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Eliminate limited regen - improving cold weather driving

Discussion in 'Future Vehicles' started by Lex, Mar 1, 2018.

  1. Lex

    Lex Member

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    #1 Lex, Mar 1, 2018
    Last edited: Mar 1, 2018
    Has this been explored previously ?

    Limited regen seems like such a waste of energy, when it seems it would always be needed when heat would be needed, so why not explore diverting the waste energy immediately to heat coils, maybe a "heat bottle" ? Even if it goes out as waste it helps the driver
    @elonmusk @Tesla
    Lex on Twitter

    I once heard the service centres have a heat coil tool to "burn off" a pack without needing to plug into motors (though I'm not even sure if that's actually true, there would be a heck of a lot of waste heat, which I'd guess they would have to vent to outside, or run outside on a removed pack ??).

    Limited regen is a cold-related issue only, right ? So why are we wasting the potential energy, why not push it out to heat coils somewhere, coils in the cooling system or other heaters that can take the "waste" regen energy. ("heat bottle" is the cooling system after more thought damn you twitter lol)

    This way the driver would never experience limited regen in the cold, and the car could warm up sooner.

    If other parts of the car are also not ready yet for full regen, then they could get the heat first or have preheaters.

    Heat coils are basic primitive electrical components, surely they can can take the surges of power that the battery is not yet willing to accept, no ?
     
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  2. boaterva

    boaterva Supporting Member

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    So, this would/could be a heating element and a vat of water to boil (away) the heat from the extra power to give better regen performance.... Gives rise to images of the old Stanley Steamer, but not used for propulsion! :D
     
  3. animorph

    animorph Active Member

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    Limited regen just forces you to get off the go pedal sooner than you would have to with stronger regen. Plenty of arguments about this, but if coasting to a stop is the most efficient then limited regen is more efficient than stronger regen. I don't think an efficiency argument can be made for stronger regen except in specific cases where you'd otherwise have to use the friction brakes.

    That said, it is annoying to have limited regen.

    The heating element for climate control is about 6 kW I think. that might give 10% regen for an X or S at full blast. Tossing around 50 kW to 70 kW would be a challenge, though it would only be for limited periods.
     
  4. MorrisonHiker

    MorrisonHiker S 100D 2020.44.15

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    No. It also occurs if you charge the battery to capacity.
     
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  5. boaterva

    boaterva Supporting Member

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    Right, which is what cold does.... no place for the 'power to go'. Artificially 'full' battery.
     
  6. Lex

    Lex Member

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    Ah ya that's why I think my original idea was for a separate heat bottle, as it could possibly also be used when battery is full.
     
  7. Rowan256

    Rowan256 Active Member

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    I think that they simply didn't expect it to become -35 that often, Elon came from South Africa and the compagnie is in California, also a heater works up to 6kWh or so I guess, regenerating works up to 60kWh or so I estimate.
     
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  8. AWDtsla

    AWDtsla Active Member

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    Many many many many times. By everyone except Tesla. Lots of the fanbase chiming in to say it must be impossible if God^H^H^HTesla didn't already do it. No significant changes in almost 6 years of Model S now.
     
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  9. MP3Mike

    MP3Mike Well-Known Member

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    Yes, my understanding is that there is a special plug on the bottom of the pack that they can plug a large heater unit into to drain the pack before they open it up to work on it.
     
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  10. Saghost

    Saghost Well-Known Member

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    Where are you thinking you can safely dissipate 30-60 kW of raw 400V DC power in a controlled fashion on millisecond timing?

    The cabin and battery heaters combined are about 12 kW I believe. You'd have to install something additional to go past that, which means more cost and weight that you're caring all the time and only benefit from in the first half hour or so of drives in cold weather.

    Now if capacitors become cheaper and more energy dense, I can see a few arguments for including an ultracapacitor stack that's big enough to eat the car's kinetic energy from freeway speed and 60+ kW DC-DC converter to support it. That improves regen roundtrip efficiency and shortens supercharger stops as well as providing the consistent experience we all want.
     
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  11. AWDtsla

    AWDtsla Active Member

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    It's almost like I can see the future... See post #8

    Resistive heating elements are both CHEAP and LIGHT. A single loop of nichrome wire pasted to the top and bottom of the pack would be able to dissipate massive amounts of heat, forget about the 100 other possible designs for resistively dumping heating without having include flux capacitors.
     
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  12. Saghost

    Saghost Well-Known Member

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    Did I say it was impossible? No. Did I say it must be impossible since Tesla hasn't done it already? No. Post #8 doesn't apply.

    Keep in mind, you need to be able to switch this heating on and off instantly and cycle it to various partial levels. Even if you achieve that, 60 kW dumped onto the pack for any length of time is going to create one heck of a thermal gradient radiating out from where the heater element is...

    You're adding cost and complexity, and possibly introducing new risks. Maybe it's worth it, maybe not.
     
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  13. AWDtsla

    AWDtsla Active Member

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    But you keep building these straw men. I guess we need someone to invent a flux capacitor to solve this issue too. To PWM control that's used anywhere else in the car won't for, reasons...
     
  14. scaesare

    scaesare Well-Known Member

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    I've thought about this before.... train locomotives have giant air-cooled resistor banks to shed excess energy for braking.

    This flat resistive heating element can dissipate 1KW in just under half a square foot. That's ~2KW per ft^2. I estimate the bottom surface area of the pack to be in excess of 40 ft^2. That's 80KW of energy you could dissipate.

    That pad is spec'ed at 0.2" thick. A pack teardown said there was about 1/4" of dead space between the bottom of the cell modules and the bottom of the pack casing inside the pack. You could theoretically use that space for such a heating unit (although I suspect that may be a buffer space in case of casing deformation due to impact. Or it was designed to accommodate 2170 cell heights...).

    Adding up to 80KW of additional energy due to deceleration, even in short bursts, would be welcome in the cold... exactly when the regen is most lacking.
     
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  15. AWDtsla

    AWDtsla Active Member

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    Electric vehicle braking resistor gets a water-cooled boost
    New dynamic braking resistors are light enough for electric cars - Cressall
    What Are Braking Resistors?
    Powerohm Resistors, INC: Off Highway Truck Resistors
    Dynamic Braking Resistors / Speed Inverters | Home – OHMIC RESISTORS, OHMIC CONTROLS
    Thermal analysis and temperature characteristics of a braking resistor for high-speed trains for changes in the braking current

    There are 10 types of people in the world. Those that can use google, and people that want to stuff their cars full of flux capacitors to fix all problems.
     
  16. scaesare

    scaesare Well-Known Member

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    All of those solutions provide resistive braking... none of them couple that with the concept of funneling that heat in to a cold pack to address the root cause of reduced regen to begin with, no?

    That water cooled one misses the boat by suggesting the waste heat be funneled to a radiator, when the point I'm making is that you could use it to more quickly heat the cold pack...
     
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  17. AWDtsla

    AWDtsla Active Member

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    Does it really miss the boat? What do you think would happen if you hooked it into the battery coolant loop instead of a radiator?
     
  18. scaesare

    scaesare Well-Known Member

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    Hence the second part of my very same sentence: "...the point I'm making is that you could use it to more quickly heat the cold pack."
     
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  19. 3mp_kwh

    3mp_kwh Active Member

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    For perspective on waste heat, ever since the observation that P100D goes 60 to 0mph as fast as it goes 0-60, and knowing how it spends most of the time on the way up pushing 400+KW, you can see how high the maximal recovery could theoretically be. So, I agree with how much sense it makes to evolve heat, especially for us folks up north. It would be even more efficient, since cold batteries start dumping you into friction braking at 50+F degrees. So, we aren't even close to 60KW of regen. A crude home water heating element takes ~4KW, for another reference. We're not all constantly doing P100D acceleration tests, but you can tell there's a lot of energy on the table, here.

    FWIW, I remember the Volt would register an additional 5KW, sometimes when heat was turned on and you had the I/O display (on '13's and later) in front of you.
     
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  20. PhaseWhite

    PhaseWhite Member

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    There's another 6kw heater for the battery pack. So that makes 20% regen that could be routed to heaters. When it's cold I'd rather route my excess kinetic energy to warm up my car and battery instead of my brake rotors.
     
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