Cheap PSU: Piece of junk or semi-decent?

[TELVM]

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

... Beef up the rectifiers on the 5V rail, so there is less voltage drop. That way 5V should stay in spec ...

That sounds very interesting . Please excuse my ignorance , exactly which one is the +5V rectifier in this 'TOOQ' PSU:

Left to right 2045CTP // 20150CTP // 2045CTP

And what could be a suitable replacement with less voltage drop?

Also you could alter the feedback ratios, so that 5V is treated as more important than 12V, but that would cause 12v to jump even higher.

I can see 2 drawbacks to this solution:

1) I haven't the foggiest what you're talking about .

2) Wouldn't like frying some +12V eating component.

Main cause would be heat, yes. There is also ripple current that the cap has to handle, which causes self-heating. This, along with the heat coming from the rest of the components, will quickly cook that 85C cap.

OK, I'm going to desolder the 85C and replace it with one of these in the 'P4' PSU:

Crappy old used caps, I know, but they are still alive and test OK.

For the price of a dozen or two new quality jap caps from Farnell, plus delivery, plus a bit more, I'd better buy some new PSU. Don't see much sense in throwing money at an old and probably mediocre PSU.


Thanks a lot for your help gentlemen .

[rogfanther]

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

Probably others will answer as well, but it is a tough call between let that 85C cap there, and use this Jun Fu one.

[TELVM]

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

... it is a tough call between let that 85C cap there, and use this Jun Fu one.

Guess that comment speaks a lot on the 'quality' of 'Jun Fu' caps .

[rogfanther]

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

Hmmm, I think you should not mix the words 'quality' and 'Jun Fu' in the same sentence. There may be some law against it.

[Behemot]

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



As for the recitifers: again, use your DMM set to diode tester and "beep your way" through. Just put one probe on +5 V (in cable or on PCB directly) and search for right rectifier with the other probe. It would be central pin of those rectifiers.

[TELVM]

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

OK I beeped my way into this:

So the extreme right 2045CTP is the +5V rectifier. From what I see in the .pdf's it's a 20A Schottky barrier rectifier with a forward voltage drop VF of typical 0.59V, max 0.65V @ 25C.

Seems that mosfets are better than schottkys for the task, could we directly replace this schottky with a mosfet of lower VF?

[Behemot]

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

There is no way how can you replace diode with transistor just like that. Whole topology has to be made that way. This supply does not seem to be so bad after all, usually you find only one shottky inside (+5 or +3,3 V), the rest are superfasts with twice the Vdrop but lower price.

Now you can either get slightly better rectifiers, or use two in paralel instead of just one. But that would mean having holes for them on the other side of the heatsink as well.

[Th3_uN1Qu3]

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

But that would mean having holes for them on the other side of the heatsink as well.

You'll find that the holes are usually there.

[Behemot]

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

Not in all cases. Drilling extra holes takes time of both machinery and personel. Those are extra costs. And as long as I haven't really seen a crap with two rectifiers in paralel ever, they don't count with them, that means they don't need to drill holes for them

Also not every time there is room for the rectifiers even if holes are present. I think I have seen some coil in there from the other side.

[goodpsusearch]

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

Also not every time there is room for the rectifiers even if holes are present. I think I have seen some coil in there from the other side.

I have managed to squeeze an extra rectifier despite the coil that was there.

[TELVM]

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

There is no way how can you replace diode with transistor just like that. Whole topology has to be made that way ...

Roger, just probing.

There are no holes on the other side of the heatsink .

[TELVM]

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

BTW I've observed that once the 21W light bulb is heated, the extra AC draw from the wall due to the bulb is 30W, both at idle and full load.

This means that the efficiency of this PSU is 21/30 = 0.7 => about 70% at these loads.

As the comp drew 75/90W idle/load AC from the wall before the bulb, the real DC draw of this PIII must be about 52.5/63W idle/load.

So the bulb not only mitigates crossloading, it also works as efficiency indicator. Car light bulbs rock!

[Behemot]

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

Only problem is, like with another bulbs, it has 10 like times startup current than nominal. Just shorted nice shottky rectifier because of that in crap I was upgrading I will be dealing with that in my passive load tester using NTC.

[TELVM]

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


The resistance of this 12V/21W car light bulb, measured when cold with multimeter, is 1.2Ω.

12V/1.2Ω=10A inrush.

The 20150CTP +12V rectifier in the 'TOOQ' PSU is a 20A one. Isn't that plenty of roof?

[Behemot]

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

I plugged in three 40W halogen bulbs m8 Halogens work on even higher temperature than average bulbs, that means its cold resistance is like none And this thing has no OPP

[TELVM]

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

Hmmm ... you sure doubling the Schottkys would cure the crossloading problem?

I have to observe that the Antec VP-350P, with group regulation and parallel Schottkys in +12V & +5V, still struggles under heavy +5V and light +12V:

[Behemot]

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

This particular one is doomed. But your still has a chance

[momaka]

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

Does anybody know if what a Radeon 9800 Pro sucks through this molex header ...

Yes, and also through the AGP slot. See this:
http://www.xbitlabs.com/articles/gra...s_8.html#sect0
It uses about 5.4 A on the 5V rail under full load and 4.35 A on the 3.3V rail under full load. So if you use that video card in your PC, it will bring the 5V and 3.3V rails down even further.
.
.
Sorry to say this, but that TooQ PSU is not very good. Reason I say that is because there are no inductors between the output capacitors and there's not even space to install ones! This means you need to have some really good caps in it or else there will be more ripple on outputs that usual.

I kind of quickly read through the whole thread, so correct me if I'm wrong, but this is your "old P4 era" PSU, correct?
http://www2.picturepush.com/photo/a/...g/11286455.jpg

If yes, then this PSU may actually be a better candidate for your PIII PC. The one you have is a Deer/Allied/L&C unit. Judging by the 30A rectifier on the 5V rail, this unit will likely work much better with your Pentium 3 PC.

You will need to do a few modifications on it, though. For example, the likely reason why one of its original caps cooked is because of the minimum load resistors. Using this photo as a reference:
http://www2.picturepush.com/photo/a/...g/11286455.jpg
note the 3 large resistors...
- 1 just below the bad Koshin cap you replaced
- 2 to the right of the orange wires
These are the minimum load resistors. More often than not, Deer/Allied likes to use low values for these so they end up generating a lot of heat and cook the caps. If you are going to use this PSU with a computer, then you can change those resistors.
Assuming you'd want to use this with your Pentium 3 PC, you can make the following changes to the load resistors:
3.3V rail: swap for 33 to 100 Ohms resistor (preferably 33 to 47 Ohms), 1 Watt or higher rated resistor
5V rail: swap for 56 to 270 Ohms resistor (100 Ohms works well, but you can go even higher than 270 Ohms if you're going to use this PSU only on 5V-based computers). Again, for power rating, you'll want 1 W or higher.
12V rail: 270 Ohms resistor or higher, 1 W rated.

Another modification you should do - change the output caps so that the 3.3V and 5V rails have 2x 2200 uF caps each. That 10 V, 1000 uF Koshin cap you swapped is on the 3.3V rail IIRC. 2200 uF would be better in its place.

Last but not least, I think there's a small 22 uF, 50V cap on the primary side close to one of the small transformers (should be close to the 5VSB transformer) - that cap is the 5VSB critical cap. If it goes bad, 5VSB can go as high as 12V and can take your motherboard with it. So if you're recapping the thing, you might as well get that cap too. I *think* it was 22 uF 50V, but it may also be 47 uF, 25V or 47, uF 50V. Double-check me.

[Behemot]

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

May wanna do flying resistor mod too

[TELVM]

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

Wow, thanks a lot for your great advice Momaka .

Yes, and also through the AGP slot. See this:
http://www.xbitlabs.com/articles/gra...s_8.html#sect0
It uses about 5.4 A on the 5V rail under full load and 4.35 A on the 3.3V rail under full load. So if you use that video card in your PC, it will bring the 5V and 3.3V rails down even further.

Argh, there goes my 'productive +12V dummy load' .

Sorry to say this, but that TooQ PSU is not very good. Reason I say that is because there are no inductors between the output capacitors and there's not even space to install ones! This means you need to have some really good caps in it or else there will be more ripple on outputs that usual.

Yep, had noticed they didn't bother to add PI coils to the output of the 'TOOQ' thing .

I kind of quickly read through the whole thread, so correct me if I'm wrong, but this is your "old P4 era" PSU, correct?
http://www2.picturepush.com/photo/a/...g/11286455.jpg

Correct. For what it's worth this is its label:

If yes, then this PSU may actually be a better candidate for your PIII PC. The one you have is a Deer/Allied/L&C unit. Judging by the 30A rectifier on the 5V rail, this unit will likely work much better with your Pentium 3 PC.

As it came with poor transient filtering and the four diode treatment I thought it was crappier than the 'TOOQ'. But as you well say it has stronger +5V rectifier, and PI coils in the output. And its very ancient design could better suit a dinosaur PIII.

You will need to do a few modifications on it, though. For example, the likely reason why one of its original caps cooked is because of the minimum load resistors. Using this photo as a reference:
http://www2.picturepush.com/photo/a/...g/11286455.jpg
note the 3 large resistors...
- 1 just below the bad Koshin cap you replaced
- 2 to the right of the orange wires
These are the minimum load resistors. More often than not, Deer/Allied likes to use low values for these so they end up generating a lot of heat and cook the caps. If you are going to use this PSU with a computer, then you can change those resistors.

I'm not sure if the readings are valid with the resistors still soldered to the PCB, but this is what the multimeter measures applied to both legs of each resistor:

Assuming you'd want to use this with your Pentium 3 PC ...

Yes, an all-out modifying to suit the PIII in exclusive is OK.

... you can make the following changes to the load resistors:
3.3V rail: swap for 33 to 100 Ohms resistor (preferably 33 to 47 Ohms), 1 Watt or higher rated resistor
5V rail: swap for 56 to 270 Ohms resistor (100 Ohms works well, but you can go even higher than 270 Ohms if you're going to use this PSU only on 5V-based computers). Again, for power rating, you'll want 1 W or higher.
12V rail: 270 Ohms resistor or higher, 1 W rated.

Err ... again excuse the noob question ... how can I find which resistor works for which rectifier? Maybe beeping my way somehow ?

Another modification you should do - change the output caps so that the 3.3V and 5V rails have 2x 2200 uF caps each. That 10 V, 1000 uF Koshin cap you swapped is on the 3.3V rail IIRC. 2200 uF would be better in its place.

Last but not least, I think there's a small 22 uF, 50V cap on the primary side close to one of the small transformers (should be close to the 5VSB transformer) - that cap is the 5VSB critical cap. If it goes bad, 5VSB can go as high as 12V and can take your motherboard with it. So if you're recapping the thing, you might as well get that cap too. I *think* it was 22 uF 50V, but it may also be 47 uF, 25V or 47, uF 50V. Double-check me.

Damn it, in for a penny, in for a pound , let's recap the whole thing with jap caps. I'm going to desolder all the cRapacitors in this PSU, identify them, make a list, and then you can suggest suitable replacements tailored for the PIII.