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Why do Roadsters make so much noise while charging?

Discussion in 'Roadster' started by gregd, Jul 6, 2017.

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  1. gregd

    gregd Active Member

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    I drove my Roadster to my daughter's for the TMC Connect weekend, and plugged it in to charge for the return trip. The fans came on, coolant pump started, A/C for the battery, etc. She asked, "Why is your car so loud?".

    She thought about it for a minute, then in a moment of inspired revelation, blurted out the answer. "Conservation of Noise!"

    Years ago, I had a similar revelation regarding my Ham Radio hobby. Radio is also known as "Wireless", but is hardly that. There are wires everywhere, just not between the stations. It occurred to me that what I was observing was a new law of physics, akin to the conservation laws of energy and momentum, Conservation of Wire! Essentially, it takes a fixed amount of wire to communicate between two points. That there is no wire stretching across the distance between them does not matter. The wire must be somewhere else, and indeed, looking up at the antenna above the roof, and the nest of wires behind the rigs and below the desk, confirms this. In addition, I observed that higher bandwidth communication modes require better signals, requiring better antennas, and hence more wire. I wrote an academic paper on this discovery, and it was published in the scientific journal "World Radio" in their April, 2004 issue.

    So what my daughter discovered is that there is apparently an EV law of noise conservation. That the cars move with utter silence does not matter; the noise must be somewhere. We hear it while charging. Higher performance requires more noise; witness the sonic difference between a top-fuel dragster and a Prius. Similarly, a Roadster vs a Nissan Leaf, which is relatively quiet during the charge cycle, and is similarly more limited in acceleration and range. The Model S is certainly a very fast car, but it is also larger, thus offsetting the sonic content with the larger volume (decibels per cubic meter). Listening to it charging, and adjusting for size, the Model S is up there with the best performance cars on the planet.

    From this, we conclude that our understanding of battery cycling is utterly backwards. We are not draining the battery of charge, we are filling it with noise. That noise must be periodically removed and vented. If not, the battery will eventually be come deaf (we call it "bricking"). This venting is what we incorrectly refer to as "charging". It is, rather, the discharging of noise, and the faster we do it, the louder it becomes. Batteries should therefore not be specified in Kilowatt-Hours, but rather in Decibel-Hours.

    So, there you have it. If anyone asks why your car makes so much noise while charging, yet is utterly silent while driving, now you have an answer. It's a matter of physics. Conservation of Noise.
     
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  2. ecarfan

    ecarfan Well-Known Member

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    Impressive. I predict that your daughter destined to join the ranks of giants like Sir Isaac Newton with your discovery of the law of "EV Conservation of Noise". ;)
     
  3. TEG

    TEG TMC Moderator

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    During the realization that EV driving is a more efficient mode of transportation, I started to ponder all the energy flows, and noise + heat from ICE vehicles are wasted energy (unless you happen to want that heat or noise for some reason.)

    The quiet drive and cool motor bay are courtesy of the amazing efficiency in getting the stored energy out of the battery and turned into motion.

    The Roadster noise while higher current charging is a bit disappointing. It is a sign of wasted energy during charging. They are running cooling pumps and in some cases the whole AC compressor to keep the battery temps more happy (and safe.)
    Better battery chemistry and more efficient cooling methods are improvements that I look forward to as EVs get better and better. More quiet charging will be a good thing.
     
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  4. TEG

    TEG TMC Moderator

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    Original post reminded me of this:


    Eventually the ghosts end up getting out when you shut it off...
     
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  5. hcsharp

    hcsharp Active Member

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    Man that was heavy.
     
  6. gregd

    gregd Active Member

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    Absolutely! And, just imagine how much louder the Roadster would be during the charging (er, noise venting) cycle if it were not so efficient!
     
  7. Stefan T

    Stefan T Member

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    fix cold weather and the sound problem is solved, best is below 0 degree C (32F)
     

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