Yes! The elusive actual unpopular opinion!
I’d rather know how long my device will have power to function. I’m under the impression most people have the same thinking, hence why mAh is the common unit to measure it.
How are joules less confusing for the purpose of battery life? I’ve heard of exactly zero devices ever that give their energy consumption in joules. I do however, know how to find the power draw of a given device in amps, and then I can very easily estimate how long I can run that device for if I know the battery capacity in amp-hours.
A watt is one joule per second. So if a phone consumes 100 watts, and its battery has 1000 Joules, it’ll run for ten seconds. If its battery has 8 megajoules (which is as much as an average person eats in a day), it’ll run for eight thousand seconds. Which is about 2 hours. It’s easy and simple.
I understand watts. I don’t really understand amps. I know how many watts My PC draws because I installed the power supply Myself. I don’t know how many amps it draws. I don’t know how many amps My phone draws, or My wireless mouse, or My body.
My phone’s battery lasts longer when I turn the screen brightness down. Does that mean the screen is drawing a variable number of amps depending on the brightness? That’s confusing! I don’t really understand what an amp is, so I can’t visualise that. I can understand the fact that a dark screen draws less watts easy, because watts are just energy per second.
I know how many watts My PC draws because I installed the power supply Myself.
You know what it’s rated for, but actual usage varies constantly. Open up your gpu overlay and it will show you the biggest users (aka your cpu and gpu).
You can install an app right now and see your phone’s battery draw in mA so you don’t even have to convert anything.
Then why joules?
Watthours is another already fairly common unit.
1Wh lasts for one hour at one watt. Half and hour at two watts. And so on.
Amps are directly related. You can get the amps from the wattage, by dividing the watt with the voltage being run.
Watthours are stupid. You’re taking the SI unit of energy, the joule, dividing it by time to get watts, and then multiplying it by a different unit of time to get energy at a different conversion rate. It’s ludicrous! I have a philosophical opposition to such confusing units.
Or, think of it as just adding time to watts.
If a thing uses 100 watts. Then in one hour, it used 100Wh.
It’s literally the simplest unit for this.
That’s not addition, it’s multiplication.
…
Adding. As in combining. Introudcing. Attaching. Affixing.
Not math.
Well, you gonna love freedom units
Actually I think of amp-hours as an imperial unit. They feel the same as imperial units.
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That is if the manufacturer is honest in their battery capability, (they aren’t.)
Why would joules help with that?
The best case I can make is that for most everyday uses, watt-hours are useful for estimating power consumption e.g. if I have a 100W light and I leave it on for 8 hours a day, that’s 800 watt hours on my electricity bill. Simple. Sure you can do the same thing with joules but it’s a little bit more unit conversion and I don’t think it makes it any easier to intuit how a device will impact my electric bill.
With all that said it rubs me the wrong way too. Same with VA vs W for AC circuits. I get why you need apparent vs actual loads, w/e, but that naming convention just bugs me. just call it a loss factor or something.
Great. Very unpopular.
Take my upvote, and now let me try it:
Joule is a French name, and French is eek, and Americans never know how to pronounce it anyway. So it must be avoided!
Wait till you find out where the name Ampère hails from
As a European, I know it already 😉
Americans never know how to pronounce it anyway
Do you have an example of an American mispronouncing joule or is that just a gut feeling
It’s the other way round: all French words are your examples. Each time when I have heard a French word spoken by an American, they did it in a very unexpected way, as if it were not French at all.
Joule jool jewel Juul what’s the problem?
Who uses amp hours? It’s watt hours everywere I’ve seen. I even forget what they are, been meaning to look it back up.
A lot of mobile devices, including laptops, smartphones, cordless drills, vacuums, whatever.
my off grid solar batteries
Why joules instead of watt hours? Also amp hours is simple to convert into watt hours. If you know the voltage then volts × amps = watts. So a 12V 100AH battery is 1200WH.
Also bear in mind that battery capacity measurements are only ever really approximate anyways because the actual capacity will vary based on how quickly you draw power from the battery. The more amps you pull the lower the capacity.
Wh is better for comparing two batteries.
If you are looking to buy a portable cell phone charger, they both might have the same Ah, but then you also need to know their voltage to compare. If you have the Wh, then the voltage didn’t matter.
Yes but when are you comparing batteries at different voltages? If you’re comparing batteries for a specific application then you’re going to be looking at batteries of the same voltage.
That’s not strictly true, the voltage of the battery changes as it discharges, so you technically need to integrate the area under IV curve. I think Watt hours or Joules (or kilojoules or whatever makes the number a reasonable size) or anything that let’s us compare across voltage would be so much better than seeing 8000 mAh 6s lifepo and you gotta know like 5 different things before you can tell
That’s not strictly true, the voltage of the battery changes as it discharges, so you technically need to integrate the area under IV curve.
Yes but a fully charged battery will also have a voltage higher than its nominal voltage which mitigates that quite a bit. Also as I said in my origional comment, the rated capacity is only ever a rough measurement anyways so while volts×amphours=watthours isn’t perfect, it’s close enough.
or anything that let’s us compare across voltage
I guess the part I’m missing is, when are you ever really comparing across voltage. Generally when you’re shopping for batteries it’s for a specific application and that application will have a specific voltage requirement. So you’re only ever really going to be comparing batteries of the same voltage anyways. It isn’t like you can just toss a 48V battery in something that requires a 6V battery.
Although I do agree that a voltage agnostic capacity measurement would be nice. My personal preference would be watt hours.
Battery banks are the biggest offenders to me. Like this, not only am I mad that 20 thousand mah is just 20 Ah and you gotta reduce them fractions, but it doesn’t mention the battery voltage, nor do we care. Usb c outputs 5,9,12 or 18 volts but none of those are the nominal battery voltage that we would want to calculate the Wh. But since the internal voltage or chemistry is never mentioned anywhere, you can’t even compare 2 different battery banks that both say 20000mAh.
It’s basically just become a “bigger number better” marketing number now, and half of them are making shit up.
Unless you are in engineering in an energy efficient application, the estimation of Ah is good enough for 99.9% of the use case.
I dunno, definitely unpopular in the sense I’ve never even heard or seen it before!
But I suspect it’s like any unit. The one you’re used to is the best. If you’re familiar with joules, then it’s best. Someone familiar with miliamps is going to find it best.
Seriously. Familiarity out ranks any other factor for quick understanding of a given thing being expressed in units. Doesn’t matter if it’s feet, meters, pounds, kilos, clicks, miles, or knots. What you know is going to be way more important than even an objectively more descriptive unit.
Now, that does mean that if everyone isn’t familiar with a given unit, communication can be snafu. But when it comes to battery capacity, nobody is going to be familiar with anything until it comes up. It isn’t like a mile/kilometer where having a distance be known is so day-to-day useful that even kids will pick the unit up in their heads eventually without being instructed.
For whatever reason, miliamps got picked, and that’s what’s on most labels. So us RC nerds and electronics geeks have become familiar with what amount of capacity is useful for a given application. Given enough time, you will too.
I don’t know if joules would be better or not, since I’m not familiar enough with using them to compare, much less estimate how many joules a given battery might have. But it’s no difficulty to estimate how long my e-maxx will run off of a given battery pack that’s X miliamps. I used to even be able to guesstimate how ambient temperatures would shift run time per battery swap, and how it would change as the motors heated up. Couldn’t now, but I can still estimate basic run time for that truck, my stampede, and a few others.
Same with power banks and a given phone.
Familiarity matters
Joules are already a unit that people use in daily life. They’re the SI unit. They’re used in science. The manufacturers should have chosen a unit that’s applicable across disciplines, so that the knowledge is transferable. That would have helped people learn science from their phones. Instead, we use a stupid unit that isn’t useful for any other application except commercial power systems, and doesn’t make people smarter when they learn it. When you learn Joules, you get smarter, because you’re learning to more easily navigate lots of energy applications.
I use Amps and hours in my everyday life much more often than Joules. The manufacturers used those units (which are both SI units) because they are the most useful in this case. If you know how many amps you are using you know how long your battery will last. If they gave the joules remaining they would need to give you a Joules/time reading to get the same information. To get that value they would have to measure how many Amps were being used so why bother converting it?
Maybe you should learn a bit more about Amperage instead of expecting everyone else to learn about Joules.
Joules are already a unit that people use in daily life
Some people, sure. You and some in your close circle of acquaintances likely use it.
Not once have I ever needed to measure something in joules. I suspect that many people, if not most, don’t use joules in daily life.
I would be okay with measuring battery capacity in calories in America.
Hipster trash.
