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Reported Fuel Consumption - BMW 330e F30

  • 10-10-2020 6:09pm
    #1
    kirving
    Registered Users, Registered Users 2 Posts: 6,125 ✭✭✭


    Something I noticed when trying to work out my overall fuel (elec + petrol) consumption on an F30 330e.

    I know the consumption meter is only a guide, and the correct way to measure real consumption is brim the tank + metered electricity. But while I'm waiting on an electricity meter, this caught my attention.

    Take the following 40km journey, split into two 20km parts.

    Part 1:
    Distance: 20km
    Battery: Start 100%, End 0%.
    Petrol: Not used at all.

    Car reports:20[kWhr/100km] + 0.0[l/100km].
    Makes perfect sense and easy to calculate the cost.

    Part 2:
    Distance: 20km
    Battery: Start 0%, End 0%.
    Petrol: Used 100% of the time @ 6.0[l/100km]

    Car reports: 10[kWhr/100km] + 3.0[l/100km].
    Again, easy to work out the cost.


    But take another journey:
    (I've divided the distance and battery usage by 10 to be a bit more realistic, but ratios are the same as before. ie: 2km = 10% battery)

    Part 1:
    Distance: 2km, downhill.
    Battery: Start 50%, End 60%.
    Petrol: Not used at all.

    Car reports: 0.0[kWhr/100km] + 0.0[l/100km].
    I've generated electricity, but the consumption meter cannot go into minus.

    Part 2:
    2km, flat.
    Battery: Start 60%, End 50%.
    Petrol: Not used at all.

    Car reports: 10[kWhr/100km] + 0.0[l/100km].

    So I've done 4km, only used the electricity that I've generated, so I haven't actually "consumed" anything, but the car says that I have.

    Or am I missing something completely? It doesn't matter on a single journey, but it adds up over time. Especially since sometimes it's the engine charginging the battery, so it gets confusing very quickly.


Comments

  • #2
    kanuseeme
    Registered Users, Registered Users 2 Posts: 1,971 ✭✭✭kanuseeme


    Its generated by the car and consumed by the car,
    the car is giving you the % of the downhill state of charge, because you regenerated, its 10% more, then you are using that 10% on the flat run so it reports 10 kWh for 100 km but in fact you only done 4 km you used only 0.4 kWh per 2 km (the flat part) but the car extrapolates for a trip of 100 km using what information it has or a programmer cares to give, a better way might be km per kWh with a - for a downhill trip and a reading of daily, monthly totals etc.

    Its confusing I know but if you reversed part 1 and 2 you will find its 0.4 kWh for the flat and going up the hill it will be a hell of lot more.

    Also your selecting a particular section of road, how did the car get up on the hill needs to be accounted for in the first instance.

    How you find the car? its crossed my mind a few times for my next car.

    What are you getting for a 100 km trip with full battery? what are you getting for a 250 km trip with a full battery?

    https://www.webdoctor.ie/online-prescriptions/#:~:text=Through%20an%20online%20medical%20questionnaire%2C%20face%2Dto%2Dface%20consultation,to%20booking%20a%20video%20consultation. not affiliated, just being helpful.



  • #3
    kirving
    Registered Users, Registered Users 2 Posts: 6,125 ✭✭✭kirving


    kanuseeme wrote: »
    ...because you regenerated, its 10% more, then you are using that 10% on the flat run so it reports 10 kWh for 100 km but in fact you only done 4 km you used only 0.4 kWh per 2 km (the flat part) but the car extrapolates for a trip of 100 km using what information it has or a programmer cares to give, a better way might be km per kWh with a - for a downhill trip and a reading of daily, monthly totals etc.

    The extrapolation I'm find with, to keep the figures meaningful. The averaging too is fine.

    As far as I can work out, it does the following: (Starting battery kWhr - Current battery kWhr) / Trip Distance.

    Just a simple calculation really, but if I regen at the start of a journey, the electric usage figure is meaningless.

    I guess it's difficult for the car to determine what it used, and where that power came from is regen, engine charging, or plug in.
    kanuseeme wrote: »
    Its confusing I know but if you reversed part 1 and 2 you will find its 0.4 kWh for the flat and going up the hill it will be a hell of lot more.

    Yeah, it's very sensitive to hills alright.
    kanuseeme wrote: »
    Also your selecting a particular section of road, how did the car get up on the hill needs to be accounted for in the first instance.

    That's probably more to the point to be honest. The reason it caught my mind is that my common commute is uphill one way, and downhill the other.
    kanuseeme wrote: »
    How you find the car? its crossed my mind a few times for my next car.

    What are you getting for a 100 km trip with full battery? what are you getting for a 250 km trip with a full battery?

    Can't say I've done enough milage to really say for sure. Very solid on the road, even in Sport trim. M-Sport look great, but my budget didn't go that far. I'll be on the motorway mostly so I don't car handling wise. Very smooth transition to the engine from battery.

    Coming from an E-class Estate, it feels compact for sure. A little down on torque compared to the Merc with 500Nm, but a boost in power is nice all the same. It's heavy, but 250bhp lets you keep up with traffic no bother, so no small car feeling.

    Get one with Pro Nav, LED's and electric seats, it makes a big difference to the experience.


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