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Towed home!

Discussion in 'Roadster' started by mgemmell, Nov 1, 2012.

  1. mgemmell

    mgemmell Scottish chap

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    Howdy

    This may sound strange but every now and then I like to run the SOC down near to 0%. Firstly to understand how the car and battery behave near empty, and secondly because the theoretical 0% and actual 0% can drift in time unless the computer gets a chance to experience a real empty.

    Rafa (of round the world in 80 days in a Roadster fame) recently said himself that he felt his Roadster was benefiting from him driving it down to near empty on his long trips. The previous times I've ran it to 0% all has gone to plan and I got expected range and predictable behaviour.

    Ok, so I took a drive last weekend and was down to 6% SOC when I lost power. I could coast off the highway and up the off-ramp, then down a large hill regenerating and up another before having to pull off. SOC was definitely at 5% then (OVMS confirmed) but the car was not wanting to move. Headlights etc all worked fine. About 1 minute later SOC snapped to 0%.

    So I got to call for the first time ever Tesla Assistance (in my case here in Spain that's a UK number). They were great, and within an hour a special sportscar capable flatbed was with me. I was only 1km from home so the rest was easy and the car recharged just fine taking in 32A straight off as soon as I put it to charge.

    This last point is a weird one... in theory if it really is empty it would charge at 7A and then 10A etc. Taking 32A from 0% SOC doesn't make sense to me or to my Ranger (logs have been analyzed and no anomalies have come up).

    Ok, so here's my lesson from this:
    1) When SOC drops below 10% and it says "Range Uncertain", it means it. I should have gotten 35kms but I had only done 15kms or so when it cut power.
    2) Don't go fast or floor it during low SOC. Even though it is Power Limited it is still not good to draw heavily from the empty pack (I confess I did step on it a little)
    3) Tesla Assistance is excellent.

    I must confess I am a little less confident about doing a full 350km or more on a charge now but if the worst case is that you get flatbedded to your destination, and it works as well as it did, then big deal right!?

    Cheers

    Mark
     
  2. Doug_G

    Doug_G Lead Moderator

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    IMHO it is a bad idea to drive into the "Range Uncertain" region. It's not good for the lifetime of the batteries to be discharged so low.

    I've only dipped into the "reserve" once, and it was an unplanned diversion from a long road trip that caused it (caused by a TV reporter). But I was within 2 km of the destination plug when the message popped up.
     
  3. NigelM

    NigelM Recovering Member

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    Duh! :rolleyes:

    In all seriousness, good that you were so close to home. You probably could have pushed it 1km couldn't you?
     
  4. doug

    doug Administrator / Head Moderator

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    That's what I was thinking.
     
  5. Zextraterrestrial

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    I would drive more conservatively when you get to that low SOC. The amount of energy left is at a lower voltage and if the car is going to perform well then the amperage draw will be higher than at a full charge with the batteries at full voltage. If you drive with quick take-offs the the power drawn will pull the battery down a little faster(than at a high SOC) I would think, higher amps = more heat and maybe the computer algorithms haven't learned this and predicted range gets messed up at a low SOC hence the 'range uncertain'

    I could be wrong about all this, just my thoughts & I'm not an EE
     
  6. hcsharp

    hcsharp Active Member

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    The software algorithms for calculating remaining miles are very sophisticated. They most definitely take into account the lower voltage. You are correct about the increased amperage draw at lower SOC which impacts motor and battery heat generated, but all that is taken into account by the software in computing remaining range.
     
  7. wycolo

    wycolo Active Member

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    mgemmell:

    > SOC drops below 10% and it says "Range Uncertain"

    > was down to 6% SOC when I lost power

    > SOC was definitely at 5% then (OVMS confirmed)

    > About 1 minute later SOC snapped to 0%.

    [cautionary tale]

    VIN appears to be the early model. Do you have Range Miles on one screen and Ideal Miles on the other? If so what are the approximate miles that you were seeing at these waypoints? I ask this since I'm always going by the miles rather than trying to interpret the graph percentages. I can barely manage to see the mile values myself and who wants to have to come to a stop to glean the SOC percentages. [Kilometers is ok; I can factor by 0.6]

    Yesterday I got home with 27/34 or thereabouts- a huge margin. I seem to recall one of the Miles being below 10 on one occasion. But I've never seen a message like 'Range Uncertain'. My graphs do change color as I drop below 40 miles. I'm now using the July 2012 firmware for the 2.0 model.

    Here in the Outback we put in a lot of miles but lack of traffic allows us to limp along at 12 mph when necessary, with heat & headlights off, in order to make it home.
    --
     
  8. mcornwell

    mcornwell Active Member

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    Unless it was uphill...
     
  9. ElSupreme

    ElSupreme Model S 03182

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    He lives in Sarasota, the only hills there are interstate overpasses, and the beach a low tide, lets give him a break. :tongue: I remember the first time I tried to push a car, after moving from Tampa to Atlanta, The damn thing almost rolled backwards over me.
     
  10. dpeilow

    dpeilow Moderator

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    The OP lives in Spain...
     
  11. NigelM

    NigelM Recovering Member

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    They're both sunny places that begin with "S" and people like to retire there. Dinosaurs are easily confused! :wink:
     
  12. mgemmell

    mgemmell Scottish chap

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    Sorry for the late response chaps... been busy.

    The VIN is an EU VIN so it isn't early... it was made late 2010.

    Appreciate the comments (although the push home would have been seriously uphill... have you guys tried pushing a Roadster?? It's heavy!).

    I know the cautionary tail sounds obvious but bear in mind that all the other times I have gone to low SOC I have not had this problem. I blame it on being more heavy footed than usual but that means that when the SOC is low we all should take it really easy or risk getting towed too.
     

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