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Fuel economy seems better with almost full battery level

Discussion in 'Gen 3 Prius Fuel Economy' started by philliphs, Nov 17, 2013.

  1. philliphs

    philliphs Junior Member

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    Hi Everyone, new prius owners. I got prius i-tech Australia (should be IV or V in US). I just noticed this morning that my fuel economy is better when I got 6-7 bars on battery level, and worsen if i only got 2-4 bars. Is it just my imagination or someone has explanation for it?
     
  2. wjtracy

    wjtracy Senior Member

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    Hows the weather down under these days?
    If you have A/C on that might make a difference, certainly A/C causes the state of charge to be less.
     
  3. philliphs

    philliphs Junior Member

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    Weather is warm now, but it could get cold at night.
    what I'm trying to say is I get better FE when SOC is almost full and I get worse FE when SOC is 4 bars below, even though I drive at the same level on econ/pwr bar.

    does Prius adjust electric assist depending on how many bars we have on SOC? Maybe someone could shed a light?
     
  4. macman408

    macman408 Electron Guidance Counselor

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    That's exactly it. The car will always try to move towards 60% SoC, when it has a choice. This is within the range where you will see 6 bars. (If you're cruising at a constant speed on the highway, it will pretty consistently end up right there.) When the battery is low, the engine will run faster than it normally would for the gas pedal's position; the extra power generated is used to charge the battery. When the battery is high (7-8 bars), the engine will run slower than normal, and it will draw some power from the battery to make up the difference.

    Now if you start and end at the same SoC, you should have about the same fuel economy whether the battery is fully charged or mostly empty - but that would be pretty hard to do. And even then, if you try to accelerate at the same rate in either case, the mostly empty case might run the engine in a less-efficient RPM range to try to generate extra power.
     
  5. philliphs

    philliphs Junior Member

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    Ic. In that case, it is better to run normally instead of trying to use EV power and deplete the battery?
     
  6. wjtracy

    wjtracy Senior Member

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    I think the answer is Yes run normally...do NOT deplete EV charge...in most cases you are reducing overall MPG unless you have a special case. The EV mode is best used to move car short distance in driveway or something like that. Sometimes running the ICE for just a few seconds then stopping causes some engine roughness on the next restart, so you are generally best using the EV mode to avoid extremely short ICE trips.
     
  7. Codyroo

    Codyroo Senior Member

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    Optimally, you want to stay in the 6 bar range. You can drain the battery down a bit IF you know you are going to be able to recharge it back up soon. For example, while sitting in slow and go traffic going up a steep hill on the freeway, it would be OK to drain my battery from 6 bars to 4 bars near the top of the hill, because I know I will get 2 bars back coming down the other side (due to regen braking).
     
  8. 32kcolors

    32kcolors Senior Member

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    That just means you're trying too hard to run on battery power, hence hurting fuel economy.
     
  9. philliphs

    philliphs Junior Member

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    Thanks for all the explanation. I will try to change my driving habit, see if it improves the fuel economy