2U PSU

[heimdali]

Which PSU would you suggest for a case that fits a 2U single PSU (or a redundant one)?

 

The case fits 16x3.5" disks and may get a board (probably Supermicro or Intel) with 1 or 2 CPUs rated for 145W TDP each, plus a graphics card.  That adds up to about 1010W, plus a couple fans and some reserve for HBAs and network cards, and I'm suddenly looking at a 1200W PSU

 

I'll probably have no more than 4--6 disks in it and probably only one CPU plus cards and fans.  That means I could get away with 650W and be on the save side with 750W.

 

The PSU must be (reasonably) quiet and must not cost a fortune.  If if it gets a bit louder when under high load that's ok.

 

Are the Zippy and Seasonic PSUs any good?

 

[RollinLower]

what chassis is this? if you can find them, Supermicro makes some incredibly silent SQ PSUs in 1KW capacities.

i highly doubt you'll be pulling 1200 watts on this system with just 16 disks.

[mariushm]

What video card do you plan to use? 

 

The drives don't consume that much power, around 6-10 watts each ( typically 60% on 5v , 40% on 12v to spin the motor) ... keep in mind this 5v requirement, get a psu that can supply at least 20A on 5v or you'd have to get dc-dc converters to convert some 12v to 5v for power to hard drives. Some cases / drive bays  have such dc-dc converters built in.

 

As for CPUs let's say you allocate 200w for each, that would mean 400w reserved for CPUs 

Reserve 50w for motherboard, ram and HBA cards (ram's around 2-3w per stick, mobo is around 10-20w for chipset and onboard devices )

No idea what video card you use, you'd have to get a 4090 to consume 450-500w and require a 1000w or higher psu. 

 

 

[heimdali]

6 minutes ago, RollinLower said:

what chassis is this? if you can find them, Supermicro makes some incredibly silent SQ PSUs in 1KW capacities.

i highly doubt you'll be pulling 1200 watts on this system with just 16 disks.

It's a Chenbro RM31616.

 

I calculate each disk with 20W --- I know they'll probably never need that much, but I have older disks, too, and it's on the save side.  I have 16 disks running in a server and it takes about 250W.  So 650W is probably enough, but I don't want to end up having to get another PSU 5 years or so from now because I got one that's too small.  Only I don't know which PSUs are good and not too loud.

 

BTW, why does, for example, AMD say that a graphics card that draws 335W should have at least an 850W PSU?

 

 

[RollinLower]

6 minutes ago, heimdali said:

It's a Chenbro RM31616

correct me if i'm wrong, but isn't this a 3U chassis?

so if it is 3U, you might be able to just fit a regular ATX powersupply, and in that case regular rules apply. (i use Seasonic in my own server)

10 minutes ago, heimdali said:

BTW, why does, for example, AMD say that a graphics card that draws 335W should have at least an 850W PSU?

because AMD does not know what the rest of your system is like, so they calculate massive overheads to account for the worst-case scenarios.

[heimdali]

2 minutes ago, mariushm said:

What video card do you plan to use? 

That depends on the development of the prices and of other things.  I have an AMD 6600XT which I might repurpose and upgrade if the prices go down because the card is a bit weak for a 4k display.

2 minutes ago, mariushm said:

The drives don't consume that much power, around 6-10 watts each ( typically 60% on 5v , 40% on 12v to spin the motor)

Some older disks would go to 12--15W.  That's still an extreme case, but it doesn't help me when things get unstable because the PSU is too small.

2 minutes ago, mariushm said:

... keep in mind this 5v requirement, get a psu that can supply at least 20A on 5v or you'd have to get dc-dc converters to convert some 12v to 5v for power to hard drives. Some cases / drive bays  have such dc-dc converters built in.

Thanks, that's really good advice!

2 minutes ago, mariushm said:

 

As for CPUs let's say you allocate 200w for each, that would mean 400w reserved for CPUs

200W for CPUs rated at 145W?

2 minutes ago, mariushm said:

Reserve 50w for motherboard, ram and HBA cards (ram's around 2-3w per stick, mobo is around 10-20w for chipset and onboard devices )

No idea what video card you use, you'd have to get a 4090 to consume 450-500w and require a 1000w or higher psu. 

Who knows, it would suck if I had to hold off an a graphics card because the PSU is too small.  But then, the question is how much it's going to cost.

 

[heimdali]

40 minutes ago, RollinLower said:

correct me if i'm wrong, but isn't this a 3U chassis?

so if it is 3U, you might be able to just fit a regular ATX powersupply, and in that case regular rules apply.

Yes, 3U --- I was thinking of using a standard ATX one, but I'm not sure if that'll fit.  If it did, why wouldn't the documentation mention it.  I don't have a standard PSU at hand but I can measure the case.  It wouldn't really matter if it didn't fit right as long as it does fit.  Since I need to buy one anyway, it would be nicer to get one that does fit.

40 minutes ago, RollinLower said:

(i use Seasonic in my own server)

Same here; I like Seasonic.

40 minutes ago, RollinLower said:

because AMD does not know what the rest of your system is like, so they calculate massive overheads to account for the worst-case scenarios.

Hmm ...

 

Ok, let me go measure it ...  Here we go, the opening for the PSU is about 125mm high and 102mm wide.  There's lots of room towards the front; if a standard ATX PSU would fit besides the mainboard, I could throw it in.

 

 

[mariushm]

The TDP is different than actual power consumption ... and processors can have "bursts" of power draw for short periods of time. Think of the scenario where the cpu was kind of idle and the cooler keeps it at 50-60c .. the processor knows that it can burst for a few seconds and be fine because the thermal mass of the cooler on top (all those fins and heatpipes) will guarantee the cpu will stay below around 100c for those few seconds. So the cpu could go up to 150-200w for a few seconds until the heatsink can't handle it anymore and it's at the 85-90c temperature and then it can lower the frequencies to give the cooler time to go down.

For example, 5950x has a 105w TDP, but will consume 120 watts in Blender and can go up to a sustained 160 watts if the cooler can handle it. If you overclock it, it can go to 250 watts. 

See for example the picture below, taken from the 5800x3D review ... you can see 65w TDP cpus go above 65w, and 105w TDP cpus hit 120-130w in well multithreaded jobs. 

 

As for video cards ... manufacturers have no idea what power supply you're gonna buy, what quality, and they have no idea what other components you're gonna use - are you gonna get a R5 4500 that consumes 50w  or are you gonna get a 12900K that goes to 243 watts? 

There's cheap 450-550 watts based on old designs that can do only 300-350w on 12v so when the video card alone consumes 200-300 watts, they can't say a 450w psu is minimum.  There's also power supplies that have 2 or more rails, and each rail has some limits .. for example, on a 500w dual rail power supply each rail could have a limit of 16-18A per rail or around 200-250 watts, so even if the power supply could handle a 300w video card, the power supply may shut down because user accientally selects 2 pci-e 8 pin connectors that are on the same rail and the video card pulls more than 200-250 watts from that rail. 

So they go and recommend 650w or more, because pretty much such power supplies will handle a 250-300w video card and they won't get RMAs and complaints and they reduce the support tickets due to crashes or computer resets which would actually be caused by crappy power supplies failing.

 

The 6600XT will consume up to around 190 watts from 12v, but it could have small bursts (for like half a second here or there, not continuously) up to maybe 210-230w 

 

 

[heimdali]

1 minute ago, mariushm said:

The TDP is different than actual power consumption ... and processors can have "bursts" of power draw for short periods of time. Think of the scenario where the cpu was kind of idle and the cooler keeps it at 50-60c .. the processor knows that it can burst for a few seconds and be fine because the thermal mass of the cooler on top (all those fins and heatpipes) will guarantee the cpu will stay below around 100c for those few seconds. So the cpu could go up to 150-200w for a few seconds until the heatsink can't handle it anymore and it's at the 85-90c temperature and then it can lower the frequencies to give the cooler time to go down.

For example, 5950x has a 105w TDP, but will consume 120 watts in Blender and can go up to a sustained 160 watts if the cooler can handle it.

That makes sense.  I haven't decided on a cooler yet; I could go with a Dynatron R-27 which is rated for 160W.  That's only because I'm fine with the Dynatron cooler in my server and the R-27 fits 2U.

1 minute ago, mariushm said:

If you overclock it, it can go to 250 watts. 

I don't plan on trying that.  I've never been successful with overclocking and it can drive you crazy ...

1 minute ago, mariushm said:

See for example the picture below, taken from the 5800x3D review ... you can see 65w TDP cpus go above 65w, and 105w TDP cpus hit 120-130w in well multithreaded jobs. 

Hm.  Maybe I need a better cooler?  When the CPU can go to double the TDP, I'd need a 300W cooler.

1 minute ago, mariushm said:

As for video cards ... manufacturers have no idea what power supply you're gonna buy, what quality, and they have no idea what other components you're gonna use - are you gonna get a R5 4500 that consumes 50w  or are you gonna get a 12900K that goes to 243 watts? 

There's cheap 450-550 watts based on old designs that can do only 300-350w on 12v so when the video card alone consumes 200-300 watts, they can't say a 450w psu is minimum.  There's also power supplies that have 2 or more rails, and each rail has some limits .. for example, on a 500w dual rail power supply each rail could have a limit of 16-18A per rail or around 200-250 watts, so even if the power supply could handle a 300w video card, the power supply may shut down because user accientally selects 2 pci-e 8 pin connectors that are on the same rail and the video card pulls more than 200-250 watts from that rail.

Yeah I have seen that happening and had to get an 1100W instead of 850W PSU once.  850W would have been more than enough, but the graphics card must have drawn too much from a rail and the PSU shut down.

1 minute ago, mariushm said:

The 6600XT will consume up to around 190 watts from 12v, but it could have small bursts (for like half a second here or there, not continuously) up to maybe 210-230w 

So far, it's been working fine with a 650W (or 620W) PSU.