How to: recapping the Mega STe power supply

[stephen_usher]

It does mean that everyone might be running these fans "backwards". I need to look at how I connected mine.

I've been wondering about the same. So what is the original direction? Is the fan sucking new air in or blowing hot air out?

Blowing out.

[IngoQ]

That's a strange one... Usually you would want the generated airstream to be as cool as possible, that's why you'd normally place a fan in a power supply, that sucks cool air in and blows at the components, at least to my (somewhat limited) knowledge...

[Icky]

That's a strange one... Usually you would want the generated airstream to be as cool as possible, that's why you'd normally place a fan in a power supply, that sucks cool air in and blows at the components, at least to my (somewhat limited) knowledge...

I think the concept is for the fans to pull out air so that the air flow is in through the case across the components and out of the power supply or any additional fans (in the case of the older TT's that had an additional fan on the right hand side at the back to also pull out air.

Even today ATX case PSU tend to have fans that either push air out the back or have a fan at the bottom that pushes the air in and out the back.

[exxos]

I did a big experiment with fans on my PC some years ago. Having fans blowing cool air in caused massive overheating... I mean, take side of PC and burn your face kinda heat. same fans blowing outwards, everything remains cool.

So you can't cool down parts by blowing cool air onto them, all you do is circulate the hot air in the case which has nowhere to escape to. You have to suck out the hot air from inside the case.

Similar problem with fans blowing on heatsinks on the CPU.. all it does is blow hot air from the CPU all over the ram and motherboard.. I always had the fan sucking upwards then another fan to suck that air out the back of the case. This way cooler air flows across the motherboard cooling it, then into the CPU cooler, then out of the back of the case.

PSU's are a bit more complicated because of smaller enclosed box. Really they should have a large fan on the bottom pushing air into the case, then 2 smaller fans on the rear sucking that hot air out.

[IngoQ]

I've seen this debated in modding forums long and excessively ;)

Of course you would need the hot air to go somewhere, so ideally I agree that you would have multiple fans establishing a defined air flow over the components. In that case, the direction of the airflow is probably unimportant, although using gravity and chimney effect is a good idea.

But in the special case, where you have a more or less small enclosure, with one fan and at least one additional opening, where you can either suck air in or blow hot air out, I wonder, which would be more efficient?

My theory is, blowing fresh and cooler air in is more efficient than sucking out the hot air. And at least with a (of course much larger) network enclosure I was able to verify this. I placed 4 pushing fans at the bottom and achieved lower temperatures than with the same set of fans on the top and pulling.

Again all of this provided, the hot air has an additional and sufficient way out (or in).

[exxos]

If we talk about the mega ST rear fan as a example.. I would say having it sucking air out the back is the way to go.

Simpley because if it was blowing air inwards, yes it may cool the PSU "better" that way, but the hot air is trapped inside the mega case, so the heat builds up and after a few hours things start to melt.

If the fan is sucking air out, the PSU may not actually be cooled as much as blowing on it, but the heat build up over time wouldn't happen, so it would overall run at a stable temperature.

If you only ran the mega for a hour, then having the fan blowing inwards would probably be more optimal, but hours later it would be worse. In that respect sucking out is overall always better.

In terms of natural convection.. my PC has vent holes in the top, so heat can escape, but its not affecting as fans running.. Even just a tiny bit of airflow can work wonders.

My CPU cooler is large...

461322_3242297771991_1072699933_o.jpg

Air is sucked over the ram, then into the CPU cooler, pushed though and hot air sucked out of the back by the rear fan.

Really the vent holes you can see should be blocked off to stop some air blowing into the case but.. well... life's to short :P

Above the cooler is also a fan which is in the top of the case, this is also sucking air out of the case.

If I only had the CPU cooler fan, most of the hot air remains trapped inside the case, and natural convection doesn't happen fast enough to remove the heat.

[Pacman]

Just wondering if after all these posts on capacitors, Pacman should change name to Capman :D

Not a bad suggestion actually :D :lol:

[Steve]

Thanks for confirming, Exxos.
Here's the corrected pinout. I'll also replace the pinout diagram in my original posting along with all the instructions to avoid any confusion (Oops: that didn't work -there's no "edit post" button there any longer. Any chance you could replace the diagram in the first posting with the one attached here?).

Noctua fan connector corrected.png

Pacman your image is still wrong. It's not -12 and +12, its GND and -12. Which means no matter what, the fan will run backwards if you connect red/positive to -12.

I have often felt the back of my TT fan grill and thought I'm not feeling much exhaust, even though my Noctua is on 100%. Perhaps what I am feeling is some indirect exhaust caused by the case design and obstruction. I'm going to try switching the power connector polarity and see the difference.

[Pacman]

Pacman your image is still wrong. It's not -12 and +12, its GND and -12. Which means no matter what, the fan will run backwards if you connect red/positive to -12.

It's been a while and I don't have my MegaSTe nearby to meter the connector, but does this look right?
The power supply PCB labelling is confusing since it says "+" and "-".

Noctua fan connector corrected_final_correction.png

[frank.lukas]

Red Wire from the Fan to GND
Black Wire from Fan to -12V