How to tell a kilowatt hour from a kelvin week henry

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Re: How to tell a kilowatt hour from a kelvin week henry

Post by Paul9 »

Thanks coulomb when writing my post I suspected I was "out" by a factor of a coupla billion!
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by EVdownUnder »

Did anyone read the RACV article on "Dictionary of energy jargon – and how to decode it."

https://www.racv.com.au/royalauto/livin ... coded.html
KwH.JPG
KwH.JPG (17.84 KiB) Viewed 1998 times

"Get fluent in the language of gas and electricity with this handy energy lingo decoder."

Well done RACV. I thought it would make me laugh but I actually started crying :cry:
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by weber »

Wow. Thanks for that, Patrick. They could hardly have got it any wronger. If you're an RACV member, it would be good to email them about it. I'm sure they don't want to be wrong any longer than they have to. At least they got megajoules right. :)
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by smithy2167 »

They appear to have made a correction. It now says kWH ... nearly there!
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by EVdownUnder »

weber wrote: Mon, 23 Dec 2019, 11:22 Wow. Thanks for that, Patrick. They could hardly have got it any wronger. If you're an RACV member, it would be good to email them about it. I'm sure they don't want to be wrong any longer than they have to. At least they got megajoules right. :)
I emailed them the same day I posted here, and cheekily asked for a year of free subscription for my editing work :lol:
I'm still waiting for a reply :roll:
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by weber »

Here's another fine point of symbol usage that relates specifically to batteries.

The relative rate of charge or discharge of a battery is often described as a multiple of its capacity, by using the letter "C". For example a "2C" charge or discharge of a battery with a capacity of 100 amp hours, corresponds to a current of 200 amps.

In this case, the letter "C" is not a unit symbol but a quantity symbol. In other words, it's a variable. It stands for "capacity", as in C = 100 Ah. So "2C" is intended to mean: multiply the capacity figure in amp hours by 2 and treat it as a current in amps. The dropping of the "h" for hours is understood.

We should not put a space of any kind between the 2 and the "C", because that would mean 2 coulombs, a measure of charge, not current. A coulomb is an amp second.

But even without the space, it could still be read as coulombs. The standard way to distinguish quantity symbols from unit symbols is to set quantity symbols in italics. So the correct form is 2C .

To ease the pain of typing this, I use yet another compose-key sequence with the free software for Windows called WinCompose, so I only need to type Right Alt c space .

<Multi_key> <c> <space>		: "[i]C[/i] "	# BBCode italic C, SPACE, for capacity (a quantity, not a unit)

Here are a bunch of other compose-key sequences I use to save keystrokes when typing units, including not having to use the shift key in most cases.

# SI Unit and multiplier symbols preceded by a narrow no-break space
<Multi_key> <space> <0>		: " °"	U202F U0080 # NARROW NO-BREAK SPACE, DEGREE SIGN
<Multi_key> <space> <a>		: " A"	U202F A # NARROW NO-BREAK SPACE, A for ampere
<Multi_key> <space> <A>		: " A"	U202F A # NARROW NO-BREAK SPACE, A for ampere
<Multi_key> <space> <c>		: " °C"	U202F U0080 C # NARROW NO-BREAK SPACE, °C for degree Celsius
<Multi_key> <space> <C>		: " C"	U202F C # NARROW NO-BREAK SPACE, C for coulomb
<Multi_key> <space> <F>		: " F"	U202F F # NARROW NO-BREAK SPACE, F for farad
<Multi_key> <space> <g>		: " g"	U202F g # NARROW NO-BREAK SPACE, g for gram
<Multi_key> <space> <G>		: " G"	U202F G # NARROW NO-BREAK SPACE, G for giga
<Multi_key> <space> <h>		: " h"	U202F h # NARROW NO-BREAK SPACE, h for hour
<Multi_key> <space> <j>		: " J"	U202F J # NARROW NO-BREAK SPACE, J for joule
<Multi_key> <space> <J>		: " J"	U202F J # NARROW NO-BREAK SPACE, J for joule
<Multi_key> <space> <k>		: " k"	U202F k # NARROW NO-BREAK SPACE, k for kilo
<Multi_key> <space> <K>		: " K"	U202F K # NARROW NO-BREAK SPACE, K for kelvin
<Multi_key> <space> <l>		: " L"	U202F L # NARROW NO-BREAK SPACE, L for litre
<Multi_key> <space> <L>		: " L"	U202F L # NARROW NO-BREAK SPACE, L for litre
<Multi_key> <space> <m>		: " m"	U202F m # NARROW NO-BREAK SPACE, m for milli and metre
<Multi_key> <space> <M>		: " M"	U202F M # NARROW NO-BREAK SPACE, M for mega
<Multi_key> <space> <n>		: " n"	U202F n # NARROW NO-BREAK SPACE, n for nano
<Multi_key> <space> <p>		: " p"	U202F p # NARROW NO-BREAK SPACE, p for pico
<Multi_key> <space> <P>		: " P"	U202F P # NARROW NO-BREAK SPACE, P for peta and pascal
<Multi_key> <space> <r>		: " r"	U202F r # NARROW NO-BREAK SPACE, r for revolution
<Multi_key> <space> <R>		: " Ω"	U202F Ω # NARROW NO-BREAK SPACE, Ω for ohm
<Multi_key> <space> <s>		: " s"	U202F s # NARROW NO-BREAK SPACE, s for second
<Multi_key> <space> <S>		: " S"	U202F S # NARROW NO-BREAK SPACE, S for siemens
<Multi_key> <space> <t>		: " t"	U202F t # NARROW NO-BREAK SPACE, t for tonne
<Multi_key> <space> <T>		: " T"	U202F T # NARROW NO-BREAK SPACE, T for tera
<Multi_key> <space> <u>		: " µ"	U202F µ # NARROW NO-BREAK SPACE, µ for micro
<Multi_key> <space> <v>		: " V"	U202F V # NARROW NO-BREAK SPACE, V for volt
<Multi_key> <space> <V>		: " V"	U202F V # NARROW NO-BREAK SPACE, V for volt
<Multi_key> <space> <w>		: " W"	U202F W # NARROW NO-BREAK SPACE, W for watt and weber
<Multi_key> <space> <W>		: " W"	U202F W # NARROW NO-BREAK SPACE, W for watt and weber
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by weber »

Serious unit nerds (like myself) may be interested to read this email I wrote to SI expert Dr Richard Brown back in September 2019. It's about what comes after yotta = 1000⁸, and so relates to this post earlier in this topic.


Dear Dr Brown,

I have just read your article, "On the nature of SI prefixes and the requirements for extending the available range".

I totally agree that the BIPM needs to standardise some well-thought-out additional prefixes before we are stuck with some poorly-thought-out defactos driven by the computer industry.

My interest in the assignment of letters to symbols began when I produced a table very similar to your Table 2, which can be seen here
https://forums.aeva.asn.au/viewtopic.php?f=16&t=6186
in the section headed "A to Ω of unit symbols".
I became interested in extended prefixes after writing this.
https://forums.aeva.asn.au/viewtopic.php?p=75349#p75349

Before reading your paper I had worked through a process of elimination, presumably similar to the one you went through. But I settled on X x and Q q and rejected R r because of the use of:

R as an alternative symbol for ohms when Ω is not available, (similar to u for µ) and
r as a symbol for revolutions, as in r/min and r/s.

Of course these uses of R r are not SI, but they are common and they are compatible with SI. I think they may appear in ISO 80000. I feel they should have appeared in your Table 2.

One reason you gave for rejecting X x was that it is rarely encountered in English. This seems irrelevant, as Z z and Q q are even more rarely encountered. But on reading your other two reasons for rejecting X x, and a third reason I read elsewhere, namely that people may assume X is the symbol for exa, I decided that you were right, and the use of R r instead of X x was the lesser of two evils.

Because r for revolutions is always followed by a slash, it can't be confused with a prefix. But ohms are sometimes multiplied by other units. The ohm metre is the unit of resistivity. If symbolised as Rm it could be confused with prefixed metres. But it can be written as R.m if Ω·m is not available.

Given that Q and R are so distant from Y and Z in the alphabet, I saw little value in continuing the reverse alphabetical order. However phonetic compatibility with the Greek numbers ennea and deka for the multiples, and the Latin numbers novem and decem for the submultiples, leads me to agree with your choice of R for 1000⁹ and Q for 1000¹⁰.

I did not understand why you mention B b as a possible future option, given that B is used for both bels and bytes and b for both barns and bits, and worse, the inevitable confusion with abbreviations for the common non-SI multiplier "billion".

And I do not understand why you think it would ever be a good idea to have a single-letter symbol for 1000¹¹ or 1000⁻¹¹ when these can be composed by concatenating the symbols for 1000¹ and 1000¹⁰ and similarly 1000⁻¹ and 1000⁻¹⁰, to give the compound prefixes kQ and mq.

Compound prefixes would continue to be disallowed except in the case where Q is preceded by a different multiplier, or q is preceded by a different submultiplier. This order of concatenation of prefixes, and their symbols, agrees with that of both Greek and Latin numbers, i.e. hendeka, dodeka, ... enneadeka and undecim, duodecim, ... septendecim, ignoring the unusual treatment in Latin of 18 as 20-2 and 19 as 20-1.
http://phrontistery.info/numbers.html

I understand such a scheme would allow the mass of the observable universe to be written as something between 1.0 YQg and 999 YQg, i.e. 1.0 × 10⁵⁴ g to 999 × 10⁵⁴ g.

While I agree with your proposed definitions of the prefix symbols R r and Q q, I have some problems with your prefix words. ronna/ronto, quecca/quecto.

Your Table 1 shows a strong preference for multipliers based on Greek words, and submultipliers based on Latin words. In fact it is possible to interpret zetta and yotta as based on the Greek words hepta and okto, instead of the Latin septem and octo, making the multipliers 100% Greek.

In each of the pairs zetta/zepto and yotta/yocto, the initial consonant and vowel are the same, and I agree we should continue that pattern. And we should continue the pattern of having exactly two syllables and ending multipliers with "a" and submultipliers with "o". But it is inevitable that these final vowels will be shortened until they become indistinguishable schwas, e.g. zettəmetre/zeptəmetre, yottəmetre/yoctəmetre, or the final vowels may disappear completely if the following unit begins with a vowel e.g. zettohm/zeptohm. So we are completely dependent on the second consonant (which may be a blend) to distinguish multiple from related submultiple.

I suggest that where the Greek and Latin for the same number, have different initial vowels and/or second consonants, we should take advantage of this. In the case of hepta/septem and okto/octo, there was no difference. But since they all have blended consonants, the rule was invoked, as used for penta → peta, and retrospectively for tetra -> tera, whereby, to create the multiple, the first consonant is removed from the blend and the remaining letter is doubled, giving zetta/zepto and yotta/yocto.

But for 9 and 10 we have ennea/novem and deka/decem, which should become renna/rovo and quekka/quesso. It's nice that the final pair is reminiscent of deca/deci which is where it all started.

So at least I agree with the pronunciation of one of your prefixes, just not its spelling. The US would change quecca to quekka anyway, like they change deca to deka. Why not beat them to it, and be more faithful to the Greek.

This scheme would allow a maximum multiplier of 1000¹⁹ as rennaquekka RQ which sounds a little like the Greek hendeka. And it would allow a minimum submultiplier of 1000⁻¹⁹ as rovoquesso rq which sounds a little like novendecim (which is what the Latin for 19 would be if it was consistent with the Latin for 11 thru 17, e.g. septendecim).

I think we should stop at 19, and leave it for future generations to decide, if they ever need to, whether to allow QQ and qq, then kQQ and mqq, or whether to come up with new symbols for 1000²⁰ and 1000⁻²⁰.

I also have a suggestion as to why the binary prefixes, kibi, mebi etc., are so unpopular, and how to fix it, but that's a topic for another email.

Regards,
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by weber »

I followed it almost immediately with this email:


I just noticed an inconsistency in what I wrote. I wrote:
"In each of the pairs zetta/zepto and yotta/yocto, the initial consonant and vowel are the same, and I agree we should continue that pattern."

But I later recommended renna/rovo, which have different initial vowels, based on the Greek/Latin ennea/novem.

So the earlier sentence should be:
"In each of the pairs zetta/zepto and yotta/yocto, the initial consonant and vowel are the same, and I agree we should continue the pattern of having the same initial consonant, but the initial vowel can vary if it varies in the corresponding Greek and Latin numbers, it just happens not to do so with the numbers 7 and 8."

Insisting on the same initial vowel would produce the pair renna/renvo. I find the latter awkward to pronounce, so renna/rovo (from ennea/novem) seems preferable to me.

Regards,
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by weber »

I received the following reply:


Hi Dave,

Thanks for your e-mail. You raise some interesting points.

The choice of symbols is an interesting one. There are very few un-used symbols! I discounted ‘x’ mainly because it is used as the multiplication symbol. I preferred symbols not already used in the SI specifically.

Names I think are less important, although they seem important at the time! If officially accepted the names would become well known and familiar.

You also raise interesting points about compound prefixes. I covered many of these in the attached paper, which you may not have seen.

Many thanks again for your input.

Best regards,

Richard
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by jonescg »

On the matter of pronunciation, I recall discussing organic molecules with a lecturer way back in 1999. Benzoyl chloride, according to Max Gunter, was "benz-oh-isle" and not "benz-oil" as I preferred. Good thing us chemists use hieroglyphics by default.
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by Chuq »

Just to bump this post :)

I've just found that the ABC has a publicly accessible style guide for their journalists: https://about.abc.net.au/abc-editorial/ ... tyle-guide

They welcome updates from the public.

At first I thought that we should provide details on a few frequently misused terms in the EV (and broadly, energy) space.

However the contents of @weber's first post - perhaps a cut down version - might be helpful - plus some detail about the kW / kWh difference. Thoughts?
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by weber »

Hi Chuq,

I'm afraid I'm too busy with other things at the moment to contribute in any way. But feel free to use anything from my post.
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by jonescg »

My wife and I were discussing energy literacy this morning - and how people can imagine a litre of water, a kilogram of rice, or how long an hour takes, but they have no idea what a kilojoule is. Energy is just one of those difficult things to imagine. While Katherine is a scientist, she's not well versed in electricity, so it seemed strange to her that we defined a unit of electrical energy as a kWh, as even she knows that kW is a rate, and the temptation to call it 'per hour' was there, despite it being a multiple, where the time unit cancels out.

A statement which needs unpacking is:
"The Ioniq has a 38.3 kWh battery, and it can be charged in 5.5 hours at 7 kW from a 32 amp supply. It has a mileage of 14.5 kWh/100 km on the highway, so an effective range of 264 km"
Where does the layman begin? :o kWh, hours, kW, amps, km...

So we had a brain wave - perhaps we should make some AEVA fridge magnets (or whatever) with the most common units translated for easy digestion?
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by Chuq »

kW and kWh are really weird ones. They are back to front to what people are used to (the h at the end is usually /h or "per hour" and refers to a rate, but in this case it refers to a multiple).

If speeds and distances were measured this way, speed limits would be in the form of "80 km (kilometres)", and the distance you travel in 2 hours at that speed would be 160 kmh (kilometre hours).

It's easy to get them back to front in your head. I see and hear experienced EV enthusiasts say or write the wrong one quite often.

The other confusing one is "km/h" when used to describe a charging rate (combining the rate in kW with the efficiency in kWh/km).
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by brendon_m »

Another problem is the reuse of units. Eg the Ioniq charges at 7kW on AC, 70kW on DC (but 50kW on most chargers) and the motor produces 88kW
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by weber »

Here's something I wrote for a battery course for Electricians, about the relationship between amps and amp hours. It could easily be reworded to refer to watts and watt hours.

Battery Capacity

The capacity of a battery (quantity symbol C) is how much electric charge it can store. We could measure this in electrons, but the amp hour (unit symbol Ah) is a far more convenient unit. An amp hour happens to be about 22.5 × 10²² electrons. That’s because an amp is a rate of flow of charge of about 22.5 × 10²² electrons per hour (not something you need to remember).

It is analogous to having an imaginary unit for the rate of flow of water, called the “water-amp”. Let’s say a water-amp is about 3.34 × 10²⁵ water molecules per hour. And then we measure the capacity of our water tanks in water-amp hours. But I didn’t choose that number of water molecules arbitrarily. We already have another name for the “water-amp hour”. We call it a litre. And so a “water-amp” is a litre per hour.

Unfortunately we have no simple unit analogous to the litre in the case of electric charge. However some people seem to want one so badly that you will hear them talk of “amps per hour” which is unfortunately nonsense. And although “amp hours per hour” are sensible, they are simply amps. A similar situation exists with watts and watt hours, although they measure power and energy rather than current and charge. Power is the rate of flow of energy while current is the rate of flow of charge.
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by weber »

This may also be of interest:

Battery capacity is called C. This is in italics because it is a quantity symbol, not a unit symbol. Its units are amp-hours (Ah).

In the case of lithium-ion batteries, we are concerned with the maximum rate (i.e. maximum current) at which they are allowed to be charged or discharged. This is usually expressed as a multiple of the capacity, e.g. 2C (pronounced “two C”) which really means 2C per hour. So, for example, if a lithium ion battery has a capacity C = 50 Ah and its maximum charge/discharge rate is 2C, then that’s a current of 2 × 50 Ah / h = 100 A. This is sometimes described as “having a (maximum) C rate of 2”.

Notice that 0.5C is the same as C/2. Both are currents, not capacities, because by convention, dividing by hours is understood in both cases, i.e. 0.5C/h and C/2h.

The capacity described above is sometimes called the charge capacity or amp hour capacity, when it is necessary to distinguish it from the energy capacity or watt hour capacity (quantity symbol E) which is obtained by multiplying the amp hour capacity by the nominal voltage of the battery.
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Re: How to tell a kilowatt hour from a kelvin week henry

Post by jsvader »

We should all go back to empirical measurements - you could then say your ICE car gets an eighth brick per buttload (about 14.3l/100km) :)
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