Some things to try: 1. Run the plotter off its own battery. Little 6 ah AGM batteries are cheap enough if you don’t have a spare battery sitting around.
2. Put a scope on the DC bus to see what, if any, AC/noise is on the line. Include an engine start with this. 3. Disconnect the NMEA interconnection and see what happens. 4. Check the NMEA connection for configuration. Does the plotter send and receive data or just send? No need to have the NMEA input line connected if there is no data headed that way. 5. Put a laptop on the NMEA connection or run the diagnostic window on the plotter, if it has one, and read the raw NMEA stream to see if it is getting some odd data or any data at all if it should not be. 6. Put ferrites on all incoming wiring. 7. Check for ground loops and NMEA isolation* * This one is a bit tricky. First off, make sure the power supply and ground connections are at exactly the same place as your other electronics. Ground loops are bit complicated to explain and hard to find, but the short version is this step will eliminate some of them. Second is check with the manufacturer to see if your plotter NMEA connections are true marine standard opto-isolated. It is very possible to use direct wiring to NMEA data and not isolate it, my laptop/plotter does just that, but optical isolation prevents various stray voltage and ground issues from messing up the data. Equipment is fairly resilient now, but back in the day an engine start could generate noise that would totally screw up electronics. Even now I will start an airplane with all radios and nav equipment off and then turn it on. I once was delivering an airplane that had a screwy alternator I had to switch off to use the radios and nav gear and then switch back on when the battery got low. BTW – my boat is wired so the engine start battery is usually separate at engine start and has no effect at all on the electronics. They don’t combine until charging voltage is present for a few minutes. Is yours like that? Joe Coquina C&C 35 MK I From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of David Knecht via CnC-List Sent: Saturday, October 01, 2016 15:14 To: CnC CnC discussion list Cc: David Knecht Subject: Re: Stus-List Chart plotter problem Let me clarify a few things that might help diagnose the problem. Previously, I tested the voltage at the chart plotter. I have a solar panel that feeds the batteries when off the boat. At the beginning of all these tests, the batteries are fully charged from the panel. So with the batteries charged (12.7 v), measuring at the chart plotter power cable, I got 12.2 volts with battery 1 only, 12.3 volts battery 2 only and 12.3 with both on. When I started the engine, I got 13.1 volts. Note that the was chart plotter unplugged so I did not confirm that it would have started acting up when plugged in (the behavior is inconsistent). I am guessing that the voltage drop is expected and 12 volts is well within the spec of the B&G. I am presuming this eliminates the under-voltage possibility. I previously have tested the voltage at the batteries from the alternator but did not write it down because it seemed OK (about 14 volts). I also did the AC voltage test by measuring AC at the battery terminals with the engine running and that was less than the 50mv that was supposed to indicate bad diodes. Is it still possible it is a voltage regulator problem and how would I test? To Gary’s message: I still think you have a noise/grounding problem. If noise gets into one of the inputs, say the NMEA, there is usually a buffer to handle excessive inputs. If that buffer gets overloaded, the chart plotter might act goofy until the buffer gets emptied. I would make sure you have a single point grounding system that all goes back to one ground point. Make sure all connections are tight. The NMEA was unplugged when it went crazy, so it is not getting in that way. I guess it is still possible to have noise from the DC input? Thanks- Dave Aries 1990 C&C 34+ New London, CT [cid:image001.png@01D21D55.1F86CF80]
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