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### Re: Why do we still confuse KW and KWH?

Posted: Mon Aug 26, 2019 12:42 pm
Aeronautics has unfortunately remained stubbornly stuck in imperial-land. This has created a few problems with space hardware when units were substituted without proper conversion - the Hubble space telescope mirror comes to mind.

### Re: Why do we still confuse KW and KWH?

Posted: Mon Aug 26, 2019 2:38 pm
css28 wrote:
Mon Aug 26, 2019 5:16 am
If megajoules were the currency of choice I suspect people would be far more comfortable with it. Example; My battery holds 108 MJ when fully charged. My car consumes 14.8 MJ/hr when I'm traveling at 60 mph.
Yep.

Fwiw though, I'm under the impression that Aussies use watt for power. They appear to have internalized the conversion ... somehow. I'm guessing they do not speak in seconds
It would be interesting to know how they calculate the time it takes to e.g add 100 MJ to an EV at 50 kW.

Anyway, while Americans are struggling with kWh, I keen for the day when the oh so cumbersome babylonian relic is discarded and we move to a base 10 system for time

### Re: Why do we still confuse KW and KWH?

Posted: Mon Aug 26, 2019 2:47 pm
Titanium48 wrote:
Mon Aug 26, 2019 12:42 pm
Aeronautics has unfortunately remained stubbornly stuck in imperial-land. This has created a few problems with space hardware when units were substituted without proper conversion - the Hubble space telescope mirror comes to mind.
Only the imperials would use the same word for a unit of volume AND a unit of weight. Not to mention the insanity of the pound meaning either weight or mass.

### Re: Why do we still confuse KW and KWH?

Posted: Mon Aug 26, 2019 3:25 pm
Pound only refers to mass in the vernacular. The technical imperial unit for mass is the 'slug', although I don't remember ever hearing the term used. It seems like anyone educated enough to know that uses the metric system.

### Re: Why do we still confuse KW and KWH?

Posted: Mon Aug 26, 2019 5:35 pm
SageBrush wrote:
Mon Aug 26, 2019 7:22 am
...I'm always amused by home heating and cooling conventions in Btu. The actual unit being measured is Btu/hour....
This use of BTU is one of the reasons it finally dawned on me that the general public probably wasn't going to bother with the distinction between kW and kWh. For them it's just a way of saying "how big". How "big" is the battery, how "big" is the charger. One unit to rule them all.

### Re: Why do we still confuse KW and KWH?

Posted: Mon Aug 26, 2019 5:49 pm
Nubo wrote:
Mon Aug 26, 2019 5:35 pm
SageBrush wrote:
Mon Aug 26, 2019 7:22 am
...I'm always amused by home heating and cooling conventions in Btu. The actual unit being measured is Btu/hour....
This use of BTU is one of the reasons it finally dawned on me that the general public probably wasn't going to bother with the distinction between kW and kWh. For them it's just a way of saying "how big". How "big" is the battery, how "big" is the charger. One unit to rule them all.
This isn't entirely incorrect. If a device outputs power at a fixed average or maximum rate, then using that rate as a per hour total doesn't really change comparisons among similar devices. As long as you stay in the same unit of measure, the numbers stay the same, relative to each other. If furnaces, say, were sold in categories like BTU/Hour, BTU/Half hour, etc, then it would get dicey, but a 35k BTU furnace is the same as a 35k BTU/Hour furnace, so the number works for comparison, even if technically incorrect.

### Re: Why do we still confuse KW and KWH?

Posted: Mon Aug 26, 2019 6:07 pm
LeftieBiker wrote:
Mon Aug 26, 2019 5:49 pm
Nubo wrote:
Mon Aug 26, 2019 5:35 pm
SageBrush wrote:
Mon Aug 26, 2019 7:22 am
...I'm always amused by home heating and cooling conventions in Btu. The actual unit being measured is Btu/hour....
This use of BTU is one of the reasons it finally dawned on me that the general public probably wasn't going to bother with the distinction between kW and kWh. For them it's just a way of saying "how big". How "big" is the battery, how "big" is the charger. One unit to rule them all.
This isn't entirely incorrect. If a device outputs power at a fixed average or maximum rate, then using that rate as a per hour total doesn't really change comparisons among similar devices. As long as you stay in the same unit of measure, the numbers stay the same, relative to each other. If furnaces, say, were sold in categories like BTU/Hour, BTU/Half hour, etc, then it would get dicey, but a 35k BTU furnace is the same as a 35k BTU/Hour furnace, so the number works for comparison, even if technically incorrect.
Yeah, that's what I mean. In terms of EVs, I'm saying the public's main concern is the "bigness" of whatever they're talking about. They're going to use the term kW for both batteries and charging, without a care for the underlying meaning. The context takes care of it. When talking batteries you know it's energy storage, when talking charging you know it's energy rate. The public says "just tell me how big". As with lay useage of "BTU", the conceptualization of rated or non-rated will be moved from the unit itself, to the context and the actual unit definition will be largely unknown because comparison is the only concern. What percentage of the population actually knows what a BTU is or can internalize the amount of heat it represents? They just know they had a 5000 BTU window box and it didn't cool for shit so they got a 10,000 BTU one next time.

### Re: Why do we still confuse KW and KWH?

Posted: Mon Aug 26, 2019 8:23 pm
LeftieBiker wrote:
Mon Aug 26, 2019 5:49 pm
Nubo wrote:
Mon Aug 26, 2019 5:35 pm
SageBrush wrote:
Mon Aug 26, 2019 7:22 am
...I'm always amused by home heating and cooling conventions in Btu. The actual unit being measured is Btu/hour....
This use of BTU is one of the reasons it finally dawned on me that the general public probably wasn't going to bother with the distinction between kW and kWh. For them it's just a way of saying "how big". How "big" is the battery, how "big" is the charger. One unit to rule them all.
This isn't entirely incorrect. If a device outputs power at a fixed average or maximum rate, then using that rate as a per hour total doesn't really change comparisons among similar devices. As long as you stay in the same unit of measure, the numbers stay the same, relative to each other. If furnaces, say, were sold in categories like BTU/Hour, BTU/Half hour, etc, then it would get dicey, but a 35k BTU furnace is the same as a 35k BTU/Hour furnace, so the number works for comparison, even if technically incorrect.
Lets say someone wants to know how much it will cost to run their new fangled Btu burner. They know it is 35k Btu.

Next step ?

---
As for your argument, my Tesla is 78 but it can be 76

### Re: Why do we still confuse KW and KWH?

Posted: Mon Aug 26, 2019 9:04 pm
Lets say someone wants to know how much it will cost to run their new fangled Btu burner. They know it is 35k Btu.

Next step ?
Flow rate of whatever fuel is used, and efficiency rating. As the parameters expand, the simple comparisons break down. There are, however, those stickers on new energy-consuming appliances that give the cost per year for a certain assumed energy cost, plus the efficiency rating, so those calculations aren't needed by the consumer.

### Re: Why do we still confuse KW and KWH?

Posted: Mon Aug 26, 2019 10:00 pm
No one is actually confused. This is just a conversation on a message board. Not the owners manual, not an operating manual, not a physics theses, not wiki, not even a general knowledge base. Simple slip of the keyboard makes way too big a deal of it. For those that are always careful and deliberate to get this right perfectly every time I commend you. For the rest... let it go.