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Crazy Charging Idea

Discussion in 'Model S: Battery & Charging' started by gavine, Aug 29, 2014.

  1. gavine

    gavine Petrol Head turned EV Enthusiast

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    I have an idea that could potentially change the way electric cars are charged but I need the smart people on this forum to tell my why it's not a good idea. I'm not sure how efficient the on-board charger is, but what if the source electricity from the charging station was used to spin the motor to act as a generator to DC-charge the battery, just like regen? The motor is somewhat efficient as a generator but I'm not sure how efficient it is vs. the on-board charger. If it is almost as efficient, then this idea would negate the need for chargers (single or dual). The motor runs on AC, right?

    To me, this seems like a cheap and simple way to charge the car and would allow you to maximize charge rates based on the amount of amps available with no need for dual chargers, etc. Plus it would sound cool having the motor spin-up as a generator while charging :biggrin:

    I know this sounds silly, using electricity to generate electricity, but you're using electricity for the same thing when charging the batteries through the charger so it's not really that much different. It all depends on the efficiency of the motor as a generator.
     
  2. rdrcrmatt

    rdrcrmatt Member

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    The laws of thermodynamics apply, plus then you'd be putting miles on the drive train and the car.

    strapping a car into a dyno isn't an easy quick process and is something that must be done with considerable care.


    The onboard chargers, while low in capacity, are quite efficient, most likely more so than turning drive train components. Direct DC charging is most likely the most efficient.


    Yea, it would look cool, and be nearly universally compatible for cars that have regent. The next question is, how much regen can an inverter do before getting too hot? How do you secure all the different types of electric cars safely?

    as i mentioned, the only inefficiency of this would be that you are turning the driveline components to charge. it takes energy to do that even if you aren't putting a load on by charging. Also, the wear and tear on tires, components, etc plus putting actual miles on the car… a full battery charge, at 60kw of charging would take about 1.4 hours.. not sure how many miles that would put on, I would guess at least 100.
     
  3. gavine

    gavine Petrol Head turned EV Enthusiast

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    rdrcrmatt, I think you misunderstood me. I wasn't talking about turning the tires with a reverse dyno. I envision the drivetrain being put in neutral and the power from the EVSE be used to directly spin the motor....the motor is fed from the EVSE instead of the battery and runs in reverse to charge the battery.
     
  4. GaryREM

    GaryREM Member

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    Uh....

    The motor either powers the car or regens... it can't do both. It doesn't drive a generator, it is the generator. When it generates it does so at fairly low efficiency. What you are asking for would require adding a generator.

    The motor runs on high voltage variable frequency AC. I.E. it cannot operate directly off the mains.

    The motor is coupled to the wheels. Can't run the motor without spinning the wheels, which implies you would have to add a clutch.

    This doesn't seem like a good solution just to replace a charger :)
     
  5. ItsNotAboutTheMoney

    ItsNotAboutTheMoney Active Member

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    EV drivetrain is:
    Battery <-> inverter <-> motor

    Why spin the motor when you can feed A/C to the inverter or D/C thorough an additional device to the battery?
     
  6. ElSupreme

    ElSupreme Model S 03182

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    Like GaryREM said you can't both generate and power at the same time.

    AC propulsion and the Renault Zoe use the windings in the electric motor to facilitate charging (if you search you can find references to these). But it basically just functions like the onboard chargers that Tesla already has in place.
     
  7. wycolo

    wycolo Active Member

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    Cause and effect, sense of proportion - work on these.
    --
     
  8. mkjayakumar

    mkjayakumar Active Member

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    Essentially what the OP is saying is, use the motor to convert AC to DC.

    But as others have said, you cannot feed power into the motor coils to make it spin and at the same time generate (DC) power in the same coils. Perhaps you could mechanically connect a separate generator to the motor and generate DC power.

    Will this eliminate the need to have an inverter completely? I don't know. And if so will the car weigh less? And more efficient? That's the bottom line
     
  9. Charger1

    Charger1 Member

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    I think you would lose a lot in efficiency. First you would have friction losses with the motor/generator spinning and then you would have electrical inefficiencies with the conversion from ac to dc. I think I read somewhere that you can never fully recover the same amount of energy with the regen because of the inefficiencies associated with the regen. Way to think outside of the box though :).
     
  10. Brass Guy

    Brass Guy Member

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    How about this though: The motor generates up to 60kW AC which is rectified to be fed into the battery. Why can't we feed all cars up to 60kW through this circuit?
     
  11. gavine

    gavine Petrol Head turned EV Enthusiast

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    Here's what I found (sounds pretty good) -->

    "The Chameleon charger is a solution developed by Renault to fit electric cars with a powerful onboard charger at limited cost. The basic idea is to “divert” the motor and inverter from their role in providing traction so that they also contribute to the charging of the battery. The Junction Box, a new sub-system developed by Renault, manages the charging process, changes the alternating current to direct current and communicates with the charging station. The Chameleon charger’s Junction Box is only slightly bigger and heavier than the 3V charger found on most other electric vehicles on the market but, thanks to the use of the inverter and motor windings, charging power can reach 43 kW."

    This is kind of what I was getting-at. Saving cost and having the ability to charge at a higher kW using the motor. My thought wasn't exactly implemented this way, but the ultimate goal is the same.
     
  12. Thud

    Thud Member

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    That would be incredibly inefficient. Grid current->Dyno motor current->Mechanical energy(dyno)->Mechanical energy(drive unit)->charge current

    Compared to: Grid current->Transformer->charge current

    Now, what would be interesting is to use some other form of mechanical input to drive the dyno. Like a waterwheel.
     

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