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Weird car compass problems with Honda Element?

9 messages,  Last post on Jul 04, 2009 at 10:26 AM

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#6 of 9 Re: Weird car compass issues with Honda Element? [cybersu] by compassadjustr Jul 03, 2009 (10:02 pm)
Replying to: cybersu (Jun 02, 2007 9:05 pm) I recently adjusted a compass in a car and found the magnetic field above the dashboard to be three times stronger than the earth's field where I was.( A small powerful magnet nearby was required to rectify the deviating force. In your Honda's case there must be a strong field from the front to the back at the dash board.   Twenty feet is a big distance magnetically as magnetic fields decrease by the inverse cube of the distance from the magnet. So if at twenty feet the field is stronger than the earth's field, at one foot it would be 8,000 times stronger. Also, if the compass was always attracted to the car, it must be closer to the car's "south pole" which would suggest a vertical axis to the car's magnetic back.   Perhaps, if you were always facing the car when observing the compass, you had the magnetic source on you. Replies to this message: tidester (Jul 03, 2009 11:44 pm) cybersu (Jul 04, 2009 7:01 am) compassadjustr (Jul 04, 2009 10:26 am)
#7 of 9 Re: Weird car compass issues with Honda Element? [compassadjustr] by tidester HOST Jul 03, 2009 (11:44 pm)
Replying to: compassadjustr (Jul 03, 2009 10:02 pm) magnetic fields decrease by the inverse cube of the distance   That's the classic dipole field which also depends on the angle relative to the dipole moment (cosine) so the orientation of the correcting magnet must also be considered. (Of course that also requires that you're not so close as to invalidate the dipole approximation.)   tidester, host SUVs and Smart Shopper
#8 of 9 Re: Weird car compass issues with Honda Element? [compassadjustr] by cybersu Jul 04, 2009 (7:01 am)
Replying to: compassadjustr (Jul 03, 2009 10:02 pm) I have a renewed desire to fix this now as I got one of the new iPhones with a compass in it, and that compass is also confused in the car. The iPhone compass works fine elsewhere and I have no "hardware" in or on me which would lead em to believe I am the source. Unless it is my magnetic personality, of course   Anyhow, about the compensating magnet. Would you put it up front or in the back? Where would you purchase a magnet with the right strength?   Thanks in advance! Replies to this message: compassadjustr (Jul 04, 2009 10:26 am)
#9 of 9 Re: Weird car compass issues with Honda Element? [cybersu] by compassadjustr Jul 04, 2009 (10:26 am)
Replying to: cybersu (Jul 04, 2009 7:01 am) A small ferrite bar magnet (magnetised along the length) would do the trick. Toy shops may have a variety in a packet.   Face the car magnetic east and place the magnet (aligned with axis of the car) beside (left or right) of the compass. Move the magnet towards or away from the compass until it reads east. In your case the magnet should be red end (N) towards the back of the car.   Now face the car magnetic west. If the compass doesn't read west, adjust the magnet to remove half the error. The fore & aft field at the compass has now been corrected.   Blutac is pretty good to hold the magnet in place.

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