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What is the target temp for the battery if the car is plugged in?

Discussion in 'Roadster: Technical' started by mg012, Jul 5, 2013.

  1. mg012

    mg012 Member

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    Its pretty hot here in San Antonio these days, varying from 90 to 106 degrees ambient outside. Looking at my OVMS app, it shows the ambient temp in my garage at 87 degrees (there is no cooling in there so I think that seems like a low reading). While plugged in, OVMS consistently shows the battery at 96 degrees, the motor at 91 or so, and currently the PEM is 98 degrees. My A/C works fine and just had a full service done in Austin in March. Also, for the record, the temps reported for the tires are: 95, 96, 98, 100. Clearly these temp readings are not very accurate.

    Why isn't the PEM and Battery (like the motor) closer to the ambient temp. Seems like they should all read the same temp after sitting there all night and this morning and that temp should be the ambient temp (unless ambient temp is over 100 in which case the battery should be kept cooler). Are the PEM and battery heating themselves up trying to cool the battery down?

    thanks in advance for educating me
    michael
     
  2. markwj

    markwj Moderator, Asia Pacific

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    In the morning, is the car awake or asleep (before you 'touch' it or the charge cord)? In the OVMS app you can see this by the color of the battery/motor/PEM temperature display - white is awake, gray is asleep.

    If the car is asleep, that means the VMS thinks the car is cool enough and won't run the circulation pump. Without circulation, the battery temps won't change much.
     
  3. markwj

    markwj Moderator, Asia Pacific

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    To help with the explanation, here is my car:

    ImageUploadedByTapatalk1373069218.584015.jpg

    TPMS is gray to indicate the data is stale and not being updated. Those were the temps and pressures a few minutes after my last drive,

    Ambient temp is white so accurate. The sensor seems to be low down and picks up a lot of pavement radiated heat.

    PEM, motor, battery temps are white so accurate. PEM is a couple of degrees cooler than the battery - it is air cooled, but sits on top of the battery. Motor is separate and closer to ambient.

    Car is awake (white PEM, motor, battery temps), and circulating hot coolant. I really don't understand Tesla's approach here - without fans or HVAC, the coolant is not going to get much cooler, and can't really bring the battery temperature down that much. All the pump can do is avoid isolated hot spots within the battery.
     
  4. mg012

    mg012 Member

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    Mark, thank you for asking these questions and clarifying the OVMS display.

    After seeing your first reply last night I waited till this morning to collect all the data. OVMS reports: Car Awake, Ambient 86, PEM 96, Motor 93, Battery 95. I could hear the pump running. I got out my HVAC technicians meter and recorded actual ambient temp in the garage at 80 degrees, but putting the sensor down in the front fans got 82.

    Could all these temps be off by 5 degrees? Various weather apps on my phone report outside temp at 75 which my meter also indicated. It might be warmer in my garage because the car is on. Is my car heating up because its trying to cool itself? It sure seems like all theose temps should be the same (ambient). I can't recall the last time I looked at OVMS and the display indicated the car was asleep (months ago maybe).

    The reason I initiated this post was because I think my pump is running all the time.

    more thoughts anyone? Sure would love a response from a Tesla engineer.
    thanks
    michael
     
  5. markwj

    markwj Moderator, Asia Pacific

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    Michael: maybe easiest if you eMail/PM me your OVMS vehicleid and I'll look at the logs.

    The temperature display in OVMS is accurate (we've verified it against what the car is showing internally). The ambient temperatures you are seeing is a few degrees higher than you measured, but that can be because of the position of the sensor. Can you try measuring lots of different points around and under the car to see if you can find anywhere hotter?
     
  6. mg012

    mg012 Member

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    Its warmer this morning and forgot to plug in until 8am. At 9:30am: OVMS reports 89 Ambient in the garage, PEM 104, Motor 95, and Battery 91. My meter showed 82 in the air, 85 on the ground under the drivers side of the car, down in the front fan assembly, and through the tail screen near the motor (all 85).

    At what temperature does the computer heat the battery and when does it think it needs to cool the battery?
     
  7. strider

    strider Active Member

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    It is my understanding that 40C is the magic temp above which which the car will begin to cool the battery.
     
  8. mg012

    mg012 Member

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    Strider: I hope your number is too low because 40C=104F and my pump is always running even when the battery is at 91F. I think my pump is always running. I guess I'll call Tesla Tech Support and see what they say.
    Is there some sort of entry in the logs telling whether the pump is turned on and for what reason? A log entry for cooling or heating the battery?
    thanks
    michael
     
  9. strider

    strider Active Member

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    I believe 40C is when the A/C is engaged to "actively" cool the pack (as opposed to "passive" cooling by just running the pump). With the latest Tesla Tattler code it can alert you when a cooling cycle starts and stops but those are just active cooling cycles. Don't recall an alert for the pump.
     
  10. mg012

    mg012 Member

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    Update:
    13 days ago I called Tesla support asking to talk to to someone about the fact that my battery and PEM were always 12 degrees above ambient and the car was always awake, even if not driven for a whole day. (Why wouldn't it settle to ambient?) I've kept the car plugged in all the time it is parked.
    Last week, Thursday, Friday, and Saturday, all of a sudden, it did that. The car was asleep most of the time and the PEM, Motor, and Battery were all approx at ambient temp whenever it was parked all night.
    Then, Sunday, yesterday, and today, its back to being always 12 degrees above ambient and always awake.
    Monday, Tesla called (but it turned out they wanted to talk to someone about their Model S, but somehow had my phone number!!!) and I told them I have been waiting for a call for 10 days. He listened to my question, said he wasn't familiar with the Roadster and asked to call me back after talking to a Roadster savvy technician. He did call back to tell me that my Roadster's behavior was perfectly normal: The car will run the pump to cool the battery which will run down the battery which will cause charging which will heat up the battery and the PEM and so forth. Crazy
     
  11. markwj

    markwj Moderator, Asia Pacific

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    Since coming back from TESLIVE, I've been nightly range mode charging at 16A - 32A for 1 hour (depending on how many miles I need the next day). That has solved it for me, and the car now sleeps both after charge and in the car park at work during the day,

    By comparison, I'll try some standard mode charges now, and see if there is any difference.
     
  12. strider

    strider Active Member

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    One nice feature of the Tattler is the "cooldown" function. You set a target battery temp (I use 25C) and when you come home and plug in the car will drop to 13A (lowest rate allowed) and charge in range mode (cools the battery more than standard) until the target temp is reached. It's actually even smarter then that as it will switch from standard to range and back again to trick the car into running the A/C more often. Once it reaches target temp it'll shut off and wait for the scheduled charge.

    So as soon as I get home the pack is immediately cooled down and the car sits silent until I open a door or scheduled charging begins. I've never had the endless pump circulating condition since using this tool.
     
  13. wiztecy

    wiztecy Active Member

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    Really "Cant Wait!" for the cool down feature to come in the OVMS :), I do believe it takes lots of stress off the pack, pump, and cooling system of the Roadser as Strider mentioned.
     
  14. Botbldr45

    Botbldr45 Member

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    I set my target cooldown temp to 25C but never make it. #992 goes thru 5 cooling cycles and rarely gets below 30C. I guess I'm being too optimistic and Tattler cooldown cant keep up with the Maryland summer....... garage is usually 80F when cooldown starts during day.

    Dont get me wrong I love the feature or the battery would sit at 37 or more when I get home....... I love cooldown feature.:tongue:
     
  15. markwj

    markwj Moderator, Asia Pacific

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    Made some good progress over the weekend. Problem is that it is bundled with a bunch of other stuff we've been working on, so lots to get right.

    Same in Hong Kong. I can get it down to about 30C without issue, but anything lower is too hard. The way I'm working on it at the moment is to just have two limits - temperature and time, and if either is hit the cooldown stops.
     
  16. mg012

    mg012 Member

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    Mark, thank you for the bit about Range charging at low current. I did that once and got the result I was looking for: the system stopped heating itself up while trying to cool itself and ran all the time. Since then, I have set my default charge current to 12 amps in Standard mode and that works great. All the components are usually at ambient (around 87 degrees) without being awake and the pump running. Since the car is always plugged it all night it doesn't need a fast 48 amp charge which probably stresses the system more than a 12 amp charge. I can always change the rate if I need a quick charge.
    thanks again for everybody's input, and yea, it would be cool for OVMS to have the cool down function.
    michael
     
  17. wiztecy

    wiztecy Active Member

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    Cool Mark! Literally :) Thanks for working on the OVMS and adding the Cool Down Feature. Please keep us updated on the progress. Yes a Time/Temp timeout would be the right way to trigger the shutdown. Would be nice if users can also set those two parameters as well. Reason being (as you both both mentioned above) is that I've noticed that if the ambient temp is above a certain temp, say 80F, that the HVAC system can't drop the battery down any further. I'd see mine sitting at 28C and it wouldn't pull down any further. If the user can modify that temp that would allow the feature to shutdown once the user has learned the behavior of the cool-down for their temperature/geological environment. Same goes with the time its running, I think a user would also like to modify that. Time could be in minutes or it also could be the number off cool-down cycles.

     
  18. strider

    strider Active Member

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    Well, there's no free lunch. It's moving heat from the batteries to the garage. If your garage is sealed then at some point it's a zero sum game where the car's A/C can't push any more hear into the garage. The Tattler cooldown function works perfectly for me in NorCal (I also use 25C as my target). Maybe arrange for an attic fan or something to evacuate some of the heat? And as you say, 30C is better than 37C :)
     
  19. mg012

    mg012 Member

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    Besides remaining cooler, I've noticed another effect of charging in Standard Mode at 12 amps instead of 48: it charges to 99% instead of 95 or 96%.
     
  20. shrink

    shrink Member

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    I just took delivery of my CPO Roadster on 8/9/2013. With Mark's help, I got the OVMS up and running late last night as well. Thanks again, Mark!

    I currently have the car plugged into a 240/30 amp EVSE and set to storage mode. This car won't be a daily driver for a while. Phoenix is hot and it looks like my battery is running pretty hot at 107 degrees. Yikes. Is there any way to cool it? For now, I have the charging set to charge on plug in. When I start driving it more regularly, I'll set it to take advantage of off-peak times.

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