EV CHARGING AND FUSE

[morqthana]

There's no such thing as kW per hour

But there is. It is a unit which makes sense. Whether or not it's ever needed, or used, in practice does not affect its validity.

One could express the acceleration of a speedboat in knots per second, no?

 

[morqthana]

Because it isn't/doesn't/whatever?

With which of the following do you disagree:

1. A unit of velocity is metres per second.
2. A unit of rate of change of velocity is metres per second per second.
3. A unit of power is Joules per second.
4. A unit of rate of change of power is Joules per second per second.
5. A unit of power is Watt.
6. A unit of rate of change of power is Watts per second.
7. 1 W/s ≡ 3.6 kW/h.

 

[EFLImpudence]

With which of the following do you disagree:

1. A unit of velocity is metres per second.
2. A unit of rate of change of velocity is metres per second per second.
3. A unit of power is Joules per second.
4. A unit of rate of change of power is Joules per second per second.
5. A unit of power is Watt.
6. A unit of rate of change of power is Watts per second.
7. 1 W/s ≡ 3.6 kW/h.

I don't disagree with any in isolation, but where they do not apply they are irrelevant.

But there is. It is a unit which makes sense. Whether or not it's ever needed, or used, in practice does not affect its validity.

Exactly.

One could express the acceleration of a speedboat in knots per second, no?

Yes, you could but there is no standard value of 'knots per hour'.



I think there is confusion with 'per'.
The dictionary defines it as 'for each' but that has differing meanings dependent on usage.

Obviously you could eat six apples per hour which could be one every ten minutes for several hours or six in the first ten minutes , and none for the next 50 minutes and then some more.
Would that be eating six apples 'for each hour'?


However what started all this is not the same:

13A socket... STRONG advise is not to do so regularly/ Emergency use. Max 10A 2.4kW per hour. Plugs and sockets can overheat.

2.4kW per hour is not quantifiable as 40W per minute or any other combination.

2,4kW for each hour or 40W for each minute is not really correct language.

 

[robinbanks]

Is that "a thing"?

Yes. You could rate a soft start mechanism in kW/h, for example. You could describe the ramp up or down of a power station in kW/h for example

I wasn't the person who first mentioned kW/h, I'm just objecting to all these nonscientific people who've come out of the woodwork to say "that's not a thing" when actually, a unit of something divided by an interval is actually a thing.

If you pick 10 kilos of apples in half an hour I might rate your useful daily output as 0.16t/day. I wouldn't say that today's output was 160day.kg/day though. I'd just say 160kg

Or are you using "per" incorrectly?

For what is being discussed here, I am not using "per" incorrectly. I have never confused any of the following: kW, kWh, kW/h, kWh/h. See the recap

Would that be eating six apples 'for each hour'?

Yes

The "per interval" aspect of a unit doesn't make any kind of claim as to when the interval starts or how long it lasts. If you ate one apple in ten minutes and I made no other observation of you eating an apple I could reasonably justify that your eat rate is a tenth of an apple per minute, 6 apples per hour, 144 apples/day etc.

If I wanted to factor in some other aspect, such as it being physically impossible for you to eat 144 apples it would be better if I said so, because the units don't import any other world knowledge to the claim, such as the size of a human's stomach or how long they can stay awake for. ("EFLI eats at 6 aph, for up to 3h. After that the consumption rate slows by 1aph/h linearly")

Absent those extra facts, and if the units seem to describe something that could happen continuously for some interval, it's ok to make the interval as long as you want when working out some other quantity

I wonder would I describe your apple eating deceleration as "1 apple per hour squared"? We do it with rates of change of velocity (metres per second squared) but "metrespersecond per second" is probably easier to understand

 

[EFLImpudence]

Yes, I confess I thought it was you who first incorrectly mentioned it.

 

[Risteard]

But there is. It is a unit which makes sense. Whether or not it's ever needed, or used, in practice does not affect its validity.

One could express the acceleration of a speedboat in knots per second, no?

We weren't talking about acceleration of the charging speed from the EVSE until it attains its maximum charging rate. Nor would we, as that takes seconds so acceleration of charging rate in kW per hour is complete and utter nonsense.

 

[morqthana]

I don't disagree with any in isolation, but where they do not apply they are irrelevant.

All sorts of things may not apply in, and therefore be irrelevant to, any particular situation.

"Pence per kilogram" might not apply in a conversation about F1 driver statistics, but that should not prompt a

There's no such thing as pence per kilogram

Nor, staying with the context of a discussion about F1 driver statistics, should it prompt an exchange like this

Though pence per kilogram is a valid descriptor of something, it is not a valid descriptor of anything here

Nor anywhere else.

Exactly.

Yes, exactly, whether or not a unit is ever needed or used in practice does not affect its validity.

Yes, you could but there is no standard value of 'knots per hour'.

What do you mean by "standard value"? Any rate of change of speed can be expressed as kn/h. It might be perverse to use kn/h, or the values might end up impracticably small or large, but it's just like any conversion between metres/yards/feet/chains/poles/nautical miles/parsecs/light-years....

Gravitational acceleration is 68,625.37 kn/h.

I think there is confusion with 'per'.
The dictionary defines it as 'for each' but that has differing meanings dependent on usage.

Not really.

Obviously you could eat six apples per hour which could be one every ten minutes for several hours or six in the first ten minutes , and none for the next 50 minutes and then some more.
Would that be eating six apples 'for each hour'?

Yes. For each hour which has passed you have eaten six apples.

Or you could eat just 1 in 10 minutes, which would be a rate or 6 per hour, just like if you drove along a 1 mile stretch of road in 1 minute your speed would have been 60mph.

However what started all this is not the same:

2.4kW per hour is not quantifiable as 40W per minute or any other combination.

Of course it's if it's a rate of change, which we're all agreed that kW/h can only be.

Assuming rate of change is linear, 2.4kW/h is 40W/min.

If a car accelerates from 0-100km/h in 5s, that's an acceleration of 20km/h/s. Or 5.56m/s²

2,4kW for each hour or 40W for each minute is not really correct language.

Nor is "70 miles for each hour", or "£2,000 for each calendar month", which is why, despite what dictionaries say, we say "70mph" or "£2,000pcm".

But the only way we've been "saying" kw/h in this topic has been "kilowatts per hour".

 

[morqthana]

We weren't talking about acceleration of the charging speed from the EVSE until it attains its maximum charging rate.

We've been talking about the concept of "kW/h" as a unit.

And there's no doubt whatsoever that you wrote:

There's no such thing as kW per hour

Nor would we, as that takes seconds so acceleration of charging rate in kW per hour is complete and utter nonsense.

Nonsensical, maybe, depending on the magnitude of the numbers, and using the meaning

ridiculously impractical or ill-advised

but not nonsense.

It might be ridiculously impractical or ill-advised to say that a EV has a battery with a capacity of 3.6 x 10¹⁵ ergs, or 2.25 x 10²⁷ electron-volts, but those values, and the units ergs and electron-volts are not nonsense.

Give a value for how quickly an EV charger ramps up, in seconds, and to what, and I'll convert it to kW/h for you.

So my point about kWh per hour is completely accurate.

No, it's completely inaccurate.

But kW per hour makes absolutely no sense

Maybe not to you.

But to those who can understand measuring a rate of change....

and is an abomination.

"Abomination is defined as something regarded with disgust or hatred. It refers to anything that is greatly disliked or abhorred, often associated with intense aversion or loathing. Examples include actions or conditions that are considered vile or shameful."

 

[robinbanks]

acceleration of charging rate in kW per hour is complete and utter nonsense

That's objectively incorrect. If I had a task to compare ramp rates of chargers, or end-of -charge-cycles of cars, I might well choose kW/h. Your 7kW charger that ramps from 0 to full in 3 seconds could be said to ramp at a rate of 8400kW/h. An EV reducing its charge rate after 80% might do so at a rate of 600kW/h.
As it's a comparison, it wouldn't matter if I'd chosen mW/year or nanowatts per second. You cannot turn round and say units are "complete and utter nonsense"; they work

 

[ebee]

I used to know a bloke who insisted that "You can`t say half a metre, it is 0.5 of a metre" and other such absurdities.
The thing is he was serious about what he said, it kept a few of us amused on a daily basis because he actually believed what he said, just another one of his silly statements (those with knowledge of plumbing joints will understand this little gem), "Eeh I have been working with end feed for so long that I can`t use "Yorkshire" fittings now!". There was a team of us could have written a book about his rambling statements.
I wish he was in on this thread.

 

[morqthana]

I used to know a bloke who insisted that "You can`t say half a metre, it is 0.5 of a metre"

You should have asked him what to say instead of a third of a metre. That would keep him occupied for a while....

 

[davelx]

Unless he knew his year 5 arithmetic:
333.33 recurring mm

 

[SUNRAY]

I used to know a bloke who insisted that "You can`t say half a metre, it is 0.5 of a metre" and other such absurdities...

Which according to another recent thread is: simple/vulgar fraction (assuming half is represented as ½) Vs decimal fraction.

 

[ericmark]

A unit of power is the Watt, and a unit of energy is the Joule, and the idea of having two times which cancel each other out and leave us with a unit with time in the name which has nothing to do with time seems rather confusing. I know working with units of 3600 Joules means we have smaller units, and gets us back to the metric idea of not having 4.184 or 60 or 24 or 365 etc, which are there because that's the way the world works, and has done for 1000s or years.

We have two units of energy in the ISO metric system the Joule and the calorie, the erg was dropped because it is 10 to the 7th not 6th, same way as we no longer have the centimetre, we only have the mm and meter.

With the demise of the BTU we clearly needed to get a replacement with small numbers, and yes it may seem to make the maths easier to have kW and kWh, but just as easy to have a kW/s which is of course a kJ so not a clue why we don't use the proper units, I had same problem going to do an 'A' level, where they used cm, and one has had it drummed into one, mm or meter the cm does not exist, and there it is on an exam paper.

 

[bernardgreen]

mm or meter the

mm or metre the