Cheap PSU: Piece of junk or semi-decent?

[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.

[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.

[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?

[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.

[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.

[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?

.

[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 :


.

[tmiha71]

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

Now, if you really didn't put insulator where it was needed, i'll skip all your posts in future :-))

[Behemot]

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

You were supposed to smack yoruself, not somebody else!

[TELVM]

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

... now smack yourself on the forehead and try it again with insulator! ...

Aye aye!



OK at last, once insulated from the secondary heatsink, the new rectifier works as advertised . ~12.3V & 5.07V with a couple fans plugged in, and no explosions thus far .

.

[kc8adu]

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

yes it does!
now smack yourself on the forehead and try it again with insulator!
i was thinking solder short.your original had an isolated tab.

[TELVM]

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

Soldered back the original MBR20150CTP +12V rectifier and the PSU works OK . Once on board the MBR20150CTP reads thus:

Legs 1 or 3 to Leg 2 (center): .213 , Ω 80.6
Leg 2 (center) to Legs 1 or 3: .390
Leg 2 to YELLOW WIRES: .001 continuous beep , Ω 01.0
Leg 2 to GROUND: .390 , Ω 1.


This means the gremlin dwells in the new rectifier somehow.


I wonder why the new STPS40M60CTN reads like it is shorted while on board ... and I'm thinking ... could it be that, unlike the MBR20150CTP, it needs to be isolated with a mica from the (grounded) secondary heatsink?

[tmiha71]

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

http://en.wikipedia.org/wiki/Avalanche_breakdown

Probably too high reverse voltage (for that part)...

[TELVM]

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

OK, removed the newcomer STPS40M60CTN and out of the board reads:

Legs 1 or 3 to Leg 2 (center): .150 , Ω 58
Leg 2 (center) to Legs 1 or 3: 1.

^ Does that sound like shorted ?

For comparison, the original MBR20150CTP out of the board reads:

Legs 1 or 3 to Leg 2 (center): .240 , Ω 88
Leg 2 (center) to Legs 1 or 3: 1.


The holes in the PCB (sans +12V rectifier) now read:

Holes 1 or 3 to Hole 2 (center): .390 , Ω 1.
Hole 2 (center) to Holes 1 or 3: .390
Hole 1 to Hole 3, or vice versa: .001 continuous beep , Ω 01.0

Hole 2 (center) to YELLOW WIRES: 0.01 continuous beep , Ω 01.0
Holes 1 or 3 to YELLOW WIRES: 0.390 , Ω 1.0
YELLOW WIRES to GROUND: .390 , Ω 1.

[domas]

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

yes, after you desolder 12v rectifier measure both pcb without rectifier and the rectifier itself separately. There might be a short somewhere else around rect.

[Th3_uN1Qu3]

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

Sounds like your replacement 12v rectifier was shorted to begin with, or there's something wrong with the soldering. Remove it and measure again. BTW, legs 1 and 3 are not "shorted over pcb" in a half bridge PSU, they are connected to opposite ends of the transformer winding. But since the winding is made with thick wire, it measures (almost) shorted. An inductance meter would tell you a different story.

[domas]

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

12V one seems to be shorted
leg 1 to 3 of rectifier and vice versa are normally shorted over pcb, that is normal.

2 to 1/3 and vice versa should not be shorted.

[Behemot]

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

Either there are minimum load resistor of quite low values or it's shorted.

[TELVM]

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

Swapped the MBR20150CTP +12V rectifier for a STPS40M60CTN.

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

No fireballs but no joy, the PSU doesn't start .

When switched on the fan doesn't move even a bit. With the multimeter on the +5V rail I see just ~a couple volts that very quickly drop to zero.

+5vsb is alive showing ~5V.


Testing with the MMF:

+12V rectifier (the new one)
Leg 1 Leg 2 (center) = 0.0 continuous beep
Leg 3 Leg 2 (center) = 0.0 continuous beep
Leg 1 Leg 3 = 0.0 continuous beep

+5V rectifier
Leg 1 Leg 2 (center) = 0.48 short beep
Leg 3 Leg 2 (center) = 0.48 short beep
Leg 1 Leg 3 = 0.0 continuous beep

+3.3V rectifier
Leg 1 Leg 2 (center) = 0.15 continuous beep
Leg 3 Leg 2 (center) = 0.15 continuous beep
Leg 1 Leg 3 = 0.0 continuous beep


+12V YELLOW WIRES GROUND WIRES = 0.0 continuous beep
+12V YELLOW WIRES Ω GROUND WIRES = 1Ω

+5V RED WIRES GROUND WIRES = 0.48 short beep
+5V RED WIRES Ω GROUND WIRES = 44Ω

+3.3V ORANGE WIRES GROUND WIRES = 0.15 continuous beep
+3.3V ORANGE WIRES Ω GROUND WIRES = 15.4Ω


What do you think?

.

[Behemot]

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

Problem are the spikes, according to the unique (sorry, not using those strange-stuff numbers ) quite high reverse-voltage spikes can occur and the rectifier has to handle them.