Flat towing a Rivian

Discussion in 'Rivian General Discussions' started by CappyJax, Mar 4, 2019.

  1. CappyJax

    CappyJax Well-Known Member

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    YOU DONT USE REGENERATIVE BRAKING ON THE TOAD WHEN THE RV ACCELERATOR IS APPLIED!!!!! How many times do we have to explain this simple principle. You only use it for slowing both vehicles. Please educate yourself and stop repeating this Bs.
     
  2. Hmp10

    Hmp10 Well-Known Member

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    So you’ll arrive at your vacation spot with, what, 20 miles of range from regeneration on your battery after using the EV occasionally to push the RV? Great plan.

    I’ve driven an EV for four years. You’re way overguessing how much charging you get from regen braking.
     
  3. stank65

    stank65 Well-Known Member

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    The one scenario it could be helpful is the following. Note: I believe this is too small a window to be worth it.

    If you use regen braking only while the RV is actually braking you are recovering energy that would have otherwise been transferred as heat in the brakes.

    If you recover that braking energy via regen and not heat in friction brakes, AND you charge the battery to whatever you consider "full", the idea would be to use some of the power in the Rivian to assist in some form. The system would in theory run the Rivian battery down to a certain point assisting, and then stop assisting while the battery recharged back to "full". On an extended trip this would result in multiple cycles of assist and no assist while the battery would fluctuate between full and the lower limit for assisting.
     
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  4. CappyJax

    CappyJax Well-Known Member

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    Not guessing at all. Is the RV and toad weigh 12,500kg, and they decelerate from 100kph, that will produce 1.3kWh. At 70% efficient regenerative braking, that is just about 900Wh of energy back in the batteries. Not spectacular if you are in the flat land on the highway. But let’s say you are in the mountains going down long grades. Going down a 5% grade for ten miles would produce over 5kWh per mile. A 10 mile run would give you 35kWh into the battles. . And that is just one downhill run. If you went for Vail to Denver, you would produce enough energy to fully charge most EV batteries. Also, you are saving a lot of wear and tear on the towing vehicles service brakes. It is free energy.

    You simply don’t understand physics.
     
  5. Hmp10

    Hmp10 Well-Known Member

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    Yes. A lot of mechanical complexity to handle push forces safely and a lot of electronic complexity to manage the charging scenario. All to a very marginal end.

    I hope Rivian is spending its time on building a reliable vehicle instead of thinking about such fringe scenarios.
     
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  6. CappyJax

    CappyJax Well-Known Member

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    Only to people who don't understand physics.
     
  7. kb78

    kb78 New Member

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  8. stank65

    stank65 Well-Known Member

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    I'd be interested to see your math on this and assumptions.

    Seems like some of the assumptions have this number significantly higher than real life application.

    What is your split between the energy absorbed by RV friction/exhaust brakes, Rivian friction brakes, and Revian regen? From the way you wrote this it seems you are counting the entire deceleration towards the Rivian Regen braking.
     
  9. CappyJax

    CappyJax Well-Known Member

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    From the way you wrote this it seems you are counting the entire deceleration towards the Rivian Regen braking."

    Yes, why wouldn't you?
     
  10. stank65

    stank65 Well-Known Member

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    Because that isn’t right. In order for the Rivian regen breaks to be engaged, the RV brakes would have to be engaged also. It is also unlikely that the Rivian would break with only the Regen but I’ll just give you that one. At the absolute very best, the Rivian would account for a quarter to a third of the braking power on the downhill.
     
  11. PaulMLAS

    PaulMLAS New Member

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    For those of us that are actually RVer's there are really just 2 important factors in this thread in my opinion:

    1. Wow, the Rivian can be flat towed!

    2. Per most (all?) state towing laws the Rivian MUST brake itself regardless of whether it's regenerating or not.

    It's fun to theorize the interesting ways Rivian could assist in accomplishing #2 outside of the currently available aftermarket solutions. So for those that question the relevance of braking, it's not just a relevant discussion, it's something that Rivian must consider when accomplishing #1.
     
  12. CappyJax

    CappyJax Well-Known Member

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    Why? Every large electrically activated trailer I have ever pulled allowed for the trailer brakes to be applied manually through the brake controller. Also, the regency braking could be applied in the brake travel of the towing vehicle before that vehicles brakes are applied.

    How so? It has 700 horsepower. That means it can provide up to 700 hp of braking power with the regenerative braking.
     
  13. Hmp10

    Hmp10 Well-Known Member

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    The batteries are a limiting factor in how much regenerative braking energy can be returned to the batteries for storage. I don’t see that accounted for in any calculations here, and in most EV’s the batteries can only absorb electrical energy at about half the rate they can release it.
     
  14. CappyJax

    CappyJax Well-Known Member

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    Well, 700 HP of regenerative braking would be a very aggressive deceleration. But Rivian has stated their batteries will be able to charge at 360kW at 800V, which means the batteries can absorb 480 HP worth of energy. And because of the regenerative breaking only being about 70% efficient, that is 490HP back into the batteries if you could get 700HP of regeneration from the wheels.
     
  15. Hmp10

    Hmp10 Well-Known Member

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    #95 Hmp10, Jun 3, 2019
    Last edited: Jun 6, 2019
    It also depends on how fully charged the batteries already are. Unless Rivian is going to use graphene ball or solid state battery technology, there will be protective circuitry to slow the charge fed to the batteries as they near full state in order to prevent their accelerated deterioration. Batteries are generally pretty poor receptors for regenerative braking energy, which is why Tesla is experimenting with adding capacitors to their battery packs, as capacitors are more optimal for capturing regenerative braking energy, especially if it’s soon going to be called upon for acceleration.

    I have read that Rivian will cut back battery charge rates once the battery pack reaches 80% of capacity. I don't see that accounted for in any of the above calculations.
     
  16. stank65

    stank65 Well-Known Member

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    You’re assumptions are just over the top. Assume the cat is a sphere. Real world applied engineering does not work like this.

    I agree with PaulMLAS. It’s great the Rivian can be flat towed. If it can regen while being towed in a safe and legal manner that is a bonus.

    I don’t want an over engineered (more expensive) solution, and I want a solution where I can hook and go as easily as possible.

    All of this functionality can be accomplished with minimal deviation from the Rivian baseline (only software and connections) and with existing proven tow arms.

    The revolutionary parts for the car industry could be a vehicle that comes from the factory with these connection points integrated and hidden, and software driven communication between RV and toad.
     
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