Recommend 500W PSU with always on fan

[SithUK]

tldr;
Time for a new 500W(ish) quiet PSU. I need the PSU fan to be running all the time at idle to stop air being drawn back through the PSU by rear mounted fans. What do you recommend for a PSU with a near silent always on fan? Preferably modular and excellent efficiency. Something tier A from the PSU list would be good (https://cultists.network/140/psu-tier-list/). I don't mind buying second hand. At the 500W capacity there are often people selling to upgrade.

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I have an old style ATX mid tower case with the 500W PSU mounted at the top, drawing air from inside the case and exhausting it outside the case. The case originally had a rear case fan just below the PSU.

I have converted the case to a custom watercooled setup. I removed the rear case fan and hung a 2 x 120mm radiator off the rear of the case with a duct connecting to where the case fan used to be. So the radiator fans pull air through the dust filter at the front of the case and exhaust the air through the radiator block. The rest of the case is air tight, except for the PSU. The PSU air intake is just above the case fan.

My PSU is getting on a bit, with the PSU fan starting to be noticeable at idle. I had a look at the PSU list (https://cultists.network/140/psu-tier-list/) and bought a Corsair RM550x PSU to replace my venerable Seasonic 500W PSU. Corsair notes in the spec sheet that the RM550x only starts its fan at 40% load. I only use the system for low load tasks the majority of the time, so I thought it would be ideal.

However, if the PSU fan is completely turned off then it is likely that the radiator fans will draw air back through the PSU, bypassing the dust filter at the front, and drawing minimal air from inside the case. So I don't think the air flow through the case will work to cool the motherboard components and hard drive. I'll also risk dust build up. Yes, I should have realised this prior to purchase.

Alternative options
i) I've ruled out placing a dust filter over the PSU rear as that would impact on the PSU airflow when its fan was needed.
ii) I could mount a case fan at the front of the case to generate positive pressure inside the case. I would then need a separate fan controller and I might impact the overall noise level of the system.

The best option is just to replicate the configuration I have, which is a PSU with an always on fan at idle where the fan ramps up when on load. That will ensure I don't get a leak path of dusty air through the PSU.

Silence is important, as is efficiency and quality of components. Modular would be nice. The majority of the time the system is at low load (web / word processing / coding).

Please recommend a PSU.

 

[SithUK]

Replace the case, cheaper than a new psu and better for it too. Having the psu at the top sucking air from inside the case is one of the worst places for a psu. The fan is for cooling the psu so removing hot air from the case while trying to cool the psu will cause the fan to run faster and louder plus the psu internals will never be as cool as they would be with the psu in the bottom of the case drawing cold air through the bottom.

I custom modified my current case to:
drill holes for the 1/2" flow and return water lines; and
mount the radiator block out the back.

If I bought a new case I'd have to modify it to mount the radiator block and accommodate the water pipes.

Then there is the effort to transfer the components over (drain the water circuit, disassemble the watercooling and other components and transfer them).

That's a few days of effort at least.

A year old second hand PSU is around £40 delivered and I can swap out the PSU in my current case in an hour or two. So that's why I'm favouring just replacing the PSU.

Why don’t you just mount a 140 mm fan to your existing PSU?

3D print a mount to make sure that the airflow is what you want.

That or buy a different chassis that allows you to achieve what you want.

I don’t know a single PSU that has an always on fan because that would just wear the fan out and need replacing which is difficult when the fan is in the PSU.

An always on fan in a PSU sounds like a fix to a problem that could be more easily corrected by doing almost anything else.

The existing PSU has a 120mm fan that runs continuously. Almost all PSU fans ran continuously the last time I was in the market to buy one, except for some exotic fanless units. By run continuously I mean the fan would be powered on and would rotate at low rpm. The PSU had thermal control that would ramp up the fan when temps became elevated.
I appreciate that times have changed. The norm seems to now be for a bottom mounted PSU that is thermally isolated from the rest of the case internals with air drawn from outside at the base of the case.
Do you mean mount a 140mm fan at the front of the case? I considered that but then I'd need to buy a fan controller and the noise might be higher than just sticking with a 120mm+ PSU fan running on idle.

 

[SithUK]

The Seasonic Core GM looks like a contender, but it's only mid tier on the PSU list.

CORE GM

Seasonic CORE GM PSU. Gold-rated efficiency for energy savings and dependable performance. Semi-modular PSU is perfect for budget-conscious builders.

seasonic.com

Or the Seasonic Focus GM. It is high tier.

FOCUS GM

Seasonic FOCUS GM PSU features semi-modular design and gold-rated efficiency for superb energy savings and streamlined cable management.

seasonic.com

Both operate with the fan always on, with the fan ramping up under load.

 

[SithUK]

There are a huge number of cases that will fit 240/360mm rads and plenty that will take 280/420mm rads with no modification needed. I would rather buy a new case than have an old case that uses the psu as an exhaust fan. A psu is one of the few things I would never purchase second hand. You can't tell if it's been loaded within an inch of it's life or how old it is, all you have is what the seller tells you be it true or not.

My current case is an Antec Sonata. It’s made from fairly solid sheet steel to keep noise emission low. Could you recommend a similarly solid built case that will take a 240 radiator without modification? My current radiator is around 80mm deep.

It’ll be interesting to compare price and effort to swap to a new case vs just changing the PSU.

 

[SithUK]

@mattyfez : I don't have case intake fans. I have two fans mounted on the intake of the radiator block that hangs off the rear of the case. The fans are connected to the case by a duct so they pull air from the case and exhaust through the radiator block.

Thank you to @pastymuncher and @Grimley for the case suggestions. I'm minded to do a simple PSU swap for now. And look again at a case change when I next upgrade CPu & motherboard.

I can source a PSU for now that has the "hybrid" switch that toggles the fan between a "fan off at low load" and a "fan always on at low low". If I get a case with a bottom mounted PSU then I can put the PSU in its "fan off" at low load mode.