrewT; 17th May 2017 at 10:01 AM.
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Old 17th May 2017, 03:54 PM   #5
Ryssen is offline Ryssen  Sweden
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Quote:
If I calculate 379v X 1.41 =I get 534v witch don make sence..
You mean that what I calculate is voltage without a load?

PSUD 2 Caculated the resistance to 35,9 ohm.

Yes I saw that error with the mF and uF ,will try to simulate again.
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Old 17th May 2017, 05:45 PM   #6
Ryssen is offline Ryssen  Sweden
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Click the image to open in full size.

Does this look ok?
I found some 600v elyts that where prettycheap they where 100uF Ill have to paralell them.
Ofcorse it gets better if I add more as C1 I tried up to 1000uF...
The trafo is now 370v ac.
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Old 17th May 2017, 09:23 PM   #7
AndrewT is offline AndrewT  Scotland
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There's still a lot of ripple from the start up.
increase your delay to 3s.
Reduce the input cap to 100uF and keep C2 at 200uF
Then compare to using 200 for C1 and 200 for C2 and finally 200 for C1 and 100 for C2
You can then assess the value you get in mains ripple per uF of smoothing.
Look at Ic1. That's your long term ripple and your ripple capacity must comfortably exceed that.
Can the current to the load increase?
What effect does that have on ripple currents and output voltage?
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Old 17th May 2017, 11:26 PM   #8
Ryssen is offline Ryssen  Sweden
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Click the image to open in full size.

I lowered the cap at output to 100uF and with 200uF at C1 the green area is at 50% of the area.
Now Im using 500uF and the gren area is less I even tried 1000uF and it got better.but that is starting to get expensive for uF..
Is it okay to load more and more at C1?

The load is a tube SE (Class A) amp thats 6P15P drivertube at 10mA/channel and 807 40mA/channel.
I increased the output to 130mA and the voltage went down 7 volts and the ripple went up a bit.(This was with 500uF C1)
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Old 18th May 2017, 06:23 AM   #9
PRR is offline PRR  United States
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> voltage went down ...and the ripple went up

As expected?

What is your goal?

Thousands of 6L6/807 amps have been run with 8uFd, 8H, 8uFd. Why do you need hundreds (or thousands?) of uFd?
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Old 18th May 2017, 08:23 AM   #10
AndrewT is offline AndrewT  Scotland
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Change "For 10000ms" to 100ms
you can zoom in on the plots, or click on the scales and manually change to the scales you want to see. eg Voltage from 495 to 496
That way you get to see the shape of the sawtooth waveform at Vc1 and Vc2.
A spiky shape tells you there is a lot of high frequency content. A rounded shape tells you there is less HF.

Look at the ripple voltage on Vc1
The diff is stated in the table as 1,6806, that is Vripple = 1.68Vpp, whereas Vc2 Vripple = 0.078Vpp, i.e the LC has reduced ripple by >26dB
What does your amplifier need?
That's what PRR is asking you to consider.
The amplifier is separated from C1 by the impedance of L1 (or the resistor if used).
The amplifier mainly draws it's operating current from the LAST capacitor in the PSU. This needs to be as big as the amplifier DESIGNER tells the Builder to use.

Look at Ic1 = 0.636A
You need at least this ripple current capability for the bank of capacitors forming C.
If your output changes from 100mA, then ripple current will change.
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Last edited by AndrewT; 18th May 2017 at 08:31 AM.
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