A Brief Electric Vehicle Geek Out

I have a response to a question on Facebook that I need to post here. This is uber geeky electric car stuff.

The Better Place electric car navigation system, Oscar, which I’ve demonstrated in a YouTube video, gives you a choice of showing either battery percentage or the raw number of kWh. A kilo-watt hour is the basic amount that is most usually spoken of in electric vehicle circles when describing battery capacity. I’m not aware that any other EV gives an instantaneous readout of this value at all times (happy to be told otherwise).

For example, my car has a 22 kWh battery and the Tesla Model S car comes in either 40,60 or 85kWh varieties. In America they’ve developed a complicated version of Miles Per Gallon to express the electric efficiency of an electric car, called MPGe. I find this number confusing and dumb.

My car reports how many kWh it takes to drive 100 km (for me and my car this is usually around 18 kWh/100 km).

Anyway here is the screen that lets me choose % or kWh:

Better Place kWh display 1

Choosing kWh or Percent as the unit system on Oscar from Better Place in the Renault Fluence ZE in Israel

Next shot is the value just after unplugging in the morning. Theoretical maximum is 22kWh but in practice I see values between 21.2 and 21.8 kWh. If I was looking at percentage, it tends to list anything above 21.2 kWh as 100%. Below this value I think the conversion from kWh to % is linear down to some cut off above 0 kWh. I haven’t really had the time to experiment with the ultra low end of kWh but I did have the car down at 3% on Sunday of this week on the way to Jerusalem.

Better Place kWh display 2

Battery at 21.4 kWh first thing in the morning (from theoretical maximum of 22 kWh) on Oscar from Better Place in the Renault Fluence ZE in Israel

After driving 2 km and stopping briefly I get back in the car and it reads 20.6 kWh (bottom left of screen). The first two km have taken 0.8 kWh and I know from experience I can reach this destination with the % display still pegged on 100% sometimes. It’s mostly downhill though my child likes strong acceleration from the traffic lights so sometimes I indulge him.

The next number to the right is 0 kW and this shows an instantaneous snapshot of current use. I’m parked so it’s 0 of course. While driving if I put my foot down this peaks at around 85 kW and if I’m decending a hill using full regen the number goes green and peaks at -35 kW.

The number on the far right, 19.2 kWh is the estimate of my battery level at my next destination in 7.3km. Though this is a very slightly different route the one I’ll actually take. The box in the top left shows my estimated arrival time and distance to destination. The system can also handle multiple destinations and will show a constantly changing estimate for each way point.

It also (as I show in the video for route planning) knows about charging times or battery switching and calculates later way points energy level based on what happens along the way!

Better Place kWh display 3

With a destination set on Oscar from Better Place in the Renault Fluence ZE in Israel

So what happened this morning? Well the estimate was a little pessimistic. I arrived with 19.8 kWh so beat the estimate by 0.6 kWh which is a 2.5% variance on a full battery. This journey is a bit short for a proper test and I believe that today’s estimate is somewhat skewed because of two trips to Jerusalem this week both of which involved some high speed driving.

Better Place kWh display 4

Final display at destination on Oscar from Better Place in the Renault Fluence ZE in Israel

The current system does try to estimate for topology but doesn’t do a great job. We are waiting for the next upgrade and I was told this will crowd source actual usage figures from all the other cars to learn what energy is used on each km of every road in Israel.

I’ve seen a sneak peak of the new system and it is prettier. It’s being tested in some of the Better Place cars at the visitor centre so here for the first time (an Israellycool exclusive I believe) is the new system:

Next version of Oscar from Better Place in the Renault Fluence ZE in Israel

Next version of Oscar from Better Place in the Renault Fluence ZE in Israel

Update: fixed the brain fart confusing kWh and kW over the display of instantaneous energy use thanks to Robin’s comment.

About Brian of London

Brian of London is not the messiah, he's a very naughty boy. Since making aliyah in 2009, Brian has blogged at Israellycool. Brian's interests include electric cars, world peace and an end to world hunger. Besides blogging here, Brian of London now writes at the Times of Israel. Brian of London also hosted Shire Network News

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How Charged Up Is Your Battery? | Israellycool
08 March 2013 at 10:03am
[...] By comparison, Oscar’s percentage or kWh readout drops in a predictable ...

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  • Robin

    I may be wrong, but I don’t think the “0kW” reading is an abbreviation of “0kWh”, it’s not kilowatt-hours, just kilowatts.
    Kilowatt (kW) is a unit of power, used to quantify immediate power, as in “right now the car is drawing 20 kilowatts from the battery”.
    Kilowatt-hour (kWh) is a unit of energy, used to express capacity, “this battery has a capacity of 22 kilowatt-hours”, which means “this battery can deliver 22 kilowatts of power for 1 hour.”
    The unit is literally defined as kilowatt x hour.

    • http://www.israellycool.com/author/brianoflondon/ Brian of London

      You are completely correct. I’ve fixed the post.

  • Eric

    I’ve been told that in a gasoline powered auto, the fuel needle hits “E” when the tank is 90% empty (that is, you still have 10% of the fuel in reserve). I wonder if they do they build in the same margin of error in the Oscar software? Or is zero really zero?

    • http://www.israellycool.com/author/brianoflondon/ Brian of London

      There is definitely a reserve below 0% on the display but, much as 100% is registered before the battery is really full, I suspect that the kWh display will show a kWh or so when the percentage reads 0%. By all accounts you have 6 to 8 km once it tells you 0%.

  • amir

    The battery display turns orange when it hits 12% capacity. Also the Oscar route calculator will not include stops, such as batttery switch stations, if it estimates that you will arrive with 12% battery or less. This margin of error, IMO, is too large, and prevents OSCar for calculating the most efficient routes. I was told (by someone who I believe no longer works at BP) that the margin of error on the new OSCar will be smaller.

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