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Dumb electrical question....

Discussion in 'Model S: Battery & Charging' started by Scothawk, Dec 10, 2014.

  1. Scothawk

    Scothawk Member

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    I am just slowly doctor so my expertise and electrical knowledge is meagre at best......question.

    The electrical power stored in the Tesla battery is it in AC or DC form? The electricity delivered to charge that battery from any source is AC or DC form?
    The inverter on the car converts the stored charge to AC or DC form to power the car?

    Thanks in advance for answering my very dumb questions!
     
  2. tom66

    tom66 Member

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    The battery, and any chemical battery, releases charge in a DC form, and accepts charge in a DC form. 320~405VDC for the 85kWh pack, and 270~360VDC for the 60kWh pack.

    The battery charger converts AC power from the charge connector to DC power for the battery charging process. In the case of supercharging, direct DC current is pumped into the battery, bypassing onboard charging equipment.

    The motor requires variable-frequency AC which is generated by the inverter by chopping up the DC input from the battery, pulling nearly 1000A at peak acceleration on MS P85 (or ~1300A for P85D)
     
  3. stevezzzz

    stevezzzz R;SigS;P85D;SigX

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    Short answer: for the single-motor S60/S85/P85/P85+ cars the main traction battery pack supplies ~400VDC at up to 320kW to the power electronics, which converts DC to variable frequency AC used to drive the car's AC induction motor.
     
  4. pgiralt

    pgiralt Active Member

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    The battery is a DC battery. As far as I know, batteries are always inherently DC.

    The power that comes from your house to charge the car is AC and is fed to the on-board chargers (single or dual depending on configuration) which take that AC and convert it to DC to charge the battery.

    The battery outputs DC to feed the inverter which converts the DC to 3-phase AC (which is different than the single-phase AC you have in your home) to run the AC induction motor.

    When you go to a supercharger, the superchargers take care of converting AC to DC, so the power coming into the car to charge the battery is DC.

    Hope that answers your question. :)
     
  5. Gerardf

    Gerardf Active Member

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    - Batteries can only store DC.
    - batteries also have to be charged with DC. As a result the AC power must be converted to DC at the correct voltage. This happens in either the on-board charger modules or the SuperCharger (that actually seem to use exactly the same charger modules, just more).

    - The inverter is actually an AC generator that drives the AC motor.


    There is is of course quite a bit more going on :)
     
  6. Scothawk

    Scothawk Member

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    Excellent thank you all for your explanations and keeping it in laymans terms. Now I know how my patients must feel sometimes!
     
  7. NigelM

    NigelM Recovering Member

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    There's no such thing as a "Dumb electrical question..."; one of the great things about TMC is that there's always a few folks around ready to explain stuff that the rest of us don't know. :)
     
  8. CliffG

    CliffG Member

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    Sure there is: the one you didn't ask, just before DZZZZT.....

    Always ask!
     
  9. physicsfita

    physicsfita Member

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    I know I'm getting slightly pedantic here, but I think I should clarify some of the responses. Strictly speaking, a battery does not store electrical charge. The energy is stored in the chemical bonds. A battery uses that energy to shove charges along. A very good analogy would be the heart -- it expends ATP's (energy stored in chemical bonds) to pass blood through it so it could do another lap through the circulatory system. Similarly, the battery takes charges in the electric circuit and does work on them to pass the charges though it so the can do another lap of the circuit.

    I tell my students that the meaning of "charge" when talking about "charging a battery" is in the same sense as "charging" a fire extinguisher -- you are rebuilding its supply of chemicals. It is not referring to electric charge (confusing, I know!).

    There is a device that does store electric charge -- a capacitor.
     
  10. ModelX

    ModelX Member

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    I appreciate this analogy, helps with my understanding!
     

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