Hi guys,
I recently bought myself the Tesla Model S and to follow up the consumption I purchased a flukso meter.
At home I have 3 phases 220V/24A, I added a transfo inbetween to have 3x380 output.
Now, following is where I get confused: (see attached pictures)
in Watt I see that it consumes 17500w
in Wh I see that it consumes 4,5k Wh
the clamps (50Amp) are connected to each of the incoming phases arriving at my fusebox.
can someone enlighten me on what is wrong here?
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Dear Profits, & others interested
It can be quite confusing indeed, since "Wh (or kWh), or J" is not a unit of power (immediate consumption, expressed in Watt or J/s) but a unit of energy (amount of energy == power x time). Thus, to put it on the Y-scale perpendicular to time, only makes sense if you incorporate (multiply) with the time scale at wich the power draw is evaluated.
* The Watt graph is scientifically more correct, in that your device draws 17kW momentarily.
* The (k)Wh scale (as I understand it), might be more intiutively for some people,
-though it could definitely use better labeling, now its very counter-intuitive-. It gives the amount of energy in Wh/kWh PER UNIT OF TIME you did use, during the period your momentarily power consumption continues at the same level, between 2 plotted points Which unit base (MIN/HOUR/etc) depends on the time SCALE you selected, but is not equal to it. It equals the smallest STEP in your current visualisation. In your case you selected DAY, where every point depicts "15mins" of time (period between 2 points), thus the Wh / 15, corresponding to "1/4 of the kWh/hr" == Watt value.
A short summary:
Year scale => Wh == Wh / 7Days
Month scale => Wh == Wh / Day
Day scale => Wh == Wh / 15 minutes
hour scale => Wh == Wh / 1 min
My opinion:
If you select the HOUR scale, the scale reverts to Wh/hr == W, then its is easy to grok.
Else, use cumulative or watt only
PS: I hope this viewpoint is correct, i'm not entirely sure, so feel free to correct me if I'm wrong.
As usual, part of my opinion is wrong ;-)
>> If you select the HOUR scale, the scale reverts to Wh/hr == W,
Is obviously wrong, it reverts to Wh/min then.
You have 4.3Wh of energy consumption in a 15 min interval. You can calculate the power value by dividing energy consumption by the time interval. So: 4.3Wh/15min = 17.2Wh/h = 17.2W. Seems ok to me.
Compare this to a Tesla Model S covering 50km in 15mins. 50km/15min = 200km/h. So the Tesla was cruising along at an average speed of 200km/h during those 15min. If the interval would not be 15min but a full day, then the distance covered would be 4800km. The longer the time interval you look at, the higher the value (distance coverered) will be. But the speed would still report 200km/h even if you take a day interval. Because you normalise it to an hour (or a second when using m/s).
Distance is the integral of speed. Speed is the first derivative of distance. Just as energy (1Wh = 3600J) is the integral of power (W). And power is the first derivative of energy. The thing that confuses a lot of people (even engineers!) is that Wh means W x h, and not W / h. Wh is a unit of energy, not of power.
Bart, could you put this explanation into the manual, please?
The usage of the units is indeed not obvious (especially when "Wh" is not "Wh", but "Wh/0.25h" ;-)
How about adding a bit more context in the tooltip (the box popping up when hoovering your mouse on a datapoint)?
Also acceptable - if you don't want to update your manual ;-)
It just should be clear what to expect when selecting a certain function from a dropdown box...