Calculation of power supply wattage needed

[turdferguson6400]

Hi,

I've been testing a server with a Z2 array of 6 Seagate NAS 4TB drives but am going up to 8(economy) or 10(x^2 + 2) drives. It has a Supermicro X10SLM-FO with 32GB of RAM.

The Seagate specs says max 12V spinup current is 2A. I haven't been able to get any figures for power consumption of the mobo.

If I assume 20A startup for 10 drives and 10A for mobo+fans, that would total 30A. What percentage of the rated output of the power supply should this 30A be?

The Seasonic X-650 650W 80 Plus Gold is rated for a maximum 12V output of 54A. 30A is 56% of that.

Is that a good percentage of the max rated or should I go higher or lower?

Thanks.

 

[jgreco]

I discuss this in https://forums.freenas.org/index.php?threads/so-you-want-some-hardware-suggestions.12276/

You are basically doing the right sort of thinking but the average end user lacks the tools to do the job right. My suggestion is to turn this around and not randomly guess at the mainboard amps.

You can CHEAT at this by hooking up the system without powering on the drives, letting it run memtest86, and checking power consumption. Take the watts, divide by 12, and that's a bad overestimate of the maximum 12V amps that the base system takes. Then you add the peak amps for all the drives, maybe add 10% more, check against the power supply rating, and there you have an easily derived pass-or-fail.

The biggest drivers of 12V current consumption on the mainboard will be the CPU and fans. You could probably assume that memory and the board aren't likely to be taking more than 4A, but with a variety of CPU's being available and fans being essentially random, you're best off doing what I suggest in that quote. By establishing a maximum possible value, which is admittedly an overestimate, you at least have a trustable number - and it's a bit big, which is rarely bad when it comes to power supplies.