[pf] no significant electric-car EMF risks, IMO

· An interesting discussion related to electric cars, on GreenViews-NZ.   D.

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At 21:16 2/4/2001 +1200, Rich Wernham wrote to GreenViews-NZ, with Subject:
[GV] Hydrogen-fuel buses :-

I love the concept of removing some of the atmospheric pollution caused by
combustion engines but I have this nagging query in my head that thinks we
may see an increase in cancer bought about by exposure to large
electromagnetic fields being generated by these new technologies !!!  Can
anyone dispel this concept that plagues my total enthusiasm for electric cars?


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At 22:06 2/4/2001 +1200, Brent Efford wrote to GreenViews_NZ :-

Yes. Coincidentally I am writing something on this for a client!
 Compared with the genuine cancer risks out there, such as 2 per 1,000 of
population from diesel exhaust, the electromagnetic field scare is a total
beatup. It is one of the most intensively studied possible causes of cancer
but no statistically valid link has ever been sustained. There is an
extremely weak possible correlation with childhood leukemia - 1 extra case
in NZ per 10 years. But even that could be due to random factors.

 Prudent avoidance of extreme EMF levels is fair enough, but it would be
absurd to continue to use fossil fuels instead of electricity on health
grounds.

 In any case, AC household wiring and appliances is the main EMF exposure
most of us experience. Riding in an electric vehicle, normally using DC,
would be an infinitesimal increase. If the electric vehicle replaced a
diesel, or petrol, vehicle, the net _reduction_ in cancer risk would be
substantial.
  
Brent Efford
TechMedia Services
Transport 2000+ NZ
PO Box 2626, Wellington 6015
New Zealand
Ph (04) 801 9331, Fx (04) 801 9344
Mob 025 887 387
www.techmedia.co.nz 

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At 05:57 3/4/2001 +1200, I (David Mac) wrote:

· Brent's right (he probably knows more about this than I do). 

· The reason is implied in his pointing out that the power source is DC
(either batteries or a fuel cell, or - I don't know - the generator turned
by a gas turbine in those buses in Christchurch NZ).

· To get from where the electricity is (in the wires and circuit-boards) to
you, any energy has to leave the metal and travel through space, i.e. it
has to be transmitted. Once it _has_ left, it is in the form of an Electro-
Magnetic Field - EMF - travelling at the speed of light (which is also an
EMF). This will have the characteristics: frequency and intensity, which
will separately affect how much energy is absorbed in living cells.

· Now, the main point. _Whether_ anything is transmitted, and if so how
much, depends on the frequency of the current in the wires - zero frequency
(DC), zero transmission. So our 50 Hz (cycles per second) mains power
transmits only a little power - this is why those thousands of km of power
lines all over the country, acting as a very extensive transmitter, don't
lose more than a very small amount of the energy they carry, as radiation;
what they lose is almost all lost as heat in the wires.

· Rich Wernham, at 21:16 2/4/2001 +1200, asked about electric vehicles.
Here I'm somewhat out-of-my-depth, because I know that there are several
ways of controlling electric motors, and I've heard that some of the more
highly efficient ones involve PWM (pulse width modulation) or some other
pulse method. I haven't heard of synchronous motors being fed AC slightly
out of phase, but I'd guess something like a wave of pulses being sent
along a linear motor might have its counterpart in a rotating motor.

· So the question is real, but depends on the details of your particular
vehicle. Such things as the frequency of the pulses. As I indicate above,
50 Hz and a few hundred Hz (as used in the newer fluorescent ballasts)
transmit _very_ little (you need to put your extremely sensitive transistor
radio quite close to a battery-operated compact fluorescent bulb, before
you can pick up anything), and I am almost certain that this is the sort of
frequency (and up to a few thousand Hz) that would be used in motor control. 

· When you /want/ to transmit, you use something above 100,000 Hz: the
numbers on an AM (or MW) radio are in kHz - ranging from half a million to
1.6 million cycles-per-second. And TV and cellphones are a hundred to a
thousand times higher than that.

· My opinion is that there is no significant risk from the power
electronics used to drive the motors in an electric vehicle. However, as
always, testing the reality is better than _just_ going by a prediction.


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sent to Positive Futures list by David.
(David MacClement) davd@ihug.co.nz 
http://www.geocities.com/davd.geo/index.html#top
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