Why are fanless Flex ATX PSUs so rare?

[seb101]

I'm confused. Laptop power supplies for gaming/workstation laptops are readily available, supplying 19V at 180W and they don't even get that hot while in use, despite being encased in thermally insulating black plastic. They can be picked up pre-owned for about $25.

However Flex ATX power supplies, even at 150W, despite being vented and able to dump most of the heat into the chassis through the metal casing, insist on having a noisy 40mm fan installed.

So despite the 150W Flex ATX form factor being a better bet for fanless performance, the only fanless Flex ATX PSU I can find is this one and it seems to be very hard to find (perhaps out of production?) and costs $100!

Why is this?!

 

[artlessknave]

because flex ATX is INSIDE the case, while laptop bricks are outside, flex ATX is typically used for server applications where noise doesnt matter, and the manufactuers haven't decided that there is enough demand so they dont bother.

 

[HolyK]

Oh nonono. I've seen consequences (001, 002, 003) of third-degree burns from laptop "brick" (got hot then shortage happened). These things can get hot ... very hot. Even my T480 adapter which is 20V/65W can get quite warm when the battery is not fully charged and the machine is under load. And it is only "warm" because it is on "open air". Close this thing into a small metal case ... well..

And the second reason is a life span i believe. Laptops are not 24/7 constant load, servers are. I *guess* the passive-cooled PSU in 24/7 server would die much earlier than the active-cooled one. The thing is that PSUs are usually at the back of the chassis so the "cold air" which is being pushed through front FANs gets the heat from disks, RAM, controllers, etc... so at the back side of the chassis it is not cold anymore. More over the air would cool-down the enclosure of the PSU but the real parts wouldn't be cooled enough (the air gets out by the easiest path and the small PSU enclosure with small holes is not the one). So i guess the 40mm FANs are there to create a negative pressure (inside the PSU enclosure) which sucks portion of the "not-that-cool" air from within the chassis which helps to cool down the PSU parts.

This is just my theory but ~3 years back we (well one of our client) had unexpected system shutdown because of failed PSU. There were 4 PSUs (2x2 redundancy) but one was dead for a while waiting for replacement and other one from the same set died as well so the system went into panic shutdown. Later examination showed that the second PSU shut down because the thermal safety got tripped. RCA was that the PSU FAN got broken (bearings wrecked). There were no thermal alerts from other parts of the server so the PSU itself got very hot.

It was a very fun night as it was sunday 2AM right after christmas and they did not had replacement available at the moment (box of 10 PSUs supposed to arrive the next week). So there was a guy at 2AM driving to other DC 50km away just to pick the same model of PSU and drive back to DC1 and replace it. In the meanwhile management came with a superb idea to "borrow" the "spare" (read as "redundant") from the other frame. Luckily there was enough of "admin power" in the groupchat to prevent this nonsense. Well at the morning on they found that one of the two PSUs in the other frame was actually dead as well and that one was the reason why they ordered new box of PSUs. :D