T&T: 12-volt cooler kills GPS input

[Rich Gano]

Thought that subject might get soma attention.

I think I solved a nagging problem I have been having with my computer-aided
navigation using a GPS input through the computers parallel port.  The two
laptops I have been using seem to have over time developed the inability to
maintain contact with the GPS.  Checking the GPS itself shows a solid bunch
of satellites with high signal strengths.  When I first started having the
problem a few weeks ago, I solved the problem by switching out the IBM
ThinkPad for the Toshiba.  Then, after a week or two, the Toshiba developed
the same problem.  Turning off and restarting the GPS and computer would
sometimes fix the problem for a few hours.  Every once in a while I'd find
the GPS turned off.

All this time, we had a battery-powered cooler plugged into a cigarette
lighter plug on the other side of the helm from the GPS. I would just hit
the GPS on button and it would come back up fine.  However, today I
noticed that when I plugged the cooler into the 12-volt cigarette lighter
socket, the GPS went off.  When I reenergized the GPS, the computer would
not regain GPS data until I unplugged the cooler.  I repeated the experiment
to be sure of what I had seen.

My conclusion is that there is an improper ground to the cigarette lighter
plug socket and that connecting a load to it creates some sort of ground
loop that interferes with the GPS data through its ground.  I removed the
cooler plug from the socket and tried the ThinkPad, which has refused to
work at all lately with the GPS input.  To my relief, it picked up the GPS
and displayed our position on Coastal Explorer all day.  I snipped the
ground wire to the plug tonight and ran a new ground to a ground block I
installed some years after the apparently shoddy installation (mine) of the
cigarette plug.  The other laptop is now plugged into the GPS and happily
computing and displaying our position on CE.

The mystery about why the two computers took such different time tables to
the same result (not getting GPS input) is unsolved.  The cooler was often
plugged in before the GPS and laptop were energized, and often the laptops
ran for extended periods with no movement of the cooler plug before giving
up the ghost on GPS input.

Tomorrow will tell if this issue is resolved.

Rich Gano
CALYPSO (GB 42-295)
Southport, FL