Dumbest use of electrical units, by marketing aimed at amateurs? - Page 1
Forum section: electronics / general

author: Freesurfer
author_rank: Regular Contributor
timestamp: May 30, 2025, 11:01:10 am
content: There are some web shops here that sell various DC products intended for off-grid cabins, campers, RVs, boats and such. It could be anything from 12V LED lights to venting fans, LPG/kerosene heaters and such, as well as batteries and solar related equipment.What I have found is that many of these shops have introduced their own set of units to measure energy and power. Rather than going by the proper units such as amps, amp hours, watts and watthours.... Power consumption may be rated as "Amp hours per hour" (Ah/h). Which by itself may not seem like that much of a problem, it's simply a matter of removing the h/h part and you are left with just amps. And it could potentially make sense for products that have average consumption even if the current rating when operating is higher than the average.But it goes further. This "Ah/h" unit that they use, is generally the "equivalent of a 12V system". So the moment they have products that are 24-48V, or solar panels that have inconvenient voltages for off-grid (and need an MPPT for efficiency) they typically rate this in "12V equivalent Ah/h". The same goes for batteries that are not 12V. Rather than saying that it is a 48V 100Ah battery, they will say it is "an equivalent of a 400Ah battery".I can understand why - a lot of people who are not familiar with electricity, energy and power, often get amps and amphours mixed up, and may not know that voltage * current = power. I can also imagine that the majority of their customers are mainly pensioners who traditionally have worked with just 12V systems, so they may be familiar with the concept of amps and amphours, but not how higher voltages affect the system. It is not until recently that we have decent, powerful and affordable solar systems and things are moving away from 12V DC. So a 48V system will seem just 1/4 as powerful as its true performance to somebody not familiar.I just find it funny when shops dumb things down in their marketing trying to target amateur users. And also annoying when trying to find the true rating. Just like power bank capacity may be rated in "number of full iPhone charges" rather than actual watt hours. And I am sure that many companies deliberately confuse people with Ah vs A to make it hard/confusing to compare products on a shelf.Another thing I find annoying, is how recent space heaters are now rated in this "BTU" (British thermal unit) rather than their actaul power rating. I understand that BTU may be a unit that other countries are familiar with and it may have been the standard way to rate heat output since the beginning of time. But in Norway where I live, we always rated our heaters in watts, and that's what you would see on the box, on the label etc. And most people will have a general idea of how running a 2kW heater for so long, results in a certain quantity of kWh on the electric bill.. So what is this BTU crap about? Trying to boast greater numbers? So I had to google it and found that BTU is a measurement for energy/heat quantity (not instantaneous power).. So for power, I would imagine BTUs would need to have an "over time" component. But those heaters don't specify the power output as "BTU per unit of time", it's just "BTU" on its own.. Does it mean it stops working once it reaches its BTU rating? I don't get it. Maybe I am the one getting old.. It just seems pointless to introduce such a unit to a region that already uses ideal, metric units.

author: Siwastaja
author_rank: Super Contributor
timestamp: May 30, 2025, 11:32:29 am
content: Had missed that "12V-equivalent Ah/h" thing - absolutely hilarious, thanks for sharingIn the meantime, li-ion world (portable devices), power banks* etc. went from Ah, A & V mess to - tadah - units of energy and power, (k)Wh and (k)W, which people are already very familiar with from their power bills and home appliances. This happened 20 years or so ago, so there is little excuse for all this crap.*) Some of it is in 3.7V-equivalent mAh, though, so the same crapI am one of those who firmly believe that dumbing down or inventing "easy" ways is often detrimental, and makes things more difficult to understand; see my comments on the dB thread for which I, unsurprisingly, got a lot of backlash.World would be much simpler to understand especially to laymen if we had originally introduced just unit of energy (SI: Joule, often with M or even G prefix), and then defined power as a derived unit J/s - what Watt of courseis, but we don't need that name. People also discuss distances in kilometers and miles, and speed as km/h or mi/h, not kiloblurbs or megaslörbs. Or knots!And for primary measurement unit of energy storage and "delivery speed" of that energy, Joules and Joules/s are the right thing. I can accept Wh and W, respectively, of course; it's minor annoyance compared to this 12V-equivalent Ah/h mess.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 30, 2025, 11:36:12 am
content: my rant is mostly the 5vdc usb adapters packs 25000ma 10000ma else ..... put a car battery and get 850000ma loll

author: tooki
author_rank: Super Contributor
timestamp: May 30, 2025, 12:00:13 pm
content: Quote from: Freesurfer on May 30, 2025, 11:01:10 amAnd they normally do have a time component: It’s actually BTU/h.It sorta made sense for cooling, because the amount of thermal energymovedby an air conditioner is not the same as the amount of electrical energyconsumedto do it. Conversely, when looking at heat pump heating, it can also make sense to have separate units of measure for the thermal energy moved vs. electrical energy consumed. I suspect it’s an attempt to avoid the bullshit seen with energy-saving light bulbs, where they write theequivalentwatts in big letters, e.g. from an actual Osram LED light bulb package in front of me:4.0 w =40w(yes, they used lowercase W)If I see a heat pump labeled as 3.5kW, what is it? The thermal power, or the electric power? In resistive heating, they are one and the same. For a heat pump, they’re not. (It’s the thermal power, by the way.)Of course, there are other SI units that could have been used instead. But the air conditioner/heat pump industry, long having been quite US-centric, is probably very used to BTU/h for sizing their machines, especially the smaller, low-cost ones that are comparatively recent arrivals in Europe.

author: TimFox
author_rank: Super Contributor
timestamp: May 30, 2025, 05:36:07 pm
content: The BTU and kcal are related, but not SI, units of energy.

author: tooki
author_rank: Super Contributor
timestamp: May 31, 2025, 12:02:19 am
content: Quote from: TimFox on May 30, 2025, 05:36:07 pmRight. But I meant there are other SI unitsbesides the kWor (kWh) that could have been used.

author: Simmed
author_rank: Frequent Contributor
timestamp: May 31, 2025, 01:24:50 am
content: how about the term "true RMS"

author: langwadt
author_rank: Super Contributor
timestamp: May 31, 2025, 02:08:39 am
content: "BTU" the energy need to heat a pound of water one Fahrenheit. "Tons" the energy need to freeze or melt a short ton of ice in 24 hourssounds like a jokes

author: TimFox
author_rank: Super Contributor
timestamp: May 31, 2025, 03:43:46 am
content: Yes, 1 Ton is 12,000 BTU/hr power (not energy).In Imperial or US conventional units, what would you use instead of BTU instead of a metric kcal?

author: tooki
author_rank: Super Contributor
timestamp: May 31, 2025, 06:07:17 am
content: Quote from: langwadt on May 31, 2025, 02:08:39 am”It’s not what I grew up with, therefore it sucks.”

author: tooki
author_rank: Super Contributor
timestamp: May 31, 2025, 06:07:52 am
content: Quote from: Simmed on May 31, 2025, 01:24:50 amWhat about it? Perfectly correct.

author: TimFox
author_rank: Super Contributor
timestamp: May 31, 2025, 02:36:17 pm
content: Quote from: tooki on May 31, 2025, 06:07:52 amWe used to have only “average responding, rms calibrated” AC voltmeters, which were not “true” for square waves, noise, or anything else non-sinusoidal.

author: tggzzz
author_rank: Super Contributor
timestamp: May 31, 2025, 02:59:51 pm
content: Capacitance measured in Jarshttps://en.m.wikipedia.org/wiki/Jar_(unit)While it was possible to calculate the required capacitance directly, it was more usual to simply have a book of lookup tables which gave the number of jars needed for any likely wavelength.

author: AG6QR
author_rank: Frequent Contributor
timestamp: May 31, 2025, 08:34:07 pm
content: Quote from: TimFox on May 31, 2025, 02:36:17 pmI'm familiar with those. I think you mean they were not RMS for square waves, noise, or anything else non-sinusoidal.RMS stands for "root mean square", that is, the square root of the mean (averaged over time, or in calculus terminology, integrated over time and then divided by the time interval), of the square of the quantity being measured. Anything that actually does that measurement is true RMS. Anything that does something else isn't doing RMS.The word "true" in "true RMS" is redundant. But I guess I understand why marketers may want to include it, because some meters have been made that use some other algorithm to display a number which will closely match the RMS value when measuring a sine wave, but produce a misleading answer when measuring something non-sinusoidal.

author: TimFox
author_rank: Super Contributor
timestamp: May 31, 2025, 08:51:36 pm
content: Quote from: AG6QR on May 31, 2025, 08:34:07 pmThat's what I said. An -hp- 400 AC voltmeter reads AC voltage in RMS Volts, but that value is only "true" (i.e. correct) for sinusoidal voltage waveforms.From the manual for the 400 HL meter, page 3-1:https://www.worldradiohistory.com/Archive-Catalogs/HP/HP-400-H-L-Vacuum-Tube-Voltmeter-1961.pdf"3-9. INPUT VOLTAGE WAVEFORM. The voltmeter is calibrated to indicate the root-mean-square value of a sine wave; however, meter pointer deflection is proportional to the average value of whatever waveform is applied to the input."That is not a true reading of the rms value for non-sinusoidal waveforms.On the other hand, the -hp- 3400A meter uses a thermal converter to measure the rms value of the input signal. It does not compute the rms by adding the square values of input samples, but by comparing the heat generated in a resistor to the heat in a matched resistor driven by DC in a servo loop.http://www.introni.it/pdf/HewlettPackard%20-%203400a%20Rms%20Voltmeter.pdfThe indication is therefore a true rms value of the AC component of the input signal (after subtracting the DC component with an input series capacitor), as opposed to an rms calibration of a mean absolute value.Other true rms meters have the switched option of including the DC component or AC only.Perhaps you would be happier if the Simpson 260 said "fake rms"? In what sense is "true" incorrect or misleading?Other voltmeters from mid-century include the "VTVMs", such as the RCA Voltohmyst range, that measured peak-to-peak values (using a 6AL5 dual diode tube in a "voltage doubler"), and the meter showed two scales, one for peak-peak and the other converted to rms, assuming a sine wave. The peak-to-peak measurement was not sensitive to the actual waveform, and did not respond to the DC level.https://www.mzentertainment.com/pics/test_equipment/rca_voltohmyst_senior_wv98a_wiz_wv98c/rca_wv98csenior_voltohmyst_vtvm_manual.pdf

author: tooki
author_rank: Super Contributor
timestamp: May 31, 2025, 11:17:00 pm
content: Quote from: TimFox on May 31, 2025, 02:36:17 pmRight. I know that. That doesn’t mean true RMS is “marketing aimed at amateurs”.

author: xavier60
author_rank: Super Contributor
timestamp: June 01, 2025, 10:10:28 am
content: BTW, Moving Iron meter readings are true RMS.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 01, 2025, 02:56:25 pm
content: Quote from: Freesurfer on May 30, 2025, 11:01:10 amYou are not even close to the reason. The real reason is (often) much more nefarious. They sell garbage, they know they sell garbage, and when you bought it, come back because it does not work, there is not much you can do. Two 18650 cells can easily deliver 50Ah/h, so you have nothing (legalese) to complain about if your batteries are depleted after two minutes. It's deliberate deception.Same for all those misspelled names on Chinese products. It's not because they can't translate. It's because those misspelled names circumvent legal issues if the customers complain. Brand names can be copyrighted, trademarked, whatever (although the Chinese law is quite flexible on this) But the misspelled names have no such protection. So if you sell your clothes as Yucci instead of Gucci then you're off the hook.Except for DMM's. Apparently you can't sell any DMM in a yellow holster in the usa if you're not from the overly expensive brand.https://hackaday.com/2014/03/19/multimeters-without-a-country-flukes-broad-trademark-bans-yellow-multimeter-imports/