[CButterworth]

I am trying to model a bunch of power supplies with PSUDII.  However, I am unclear which voltages to input into the transformer section.  For full-wave bridge, I have been entering total off-load voltage such that for a 125-0-125 transformer, I enter 250 V.  However, for a regular full wave PSU, do I enter this, or half ie., 125V.

Of course, transformer resistances can have an effect, but I do not know these unless I actually go out and buy and measure.

To make matters worse, I have forgotten my password to the DuncanAmp Forum and he's not taking new registrations or giving access to password retrieval anymore due to excessive amounts of spam - isn't it amazing how we humans can take a great system and trash it.  I hope this simple question makes it through the internet to the newsgroup without being lost and slowed-down by people downloading TV shows, music, and videos 

Thanks,
Charlie

[JoshK]

If you are using two VT diodes (i.e. a typical tube rectifier) in a full wave configuration it is 125V, if you used 4 VT diodes like a SS bridge then it'd be 250V.

[CButterworth]

Josh,

That is exactly as I thought.  When I modelled some PSU's a simple non-bridge gave out too much voltage at the end.

If you haven't read my posting to the DIYAudio circle,  I have one of three options to correct the buzzing/hot transformer:

1.  Don't redesign - simply change the transformer from the Hammond 263 series to the same value of the 300 series. This would allow for 120VAC input.  It is also a physically larger unit and according to many would be less prone to buzzing for that reason (and the better tolerance of 124VAC input).

2. Choke input PSU using 350-0-350 into 5V4GA into 10H (103R) choke: 60uF cap; 10H (103R) choke; 60uF cap. With 32mA current, PSUD gives me 300VDC with 3.61mA ripple.

3. "Cap" input PSU using 275-0-275 into 5V4GA into 1.5uF "tuning" cap; 10H choke; 60uF cap; 10H choke; 60uF cap. With 34mA current, PSUD estimates 308VDC with 1.04mV ripple.

All these options would only force me to buy a new transformer.

Option 3 give the least ripple.  However, I do note that in PSUD I get high amount of current at the transformer (lT1), much higher than the 100mA rating.

What are the key things to guard against in a PSU???

I have decided not to try to adapt the Cornet2 PSU for my Aikido, as I think that my current PSU should be as good or better, well at the very least, I already have the parts (caps, chokes) to make one that is as good or better.

What I will try to adapt from the Hagerman PSU is the LED system, but only if I go for tube rectification.

I can send .psu files for all three of my modelled PSU's.

Charlie

[Occam]

...
Of course, transformer resistances can have an effect, but I do not know these unless I actually go out and buy and measure.
......

Charlie,

Actually, those parameters can be calculated from the transformer 'Regulation %' where you use that to calculate the effective source impeadance of the transformer. I don't recall specifically (its been a few years) but Ohms Law is sufficient. The plitron.com site has enough to suss out wtf 'regulation' means. [actually Reg% = 100 x (Vnoload - Vrated) / Vrated ] On a small hv transformer with 20-30% regulation you'll find enough source impedance to throw your voltages way off.

Regards,
Paul

[CButterworth]

Occam,

Thanks for the info.   However, Hammond don't even specify % regulation!  They do not even state voltage unloaded.

Charlie

[JoshK]

In Bas's online diy rag, there is a tutorial on how exactly to use the calculator in PSUDII to get the source impedance once you measure the DCR of the primary and secondary.

[CButterworth]

Josh,

I found the article.  It was very interesting, thank-you.  The problem is that I cannot measure resistances across the primaries and secondaries unless I have access to the transformer, which doesn't help with chosing parts.

Anyway, I am going to wait a while before re-doing my Aikido PSU.  I am thinking and have been modelling in PSUDII the following:

1. 275-0-275
2. 5V4GA
3. 1.5uF
4. 10H choke
5. 80uF cap
6. 10H choke
7 100uF cap

I get something like 600uV of ripple and about 320VDC.  What I would do is to buy a couple of smaller electrolytic caps at the 80uF and 100uF - they're not expensive.

Regards,
Charlie

[JoshK]

My 273BX (350-0-350 @175ma) has a source impedance of 91 ohm, fwiw.  But its the high current version which may mean it has lower source impedance than the lower current version. 

[CButterworth]

Josh,

Thanks.  The problem is knowing for sure.  I have the 369BX  (275-0-275) at 50mA on my Cornet2.  However, for the Aikido, I may go with a little higher power rating, say 275-0-275 @ 125mA.

275-0-275
5V4GA
200R resistor in series with "+ve"
1.5uF cap
10H choke
80uF cap
10H choke
100uF cap

with 30mA current, I get around 323VDC with 413uV of ripple.

Do you think that this would make a good PSU?  I can tune the B+ up and down using the 1.5uF cap, lower uF for lower B+.

Charlie