Amps or Volts, or Does it matter

[SamirD]

I think saying "watts per hour" is like saying "horsepower per hour", the only way it makes sense is if you're talking about the rate of change of power over time.

It is, especially considering the nature of a watt being a joule over a unit of time already. Pretty interesting that even a kilowatt-hour has got time in there twice.

[sdold]

However while the common nomenclature may be kilowatt-hour with a hyphen, the slash is what we would use when doing the actual equations since the number is actually a fraction or ratio of watts per hour. Just like mph is actually mi/hr.

I think saying "watts per hour" is like saying "horsepower per hour", the only way it makes sense is if you're talking about the rate of change of power over time.

[J.P.M.]

I managed an A in high school physics, but I never saw a situation
where watts per unit time was legitimate. Bruce Roe

Well, time is already one dimension of the watt unit.
1 W == 1 joule /sec.
1 joule == 1 newton-meter - the S.I. unit of work.
So, 1 N-m/sec == 1 watt.

Since 1 watt == 1Joule/sec or 1 N-m/sec per second (and similar to acceleration being the 2d derivative of displacement with respect to time (= displacement per sec per sec)), 1 W/sec could be thought of as the second derivative of work (the newton-meter) - or energy in some contexts - with respect to time.

All this stuff may serve as an example of why and how there's a (minor perhaps) disadvantage in using the S.I. over the old Imperial system: It's difficult to do an additional check of a computation by doing a units cancellation check in S.I. because so many units get their dimensions buried or masked.

Like you I have yet to come across an application for W/sec, but I suppose the term W/sec could possibly have some application as the rate of power change (increase or decrease) for a energy process or for a prime mover, but I've never come across that usage after an engineering career in the power and process business as an identified and named dimensional unit.
Closest I can think of (and really not that close) is the rate of torque dissipation in the analysis of power system oscillation/stability studies, but that's pretty obscure and mostly above my pay grade, and I bet the OP doesn't care as much as the north end of a southbound rat about any of this anyway.

[J.P.M.]

I managed an A in high school physics, but I never saw a situation
where watts per unit time was legitimate. Bruce Roe

Well, time is already one dimension of the watt unit.
1 W == 1 joule /sec.
1 joule == 1 newton-meter - the S.I. unit of work.
So, 1 N-m/sec == 1 watt.

Since 1 watt == 1Joule/sec or 1 N-m/sec per second (and similar to acceleration being the 2d derivative of displacement with respect to time (= displacement per sec per sec)), 1 W/sec could be thought of as the second derivative of work (the newton-meter) - or energy in some contexts - with respect to time.

All this stuff may serve as an example of why and how there's a (minor perhaps) disadvantage in using the S.I. over the old Imperial system: It's difficult to do an additional check of a computation by doing a units cancellation check in S.I. because so many units get their dimensions buried or masked.

Like you I have yet to come across an application for W/sec, but I suppose the term W/sec could possibly have some application as the rate of power change (increase or decrease) for a energy process or for a prime mover, but I've never come across that usage after an engineering career in the power and process business as an identified and named dimensional unit.
Closest I can think of (and really not that close) is the rate of torque dissipation in the analysis of power system oscillation/stability studies, but that's pretty obscure and mostly above my pay grade, and I bet the OP doesn't care as much as the north end of a southbound rat about any of the anyway.

[SamirD]

I managed an A in high school physics, but I never saw a situation
where watts per unit time was legitimate. Bruce Roe

Was just an example. You remember having to convert whatever the number was to the requested units--that's what I was talking about.

[bcroe]

I managed an A in high school physics, but I never saw a situation
where watts per unit time was legitimate. Bruce Roe

[SamirD]

The accepted convention from the NIST, the recognized body that sets the naming and convention rules and which are the common convention rules used and accepted by knowledgeable technical individuals - at least for the U.S.- is what is used for technical communication.

The watt-hour or kilowatt-hour represents a quantity of energy, not a ratio or a rate or a duration of power use.
There is a difference.
The context is important.

See the NIST for details.

But all this is off topic. If you want to have further discussion about proper unit conventions and use, I'd respectfully suggest you start a new thread.

Oh I totally agree with using NIST terms--after all that's what standards bodies do. Really is a mess when people get Mb mixed up with MB on computer forums when they're having speed issues.

And while a KWh may be a unit of energy per the NIST, in the math/physics world it's just another 'something over time' unit. This is important in that realm as it typically gets converted to something like Wm (watts per minute) in those pesky high school physics problems. Unit conversion was a bit part of the whole course. And fwiw, energy in high school physics was all in joules, and I've forgotten what the joule equivalent is.

All off-topic for sure, but just some context outside of this realm.

[J.P.M.]

However while the common nomenclature may be kilowatt-hour with a hyphen, the slash is what we would use when doing the actual equations since the number is actually a fraction or ratio of watts per hour. Just like mph is actually mi/hr.

The accepted convention from the NIST, the recognized body that sets the naming and convention rules and which are the common convention rules used and accepted by knowledgeable technical individuals - at least for the U.S.- is what is used for technical communication.

The watt-hour or kilowatt-hour represents a quantity of energy, not a ratio or a rate or a duration of power use.
There is a difference.
The context is important.

See the NIST for details.

But all this is off topic. If you want to have further discussion about proper unit conventions and use, I'd respectfully suggest you start a new thread.

[SamirD]

It's hard to take people seriously when they can't even take the time to try to get the basics of technical communication right.

I blame ebonics.

[SamirD]

But it looks like you don't yet know that the nomenclature convention is that S.I. units named after individuals have their abbreviations capitalized (but when spelled out, the word is not capitalized).

Thus: kWh, not kwh.
Also, and also just for the record, you know wrong. It's kilowatt-hour with a hyphen, not kilowatt/hour with a slash.

Seems like a small thing to the uninformed but not getting this stuff right can cause big problems as a lot of working technical folks and engineers have seen.
If you're going to attempt communication about technical stuff, start by getting the basics and communication rules right.

See: "NIST Guide to the S.I., Chapter 9: Rules and Style Conventions for Spelling Unit Names"

Thank you for the corrections--this was actually a big part of our high school physics class--getting the capitalization right. I did well in that class, but it was 30yrs+ ago so some of it slipped.

However while the common nomenclature may be kilowatt-hour with a hyphen, the slash is what we would use when doing the actual equations since the number is actually a fraction or ratio of watts per hour. Just like mph is actually mi/hr.

[J.P.M.]

So true, I am working on my capitalization out of respect, but getting the
units right is critical to communication and calculations. Bruce Roe

It's hard to take people seriously when they can't even take the time to try to get the basics of technical communication right.

[bcroe]

Thus: kWh, not kwh.
Also, and also just for the record, you know wrong. It's kilowatt-hour with a hyphen, not kilowatt/hour with a slash.

Seems like a small thing to the uninformed but not getting this stuff right can cause big problems as a lot of working technical folks and engineers have seen.
If you're going to attempt communication about technical stuff, start by getting the basics and communication rules right.

So true, I am working on my capitalization out of respect, but getting the
units right is critical to communication and calculations. Bruce Roe

[J.P.M.]

Yep! Users need kwh to 'kill a watt-hour' (just for the record, I know kwh=kilowatt/hour)

But it looks like you don't yet know that the nomenclature convention is that S.I. units named after individuals have their abbreviations capitalized (but when spelled out, the word is not capitalized).

Thus: kWh, not kwh.
Also, and also just for the record, you know wrong. It's kilowatt-hour with a hyphen, not kilowatt/hour with a slash.

Seems like a small thing to the uninformed but not getting this stuff right can cause big problems as a lot of working technical folks and engineers have seen.
If you're going to attempt communication about technical stuff, start by getting the basics and communication rules right.

See: "NIST Guide to the S.I., Chapter 9: Rules and Style Conventions for Spelling Unit Names"

[solarix]

Power loss is proportional to the square of the amps so its best to run as high of a voltage as you can. This is why transmission lines run at 100's of thousands of volts. Of course NEC code comes into play when ever a system is over 50 volts.

[organic farmer]

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