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OVMS Cooldown Alternating 70A/13A. Huh?!?!

Discussion in 'Roadster: Technical' started by jimmyz80, May 27, 2015.

  1. jimmyz80

    jimmyz80 Member

    Joined:
    Dec 26, 2014
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    179
    Location:
    Apex, NC
    Last night I decided to enable ACC on OVMS in my roadster, so that I could have the car run a cooldown cycle upon plugging in and prior to charging. This functionality works great. But I'm seeing something really wacky if I manually initiate a cooldown via SMS after the automatic cooldown has completed.

    Say for example I plug in with the battery at 37C and the automatic cooldown runs for its 60 minutes and only gets the battery down to 34C. If I look at the app and see this, I might then send an SMS to run another cooldown cycle. When I do so, the car goes into this endless loop of alternating between charging limits at 13A and 70A. I've seen this behavior both at home using a UMC and at work using a 208V-30A J1772 EVSE.

    Has anyone seen this sort of behavior or have any explanation as to what might cause it? Below are a couple videos I shot of the weirdness...

    Video upload (QgsF) - vidme

    Video upload (1m3R) - vidme
     
  2. Doug_G

    Doug_G Lead Moderator

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    Pretty sure the OVMS has to "trick" the car into cooling down.

    The way the Tesla Tattler (a predecessor to the OVMS) does it is to trigger a Range Mode charging cycle at minimum charging current. The car starts up the A/C cooling immediately, but then it cycles off after a while. As soon as this happens the gadget detects that the A/C has shut off, and aborts the charging cycle. Then it restarts the Range Mode charge again, and the A/C compressor starts up. Lather, rinse, repeat.

    In other words, it's probably normal.
     
  3. jimmyz80

    jimmyz80 Member

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    Apex, NC
    Notice in the video though, that it stays in Standard mode the whole time that it's flipping back and forth. Normally when I see cooldown mode doing it's thing, I can see it switching to range mode at 13A.
     
  4. rgjones

    rgjones Member

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    San Diego
    FYI Tattler was updated when we learned that you don't need to add cycles to the charging contactors with stop/start charge.
    The algorithm is start charging in range mode (only mode where battery cooling occurs normally) limit 13A (minimum allowable current for minimal power consumption) then monitor the cooling cycles and stop either on target temperature, time or # of cooling cycles. I have mine set to 25C and 45mins which works well in mild San Diego.

     
  5. Doug_G

    Doug_G Lead Moderator

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    Okay cool. I kept having trouble with my Tattler going into piracy-protect mode. Would like to get it running again at some point, just too busy to keep fiddling with it.
     

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