Portable energy meter for measuring the consumption of consumer devices? - Page 1
Forum section: electronics / testgear

author: nightfire
author_rank: Frequent Contributor
timestamp: August 13, 2022, 11:10:04 pm
content: In response to the currently rapidly rising energy costs here in Europe, at work my boss decided to be prepared for the winter, where costs are expected to be even higher than now- and if some computers or other stuff is old and verrrry energy-inefficient, it would be the best course of action to buy replacements in the summer, when the suppliers still have stock at low prices...So in preparation I suggested that we go and "Round Up The Usual Suspects." This would mean measuring the power consumption in operation, and in case of illumination probably over the course of a workday.With devices like PCs or similar it is no problem, but when we take standby consumption into account, like printers idling around (and in case of inkjets that need to be switched on periodically for cleaning) or monitors that are not switched off at the end of the day, we are talking about single digit Watts that are consumed, but ultimately will add up.And given the fact that the power supplies are not exactly taking the power in with cos Phi=1, I would like to have some measures that are usable in that range.We also have lots of uplighter in use due to workplace regulations regarding quality of lighing and avoidance of reflections at computer screens. These are usually powered by EVG and some GX11 tubes, so I do not know how well the EVG behaves and draws continuous current...Here in germany there are some devices readily sold at every corner, like this:https://www.amazon.de/-/en/Brennenstuhl-Primera-Line-protection-individually-electricity/dp/B007459MH6/Are there any other devices that can be recommended from experience, that honor the power factor/cosPhi at low consumption and do not break the bank?(->approx 50 Euros)Or are there situations where those digital devices fail miserably and some good old Ferraris-based meter should be used for some longterm usage?https://www.bauhaus.info/sicherungskaesten/wechselstromzaehler/p/12158819

author: Alti
author_rank: Frequent Contributor
timestamp: August 14, 2022, 02:01:31 am
content: I do not think there is a point tracking sub 1W standby loads because there is no viable alternative. An upgrade of 1W won't save even 1W, right? Track those devices that draw 200W and replace with sth that draws 100W. For that a regular kill-a-watt would do.If you really, really need to measure sub 1W standby load with kill-a-watt then temporarily take several of those loads and plug them into same extension cord and this is going to add up.

author: ledtester
author_rank: Super Contributor
timestamp: August 14, 2022, 02:23:43 am
content: You might have success in measuring low wattage devices by taking a power meter which uses a current transformer and adding more turns through the transformer to magnify the measured current.Also, I think that pretty much any recent power meter will correctly measure the power factor and cosPhi simply because there are power meter chips like the Vango V98xx series which perform all the calculations for you and make designing a meter dead simple. Just witness all of the different power meters available on aliexpress:https://www.aliexpress.com/wholesale?SearchText=power+watt+meterTo get an idea of the accuracy of power meters designed around that chipset, have a look at this video:How accurate is the Peacefair PZEM-004T AC Comms Module? -- TheHWCavehttps://youtu.be/j0_y8dPfpKc

author: nightfire
author_rank: Frequent Contributor
timestamp: August 14, 2022, 03:41:39 am
content: Thanks for the input so far!This confirms mostly the assumptions I already made, , but probably not all of the suggestions would be deployable, as we rent the office space of 3 floors where my company resides. Would mean that some modification in the mains distribution level would be dependent on the landlord.The big plan is some assessment of the stuff we have- luckily the assortment of PCs, Notebooks and monitors is not that big, as most stuff was bought in certain waves, meaning that lots of similar models are available.So a general check of what the things will consume should be sufficient to get some general numbers.As I did some homework about the sensitivity and the minimum amount of consumption needed that the meter will measure, I came across a bandwidth of something between 0,1 Watt and 1 Watt- and some wall warts with USB outlet probably use some idle consumption in that dimension.Fun fact: Most desks in my company are equipped with power bars that can be (manually) switched on/off, but most employees do not use them, so it would be some project for management to enforce this.I already told management that it would be necessary to get some realtime monitoring of the general power consumption in the building, ideally enhanced with the outside temperature, to get some idea whats going on whilst looking at some curves...

author: Alti
author_rank: Frequent Contributor
timestamp: August 14, 2022, 09:48:24 am
content: Quote from: nightfire on August 14, 2022, 03:41:39 amI would discourage using those switches for this purpose. Literally all loads that include a rectifier have a bridge and capacitor at the input and this generates a massive inrush at turn on. The switches won't survive inrush from several loads long term as this adds up in square. So 5*1A inrush loads heat up the switch 25 times more than from 1A inrush load. Usually cheap power bars come with switches rated for AC-1 switching category (resistive loads). Maybe with low prospective short-circuit current this could survive but something tells me such offices are wired with thick cables and small count of circuits.

author: nightfire
author_rank: Frequent Contributor
timestamp: August 14, 2022, 10:51:05 am
content: Quote from: Alti on August 14, 2022, 09:48:24 amUsually/Theoretically each desk has one power bar from a reputable manufacturer (Bachmann/Brennenstuhl as they are good to get in germany) that is used for PC/Notebook Docking station, 2 24" screens, and some Ligh or USB wall warts.