Cheap PSU: Piece of junk or semi-decent?

[TELVM]

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

Guilty as charged . I can only plea as extenuating circumstances that this is my first ever rectifier swap, and that all three original rectifiers came without insulating pads , so I didn't even think about it at first :


.

[TELVM]

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

Fresh Panny primary caps, perhaps a bit oversized for the application :



Smaller electros replaced with Panny FCs, and an extra ghetto-modded fan to let the air flow:

>Expand . . . >Expand . . . >Expand

Now with larger primary caps, 12A switchers, a 40A +12V rectifier, and overkill cooling, what do you think might be an honest max continuous wattage for this thing?



On the Vrrm subject, I've read elsewhere this piece of info:

"... the diodes used in a rectifier circuit must have the proper ratings so that they will not fail. The main considerations for a rectifier circuit are the maximum average forward current and the peak inverse voltage (PIV), or maximum repetitive reverse voltage (VRRM).

The maximum average forward current is roughly 1/2(Vav/RL), where Vav is the average voltage and RL is the load resistance, since each pair of diodes conducts only half the time. As for the other rectifiers, if we add a capacitor to filter the output, the PIV is twice the peak voltage, since the capacitor holds the output at peak voltage while the opposite side of the bridge swings down to negative peak voltage. Because there are two diodes in series with the load, however, each diode sees only half the applied voltage, or just the peak voltage ..."

^ If I get it right, the more rectifiers we lay in parallel, the less reverse voltage each individual diode will see.

So if peak reverse voltage PIV or Vrrm is say 100V ...

· 1x rectifier = 2x diodes => each diode will see 100/2 = 50V of peak reverse voltage

· 2x rectifiers in parallel = 4x diodes => each diode will see 100/4 = 25V of peak reverse voltage

· 3x rectifiers in parallel = 6x diodes => each diode will see 100/6 = 16.6V of peak reverse voltage

Is the above correct?

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[goodpsusearch]

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

I don't think it can do 300W due to the small main transformer size.

[Th3_uN1Qu3]

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

Note that they said series, not parallel... So no, putting diodes in parallel will not magically increase their voltage rating. Putting them in series will, however, this is suboptimal for many reasons and thus is not used unless there's really a need for it, usually in high voltage circuits.

I think it'll do close to 350W... However those output inductors will likely get pretty hot.

[TELVM]

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

Note that they said series, not parallel...

I misunderstood what I read. Please chalk another one in my long list of stupid questions .

I think it'll do close to 350W... However those output inductors will likely get pretty hot.

Yep, I noticed how, after a time powering the Preshott, the glue on them was roasted alive:


In this IR pic inductors are even hotter than voltage regulators :


Guess the extra fan will help here.

I don't think it can do 300W due to the small main transformer size.

Well this PSU with 13009s, similar heatsinks, '35' transformer, and one 20A +12V rectifier managed 377W.

Let's make a deal at 300~350W, OK?

[goodpsusearch]

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

This is real 35 size transformer on the link you posted: http://www.clubedohardware.com.br/fu...hp?image=70239

Your psu has fake 35 size transformer judging from the pics.

[kaboom]

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

Your psu has fake 35 size transformer judging from the pics.

For sure! That looks like a 25, maybe a 28.

[TELVM]

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

LOL, the main transformer is a fake? The more I know her the more I love this PSU .

OK, will it work better or will it if I kick off the fake and fit a real '35' trafo?

[Pentium4]

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

It actually looks like 33 to me. Still not good....Although I have seen half bridge with 33 transformer do almost 350W. Unless you're loading this thing over 250W I'd leave it. If you were in the USA I'd send you a transformer, I have quite a few 35 and 39 transformers just sitting here!!!

Edit: I would also try and get the secondary caps a little closer to the PCB. Having them like that shouldn't cause too many issues but having the lower ESR definitely wouldn't hurt

[TELVM]

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

Do we agree this is a true legit bona fide authentic 35 size transformer ?

It comes from a 10~15 years old deceased PSU, can I test it somehow to verify it is still OK?

What do I do with that thick wire, put it to ground?

[goodpsusearch]

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

Please don't replace transformer with another one if you are not sure that they are compatible.

Compatibility has to do with the psu desing, if it is a half bridge, transistor forward etc...

[kaboom]

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

LOL, the main transformer is a fake? The more I know her the more I love this PSU .

I wouldn't say fake. At least not in the usual "prints whatever on the label" sense. Just keep the load reasonable and it should be ok.

OK, will it work better or will it if I kick off the fake and fit a real '35' trafo?

Do not do this unless you are certain about the two transformers being compatible!

Obviously, you need to consider pinout and ratio. Number of primary turns vs core area are exceedingly important also, since this determines the minimum freq the supply must run at. Get this wrong, and the core'll saturate- no more transistors. Depending on how the replacement is wound, you may also need to modify the primary snubber due to leakage reactance.

[momaka]

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

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

+1
That's how I always pull mine.
... okay, by always I mean I only tried it like 2 or 3 times . But still, it is easier than whatever other methods I tried before).

[kaboom]

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

+1
That's how I always pull mine.
... okay, by always I mean I only tried it like 2 or 3 times . But still, it is easier than whatever other methods I tried before).

Yeah, but sometimes, ya gotta "improvise..."




...you know, for the stubborn ones.

[TELVM]

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

P... Compatibility has to do with the psu desing, if it is a half bridge, transistor forward etc...

The donor PSU claimed 350W and was also half-bridge topology with two NPN transistor switchers.

... you need to consider pinout and ratio. Number of primary turns vs core area are exceedingly important also, since this determines the minimum freq the supply must run at. Get this wrong, and the core'll saturate- no more transistors. Depending on how the replacement is wound, you may also need to modify the primary snubber due to leakage reactance.

Pinout is identical, six pins at one side, two pins at the other side. However it has that thick grounding wire that the fake 35 lacks.

How can I identify turn ratio and number of primary turns vs core area in a transformer?

[Th3_uN1Qu3]

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

Pinout is identical, six pins at one side, two pins at the other side. However it has that thick grounding wire that the fake 35 lacks.

Not gonna work then.

[ben7]

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

Not gonna work then.

You sure?

I guess it would be possible to re-wire the output connections on the PCB so they match those of the newer, larger transformer.

[goodpsusearch]

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

Even if you replace the transformer have you got a load tester to check that the new transformer combined with the psu you put it into will provide 300W+ without saturating?

[TELVM]

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

... I guess it would be possible to re-wire the output connections on the PCB so they match those of the newer, larger transformer.

(Potential absurdity ahead): If the problem is the lack of a hole in the PCB close to the transformer to solder the thick ground wire in, I could connect it to the secondary heasink, which is grounded.

[momaka]

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

I guess it would be possible to re-wire the output connections on the PCB so they match those of the newer, larger transformer.

+1
If you match the pinout correctly (that is, connect the pins from the 5V windings to their corresponding 5V holes on the PCB, the 12V windings to the 12V holes, ground wire to ground, and etc.), then there is no reason why the transformer from one half-bridge PSU won't work on another one.

Now, as far as how well it will work (as kaboom mentioned, there's some other things to worry about too), that's another story. This you will know only with a load tester until the PSU goes bang .

(Potential absurdity ahead): If the problem is the lack of a hole in the PCB close to the transformer to solder the thick ground wire in, I could connect it to the secondary heasink, which is grounded.

Yes, that would work. And you'll probably also have the transformer standing a bit off the PCB as you rewire the pinout on the bottom to match the PCB holes. But this crosses quite far into the ghetto mod thread territories .