Voltage Drop

Willhound

Noticed last year while running that my voltage while under way was consistently  reading about 12.8v on all 3 of my voltage guages. The stock dial, on my plotter and on the little temp/volt meter that plugs into my accessory socket. I was reading 13.4 to 13.8 at yge alternator  but just to see I changed out the alternator and one house battery that had come with the boat. I had added a second house battery the year before. So one is a year old and the other 2 years old. Both pass a load test and readily charge.
As soon as I shut the engine down voltage drops to 12.4 and then quickly to 12.2 to 12.1 but will stay there all day. That's with fridge, stereo, plotter and VHF all running. 
Should I be concerned? Maybe isolator?
I did pull the battery switch panel last year and checked connections and also clean and grease my battery terminal connections every spring.

Dream_Inn

Have you taken a meter and looked directly at the voltage on the batteries?  I'd start there before going any further.

Willhound

I'll check again but in sure when I checked when I joined things up I was getting 13.5 at the batteries from the alternator.

kordo

Had a similar situation, the analog gauge on the electrical panel and my small volt meter that plugged into the accessory socket were both wrong.  Instead of checking the battery, you can check the voltage at the accessory socket using a good volt meter.  Just use the leads and poke around until you fine the positive and negative,  The plug in volt meter I bought on line was junk and the analog gauge on the electrical panel was inaccurate.  Hope this helps.

Willhound

Thanks @kordo hope that's all it is. But the hardwired Chartplotter is showing the same. Will try tomorrow when I'm sober. Off work tomorrow and hit a major party when I got back to Marina this evening. 

Black_Diamond

Check your ground block and your grounds to the engines for clean connections. Bad/poor grounds in DC is almost always the problem for voltage issues. 

Willhound

Had a rain day here yesterday on my day off, so spent it getting at all the little boat jobs I've been wanting to tackle. My multi meter showed I was getting 14.4 to 14.8 volts out of the alternator and 14.4 or so from on-board charger and that it was getting to the batteries. But dropped off from batteries to dash.
Started at batteries and right away found that two of them I was able to get at least a couple of wrench turns on the connections. Just to be safe I also pulled out the battery switch panel and all those connections were good.
Now showing 14.2 to 14.4 from batteries.
So the moral of the story is start with the simple and most logical explanation. Even though I thought I had taken care when installing the batteries this spring I obviously either didn't tighten them enough, or at least should have checked them again after a few weeks.

kordo

Good news and good reminder for the rest of us.  Thanks.

Ian

I had the same issue on my Harley - didn’t tighten up the battery properly when I changed it out. I lead a technical support team and too often the basic are overlooked. 

cmelt2003

Anyone know where the grounding blocks are on a 99 270? I’m have weird dash electrical gremlins as well.