Weird compass question

[PoorDick]

Have been enjoying my truck for four years now (March of 22) and just "discovered" something strange, at least to me. Pulling out of my garage faces due north, and the truck compass agrees, but for the first time I happened to have a GPS app on my phone running and it said due north was to my left, pointing due west. I thought the app had gone wonky, so turned it on and off again, but the same result. I stepped out of the truck and - voila - the app suddenly adjusted and pointed true north correctly, but as I sat down in the truck it again said north was due west. I waved the phone around while sitting in the truck and the phone compass was going nuts, flipping around like it was stuck in the Bermuda Triangle.
So...is it simply the battery pack in the truck causing the compass to lose it's composure or something else? Just curious more than anything.

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[BigSkies]

Being near big metal objects is known to reduce the accuracy / functionality of magnetic compasses.

On top of being a big metal object, an EV is a giant ball of various magnets & electromagnetic fields.

I've never thought to test it, but I wouldn't call your experience surprising.

 

[37.773972 -122.431297]

GPS is True North, not magnetic north. It gets info from satellites, not the magnetic pole. Were you still in your garage? Between the garage, and the car, some satellite reception may have been affected.

 

[Joules Burn]

Try the same situation with an old fashion magnetic compass.

 

[Polar]

It’s the giant metal box you’re in - when you’re in the truck.

That aside, it’s interesting to see the behavior.

 

[VSG]

GPS is True North, not magnetic north. It gets info from satellites, not the magnetic pole. Were you still in your garage? Between the garage, and the car, some satellite reception may have been affected.

No, this is not the case.

GPS doesn't provide orientation information, except as a derived quantity when moving. Handheld GPS units and cellphones also have a magnetometer to detect magnetic fields, which is what is used for the compass function. This data is *combined* with GPS information when moving to provide a more accurate heading determination. But the software inside the unit corrects for magnetic declination (this correction is part of the datum, which also corrects for the shape of the Earth) so the readout you get will always be true north unless your software settings allow you to override this and display magnetic north.

The behavior the OP is seeing is totally due the the large metal mass of the vehicle distorting the local magnetic fields. There are also strong permanent magnets in your motors - even the fringe field from these is probably stronger than the Earth's field. As @Joules Burn said above, you will see the same phenomenon with a magnetic compass.

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