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Draw power from battery and external charger at the same time?

Discussion in 'Model S: Battery & Charging' started by rnortman, Sep 21, 2017.

  1. rnortman

    rnortman Member

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    If I'm plugged into a low-power charger (e.g., 110V/12A adapter) and I turn on the heater, which I believe draws more power than that outlet can provide, will the car use as much power as the charger can provide and then draw the rest it needs from the battery, using both power sources at the same time? Or will it switch to drawing entirely from the battery? Or will it perhaps run the heater in a low-power mode? (I kinda doubt that...)

    Before you answer "of course it can draw from both", which is the intuitive answer, have you actually confirmed this? Power/charging circuitry is complex and things that seem like they should be easy aren't always.
     
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  2. pers1

    pers1 Member

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    My advice is to check the inside temperature and choose only one step up.
    If I see that the interior temperature is 17C i’ll set it to 17Cin the app. When it reaches 17,5 or above I move it to 17,5 and so forth. I have 3kW from the outlet, but that keeps it down to 5A (230V). The Tesla heather can draw as much as 6,34KW at high (max heatsetting)

    PerS
     
  3. Brass Guy

    Brass Guy Member

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    Yes, it will continue to draw from "shore power."

    A few years ago (3?) I had turned on the heat from the app during a typical winter morning. When I got to the car, the screen reported charging complete, while drawing the UMC max of 40A at about 240V. (I was confused by this at the time.)
    The cabin heater is about 6kW, and the battery heater is another 6kW; so over 12kW. I was drawing over 9kW from shore, so the other ~3kW would've come from the battery.
     
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  4. scaesare

    scaesare Well-Known Member

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    Yup, as @Brass Guy noted in his experience, it draws from both.

    You can watch this yourself if you have a pre-AP car (like mine) with the older dash "power gauges", which show real-time power draw.

    If you plug in to your example 110v/12a circuit, you are getting less than 1.5KW from shore power. Max out the heater and watch the power usage jump up to ~6KW. If you do this on a cold morning and the pack heater kicks in you can watch the power usage increase even further, all the while you are charging with the 12A draw being reported.
     
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  5. rnortman

    rnortman Member

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    Thanks to both of you! This is exactly the kind of answer I was looking for.
     
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  6. scottm

    scottm Active Member

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    #6 scottm, Sep 22, 2017
    Last edited: Sep 22, 2017
    There's one other clue that is probably universal for all Tesla S X, the green ring around charge port is pulsing green when charging / drawing through the port. So flick on your HVAC to max heat and get out and see if that ring is still pulsing. If so (it is!) you are drawing from shore AND battery at the same time!

    Since we're on the topic, you may wonder if/when HVAC demand exceeds UMC delivery capability, what is the blend of what power being drawn from what? Does the HVAC begin pulling directly from UMC / charge port for all it has to offer with nothing excess actually flowing into main pack to charge it, and main pack also delivers the difference that is needed to satisfy HVAC... ??

    This is perhaps splitting electrons worrying about this.. but I believe the on-board charger is dutifully trying to stuff all UMC capacity into the car battery, and all HVAC is drawing everything it needs from the car battery. If HVAC demand exceeds UMC offering then those electrons gained by UMC are simply scooped up really fast by HVAC equipment. It's philosophical arguing if they reached the battery first.

    Also on this topic... suppose you're at full charge (whatever you set the dial to) and the pulsing green is now solid green ring but you remain plugged in. Now turn on the HVAC (using App or in-car while parked and still plugged in)... supposing the UMC / HPWC / public / supercharge that can deliver more than HVAC needs... What's happens now?

    Look at the ring. And look at the status of the charging under the lightning bolt icon on the console. The combination of those two things tell you if any battery top up is happening (there will be some charge flow indicated on the console), or not. If you're not topping up (no charge flow) and the ring is pulsing then all electrons needed by HVAC are flowing from shore power. The best place to be.
     

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