Re: Empirical results, Re: How much current does a 170 draw? Or an E4A?

Patrik,
Here's some reading on how IBM i handles it when a UPS warning cable is
properly installed
https://www.ibm.com/docs/en/i/7.5.0?topic=concepts-uninterruptible-power-supply

The message queue allows you to write a program which waits on that message
queue and performs an orderly shutdown. Often you delay and see if you get
a power restored message to avoid shutting down for a quick power blink.

QPWRRSTIPL encourages to think before blindly using. If your UPS is
drained, and power gets restored but it's still a bad storm, you may not
want to power up until the UPS has some time to charge up.


On Thu, Aug 7, 2025 at 3:28 PM Patrik Schindler <poc@xxxxxxxxxx> wrote:

Hello James,

Am 07.08.2025 um 19:42 schrieb James H. H. Lampert via MIDRANGE-L <
midrange-l@xxxxxxxxxxxxxxxxxx>:

I just powered up the "MERCURY" 170 with an "amp clamp" (and an adapter

allowing me to use an "amp clamp" on a corded device), and I'm in the
middle of doing so with the E4A (with one PSU unplugged).

Interesting readings. But simply doing the math is not giving you correct
power values for AC. Something you need for UPSes — and what you eventually
pay for per kWh.

There was some discussion about this very topic not too long ago. In
short: Amps times Volts is only valid if tension and current are in perfect
sync for phase as well as amplitude. This is the case with e. g. a classic
electric stove or other pure resistance based devices. Once you have
nonlinear devices such as caps, coils, or diodes, this is no longer the
case, and you most often get higher values with simple math compared to
what's really drawn.

The key is the term "reactive power". See
https://en.wikipedia.org/wiki/AC_power#Reactive_power — I admit that the
article is overly mathematic.

I suggest to buy a proper power meter, the household type "in between
plug" type. The cheapest ones are not very precise, especially when
measuring low power values (standby). Can be reused many times to get a
better idea what device uses how much energy.

Obviously, a "fat" 170, like MARS, would draw quite a bit more, since

the second PSU is *not* for redundancy's sake.

Now I understand what you mean with "fat". You're referring to the
expansion box I usually name "sidecar". :-)

Running, but quiet, on both PSUs: 1.5-1.7A (180-204VA) per PSU.

This is surprisingly close to my 400 W I remember to have measured.

So if the box is only in intermittent use, and not usually left powered

up unsupervised, and you plan on doing an immediate PWRDWNSYS at the first
sign of flaky AC, it's probably not necessary to use that big of a UPS.

Rule of thumb: Buy an UPS which gives you enough runtime for a clean
shutdown, and some extra headroom. I admit, I have no experience with IBM i
and how it decides when it's time to shut down. Maybe immediately after an
"on battery" is signaled? But then, this happens once a week with the usual
UPS self test. Which is alt least signaled as short outage via SNMP with
APC devices. I assume it's also via serial port.

:wq! PoC

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