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Author Topic:   mounting of compass near battery
13sport posted 01-13-2002 06:22 PM ET (US)   Profile for 13sport  
How close can a compass be mounted to a battery? I would like to add a compass to a 13 sport where the battery is next to the console. The ideal location for viewing would be very close to the battery.
jameso posted 01-13-2002 09:15 PM ET (US)     Profile for jameso  Send Email to jameso     
Mounting the compass near the battery should not effect the compass. The compass senses a magnetic field not an electrical source. Beware of electrical/magnetic fields i.e. some depth finders that may have a motor driven display and other sources of EMI (electro magnatic interference). A good test of this is to temporarily put the compass in the desired location, leave all power off of the boat, even disconnect the battery. Take a compass reading of an object some distance away, then power up all electrical systems, If you have a deviation trouble shoot by starting at step one and turning on each item seperately, but I doubt you having problems with just the battery. Being of the Avaition school I always "swing" or test a new compass installation.
my 03 jim armstrong
13sport posted 01-14-2002 12:52 PM ET (US)     Profile for 13sport    
I thought that the current flowing through the wiring would, in effect, be a electro-magnet. I sort of remember this from grade school.
jimh posted 01-14-2002 01:33 PM ET (US)     Profile for jimh  Send Email to jimh     
The composition of a typical lead acid storage battery is probably not highly magnetic, however the strong currents that can flow in and out of the battery on the heavy cables attached to it can affect compasses nearby.

If the battery wires are closely coupled the currents will tend to cancel. Even better cancellation results if the conductors are laid up in a twist, but this is not practical with most battery cables.

The magnetic field exists only while the current is flowing, but heavy starting currents may induce residual magnetism in other surrounding objects that will persist when the current stops.


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