lithiums messing with compass?

[rala]

both my sons left thursday for a camping trip so of course i had to pack them some lights and some extra batteries. as i packed some of their gear, i noticed the north heading on one of the compasses was way off. so i took it out of his bag and it was fine. as i put it back in, i noticed it was off again. it took me a while to figure it out but anytime the compass was near the cr123's i had packed, the compass would point towards them. i tried two other compasses with the same results. can anyone explain why? i was never really good in science class.

 

[Icebreak]

I believe it is a combination of the content and shape of the material used in the components that make up the battery and the electromagnetic field in the battery as well as the electromagnetic field around the battery.

With a primary lithium battery the positive end of the magnetic needle in the compass seems to be mostly attracted to the center of the battery. The negative end of the compass needle seems to be more attracted to each of the ends of the battery and more attracted to the anode than the cathode.

An alkaline gives a similar result.

With an AW protected RCR2 the positive end of the magnetic needle is repulsed by the anode and attracted to the cathode.

Conversely, with an AW protected RCR123 the positive end of the magnetic needle is attracted to the anode and repulsed by the cathode.

 

[defusion]

i've just tried lithiums, li-ion, and nimh's.
All gave the same result.

Some other object do the same, i tried a pen, and a screwdriver, and also some coins.
the pen and screwdriver both produced pretty big deviations, and the coin did affect it, but not really by much.

 

[Daniel_sk]

Every piece of metal will distract a sensitive compass, you always have to take it out and hold it with hands away from you when looking for a direction. I prefer to have a small backup compass. The reason is that the needle on the compass is a magnet, so metal parts will mess it up.

 

[Handlobraesing]

Magnetic attraction to the battery can. Most battery housing is steel, including the CR123A

 

[Genes]

Only ferromagnetic metals

 

[Gimmy]

Remind them not to wear a watch or stand near powerlines when using a compass also.

 

[jason9987]

also the bigger the metal the further you should be away ie. for a car/truck you should be about 15 feet away for smaller stuff a foot or two is good

 

[McGizmo]

This is a real problem on small boats at sea where the compass is the primary means of navigation. With the advent of GPS, it isn't nearly as critical but when you use a compass to steer by even if the course to steer has been determined by a GPS, it really helps if the compass is indicating the real course!!

A good boat compass as well as the newer fluxgate compasses can be "swung" to make adjustment for local anomolies in the magnetic field induced by metal and electrical interference of devices near by but you still need to keep other items of ferrous or electrical nature away from the compass! Some stainless steels are magnetic and will cause the compass card to swing if they are brought near. If you approach the helm and see the card rotate, you have trouble!!

 

[rala]

thanks all for the quick science lesson. i have never really used a compass before so i had no idea that so many different things can cause interference. today i can say i learned something new.