Anti_Climax
Posts: 20
Joined: Fri May 20, 2016 12:22 pm
Location: The Valley of the Sun

Revisit of FFE Energy calculations with EVTripPlanner

Fri Feb 22, 2019 11:47 am

Hello All,

You may recall that I did coastdown testing and calculations to determine how much energy was needed to maintain a given speed on flat road:

http://www.myfocuselectric.com/forum/vi ... php?t=4210

I put this data into EVTripPlanner (the site owner even added it as a selectable model) but it needs additional points to calculate correctly - in particular the amount of energy use that is independent of mechanical and aerodynamic loads. I hoped to get a scanner going to capture that but have not been able to.

Instead, I took some distance and energy readings through a decently varied round trip using cruise control and compared them to the EVTripPlanner estimates for those segments. While they disagreed significantly without a "constant" value added to the car data, adding a constant draw of 1100 watts had them all matching to within a fraction of a percent.

The trip segments included some city driving, some relatively flat highway speed sections and several miles to the top of an uphill section, with measures of the same sections on the return. I also ran some checks against known trips I've taken in the past and those results similarly match up.

While the 1100 watts seems a bit excessive, the "other" energy segment on the "MyView" screen is consistently around 500 watts and I can't be certain that is really capturing all the draw. In particular the battery cooling and such. I also have some assumptions about efficiency of regen and the motor. Regardless, these values seem to spit out very accurate estimates for me:

Usable Battery - Set this to match *your* car's battery
Cubic Parameter - 0.423
Quadratic Parameter - 0
Linear Parameter - 272.665
Constant Parameter - 1100
Motor Efficiency - 0.9 (based on cursory googling, open to suggestions)
Regeneration Efficiency - 0.95 (same)
Heating Power - 0 (I zero these so I can factor it on myself because Arizona)
Cooling Power - 0
Weight - 1644
Temperature Sag - 0
Temperature Exponent - 0
Watt Hours per Rated Mile - 282 (seems to just be used to compare the estimate to what the car would tell you)

Most of the values are available under "2012 Focus" on EVTrip planner if anyone else wants to see how well it matches up for them.

I'm curious to see if we can collectively refine it - perhaps different regen/efficiency/constant values.
2012 Candy Blue FFE with a 33.5kWh battery pack

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