What could cause this PSU to output 12.5V on the 12V?

[Wester547]

Re: What could cause this PSU to output 12.5V on the 12V?

2x470uF primary caps: (maybe) 300watt peak

I know I've questioned this before but I think it's intriguing: do primary capacitors affect the overall wattage that much or does that depend a great deal more on the rest of the components and do they just augment efficiency? I've read that 560uF/470uF primaries achieve 350-400W+ (respectively) in some reviews of other power supplies, albeit in very well designed power supplies. And yes, TKs are utter garbage. As bad as Fuhjyyu. I don't think they're rebranded OSTs but worse. As for the 12V rail, it's pushing it a bit but it's within spec. I think this PSU is probably 270W continuous / 300W absolute max as is. And I imagine the two 30As would be for the 5V/3.3V rail, the 20A for the 12V rail, and 5A a voltage regulator of sorts for something else.

[Pentium4]

Re: What could cause this PSU to output 12.5V on the 12V?

I know I've questioned this before but I think it's intriguing: do primary capacitors affect the overall wattage that much or does that depend a great deal more on the rest of the components and do they just augment efficiency? I've read that 560uF/470uF primaries achieve 350-400W+ (respectively) in some reviews of other power supplies, albeit in very well designed power supplies. And yes, TKs are utter garbage. As bad as Fuhjyyu. I don't think they're rebranded OSTs but worse. As for the 12V rail, it's pushing it a bit but it's within spec. I think this PSU is probably 270W continuous / 300W absolute max as is. And I imagine the two 30As would be for the 5V/3.3V rail, the 20A for the 12V rail, and 5A a voltage regulator of sorts for something else.

Thank you for your input. I might throw some 560's on there. i'd definiitely want to upgrade the switching transistors before the output diodes. maybe even the transformer too, I'll post questions here about that later, I got a decent amount of parts lying around

[Pentium4]

Re: What could cause this PSU to output 12.5V on the 12V?

Okay, so I still have a lot to learn. I have a transformer here from a half bridge powerman that I parted out. The transformer from this L&C has a wire coming out of the transformer going straight to the board. How come the transformer from the powerman doesn't, what is the difference?

[Th3_uN1Qu3]

Re: What could cause this PSU to output 12.5V on the 12V?

That wire is the median of the secondary which is connected to ground. It's the most common approach in half bridge PSUs because of commodity - since you have a bunch of ends that need to be connected to ground, it's easier to break it out from the top.

Being the most convenient way doesn't make it the only way tho - the transformer from the powerman likely has the ground wires on one or two of the pins.

[Pentium4]

Re: What could cause this PSU to output 12.5V on the 12V?

That wire is the median of the secondary which is connected to ground. It's the most common approach in half bridge PSUs because of commodity - since you have a bunch of ends that need to be connected to ground, it's easier to break it out from the top.

Being the most convenient way doesn't make it the only way tho - the transformer from the powerman likely has the ground wires on one or two of the pins.

Sweet, thanks! I'll keep an eye out for some transformers that will fit, the one from the powerman didn't line up. I'm wondering if I can replace the small coil on the secondary with this one from a Bestec. They both just have a pin on each side. Does it matter that the Bestec is a Single Transistor Forward and the L&C is a Half Bridge? It looks quite a bit bigger.

[momaka]

Re: What could cause this PSU to output 12.5V on the 12V?

Does it matter that the Bestec is a Single Transistor Forward and the L&C is a Half Bridge? It looks quite a bit bigger.

No, but the input/output wires have to match, which I don't think will be the case, even if the chokes do have the same number of wires. The L&C likely has wires for the -12V (and possibly -5V) rail while the Bestec might not. Check before swapping!

[Pentium4]

Re: What could cause this PSU to output 12.5V on the 12V?

No, but the input/output wires have to match, which I don't think will be the case, even if the chokes do have the same number of wires. The L&C likely has wires for the -12V (and possibly -5V) rail while the Bestec might not. Check before swapping!

Thanks for the reply. How would I check? Follow the traces?

[momaka]

Re: What could cause this PSU to output 12.5V on the 12V?

Thanks for the reply. How would I check? Follow the traces?

Yes, that's one way.

If you haven't removed those chokes from the power supplies yet, there is actually an easier way with a multimeter...
1) Set multimeter to continuity or lowest resistance setting
2) pick a wire on the choke and put one of the multimeter's probes on it.
3) connect the other probe to the 3.3V rail, then the 5V, then 12V, then -12V (one at a time, of course), and so on until you find on which one get zero resistance/good continuity. The rail that gives you zero ohms/good continuity is the rail that is associated with that wire on the choke.
4) move to the next wire on the choke and repeat steps 1 to 3 until you find what each one is connected to.
5) do steps 1 through 4 for both PSU chokes.

Checking the wires is actually necessary, because when you are transplanting a choke from one PSU to another, it is imperative that you match the wires on the choke from the donor PSU to the correct voltage rails in the acceptor PSU. Otherwise, you likely won't get proper regulation. Moreover, the choke will probably begin to heat up quite badly too.

[Pentium4]

Re: What could cause this PSU to output 12.5V on the 12V?

Yes, that's one way.

If you haven't removed those chokes from the power supplies yet, there is actually an easier way with a multimeter...
1) Set multimeter to continuity or lowest resistance setting
2) pick a wire on the choke and put one of the multimeter's probes on it.
3) connect the other probe to the 3.3V rail, then the 5V, then 12V, then -12V (one at a time, of course), and so on until you find on which one get zero resistance/good continuity. The rail that gives you zero ohms/good continuity is the rail that is associated with that wire on the choke.
4) move to the next wire on the choke and repeat steps 1 to 3 until you find what each one is connected to.
5) do steps 1 through 4 for both PSU chokes.

Checking the wires is actually necessary, because when you are transplanting a choke from one PSU to another, it is imperative that you match the wires on the choke from the donor PSU to the correct voltage rails in the acceptor PSU. Otherwise, you likely won't get proper regulation. Moreover, the choke will probably begin to heat up quite badly too.

Thanks for the awesome informative reply. I'm going to leave it for now but probably come back to it. First I want to look at replacing the transformer and the switchers. I was wondering if 13007's and a SW2N60 are better than the current ones in there? I'm parting out that Logisys and wanted to use some of those parts

[Pentium4]

Re: What could cause this PSU to output 12.5V on the 12V?

How much would it increase the efficiency if I replaced the DFF2N65, and two D304X's with three 13009's? (Still looking for a transformer for it) Then I'm going to take momaka's advice to see if I can replace the chokes

[momaka]

Re: What could cause this PSU to output 12.5V on the 12V?

How much would it increase the efficiency if I replaced the DFF2N65, and two D304X's with three 13009's?

The DFF2N65 is a MOSFET, I believe (can't find a proper data sheets for it, though... only bits of info on the web). You can't replace MOSFET with a BJT.
Also, I doubt the 13009s will increase the efficiency much (if at all). Better off just replacing the silicon on the secondary side with good, low-voltage drop schottkys. That will increase the efficiency for sure.

[Pentium4]

Re: What could cause this PSU to output 12.5V on the 12V?

The DFF2N65 is a MOSFET, I believe (can't find a proper data sheets for it, though... only bits of info on the web). You can't replace MOSFET with a BJT.
Also, I doubt the 13009s will increase the efficiency much (if at all). Better off just replacing the silicon on the secondary side with good, low-voltage drop schottkys. That will increase the efficiency for sure.

That was gonna be my next step And those Fets installed are good for up to around 300W?

[Th3_uN1Qu3]

Re: What could cause this PSU to output 12.5V on the 12V?

I was able to pull 650W continuous from 13009s, at 35C ambient. Would have gone higher but i designed the transformer for 600W tops, and it started getting quite hot.

It's all about the secondary. Lower voltage drops on the secondary = higher efficiency = less wasted power = more power output from the same primary parts.

[tom66]

Re: What could cause this PSU to output 12.5V on the 12V?

And the transformer. I figure that the drop in efficiency near when a PSU fails must be, at least in part, related to the transformer saturating.

[ben7]

Re: What could cause this PSU to output 12.5V on the 12V?

And the transformer. I figure that the drop in efficiency near when a PSU fails must be, at least in part, related to the transformer saturating.

Oh yes, indeed it is! When it saturates, it can't 'hold' any more magnetic flux, and so the windings basically act like a simple wire. That is, the current isn't 'limited' by the reactance of the transformer anymore! Then the current goes up very high, efficiency drops, and usually the increase in current causes the primary switchers to blow up. That's as far as I know...

[Pentium4]

Re: What could cause this PSU to output 12.5V on the 12V?

Thanks for the valuable knowledge guys First things first, this thing needs a new transformer. That sticker isn't fooling anyone, that thing isn't even close to a 35. It's probably a 28. And just for kicks I put a much nicer input coil on the primary, the one it had was tiny

Edit: Added updated pictures

[goodpsusearch]

Re: What could cause this PSU to output 12.5V on the 12V?

It's 33.

[Pentium4]

Re: What could cause this PSU to output 12.5V on the 12V?

So only good for around 275W? I should probably upgrade the input caps too, I never trust the label on an input YC cap

[ben7]

Re: What could cause this PSU to output 12.5V on the 12V?

So only good for around 275W? I should probably upgrade the input caps too, I never trust the label on an input YC cap

The heatsinks need to be upgraded. I bet they'll be smokin hot at 200w!

[goodpsusearch]

Re: What could cause this PSU to output 12.5V on the 12V?

The heatsinks could be fine as long as the fan is moving some air.

250W continuous, as long as the caps are real 470uF.