EMF Radiation

[vfx]

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.

 

[bonnie]

Easily and cheaply mitigated Electromagnetic shielding - Wikipedia, the free encyclopedia

A tinfoil hat won't work?

 

[Doug_G]

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.

 

[doug]

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

 

[vfx]

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

 

[bonnie]

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

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.

 

[hcsharp]

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.

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.

 

[brianman]

And the normal usage model would not be to sit in the car or hang out next to it while charging.

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."

 

[Doug_G]

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.

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.

 

[vfx]

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.

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

 

[Bearman]

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.

 

[Robert.Boston]

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.

 

[rolosrevenge]

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.

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

 

[Doug_G]

There has been a decent amount of work around these issues regarding power lines.

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.

 

[Doug_G]

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).

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.

 

[Incredulocious]

So I have a "friend" who is a bit of a whacko about EMF and he came out and "measured" my Roadster with some sort of instrument. He determined that while driving there was very little EMF and not to worry (like I said, he's a whacko so if it was elevated at all he would have freaked out). However he did measure the car and UMC while charging and recommended I not sit in or be really close to the car while charging. Again, he's a whacko, but it would seem that the car does emit some EMF radiation while charging but very little while driving. Please don't ask for real numbers as I don't want to talk to him about this ever again....

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:

 

[doug]

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:

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

 

[NigelM]

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.

 

[Doug_G]

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.

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

 

[bonnie]

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:
View attachment 7539

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?