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Comment by wltr | Hacker News Reader

How would you guys properly measure that? I have my suspicion that my Intel processor also quite not too heavy at idling.

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I have a regular i5-6500 in an HP 800 G2 SFF. It has 32 GB RAM (2x8+16), two Samsung 840 SSDs and a 4-port i350 network card. It Linux as a KVM host with OpnSense and Home Assistant on top.

According to some watt-meter I got off Amazon it idles at 14W with the 4 interfaces UP but next to no traffic. I consider it idling when the CPU usage as reported by the host is under 5%.

Now the watt-meter isn't some top-of-the-line exotic model, just a random Chinese thingy, but it seems to measure close enough to what I expect some other devices to pull.

I can vouch for the power draw in this type of system. I have a Dell OptiPlex 7070 with i5-9500, 32GB and running Proxmox with a Windows VM and a couple smaller instances. I measure 8w idle from my Kill-a-Watt on the system. I was really surprised at how low it is.

Which form factor? Tower, MT, SFF or Mini?

SFF

Thank you! The Dell SFF can only hold one 3.5 inch HDD right?

Yeah, just one. Here is the service manual: https://www.dell.com/support/manuals/en-us/optiplex-7070-sff...

I got a refurbished unit for $180 last year, using this deal (now expired): https://slickdeals.net/f/17490348-dell-coupon-50-off-refurbi...

The easy path, as someone suggested, is a kill-a-watt that you just plug it into.

The less intrusive path for some definition of less intrusive is a clamp ammeter if you can expose one of the AC wires (you have to clamp around an individual wire, not both hot and neutral). But then you don't need to unplug the system to measure it.

The third overkill option is to have it plugged into a full-time power monitoring and control device, such as a zigbee home automation plug switch. ;)

This can actually be life threatening if done without proper tools and working fast fuses. So just use a kill-a-watt or any other such tool for safety! NB they're maybe not 100% exact but good enough to give an estimate.

A clamp meter does not expose you to any live uninsulated wires unless you are doing it very wrong.

(Although they also tend to be not very accurate for low current measurements. So this isn't a use case I would recommend them for.)

Clamp meters are completely safe. The only risk is if you DIY your power cable so you can clamp one lead, but that's not necessary if you just buy an AC line splitter plug. And those often come with the hot looped around so you can get a 10x reading for better fidelity at lower current draw.

But these days I just skip the clamp meter and throw Ikea Inspelning zigbee plugs anywhere I want power measurement.

Doing anything can be life threatening. We don't need to assume that people who decide to do a thing are the same as you.

There are $10 Chinese kill-a-watts with color display, and live Bluetooth data recording.

It's fun stating a CPU intensive job and watch the graph spike.

Do you have any names or links? I tried a Temu version a while back and even getting it connected to wifi was hopeless.

I use an electrical outlet meter. It's roughly €10, the only annoying thing is everything rebooting each time I want to move it.

i wonder if there's a market for pre-made cables with a "loop" in the hot wire, for using clamp ammeters, or a cable where in addition to the choke ferrule, there's another "ferrule" - current transformer - on the hot wire with "test points", where those test points are to a transformer winding around the hot wire. That way you could just put those cables on things you want to know the power consumption of, rather than having to move a kill-a-watt or whatever.

I could make either, but they wouldn't be "certified", as i'd be either replacing plugs or cutting into the wire itself to add a pigtail.

Matthias Wandel measures power that way: https://www.youtube.com/watch?v=P47pjVyPP3w

You may be looking for "AC line splitter".

One example: https://www.harborfreight.com/15-amp-professional-ac-line-sp...

Edit: s/splicer/splitter, damn autocorrect.

Yup. They even typically come with separate 1x and 10x loops.

They're a common pack-in item with low- and high-end clamp meters.

the author has a previous blog post about his monitoring setup:

https://www.jeffgeerling.com/blog/2025/how-i-monitor-and-con...

I can recommend those Third Reality outlets as well, I have about a dozen now and they Just Work with my Zigbee dongle (Sonoff ZBDongle-P) and zigbee2mqtt / Home Assistant setup. I use Home Assistant's Prometheus integration to get the data into VictoriaMetrics, which lets me build Grafana dashboards showing the usage of each plug over time.

> How would you guys properly measure that?

I'm using smart plugs that have an open source firmware called tasmota. I can scrape the values using prometheus and can build dashboards with historical data.

USB-c cables with live PD power display can be chained with PD-to-barrel converters for fixed voltage.

Buy a kill-a-watt wall wart.

At Walmart.

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