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Small, quiet, high-quality PSU that supports PMBus?

Scramblejams

Newbie
Joined
Apr 20, 2021
Messages
2
Hi all,

I've lurked on these forums for many years and been impressed with the knowledge here. Now I have a question that my Googling hasn't answered, and I'm hoping you can.

I'm looking at putting together a Supermicro SC510T-203B with an X10SLM+-LN4F. So far so good. I have a few X10SLMs in service and I love 'em. But the PSU in that Supermicro chassies does not seem to support PMBus, which means I won't have power consumption data through IPMI. I'd like to have that data. So I'm looking for a recommendation for a power supply that:

1) Is high quality. I learned my lesson on this long ago, and I'm willing to pay more to get good power.
2) Supports PMBus.
3) Is sized efficiently. This system will probably idle at ~30w, I expect it to spike no higher than 100w (probably lower, the internal config is 2 SSDs, no PCIe cards, and an E3-1220v3), and based on some test results I saw, larger power supplies can easily waste 10-20 watts at this idle load. Where I live power is pricey (~$3/watt-year) and since the system will be mounted in a living space, I'd also like to not generate unnecessary waste heat. ~150w would probably be a good target.
4) Is reasonably quiet, since it's going to be in a walk-in closet. Doesn't need to be silent, just shouldn't be a nuisance.
5) Hopefully fits in a 1U, but this isn't a deal breaker. I could upsize the chassis if I really have to.

I've looked around but been unable to find a PSU with these attributes. Any thoughts or suggestions would be appreciated. Thanks!
 

jgreco

Resident Grinch
Moderator
Joined
May 29, 2011
Messages
14,159
You're not going to find that in the Supermicro lineup, because that is mostly seen as a "value" chassis, and PMBus support is more of a premium feature. Most buyers also aren't that interested in detailed power information at the low end, seeing as how those supplies are already extremely efficient.

https://www.supermicro.com/en/support/resources/pws

The smallest one I'm aware of with PMBus support is the PWS-341P-1H, which I've got running in some older 1U X9SC* hosts. It is probably too long for your short-shot chassis application, but perhaps you could use a deeper 1U chassis.
 

Scramblejams

Newbie
Joined
Apr 20, 2021
Messages
2
Thanks for your reply! Yep, there are some options if I were willing to up the wattage, I'm just hoping to avoid the efficiency hit that comes from pairing an oversized PSU with a system that idles really low.
 

jgreco

Resident Grinch
Moderator
Joined
May 29, 2011
Messages
14,159
There really shouldn't be much of a hit, unless you're looking to do something crazy like a 700W PSU for a system that only needs 50W.

The rest of this message is just discussing efficiency; do not make the mistake of assuming that any PSU mentioned other than the 341P supports PMBus!

The PWS-341P-1H is rated at 85.3% efficiency at 10% load, and 90.45% at 20%. Most Platinum supplies top out around 94% efficiency when they are at around 50% load.

The 341P is a 340W PSU.

Assuming you can get your system to hit an idle of 30W, which I suspect is somewhat low, but if you're doing passive cooling and only SSD's without an HBA, I guess you could probably get there... that puts you around 10% capacity of a 341P.

What this means is that your usage "at the plug" would be 35.17 watts (30W / .853). If you could hit the very best efficiency afforded by a Platinum supply, this would instead be 31.9 watts, or a savings of 3 watts. But you can't do that, because you'd need to be in the 50% usage of a hypothetical 60W Platinum PSU.

There are 1U PSU's made in the 90-100W range. For example, the Phihong PSF115-332-R is a 95W Bronze PSU, but at 20% load it is 82.9% efficienct, at 50% load it is 85.6%, so maybe it is let's say 84% efficient at your ~33% load. This means that draw "at the plug" is 35.71 watts (30W/.84) -- actually HIGHER than the 340W platinum PSU.

So even if you do find the unicorn in the form of the Lite-On PA-2251-2, which is a non-ATX PSU, Titanium rated 250W, 95.5% efficient at 10%, 91.3% at 20%, this gives you maybe a 94% efficiency at your 30W workload. That works out to 31.91 watts, which is indeed 3.26 watts better than the 341P.

So. If we circle around to your original post,

based on some test results I saw, larger power supplies can easily waste 10-20 watts at this idle load.
there is a lot of stupid floating around out on the Internet, especially when people have agendas.

My agenda is simply putting sensible information out there; the PSU numbers above were taken from Plug Load Solutions, you are not my customer, I am not going to sell you anything, even though I do this professionally, and I do not own any stock in PSU companies.

I typically argue for larger PSU's for NAS units, complete with homework, and indeed we have an entire article and discussion of this here on the forums:

https://www.truenas.com/community/threads/proper-power-supply-sizing-guidance.38811/

Also, in your original post, the chassis you suggested comes with Supermicro's PWS-203-1H, which I'm going to guess is 88-88.5% efficient at your intended load, or 34.1 watts "at the wall". So my opinion is that the best thing you could do would be to Just Use The Provided Power Supply and just forget about PMBus. But if you really must have PMBus and are willing to burn a few more watts to get it, then the 341P is the option I'd suggest, although if you look long enough, someone else probably makes something similar.

I have taken some extra time here to discuss this with you because you seemed to be laboring under the quoted misconception about PSU sizing.
 
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