[ausev] Riding close to 96v EMF vs 120v EMF

[Chris Robison]

Dan,

"EMF" as a term is not completely clear in your message.  The usual
meaning "electromotive force" is otherwise known as "voltage" (your 96V,
120V, etc) and isn't something that floats around in the air unless said
voltage is high enough (thousands of volts) to ionize the air and cause an
arc.  If your bike is producing lightning, I suspect you have some design
issues to re-hash.

I suspect on the other hand, that you're referring to "electromagnetic
fields" -- however:

- The steady polarity magnetic fields you'd be able to pick up with a
compass as you describe are not worth worrying about (you can buy on eBay
giant neodymium magnets powerful enough to break your arm if you hold one
within a couple feet of a large metal object; their enormous magnetic
field is otherwise harmless)
- The fluctuating electromagnetic fields (essentially high-amplitude
low-frequency radio waves) generated by the controller's PWM wouldn't be
detectable with a compass, and do not have a well-documented negative
effect on humans or animals.

More on that last point -- such fluctuating electromagnetic fields are not
only produced by the motor.  They're produced by the motor leads and the
controller, and to some extent in the battery wiring as well. They're
everywhere around the vehicle, even coupled to the body of the car, which
means that even "ground" is very electrically noisy, which is one of the
challenges in designing electronics that operate in an EV.  There are ways
to reduce these fields somewhat (ways of routing wires, etc) but no way to
eliminate them.

If you're worried about electromagnetic fields, EVs are probably not a
good hobby for you.

  --chris



On Tue, November 7, 2006 5:17 pm, jtp said:
> Mark,
>  We had discussed 4 years ago (when you had offices in San Marcos),
> regarding an electric motorcycle and sitting to the close proximity to the
> motors' EMF, that,  a copper mesh-surround-to-ground may be the direction
> to
> go within the fiberglass body housing over the motor, to ground magnetic
> fields. To what extent might that be effective?
> I'm sure that some emf would get through, as I've noticed a compass needle
> swing from north-magnetic to point to the electomagnetic clutch (in my
> motorhome) when the a/c compressor is engaged, (a foot away from the
> compass).
>    Is there any great difference in voltages applied in the production of
> field strength, or is it a matter of watts from demand?
> Dan.
>
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