Cheap PSU: Piece of junk or semi-decent?

[PeteS in CA]

Re: Cheap PSU: Piece of junk or semi-decent?

1 is for the common mode choke for the 12V, 5V, and -12V rails ...

Actually, a common mode inductor has 2 (or more) in-phase windings that are the same number of turns of the same wire gauge on the same core. While the windings of the inductor to which you refer are on the same core and wound in-phase, the windings are of different wire gauges and number of turns. It's called a coupled inductor. It saves PCB space (I know, Duh!), keeps the inductor continuous down to lighter loads, and if the windings are properly proportioned relative to each other cross-regulation is improved.

The different main transformer windings for positive voltages are built atop each other. In one sense it looks like the +12V winding has taps for the +5V and +3.3V, but it's actually the other way around, the +12V and +3.3V come from windings that are part of, or connected to, the +5V winding. Because the voltage from the +5V winding is regulated, the cross-regulation of the +3.3V and +12V are improved.

The +3.3V could be derived in maybe 4 ways. There could be separate taps for the +3.3V, but that complicates the transformer - two extra O/P pins and sets of wires going out and back in the transformer body. I doubt it is done that way, possibly excepting server power supplies. The 3.3V could be linear regulated from the +5V, but that would waste a lot of power (1.7V x I - 17W wasted with a 10A output!)! A buck regulator could be used, would be pretty efficient, but would be a bit complex (the regulator circuit as well as suppressing the extra noise and interaction with the main regulator - synced or not synced with the main regulator?) and take up board space. A mag-amp is simpler, pretty efficient, and the board space required is reasonable, so that's the more common choice.

[Wester547]

Re: Cheap PSU: Piece of junk or semi-decent?

The different main transformer windings for positive voltages are built atop each other. In one sense it looks like the +12V winding has taps for the +5V and +3.3V, but it's actually the other way around, the +12V and +3.3V come from windings that are part of, or connected to, the +5V winding. Because the voltage from the +5V winding is regulated, the cross-regulation of the +3.3V and +12V are improved.

The +3.3V could be derived in maybe 4 ways. There could be separate taps for the +3.3V, but that complicates the transformer - two extra O/P pins and sets of wires going out and back in the transformer body. I doubt it is done that way, possibly excepting server power supplies. The 3.3V could be linear regulated from the +5V, but that would waste a lot of power (1.7V x I - 17W wasted with a 10A output!)! A buck regulator could be used, would be pretty efficient, but would be a bit complex (the regulator circuit as well as suppressing the extra noise and interaction with the main regulator - synced or not synced with the main regulator?) and take up board space.

There isn't a second toroidal coil on the secondary of those Hipros momaka speaks of, though (the ones that use DC-DC conversion for +3.3V). Most of them have what seems to be an extra tap in the main transformer as part of the DC-DC conversion for the +3.3V rail..... but usually they have two +5V rectifiers: one for the +5V rail, one for the +3.3V rail.... so even though technically speaking +3.3V would still be generated from +5V via linear regulated DC-DC conversion and Hipro's own tap (that momaka estimates to be roughly 3.6V), since they have a separate rectifier for the MOSFET to regulate down (voltage wise), doesn't that mean less squandered power?

A mag-amp seems fine to me, but as far as I understand it, using DC-DC conversion means less noise on the +3.3V rail and better group-regulation, maybe...

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

Guetto-modded a bit the 'TOOQ' thing. To add PI coils for +12V, +5V & +3.3V outputs in a PCB lacking any parking slots for them, I brainfarted what I call 'the inglourious basterdaughterboard':

Scrounged the PI coils from an old deceased PSU, and soldered them bridging the positive legs of each pair of caps (2200uF Pannys & Rubys now, replacing the 1000uF 'ASSIA' & 'ChungX' crap).

=>LARGE =>LARGE =>LARGE

Cut the traces under the PCB, so that the juice has to go up from the PCB through the + leg of first cap, then pass through the PI coil, then go down through the + leg of second cap back to the PCB downstream of the trace cut.

=>LARGE =>LARGE

Also added a small daughterboard for extra input filtering components, with two Y-caps, a common mode ferrite choke, and a ferrite bead for the main wires:

A MOV across L-N downstream of the fuse:

=>LARGE =>LARGE

DIY heatsink for the bridge rectifier:

=>LARGE =>LARGE

Top view of the thing once modified to the perpetrator's delight:

A potentiometer for 'digital' control of fan speed:

=>LARGE =>LARGE

The thing under test to discover in how many pieces it explodes:

But again in a most amazingly way the thing works , with the DMM reading coherent voltages.

A pity I lack the equipment to find if ripple & noise have improved or what.


Man do I love this shit .

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

Guetto-modded a bit the 'TOOQ' thing. To add PI coils for +12V, +5V & +3.3V outputs in a PCB lacking any parking slots for them, I brainfarted what I call 'the inglourious basterdaughterboard':

I kinda thought about something liek that from time to time…I definitelly like this

[momaka]

Re: Cheap PSU: Piece of junk or semi-decent?

Guetto-modded a bit the 'TOOQ' thing. To add PI coils for +12V, +5V & +3.3V outputs in a PCB lacking any parking slots for them, I brainfarted what I call 'the inglourious basterdaughterboard':

Haha, nice! I always wanted to do something similar for a few PSUs that I have that don't have their PCB silkscreened for coils.

Very well done, sir! Your projects inspire .

[c_hegge]

Re: Cheap PSU: Piece of junk or semi-decent?

I have considered doing this myself. The only problem is I simply lack the storage space for any more PSUs. I already have a lot of spare repaired 300-400 Watters which were decent to start with (Antecs, a Bestec, a few Hipros, a few Deltas) which I just can't seem tro get rid of. Unfortunately, all too many people think "Why get a used 300W when I can get a new 700W for $20?"

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

... Very well done, sir! ...

Thanks a lot , coming from you that really means something for me . But there is no merit on my part, barely a month ago I was (even more than now ) PSU illiterate, and would have been unable of anything without learning in spades here in badcaps.net from masters like you .

[Pentium4]

Re: Cheap PSU: Piece of junk or semi-decent?

That thing looks GREAT! I can't help but not trust those Cheng caps though, and if they are really as much uF as they claim. Wouldn't want them limiting your awesome mods

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

(Double post)

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?


As implausible as it sounds, both pieces of junk starring in this thread are still alive & kicking and stubbornly keep working like a charm .

The 'TOOQ' thing, complete with with its world famous ghetto-modded secondary PI coils , is now propelling a P4 Preshott overclocked to a non trivial 4.25GHz .

Most amazingly the 'TOOQ' hasn't exploded yet . But judging from the tropical heat that comes from PSU rear and the 311W from the wall that the Kill-a-Watt shows at full Preshott burner (311 x 0.8 = ~250W DC) it must be on the very edge of .

So I think the time has come to plunge into more serious PSU tinkering: The black art of switchers and rectifiers replacement .



The 'TOOQ' thing has this on the primary:

I think the 8A 13007s could perhaps be replaced with 12A 13009s.

The MJE13009G is out of catalog in Farnell. How about the Fairchild FJP13009H2TU, could it do the job?

.

[c_hegge]

Re: Cheap PSU: Piece of junk or semi-decent?

Yup, it would do fine as well.

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

Thanks c_hegge .

I'm also thinking on beefing up the +12V rectifier:


If '20150CTP' is something like the MBR20150CTP, it is a Schottky 20A, Vrrm=150, Vf=0.9 .

How about replacing it with a STPS40SM60CT? Double the amps and half the Vf. Would lowering the Vrrm from 150 to 60V make it go ?

[goodpsusearch]

Re: Cheap PSU: Piece of junk or semi-decent?

My guess is that it will be ok.

[Behemot]

Re: Cheap PSU: Piece of junk or semi-decent?

I think that 60 V is usually suggested minimum for +12 V rail and STMiro part should not have any problem with that…

Just a notice, you should compare under same circuimstances. MBR has voltage drop specified as maximum at 10 A/25 °C. STPS has 0,405 V on the frontpage, but it is typical under different circuimstances. Under same conditions, it is 0,535 V. So be aware of that, quite often you can find parts are not that impressive as they seem on first view.

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

Thanks a lot pals .

One last detail if you don't mind. To replace this crap :

Would a couple Panasonic EE-TS 800uF 200V 105C 22x50mm Ripple=3.08 ESR=0.15 do the job OK?

[momaka]

Re: Cheap PSU: Piece of junk or semi-decent?

Most amazingly the 'TOOQ' hasn't exploded yet . But judging from the tropical heat that comes from PSU rear and the 311W from the wall that the Kill-a-Watt shows at full Preshott burner (311 x 0.8 = ~250W DC) it must be on the very edge of .

Yeah, it really is right on the edge - particularly the 12V rectifier. Efficiency of a cheap PSU is usually around 70%. With that in mind, 311 x 0.7 = 218 W. Most of that is from the 12V rail, so let's say 200 W. That means the 12V rectifier is providing almost 17 A.

So yeah, the 12V rectifier is probably the only thing you need to upgrade.

[c_hegge]

Re: Cheap PSU: Piece of junk or semi-decent?

Would a couple Panasonic EE-TS 800uF 200V 105C 22x50mm Ripple=3.08 ESR=0.15 do the job OK?

Yes, those would be fine. The ESR isn't that critical for the primaries.

[TELVM]

Re: Cheap PSU: Piece of junk or semi-decent?

Thanks Momaka & c_hegge!

Harsh profanity was required but managed to unscrew the 13007s without desoldering the heatsink :

[Th3_uN1Qu3]

Re: Cheap PSU: Piece of junk or semi-decent?

I always unsolder the whole heatsink, saves a lot of sweat.

[kaboom]

Re: Cheap PSU: Piece of junk or semi-decent?

Thanks Momaka & c_hegge!

Harsh profanity was required but managed to unscrew the 13007s without desoldering the heatsink :

While you're at it, replace those two small electros. They, along with some resistors and diodes, bias the two switchers.

Miniature long- and needle-nose pliers are excellent for removing and replacing the screws and insulators for the power transistors.

Something like this, but with less bulky handles:
http://www.harborfreight.com/6-piece...set-94931.html