Wierd Magnetic Fields?

When you move it around to various locations in front, does the direction deflect slightly? If there were something inside the car that created a magnetic field - under the dash or hood, etc. - it seems to me that the lines of magnetic force would not all be lined up. In other words, in an area that small, there should be a 'point' of origin somewhere. You could even approximate the location by observing the compass deflection.

Unless the car is somehow acting as a coil, and the compass is 'inside' the coil.

What about close to the car? Is there a clear line of working/not working as you leave the car, or does the effect 'fade out?'

-- R Flowers

there's two things, the second being most likely:

1. the car's full of electrical gear - all of which generates electromagnetic fields of some degree. you can figure out if that's the cause by turning everything off and seeing if the needle moves.

1. the car's made of ferro-magnetic steel. that always has some degree of "set" to it. theoretically, it's possible to neutralize this with big electromagnetic coils running around the perimeter of the vehicle [as used in shipping], but reality of course is that it's not practical.

Does it make a difference if the car is on or off? that could lead you in the direction of what is causing the pull.

Dave DeJonge

" I don't like guns" - Dave DeJonge

My guess is that the car body is magnetized. I used to work in aviation and would periodically see the problem in fabric covered planes that had steel tubing frames. We would try to compensate the compass and we wouldn't even get in the ballpark. (If the problem is electrical, you will see the compass jump when you turn things on and off.)

It is theoretically possible to degauss the car body - it's the practical part that gets in the way. The essense is to wrap the body with wire (the way you are probably already thinking, from the side over the top and down and around). The wire is connected to AC power - you'd want a few amps flowing - that is slowly decreased. I've never done it because it was beyond the authorization of our avionics/instrument shop. Whether you want a compass enough to pursue that is up to you.

Mike

It's the radio speaker.

Al

You'd think, wouldn't you? ;-)

I do not find any serious movement from location to location. It always shows ENE.

As soon as I get out of the car with it (even holding it out the window) it acts normally. Strangest friggin thing I have ever seen...

That certainly sounds most likely to me, too. The effect is the same with the car on or off...

Thanks for the possibility...

This one? It isn't yellow, but it looks like what you are describing. I think I'll go get one tomorrow.

Thanks!

Nope...

I thought that, too, but considering that it doesn't change anywhere in the car, including far away from any speakers, I think the magnetized body is most likely...

When the outside of your car gets dusty, do you see the magnetic lines in the way the dust settles? Just curious.. Nick

Joe LaVigne wrote:

There you go! Get some fine metal filings and throw them on the car in various places.

-- R Flowers

the yellow digital one with the 2 rubber

driving in a circle and it compensates for

If the body of the car is magnetized, I don't think this would help.

I agree. Speakers have a very localized field and moving the compass even a couple inches swings the compass a lot.

Mike

I am going to jump in here late. I do not think any of the answers explain what the OP experienced. There are several issues with compasses in cars, airplanes, boats, etc.

1. The compass needle is a magnet. It will point to the nearest peace of ferromagnetic material. It will point to a magnet, but it will also point to a nail, car pillar, anything made of iron or steel whether magnetized or not.
2. The car is full of magnetic fields caused by wiring, speakers, etc.

Both of these issues are resolved by placing the magnet as close to the outside world as possible, stuck to the windshield for example, and then calibrating it.

But, the OP said the compass always pointed ENE (if I recall). I assume this is regardless of the position of the car. This sounds like a stuck compass needle. In other words, take it back and get a refund.

Elliot Richmond Itinerant astronomy teacher

Not sure he said that (points ENE at all times) but I may be wrong. What I do know he said is that it works just fine as soon as he removes it from the car. There, I think, goes the stuck needle theory, right?

The OP said he tried it outside of the car and it worked fine.

I'll stick with the magnetized body. Steel vehicles are problematic for compasses because they always introduce errors. Mostly the errors are not big enough to cause trouble for a driver. Aircraft pilots have to know the heading with precision but car drivers are happy with "kinda northeastish."

The problem is that when a car body is magnetized the compass is effectively inside a magnet. That will make the compass point in one general direction... in this case, ENE. How the car got that way and how to degauss it, I surely don't know.

Mike