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Laptop trips GFI
w_tom wrote in :
First, to have a common mode noise (leakage), the computer must have separate incoming and outgoing electrical paths. Incoming is AC electric. What is the outgoing path? The ground in the computer is hooked to the ground in the NMEA bus, the printer through the printer cable, the computer's own troublesome charger. Because of any NMEA connections, it's also connected to that AC battery charger under the quarterberth, which is also hooked to AC ground. How many paths does it need?? Second, leakage through a resistance is rare. Leakage occurs more often through reactive devices. That means the ohm meter will not measure leakage through components whose conductivity increases with frequency and voltage. IOW these leaks would appear as high resistance (notice I did not say impedance) to the meter. This troublesome computer has a 3-prong grounded power plug, so we may assume it also has in input double pi line filter, or at least some disc ceramics in the .01 to .05 uF range between "hot" and neutral and ground. The ac current differential caused by the input filter's capacitors is more than enough to cause trips, which is why I wanted him to first plug the computer into a ground buster to eliminate the connection between the computer power supply ground and the boat AC ground to isolate this type of tripping. If the ground buster fixes the problem, he merely leaves it plugged into the ground buster and goes about his business, occasionally getting a tingle from the ground on the RS-232C shell, maybe. He'd be fine. Then, I was going to have him measure the voltage between the unconnected ground pin and boat ground to see how hot it was. You can imagine the $24 switching power supply of the bargain laptop has nothing but the finest, mil-spec line filter parts....totaling, probably, 10 cents, tops.... Third, all appliances have leakage. GFCI trip is not just from one device. Sometimes it is leakage from numerous devices combined. And yet the meter would test every device and see no leakage from any of them. Maybe nothing else is plugged into this OUTLET GFI. It could serve more than one outlet from its internal terminals, though. The GFI outlet in my bathroom services the AC outlet on the side of my house, too. Notice - without numbers then one can only speculate. Everything we do on this newsgroup is speculation...an exchange of guesses and ideas that usually come up with a solution or prod the asking party into taking a different path to the solution than the one he was taking.... |