Rectifying multiple secondaries..

[DigitalJunkie]

So,for a pair of Tube Monoblocks I'm planning,I've got a couple of big Tektronix power transformers with multiple secondaries. I'm wondering if it would be better to series all the secondaries (3x), before the bridge rectifier (basically series them all up,and treat them like one secondary winding) or rectify each one separately,and series them up after the rectifiers.

Connecting them in series post-rectifier,I would incur higher diode losses(3x as much),but I'm wondering if there might be some benefit to doing it that way?
(One I can think of,is the ability to use lower voltage caps.)

Here's a crappy diagram of what I mean;
http://i199.photobucket.com/albums/aa154/Nothing40/TubeStuff/PSU2.jpg

And some data on the power trannies in question,from Pete Millet's site (I hope he doesn't mind!):
http://i199.photobucket.com/albums/aa154/Nothing40/TubeStuff/tek545A-test.jpg

I am planning on using the 3 windings= 5-10 , 7-14 , 8-15 (Marked in Blue on Pete's graph) as they have lower DCR.


Any thoughts either way?

 

[dtproff]

Personally, I don't like stacking caps. For me... One big winding.

For what it's worth.

Tony

 

[DigitalJunkie]

I see what you're saying. But considering that the B+ is going to be in the 450V neighborhood,I will most likely have to stack some caps to get to (above) that voltage rating anyways. :-/
Although,I suppose I could get some oil motor run caps.I might also be able to use the JJ multisection caps,since they're rated to 500V-That might be a bit close though.
Hummm.. decisions,decisions!

 

[dtproff]

FYI...

Digikey has 630V caps but anyway... There really isn't much difference between the two other than possibley a lower ESR for the single HV cap.

Good luck.

 

[AndrewT]

440Vac motor run caps should have a DC rating ~ 600Vdc.
I wonder if that's where the 630Vdc rating comes from?

 

[Tweeker]

As you get to higher voltage AC rated caps the DC voltage rating is often much higher than 1.4 * RMS. AC duty is typically much more strenuous.

The AC rating is often limited by dissipation etc.

An extreme example, pdf.

 

[DigitalJunkie]

Wow,2 to 4 times the AC voltage!

440Vac motor run caps should have a DC rating ~ 600Vdc. I wonder if that's where the 630Vdc rating comes from?

I have wondered that too,and sort of 'assumed' that was the case.

I'm still pretty undecided,but I'm thinking I'll just rectify each winding,and series up the resulting DC.