Prius Magnetic Fields

June 19th, 2009 by Potato

Previously, I wrote about the fear surrounding hybrid cars, specifically the magnetic field exposure:

For the hybrid car issue, we have the question “what are the fields?” and we don’t even have a good answer to that, from which point some people fall into hysterics (up to selling their car). The real issue is then several steps removed: the Prius may have higher magnetic field exposures than other cars, and those fields have an unknown but probably small effect on human health, and that might outweigh the positive aspects of the technology.

I was understandably baffled that some people would make a mountain out of a hypothetical mole hill, especially in light of the fact that there are many other EMF “risks” that are obviously higher in everyday life, such as using a hairdryer, cell phone, or riding on a subway, which may not offer the benefits of a hybrid drivetrain. I was upset that the few people that have actually taken the measurements have not published or shared them in any way. I figured that when I eventually get a Prius for myself, I would have to borrow the magnetometers from the lab and do the job myself (and possibly get a published paper out of the deal!). (Un?)fortunately, someone has beaten me to the punch: G. Schmid and colleagues from the Austrian Research Centres in Seibersdorf have measured the fields in a Gen2 Prius under various conditions and reported the results at an international conference.

The exposure frequencies can go up to 1000 Hz due to some of the power switching. They found that near the floor in the backseat the exposure was highest, averaging 10% of the permissable general population chronic exposure according to the ICNIRP guidelines (which are frequency dependent), and could reach 30% in the maximum case (a switch from maximum acceleration to maximum braking). Even just at lap level the exposure is <5% of the guidelines (since children have short legs, this is perhaps the more appropriate measure).

They accounted for the effect of the tires (rotating tires with steel belts/cables in the makeup produces magnetic fields of up to 4% of the guideline exposure), which would be present in all cars. They also compared to some conventional cars — and the Audi A4 and VW Passat both had significantly higher exposures than the Prius! In fact, the Audi A4 exceeded the ICNIRP guideline in some conditions. The main source of exposure in those cars was from the air conditioning systems, which are “not as sophisticated” in their electrical management as in the Prius. One factor in particular that they mentioned was that the conventional cars tended to use the chassis as a current return, wheras the Prius has dedicated, shielded wiring loops that return to the battery.

In other hybrids it was found that magnetic field exposure does not correlate with installed electric motor power — the Honda Civic Hybrid has nearly 3X as much magnetic field exposure as the Prius does.

For comparison, another presenter looked at exposures on British Rail cars (not the underground — the motors are in locomotives separate from the passenger cars) and found that the fields were also in the 5-10% of ICNIRP guidelines range.


One Response to “Prius Magnetic Fields”

  1. Jonathan Says:

    Hows the Honneymoon?