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Climate control and other accessory power sources when parked

Discussion in 'Model S: Battery & Charging' started by Todd Burch, Jan 5, 2013.

  1. Todd Burch

    Todd Burch Electron Pilot

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    I often take a 20 minute ferry ride to work. On the ferry, you cannot run your engine. During the hot summer days, or cold winter days, the cabin would get uncomfortably hot or cold in my ICE. This is one reason why I like the Model S...I can keep the cabin comfy even with the "engine" off.

    If I'm parked and have the air conditioning running, is the A/C fed from the 12V battery or the main pack? I would assume the main pack, but want to make sure. It would be a pain (not to mention embarrasing) to reach the end of the ferry only to find my car won't start, blocking traffic behind me. Much more, jumping it would be interesting as the manual has no instructions for it...Nor instructions for removing the nose cone...

    So the question is: what is the power source for everything in the Model S? My assumption is:

    -Climate control power is fed by the main pack.
    -Stereo, interior lights, headlights, taillights are fed directly by the 12V battery
    -Computers/touchscreen are fed by the pack.

    But who knows? Any ideas?

    Since as I understand it the 12V battery is slowly charged by the main pack (let's just call it a trickle charge for lack of a better term), if the accessories that are fed by the 12V battery exceed the recharge rate of the 12V battery for a certain amount of time, you'll kill the 12V and your car will not start.
     
  2. jomo25

    jomo25 P4398

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    Good questions. Perhaps the Ownership team can answer these? I sent 2 sets of questions to them on Thursday. I got one set answered on Friday. I was told by a Scottsdale rep that the Ownership group is happy to answer these use case types of questions.

    Of course if anyone here knows for certain, that would be great. I just dont know if anyone would.
     
  3. harry

    harry Member

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    There is a DC/DC converter which is sized to provide plenty of 12VDC power to keep the battery charged to run the 12V stuff (lights, screen, apps, etc.). The main battery pack powers that DC/DC converter. On the other hand, the climate control (except perhaps for the blower?) is powered by the high voltage pack, not the 12V battery. Everything except the climate control and battery temp management is trivial in terms of current draw. As long as you have charge in your battery pack you can't run your 12V battery down.
     
  4. Todd Burch

    Todd Burch Electron Pilot

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    Thanks Harry--is this info from an official source?
     
  5. harry

    harry Member

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    Todd Burch --

    Mostly surmise, intuition and past experiences. First, the DC/DC converter is active anytime the car is active, so the 12V battery is being charged as power is drawn from it. From my quick view of the converter while Chicago was replacing our 12V battery I'm guessing that the converter is about a 45-55 amp unit. That would be plenty of power for the ancillary systems on the car. So... you can't run the 12V battery down as long as you have any power in the high voltage pack.

    With respect to the climate control, I just installed a variable speed scroll compressor on an EV I'm rebuilding, and it is a high voltage unit. That seems to be the customary approach. Since A/C-heat pump compressors pull anywhere from 2KW - 5KW, if they were powered by 12VDC then the amperage required could be over 400A. That would require some pretty large cables, fuses, etc. Using -- for example -- 300VDC instead, the same wattage would require something roughly in the range of eight to eighteen amps. Easier to cable, fuse and with less transmission loss.

    For the other ancillary systems, the lighting is almost all LED. The touchscreen and all firmware, etc., is computer based, and 5VDC and 12VDC are the requirements for that equipment. It wouldn't make sense to step down from a high voltage pack to get that low voltage when there is already a DC/DC converter doing that job for the 12V battery. The cabin fan, wiper motor, etc. are based on proven 12VDC designs, and I assume that Tesla wouldn't redesign those to use a high voltage supply.

    So there it is... Maybe that's all wrong -- just one view of it, anyway.
     
  6. Todd Burch

    Todd Burch Electron Pilot

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    Thanks---that all makes sense!
     
  7. TSLA Pilot

    TSLA Pilot Member

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    I suspect he's correct.

    The only really high demand item is the HVAC compressor and that's got a sticker on it that says "400V" if I recall correctly. Thus, it's powered directly by your large battery. (There are pictures somewhere on the forum I'd suspect.) The fans and such are likely to be 12v units due to industry practice and cost considerations, despite the much greater efficiency of higher voltages.

    Sit in comfort and enjoy driving the future!

    If you could, however, do please post the mileage you lose on really hot and cold days so that we might get an idea of the mph loss due to HVAC use.

    Thanks!
     

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