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The old 8 bar blues (well actually 8 bar greens).

Discussion in 'Gen II Prius Technical Discussion' started by uart, Nov 7, 2011.

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  1. uart

    uart Senior Member

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    I got the overheated battery thing happening today after I left the Prius parked in fairly hot weather with a full eight bars SOC showing. The place I was visiting was at the bottom of a fairly long descent and the SOC went to 8 green shortly before I stopped. When I returned to the car approx 90 minutes later I immediately noticed the rear vent fan running full blast, something that rarely happens and that indicates that the HV battery is too hot.

    When I started driving there were some anomalies that lead me to think that this overheating was something a bit out of the ordinary. I'm thinking this was because when the car was off the fan couldn't continue to cool it, even though some heat may still be building up back there.

    The anomalies were interesting. With the rear vent fan running full blast I noticed that the engine was running all the time as well. After a while I even pulled over and stopped to see if the engine would eventually cut out, but it wouldn't. And all this time the battery SOC just kept dropping, from 8 bars eventually down to 3, even though I was driving it fairly gently and the engine was running continuously. This was only a short trip but the fuel consumption was really messed up, probably only about 25 MPG (whereas I normally I get 55 MPG).

    Anyway, after that short trip the car was then parked for another 90 minutes and when I returned the battery must have cooled down somewhat. The rear fan was still running, but not full blast, and the car was driving normally (engine cutting out when gliding and fuel economy was just about back to normal). The EV function (via EV button) was out of action, but apart from that it was driving ok.

    Several hours later (in the evening) I took the car for a run and everything seems 100% back to normal. Anyway I just thought I'd let others know about this experience as I know that this situation has been discussed here recently. That is, the possible dangers of turning off the car and leaving it parked while the battery is the full 8 bars and still possibly heating up
  2. Hal W

    Hal W New Member

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    Hey uart:
    I don't really understand what the colors mean with the Pack ! Mine are showing normally grn. I have notice purple on occasion as well as blue. I think blue means full SOC and purple low SOC? I would really like to know what this all means! I cannot find anything about it in the manual! Hal
  3. edthefox5

    edthefox5 Senior Member

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    There must be a level of "supercharge" of maybe super long hill in regen that causes this as I routinely park my car with all green overnight. I forget to ev and burn it off the last leg of my commute.
    And I have never heard the battery fan come on. Casual full charge does not seem to affect the battery fan or force the engine come on.

    But isn't this is why we have a B gear? The Braking gear? Have you tried
    using the B gear down a big hill? It's hard on mileage but takes the load off the brakes and regen. I have never gone down a big hill in the 4 years I have owned my 07 so do not know how effective the B gear works but its there for big hills apparently. I wish they disabled regen completely in the B gear. That would have worked really good to prevent overcharge.

    But if regen disabled the brakes would suck. Millions of Americans shouting my brakes went out!!

    And your anomalies are pretty common based on reading this many times here.
    The engine's constant running to spin mg to to load the hybrid battery trying to burn off the extra charge. Mileage goes in the dumper.
  4. uart

    uart Senior Member

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    Hal, the number of bars on the battery graphic in the energy monitor display gives an indication of the state of charge. It's the number of them that's important, but the color is just to give a quick overview of the level.

    1 or two bars = purple
    3, 4, 5 or 6 bars = blue
    7 or 8 bars = green

    Six bars (blue) seems to be the optimal level that the prius tries to maintain.

    Here is a graphic that depicts the approximate correlation between percentage battery charge and the bars displayed.

    Attached Files:

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  5. edthefox5

    edthefox5 Senior Member

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    Green is battery fully charged. I see it constantly and is not a bad thing.
    (See my "overcharge" post above)
    Blue is normal charge remaining depending on how many bars.
    Purple is very low soc. Empty. Will happen quite often and will force engine on to recharge.
    A healthly car should charge back to a few blues from a purple in a mile or so.

    Be aware there are software limits to being empty and being full. Reserves if you may.
    The software will never allow the battery to be completely empty nor overcharged but apparently you can "overcharge" the hybrid somewhat.
    Causing the hybrid pack to heat up turning the fan on.
    Then the software turns the engine into an air pump which loads the mg drawing alot of current out of the pack to kill off the supercharge.
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  6. uart

    uart Senior Member

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    Parking overnight is a bit different as the battery will have time to cool down before you next use it. In my case it was parked out in the 90 degree heat.



    It does for me. Most times (except for winter) that I've driven a few hills and had all eight green I've had the rear fan at least on low, and usually (a short time later) the EV button goes into denial as well (Beep-Beep: "EV mode is not available at this time"). So I'm pretty sure there's a correlation between full 8 green and warming of the pack. The only difference is that under regular driving it never usually gets bad enough to make the fan go full blast. That's because the fan is running enough to keep it manageable, but this time I guess that, with the car switched off so no fan - but still sitting in the hot weather, that the temperature got a bit worse than normal.



    B can definitely help here, but you have to think ahead to use it. Today I was traveling a different route to normal and wasn't anticipating so much regen.



    Yeah I've had that happen before but normally it only spins the engine for a little bit, maybe enough to drop it to 7 green if that. Today was really different, Even though I was driving it pretty gently, it just wouldn't glide or use EV. The engine kept running and the SOC just kept dropping, it was really weird. I've had the whole maxed out battery and all that before, but it's never behaved like today.
  7. Hal W

    Hal W New Member

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    I use B position on the stick for very steep hills! Works great to keep speed under control without brakes. I live in the mountains! Hal
  8. edthefox5

    edthefox5 Senior Member

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    Thats it! Whats the SOC look like after using it?

    I have never seen a hill with my car. Damn flatlander.
  9. edthefox5

    edthefox5 Senior Member

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    Roger that.
  10. qbee42

    qbee42 My other car is a boat

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    Was the engine really running, or was it being spun to burn off excess charge? My guess is that it was doing the burn-off dance, where MG1 spins it fast for a bit, stops, spins again, and so forth until the SoC gets down to a reasonable level.

    Tom
  11. SageBrush

    SageBrush Senior Member

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    ^^
    I drive lots of hills and the occasional mountain. When the ICE revs as part of a SOC lowering cycle, the instant GPM on my scangauge is not zero even when in motion. At the moment I cannot remember a figure
  12. Hal W

    Hal W New Member

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    I only use B on short steep hills in town. On the open road I prefer to tap the brakes to keep speed under control. The Prius seems to have some engine breaking at all times. My HCH2 just takes off when the SOC fills.[Free wheel] Hal
  13. edthefox5

    edthefox5 Senior Member

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    I made a mistake. I don't get 8 green bars I get 7. I counted them tonight. I thought that was 8 bars but there's a little white bar on top I never noticed.
    So I guess you have to go down a really big hill and be in regen a fairly long time for it to charge up to 8 bars.
  14. seilerts

    seilerts Battery Curmudgeon

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    uart, you have it spot on, the battery was overheated, and you noticed the driveability problems. It is precisely this type of scenario, repeated several times, that leads to a dead cell, typically for drivers in US mountain states or the superheated South. What gets me is, electric engine cooling fans will run even after the car is turned off...so why not the HV battery fan? I think so many failures would be prevented that way.

    A feature of NiMH chemistry is continued heating due to production and reabsorption of oxygen at near full charge. Excessive heat also causes cells to vent, which leads to lower capacity, which leads to eventual failure to do overcharge/discharge.

    Question is, why does this seem to happen to older Prii? My working theory is that older batteries suffer from NiMH voltage depression, which leads to a mismatch between calculated SoC and actual. At 8 Green bars, instead of 80% SoC calculated, it might be 95% actual -- the battery is almost fully charged even though the computer thinks it is not -- which is well into the oxygen production region and would explain why the battery temperature goes up after the car is turned off.
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  15. fjpod

    fjpod Member

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    I've had something similar to that happen, once...but not quite as severe. It only happened to me the other day after driving my 2010 for two years. I was driving in a very hilly area that I normally don't drive in. The battery got fully charged for quite some time, and when I slowed down to work into town traffic, I could not stay in EV mode over 10 mph, in spite of having a full charge. I did not hear the battery fan though. I happened to park the car for about a half hour and it still showed a relatively high SOC, but again could not use EV above 10 mph. After several hours cooling, everything was back to normal.

    In my mind, it is better to disable EV if things get overheated than to burn something out.
  16. Southern Dad

    Southern Dad Active Member

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    In my 2008, I've only seen 8 bars one time. I actually was beginning to believe that 8 bars didn't exist. Now from reading this thread, I get the idea that if I should hit 8 bars it is a good idea to do a bit of ELECTRIC driving to burn it off so I don't have an overheating issue.
  17. qbee42

    qbee42 My other car is a boat

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    A full SoC will not cause overheating. Overheating, on the other hand, will influence SoC. Drawing power for EV mode would only make the problem worse.

    Tom
  18. seilerts

    seilerts Battery Curmudgeon

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    True on a new battery, questionable on an old one.
  19. qbee42

    qbee42 My other car is a boat

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    True. With a failing battery all bets are off. A bad battery can overheat while sitting idle.

    Tom
  20. uart

    uart Senior Member

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    I'm now wondering if it was trying to a battery recalibration, or something like that, when the SOC kept dropping even though the engine was running and I was driving gently?
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