• 24 NOV 14
    • 0

    Magnetic fields and other issues regarding hybrid and electric cars

    From Alasdair Philips

    (In response to a question posed to him on the effectiveness of shielding against EMF levels inside hybrid cars)

    Nothing really screens ELF magnetic fields in practice. Most materials are for RF fields only and screen the electric component that therefore stops the radiated wave. This is not the case for ELF and VLF fields. (c. 3 Hz to 300 kHz). You need to enclose either the source or yourself in a “mostly sealed” high permeability metal box (e.g. like mu-metal). That shorts out the magnetic flux so it can’t really escape. Published EMF adverse-health-effects science is strongest for ELF fields.

    You need to be very wary of trying to measure EMFs in hybrid vehicles with a simple Gauss meter. There are enormous DC switching changes that can create large impulse magnetic fields that many meters will ignore and are likely to have biological consequences. They also usually have high-speed switching power trains for motor speed control that create magnetic fields in the range 2 kHz – 200 kHz that again almost no common magnetic field meters will measure. You need a VLF meter for those. Gigahertz Solutions manufacture some good ones. Many cars (including hybrids) still use the chassis as the negative connection with a single large cable through the cabin for the positive. So you are effectively sitting inside a co-axial cable.

    Unless you have to drive a lot in cities and need to meet strict new emission restrictions, I would be wary of choosing a hybrid.

    People should also look at the battery warranty in close detail. Lifetime use often brings the financial cost per mile up to at least the same as a modern diesel car. Some companies lease you the battery and some sell it to you with a warranty – but usually that devalues with mileage and time so that if you claim in, say 5 years, as your battery fails, you only get a small contribution towards a replacement. The battery is very toxic inside and very expensive, though the costs have fallen from about $10,000 USD to about $3000 USD – though I have been told that they have recently been rising again. So, about twice the cost of a replacement engine – again reducing long-term re-sale value. Current owners are very positive about the cars – well they would be, wouldn’t they!

    CarGurus.com examined the purchase price and operating costs of 45 popular hybrid models and discovered the average petrol-electric automobiles costs 25 percent more to own and operate than its petrol-only sibling. “The hybrid premium tends to considerably outweigh any savings you might see in reduced fuel costs,” said Langley Steinert, founder and CEO of CarGurus.com. “In 76 percent of the cars we examined, the cost of ownership was significantly higher than the cost of ownership of the same petrol-only model.”
    In practice the Prius is reported as doing about 50 mpg – less than you will get with a modern diesel of similar size and better performance.

    That’s my take on the issues. I was surprised how low the fields were that they were reporting – then I saw that they were usually only reporting ELF fields and not VLF fields.
    Alasdair Philips BSc(Eng), DAgE, MIAgE, MIEEE

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