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Liquid cooling the Roadster PEM

Discussion in 'Roadster' started by adiggs, Jul 3, 2013.

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  1. adiggs

    adiggs Active Member

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    Something I figured out in the heat of the day, during Stage 2 of the BC2BC rally - using water to cool down the PEM while charging. Is this a well known trick for helping along the charging process on a hot day, and I'm just late to the party?

    http://asokasblog.wordpress.com/2013/07/03/liquid-cooled-roadster-pem/


    For anybody who doesn't yet know about this, I have good news and bad news. The bad news is that it appears it can get hot enough outside that the battery will be fine, but the charging system will slow down the rate at which it recharges the battery. The good news is that the Roadster PEM has a flat top and is easily accessible (open the trunk), and that means you can keep it damp / wet to help it radiate that heat away.

    For standing water, what I did was use a wet cloth and squeeze the water out onto the PEM (rather than trying to pour water from a bottle). Much better control over how much water gets onto the surface and how far it spreads. You need a flattish surface, and if any of this is sounding way out there for you, then maybe just consider a wet cloth and keeping your PEM excessively clean (and damp) while it's charging :)
     
  2. TEG

    TEG TMC Moderator

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  3. jbadger

    jbadger TR#506, 3#1206

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    The last couple of days i've been getting the power reduced message as the battery is getting too hot. This is after I paid $1500 for a new PEM double fan assembly. Is 90 degree weather really that hot for the Roadster? I'd love to see a liquid cooled PEM.
     
  4. wiztecy

    wiztecy Active Member

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    Hows your driving habits in the past few days? I know that when my car's sitting idle for 8 hours outside in Campbell after these 95+ days that the PEM temp sits right below the 1st yellow marker, still in the blue but its already at a high temp... same with the motor, the battery temp sits one blue bar away from the yellow which around 36 - 38 degrees C just sitting. Then once I get moving on the highway I then get the needed airflow to breath all the heated components and my battery, pem, and motor temps begin to drop. I do get on it and typically driving 60-80mph but not racing it. I suspect if your in city/stop and go traffic things would heat up on your much faster in this blistering heat.

    Trying to find a shady spot to park but that's really hard to find where I work... bummer. I may bring my car cover, at least that should reflect some of the sun's rays. I'll have to experiment with that.
     
  5. jbadger

    jbadger TR#506, 3#1206

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    My car is generally parked in the sun, don't have a lot of options where I park as I only charge at work. As far as driving goes, i'm a bit spirited but lately been stuck in traffic as i'm working out of Sunnyvale more than Cupertino now.

    A few days ago I got in my car and saw outside temperature of 132 F, so with the stop and go traffic it must not be able to cool down. I remember my motorcycle having this problem when I was behind a few cars in a parking lot on a hot day.

    IMG_0857.JPG
     
  6. ggr

    ggr Roadster R80 537, SigS P85 29

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    But you say that the message is about the battery getting too hot, not the PEM, so the new fans or water cooling the PEM won't help? The battery is cooled by the air conditioning, maybe you've lost some pressure in the A/C system.
     
  7. jbadger

    jbadger TR#506, 3#1206

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    Oh had no idea that the A/C cooled the battery. My A/C doesn't produce cold air, could that be why? Is the A/C cooled like traditional cars, or is it somehow different?
     
  8. wiztecy

    wiztecy Active Member

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    #8 wiztecy, Jul 4, 2013
    Last edited: Jul 5, 2013
    The Roadster will use the onboard AC system to cool the battery pack and the pack has priority over the passengers as for cooling. The Roadsters don't blow cold air really, I'd say it blows mildly cold air and the 1.5s are worse.

    The true way to see if your AC is functioning is to ask Tesla to look in diags to view the bar pressure of the AC system. Another way is when you connect your Roadster up for charge after the Battery pack has been heated up.

    1) Before the charge look at the bars the battery pack is in, the higher the better for the test.
    2) Connect your Roadster to a 240v 12 or more amp charger. (you can also dial your amps down to 12 so that the pack doesn't charge but the energy goes to supporting the cool down function of the AC/Roadster. I do this after I finished driving my roadster home from my daily commute to condition and keep the battery temps where they like to be).
    3) Set your charge options to charge in Range mode, this aggressively runs the AC system on the pack vs. a conservative approach in STD mode.
    4) Execute your charge and come back withing 40 - 60 mins.

    I believe you'll need to turn the charger off, turn the key on, and drop the e-brake to see the vitals / temps of the system. After doing that view where your bars are for the battery temp. They should have been driven down, ideally it should now be at the 1st blue bar which typically represents around 26 degrees C plus or minus some degrees or sitting on the second blue bar. This also depends on the ambient temp to some degree, in the winter I can drive my pack down to 20-23C but can't seem to drive it that low in the summer heat.

    If the pack temps were driven down in this test your AC is functioning properly.

    Yes its a traditional AC system, the front Radiator is the condenser for the AC system with the exception that it uses a heat exchanger... meaning the AC system also works as a heater. But the the system is the same, AC refrigerant running through a condenser.

    I'd also find a way to keep out of that heat, 132F is not good for the packs longevity. I'm guessing thats with the sensor and was heated up by the body panels etc... But still that is way too hot for the Roadster. Your pack is under your hood trying to do the best for cooling... Now if your can keep the roadster on a charger at work you can cool the pack down like I mentioned before.... I'd cool it when I arrive at work and then towards the middle/end of the day.

    I'll also bring my car cover into work next week and take some metrics on the Vitals.... to see if it helps keeping the Roadster cooler. I was in an underground garage at my last job which was nice... I still wanted to cool the pack down but couldn't with 110V @ 15Amps. Now I'm at a new job/location I'm getting hammered really bad with the sun's rays pounding on the poor thing so I really want to find an escape from it soon. Electronics and batteries hate the heat.
     
    • Informative x 1
  9. ggr

    ggr Roadster R80 537, SigS P85 29

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    The only difference in the unit itself is that it's driven off an electric motor, not power taken from the engine. It then goes through a heat exchanger to blow cool air on the people and/or cools the coolant that circulates through the battery pack. If you can't get at least slightly cool air from it, this will be the problem. You'll need service.
     
  10. jbadger

    jbadger TR#506, 3#1206

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    Even after 20 minutes it is still blowing warm air, so i've emailed the service guys over at Fremont and will try to take it in next week.

    Wiz, thanks for the informative post. I'll definitely try to keep it cooler.
     
  11. wiztecy

    wiztecy Active Member

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    #11 wiztecy, Jul 4, 2013
    Last edited: Jul 4, 2013
    FYI:
    "According to our research, lithium ion batteries perform optimally, and will last longer, if they are kept at temperatures between -10°C and +30°C. This range is consistent with findings by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE)."

    Lithium Ion Batteries Can’t Stand the Heat | PluginCars.com

    http://www1.eere.energy.gov/vehiclesandfuels/pdfs/thermoelectrics_app_2012/wednesday/cunningham.pdf

    As for keeping the PEM cooler, keep it out of the sun and try to get air circulating around it... the 1.5 PEMs are built like a tank, so I'm not concerned with mine going out... but I am concerned about the heat buildup with the battery.
     
    • Like x 1
  12. backmost

    backmost Member

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    High temperatures here in New York have made my PEM get too hot. The last two days I'll get to work, plug in, car starts the HVAC and brings the battery temp down to around 37C. But after maybe half an hour or so I'll look on my Chargepoint app and the car stops drawing power.

    When I go out to the car to check what happened the VDS says System too hot, restart when safe. My PEM was at 61C when the message fired. It's charging fine now that it's night and the sun has gone down, but this afternoon it was almost 100F ambient temps.

    In this example would using alcohol have a greater evaporative cooling effect on the PEM?
     
  13. adiggs

    adiggs Active Member

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    Being a huge non-expert, the water on the PEM thing was a hook or by crook thing I gimmicked up on the spot. I would park in shade if that's an option - part of what made that day go so badly for me is (as you can see from my avatar) my Roadster is black, it was 100+, AND I don't think there was any shade in sight, much less something in range of where the car was charging.

    At least in that circumstance, it seemed like the AC cooling the pack, the ambient heat, and the heat gain from the black car body balanced out and I was at best trickle charging.


    Yeah - I'd expect alcohol to have a better evaporative effect, but whether you'll notice the difference or not is a different question. I was babying the car in person pretty much full time, and it seemed to help. I think the only quantities of anything that'll make a different are so small that they will require continuous application as they evaporate to make a difference - even rubbing alcohol sounds expensive in that situation.


    Oh yeah - leaving the trunk open probably helped too - easier for the 100 degree breeze to carry away the excess heat above the battery than keep it locked away in there :)
     
  14. backmost

    backmost Member

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    I noticed a 5 degree drop when I opened the trunk to air it out. My Roadster is black as well!
     
  15. DanielFriederich

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    The AC system will kick in at 41 degrees battery temperature while driving or charging. If not check the pressure of the HVAC in the service menu. it should measure about 2-3 atmospheres when idle. if value is 31.8 atmospheres the HVAC coolant has gone caused by a leackage or HVAC compressor failure.
    IMG_6627.jpg
     

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