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EMF Radiation

Discussion in 'Energy, Environment, and Policy' started by Ben W, Feb 27, 2009.

  1. vfx

    vfx Well-Known Member

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    We went through this with the Roadster launch.

    Owners and friends of owners had EMF devices that measured different kinds and had different sensitivities. I would like Tesla to release some Model S numbers ahead of the Dougstorm that is coming.
     
  2. bonnie

    bonnie Oil is for sissies.

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  3. Doug_G

    Doug_G Lead Moderator

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    People should bear in mind that the frequencies involved are extremely low. If the motor is turning full speed at 14,000 RPM, that's 233 rotations per second. The motor has four poles, which means the magnetic fields being generated are at most only 933 Hz.

    At that frequency, the skin depth in aluminum is about 2 mm. I'm not sure how thick the motor casing is, but it's pretty rugged. It's going to diminish the fields significantly.

    Also we're not really talking about electromagnetic fields. We're talking about magnetic fields, which drop off cube-law. So a few feet away from the motor they're going to be insignificant even if the motor wasn't shielded by the casing.

    There will be some amount of electric field from the wiring, but the voltage isn't that high and they're too far short to efficiently emit energy at those very low frequencies.

    Assuming that some measurable level of these fields actually reaches your body, could you absorb the energy? Nope. It takes 2 mm of highly conductive aluminum to absorb significant energy from these fields. Your very poorly-conductive body isn't going to absorb any significant energy - it's going to simply pass through you undetectably.

    You're getting a far higher "exposure" to electromagnetic fields just sitting in your house.

    In short, all of this is completely bogus.
     
  4. doug

    doug Administrator / Head Moderator

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    I'm pretty sure this is a non-issue.
     
  5. vfx

    vfx Well-Known Member

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    Best to have it in the specs somewhere. It's gonna come up and they should have an answer ready.
     
  6. bonnie

    bonnie Oil is for sissies.

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    No! Because to put it in the specs means that they think it is important, and then every EV manufacturer will have to do it, and then there will be articles about who has less emissions (even though it doesn't matter), and it will be the source of a LOT of fud. Please, no, not in the specs. Nooooooo.

    No.
     
  7. hcsharp

    hcsharp Active Member

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    I thought they used PWM at much higher frequencies to control power levels. If so, your example would only be true if they were applying full power or 100% duty cycle PWM in addition to max RPM.

    Note I'm making a technical comment. Not arguing validity of EMF radiation exposure concerns.
     
  8. brianman

    brianman Burrito Founder

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    The joke almost writes itself...

    Neighbor walks up and asks why the Roadster owner has his lawn chair positioned so that he straddles the charging cable. Roadster owner points across the lawn to his lovely 3 children and replies, "3 is enough."
     
  9. Doug_G

    Doug_G Lead Moderator

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    Yes, the power is controlled via PWM at higher frequencies, because it's efficient. However, the inductance of the motor itself acts as a filter, preventing very rapid changes in current. That's why PWM works. So the vast majority of the current cycles at the lower frequency, and the high frequency switching is more of a voltage ripple on top of that.
     
  10. vfx

    vfx Well-Known Member

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    Agree if the number has any significance but if it's near zero it should be buried somewhere for those looking for it.
     
  11. Bearman

    Bearman Member

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    There is no radiation close to the source (pem/cables/engine) because the magnetic and electric fields don't couple to become radiation until some distance, around the wavelength/2 which is usually very far away with these low frequencies, what you should physically be mildly concerned about is the low frequency magnetic near field which is something else and can also be negated/damped by design. Also very little energy is lost in the lower frequencies to radiation because the product of the E and B fields are proportional to the dipole moment^4 which in turn is proportional to frequency. There has been a decent amount of work around these issues regarding power lines.
     
  12. Robert.Boston

    Robert.Boston Model S VIN P01536

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    I was on an airplane next to an EMF crazy one time, who was wearing special crystals to ward off the huge EMF fields emitted by the jet engines (which, effectively, are electric generators). He cited as proof of the intense EMF the fact that people doze on airplanes -- the EMF doing its evil work! Unfortunately, his crystals appeared to work, keeping him awake the entire flight so that he could discuss his many other theories of the ordering of the universe. That was a very, very long flight.
     
  13. rolosrevenge

    rolosrevenge Dr. EVS

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    Lol! Never mind the fact that the engines are external the aluminum Faraday cage that is the airplane fuselage.
     
  14. Doug_G

    Doug_G Lead Moderator

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    All of which got started because of a bogus epidemiology study that incorrectly concluded that there was some cancer risk associated with power lines. It's basic statistics that, if you collect a sample and then test an endless series of hypotheses against it, you will inevitably end up with a correlation. That doesn't mean any cause and effect, it means you have to collect another set of data and test the hypothesis again, which they didn't do. Other studies found no such correlation, which isn't surprising because it's hard to understand how humans could even absorb any significant energy from 60Hz fields.
     
  15. Doug_G

    Doug_G Lead Moderator

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    How so? Once they're started they're basically a thermodynamic engine. Fuel and air is burnt at high pressures and temperatures to create thrust and power a mechanical compressor. No electricity is involved in that.

    One of the engines on the plane will typically have an alternator attached to generate electricity for the rest of the aircraft, but that's in principle no different from an ICE car.
     
  16. Incredulocious

    Incredulocious '11 LEAF → '13 RAV4EV → '18 Model 3

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    For what it's worth, Nissan includes a warning in the LEAF manual about being in the car while charging if you have a pacemaker:
    LEAF-manual.JPG
     
  17. doug

    doug Administrator / Head Moderator

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    That's a separate issue all together. EMI for many types of electronics is a legit design concern.
     
  18. NigelM

    NigelM Recovering Member

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    Just a little true story from today that illustrates 2/3 of the population has no idea what EMF is:

    We're out on a boat with a metal tower when a sudden storm blows up and it's thundering pretty loud. We pull over to a spoil island and disembark in case of lightning (typical here at this time of year). 3 people pull out their phones and start checking messages etc. I said "You know that the EMF that your phones give off attracts lightning right?...." Two people immediately put their phones down.
     
  19. Doug_G

    Doug_G Lead Moderator

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    Actually cell phones won't attract lightning, but apparently they can make the risk of injury greater. http://www.snopes.com/horrors/techno/ipod.asp
     
  20. bonnie

    bonnie Oil is for sissies.

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    There are standards in place regarding emissions and immunity for medical devices - and pacemakers have specific immunity standards on top of that (that's why you rarely see warning signs on microwaves anymore). Same with defibs.

    So either Nissan is exceeding a reasonable level or their lawyers are overly conservative. What if you wear a pacemaker, have to go somewhere and the car is still charging?
     

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