Cheap PSU: Piece of junk or semi-decent?

[momaka]

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

I suspect this comes from the new 40A +12V rectifier, beefier and with lower Vf.

Yeah, the lower Vf helped save a few watts.

[TELVM]

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

Well the TOOQ thing works fine after all the tinkering. Voltages are well inside ATX specs at any load. With the extra 80mm fan the air exiting from the PSU at full steam is now cooler, barely warm @ 21C ambient.



I've noticed that, even with the added fan drawing one or two extra watts, the Kill-a-Watt now shows ~15W less power draw from the wall at full steam (296 vs 311W previously), a ~5% efficiency improvement.

I suspect this comes from the new 40A +12V rectifier, beefier and with lower Vf.

[Th3_uN1Qu3]

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

Good luck with that, most halfbridge PSUs have that grounding wire on the transformer.

[TELVM]

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

By visual tracing it may be that the two center pins of the 'fake' go to +5V. Most definitely two pins go to +12V, and two to ground.

The two dubious pins in the 'true' seem to go to a resistor and a small lenticular ceramic cap, then seem to go to +5V. I can't tell for sure, the donor PCB is now almost empty of components and heavily mauled.

I don't know, sounds too baroque and risky a trasplant with my very limited tools and knowledge . Better I'll wait till I can scrounge some true 35 with a clearer pinout and no hanging wire.

Thanks a lot for your interest and your help , this is a fantastic forum for learning!

[momaka]

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

Hmmm ... I've been beeping my way and the two PSUs are very dissimilar :

That won't do. Windings are all connected together so you can't use a multimeter.

What you need is to have both PSU boards in front of you and physically (i.e. with your eyes) trace the 3.3V, 5V, and 12V rails to their corresponding transformer pins. Start from the rectifiers for each rail and work your way backwards to the transformer.

For the transformer that doesn't have the separate ground tap, you should have 2 pins for 5V, 2 pins for 12V, and 2 pins for ground . On the one that does, it's possible that 3 of the pins are for 12V and 3 are for 5V... or 4 are for 5V and 2 for 12V. Or just 2 for 12V and 2 for 5V, and 2 unconnected.

[Behemot]

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

Those are often not independent windings rather than single winding with several outputs. It is also usually thick wire, you won't be able to measure that unless you have precise meter (like ESR metr, inductance meter is better). Ordinary resistance meter is not precise enough and has higher transitional resistance on probes than the measured winding.

[TELVM]

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

Hmmm ... I've been beeping my way and the two PSUs are very dissimilar :


In the TOOQ four of the six 'secondary' legs of the main trafo seem to be put to ground, two go to +12V and apparently none goes to +5V.

Too baroque to tangle with, I think I'll live with the fake 35 for the time being .

[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 .

[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.

[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?

[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.

[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.

[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?

[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.

[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?

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.

[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...

[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?

[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?

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?