History of power

[Kristian]

I dont understand the historical power diagram. It has the unit kWh. A unit for power would be kW. kWh is a unit for energy. Also max values like 2 kW (kWh?) seems a bit low. it is probably averaged over 6 or 5 min interval, but still. Anybody who knows what is the correct interpretation?

 

[Wuduslad]

KWh means KiloWattHour, therefore 6KWh means 6KiloWatts used (or produced) in one hour (6,000 Watts per hour). 1000Watts is 1KW.
Think in terms of a light bulb. A 100watt light bulb would have to be on for 10 hours to consume 1KWh of electricity ( 100Watts x 10 = 1000 which is a KiloWatt ) .
A unit of electricity from the grid is 1KWh. If a 1KW heater is on for an hour, it would use 1 unit of electricity, (1KWh), costing about 12p depending who you purchase it from.
A 3 KiloWatt electric fire left on for an hour would cost 36p from the same supplier.Thats 3 x 1KWh at 12p a unit. The car's supplied home charger costs about a pound to charge from empty over a 5 hour period because as the batteries charge, the required current drain decreases. It doesn't draw 3kw for the whole cycle.
Wattage is a measure of electrical power, not voltage or current.

 

[Kristian]

Yes I know all that Wuduslad. That is why I am asking. Under the heading POWER if you look at the history graph, the Y-axis has the unit kWh, is this just wrong and it means kW? Because as you say kWh is NOT a unit for power while kW is. Also the numbers I read seem low if it is indeed kW. That was my question. btw Watt is the product of voltage and current, so Watt can also be called VA, but that does not help us here.

 

[Grigou]

Kristian, 2 kWh every 5 mn make 24 kWh in an hour.

About 3 times the battery's capacity.

Another calculation : with an average power of 10 kW (about 13 hp), the value per 10 mn will be 10/6 = 1,7 kWh.
Coherent.

The unit seems to be in kWh per 5 mn (but isn't it 10 mn ? I don't remember exactly, I'am not in my car at this time )

 

[PeterGalbavy]

To clarify the language kWh is NOT kilo-Watts *per* hour but kilo-Watts *for* an hour.

A Watt is defined as a Joule per second - Joules being the standard unit of energy. More on Joulers in https://en.wikipedia.org/?title=Joule

Since Watts in turn have a "per second" component it makes little sense to add another, else you are saying "Joules per second per hour". What we mean is "Joules per second for an hour".

So, 2kWh is 2,000 Watts (Joules per second) delivered continuously for the period of an hour.

 

[Grigou]

Nobody wrote that the definition of the kWh unit was "kW per hour" (I think).

Nevertheless, I think that it is perfectly accurate(*) to speak about "kWh per 5 mn" for example, when we want to discuss of the energy used each 5 mn.

And consequently, one could speak of "kWh per hour" if we would speak about the energy used each hour.
In this case, it's obvious that the "kWh per hour" is not a unit, but just a measurement.

(*) english is not my native tongue and all my scientific studies were in french, so I can make a mistake about the "per". But in french, il n'est pas interdit d'écrire "la voiture a consommé en moyenne 15 kWh par heure pendant les 45 km de trajet"

 

[anko]

Nobody wrote that the definition of the kWh unit was "kW per hour" (I think).

Well, technically somebody did ....

KWh means KiloWattHour, therefore 6KWh means 6KiloWatts used (or produced) in one hour (6,000 Watts per hour). 1000Watts is 1KW.

The word in should have been replaced by during :ugeek:

 

[Grigou]

Oh ! I didn'see this horrible mistake ! :mrgreen:

 

[Kristian]

So people are suggesting that the POWER screen shows energy usage per 5 min periods. Not quite scientific (trust me I am a scientist) to call it power. For example an energy usage of 1kWh used up during a 5 min interval represent a POWER of 12kW, so perhaps what is now called 1kWh on the screen means 12kW average POWER during that 5 min period. Well, that is usefull too, if you have a steady power of what Mitshubishi call 1kW you use up the battery in 1 hr I think.

To introduce yet another power unit. On the three strange tacky dails each tick mark of the double circle represent 10 horsepower for the motor dail and 1 hp for the AC dail. The representation of this screen is not very elegant, but it gives you horsepower for those who are old fashioned.

 

[Grigou]

So people are suggesting that the POWER screen shows energy usage per 5 min periods. Not quite scientific (trust me I am a scientist) to call it power. For example an energy usage of 1kWh used up during a 5 min interval represent a POWER of 12kW, so perhaps what is now called 1kWh on the screen means 12kW average POWER during that 5 min period. Well, that is usefull too, if you have a steady power of what Mitshubishi call 1kW you use up the battery in 1 hr I think.

Why do you say "if you have a steady power of what Mitshubishi call 1kW" ? Mitsu shows kWh !!
The only little error is to call the screen "power" instead of "energy". Et alors ... ?

The important thing is that it shows energy per period, isn't it ? For me it's obvious since I have seen this screen for the first time

 

[Kristian]

Why do you say "if you have a steady power of what Mitshubishi call 1kW" ? Mitsu shows kWh !!
The only little error is to call the screen "power" instead of "energy". Et alors ... ?

The important thing is that it shows energy per period, isn't it ? For me it's obvious since I have seen this screen for the first time

It is strange how defensive people become when they have spent a lot of money on a car. I like that car a lot but I think the MMCS interface sucks. You are right the screen should have been called ENERGY, and it would have been helpful if the manual explained the screen, it does not. The manual really sucks btw. Since you understood the graph so quickly maybe you are smarter than me, or maybe I am biased because I am used to scientific writing and expect a power unit in a graph on power. You are right that the graph is sort of presenting a qvasi POWER where the a unit is 12 kW, a unit invented by Mitshubishi. The graph would also be more intuitive if it had colums and not points and lines. The information in it is of a binned nature. But I think it is great that me and the people reading this forum now get a crystal clear picture of the screens information.

 

[Grigou]

Kristian, I agree with your last post, the MMCS is a piece of s.... in many aspects. And I think that most of the people will agree with that !

So it seems you haven't understood something if you say that I am "defensive" on this subject. I love my car but hate many aspects of it

I just wanted to explane that for me, it was obvious that the unit was kWh and not kW (and have tried to explane why in my first reply, even if it was more an illustration than a demonstration). And for me the most important thing was that you had the answer for your first post, not that the screen is named power or energy !

And finally I am happy to be just an engineer and not a scientist : I am perhaps more able to interpret conficting informations. It seems that a pure scientist can be quickly disturbed by an inappropriate word

 

[Kristian]

Yes words and units are important, and I spend a lot of time making my own graphs as precise and illustrative as possible. Enigneeres are used to reading graphs that are more pragmatic I guess.