Electrical Gremlins or Bad Ground?

[Valmika]

This is on the Beneteau. I have recently encountered a problem where if I put any large load (Macerator or refer compressor specifically) on the 12 volt system it seems to draw it down to a point where it shuts the system down momentarily. MFD reboot fans stop Etc. It comes right back up until the draw again. Reefer is not working because it can't pull enough power from the system. It did seem to work the other day while motoring but not sure if that was a fluke because yesterday it wouldn't.


Battery bank is 2X 4D 400 Amp hours. (new yesterday, That wasn't the issue but an expensive guess)


Magnum 2000 something modified sine wave inverter charger.


It also seems I am reading a lower voltage at the panel then at the batteries.



I replaced a couple of iffy battery posts when I replaced batteries and cleaned all contacts there



I thought it might be a bad compressor on reefer but the same issue happened when I turned on shower sump.



What is the best way to test cables and such for a major resistance beside just a visual?


Anybody else have a problem like this. Its making me nuts and its 95 degrees here now. Be nice to have some ice.


Just an FYI probably not related but cockpit stereo speakers not working although cabin one are.

[old frog]

From the outside looking in, & if I were troubleshooting, I would start with voltage drop testing the major circuits. n If you are not familiar with it: internet search with get you videos & how to tutorials. https://www.hagerty.com/articles-vid...g-voltage-drop

[thomm225]

You might try isolating everything.

That is turn everything off or remove the fuse from each and then test one thing at a time and see what happens

If it still does it with each large load item, it's probably a bad connection from the power source/battery (if the batteries are good)

Or if it does it with everything off (except maybe one fan to show effects) and say with just the fridge on pulls the power down, you can then just troubleshot back to the power source from the fridge. This eliminates the confusion of so many things not working

[Mariano]

Could be the ground. Bad ground usually makes things work funny: Gauges all the way up or down, lights that dim o go bright by themself. Had that problem once with a ground terminal with the wire loose inside, hard to see on visual inspection. Two tech guys spent almost two hours looking around and troubleshooting and they din't see it. Their boss, old school mechanic ( and really old, maybe 85), found the problem in 5 min.

[Valmika]

Originally Posted by old frog

From the outside looking in, & if I were troubleshooting, I would start with voltage drop testing the major circuits. n If you are not familiar with it: internet search with get you videos & how to tutorials. https://www.hagerty.com/articles-vid...g-voltage-drop

Thanks Old Frog. This is a great link!! I did end up finding the problem yesterday. One of the large ground cables going to the ground bus behind the panel had a loose hold down screw. The only reason I found it was that the previous owner had wired a blue ground wire into hole for something and that smaller wire looked loose. Tightened the screw down and everything works. Sometimes it's better to be lucky than smart. (but not usually)