Hello Steve,
Am 01.07.2025 um 18:59 schrieb Steve Richter <stephenrichter@xxxxxxxxx>:
How much power will an S822 power 8 actually use? Much more than a power 7
8202-E4B? The S822 would be running the same workload as the power7. Which
is IBM i running on a single core.
I am asking because the S822 needs 240V utility power and the electrician
wants to know the amperage.
What the electrician wants to know is the absolute maximum rating, including the so called "inrush power" when you freshly plug the system into mains, and empty capacitors being charged quickly. This creates a surge. You don't want your fuses to blow because of that. Hence the question of the electrician.
I firmly believe that this has not changed much from e. g. Power 7 to 8, because it is related to the electrical PSU design and not the "computer" behind.
The amperage can be calculated by dividing the 1400W power supply by 240V?
Roughly, yes. Then you get the VA (Volts times Amps) value, mentioned in Bryan's documenation links. But since PSUs use rectifiers and other "electronic magic", tension and current are not necessarily "in sync". Here comes "reactive power" into play.
https://en.wikipedia.org/wiki/AC_power#Reactive_power
(This is a very mathematics-centric explanation and might create more questions than provide answers.)
Reactive power is usually something you're not charged for, but wire thickness, fuses, switches, etc. need to be chosen according to the maximum permissible current. That's what your electrician is after. Long term power dissipation is less relevant here.
But if your electrician is about to install a step-up transformer, the information he needs to know is "1.88 kVA maximum". Number taken from redp5102.pdf, the Technical Overview and Introduction for the S822. Chapter 1.2 Operating environment. Possibly show that to your electrician.
Then x2 because there are two power supplies? Or is the 2nd power
supply for redundancy and the max amps the S822 will draw will be the power
supply rating divided by utility power voltage?
Multiple power supplies are almost always there for redundancy purposes: It would have been cheaper to build one big PSU.
See also the links provided by Bryan:
"These dual-power installation configurations allow you to leverage the fully-redundant power features of your server."
What is confusing me is an actual S822 user, a linux developer, says the
system generated a lot of heat and spiked the electric bill.
These are both rather subjective terms. No solid numbers. But even 300 W can be a considerable amount of heat when endured in summer. :-) (See below for the numbers.)
He said 16 amps. I assume that was on a 110V circuit going through a transformer to step up the voltage. But even 8 amps at 220 or 240V is 1600W. Which is much more than the power 7 I had been using.
I assume 16 amps is the rating for the fuse and wiring according to my explanations from above. I barely believe a fully equipped Power 8 draws the full 1400 W a singe PSU can deliver all of the time.
I have measured a 4 core Power 6 with all 3.5" disk slots filled. Roughly 400W, if I remember correctly. AFAIK, the Power 6 CPU has no energy saving facilities, so it converts electricity to heat all of the time, no matter if it does useful work or not.
I have measured a 4 core Power 7 with all disk 2.5" slots filled. Was around 350 W, idle. Power 7 has some minimal power saving functions when idle. Had not enough time for more detailed measurements.
I estimate, a Power 8 might be in the 300 W ballpark when mostly idle.
But yes, IBM documentation lacks some helpful parameters, such as maximum inrush current, and typical power dissipation for real world scenarios.
Sorry, can't be more specific.
:wq! PoC
midrange.com
