• On September 1st, Maine Sail suffered a major hemorrhagic stroke. One of the most generous members of our sailing community, he has helped thousands. Now it's our turn. Click here to learn more

basic marine electrical system help

Dil

.
Jul 13, 2020
38
Hunter 30T Neptune
so on my way back to dock the other day I got a low battery warning. I started the motor and continued on assuming this would charge my batteries. I had the motor running for a few hours. when I got back to dock I noticed the batteries did not seem to have taken any charge. I plugged the boat in to shore power and have turned on the charger. I have not been back to the boat so do not know if they have charged am going later today. I am assuming if the batteries have charged the alternator or the voltage regulator from the alternator has gone bad. if the batteries are not charged I assume I have a loose wire somewhere or the batteries them selves are bad or need fluid. beyond this I am not sure of what it could be. I have a 1991 hunter 30 with a yanmar engine. any other input of what I might check beyond this would be appreciated.
 
Jul 7, 2004
8,020
Hunter 30T Cheney, KS
We have the same boat but I'm sure we're wired differently. First see if they are charged when you get out to the boat. That may tell you if the batts are good. I have 3 on board. Bring a good multimeter out in case you need to check the alternator output. Good luck. Electricity is dark and mysterious.
 
Sep 25, 2008
6,315
Alden 50 Sarasota, Florida
First things first - I would go back to the boat ASAP because running a shore powered charger (which isn’t temperature compensated) into a bad battery would cause it to overheat which can lead to some bad outcomes.
 
May 17, 2004
3,483
Beneteau Oceanis 37 LE Havre de Grace
What were your voltage readings before starting the engine, with the engine running, and with the shore power charger on? If you don't have a volt meter (preferably a handheld digital volt meter to measure the actual batteries) you're going to need one to troubleshoot. How are the batteries wired? One large bank? Two banks with a 1-2-B switch?
 
Nov 8, 2010
11,385
Beneteau First 36.7 & 260 Minneapolis MN & Bayfield WI
Could I respectfully suggest a basic level of understanding regarding electricity and marine wiring? Find a pro or a willing dockmate? It's hard to give answers when you can't ask the questions.
 
  • Like
Likes: Justin_NSA

JRacer

.
Aug 9, 2011
1,239
Beneteau 310 Cheney KS (Wichita)
Can recommend the Boatowners Illustrated Electrical Book - Charles Wing or the Marine Mechanical and Electrical book by Nigel Calder.
 
Apr 8, 2011
468
Hunter 36 Deale, MD
If the batteries are charged when you get back to the boat that tells you something - its likely your alternator/regulator/wiring on that side, and not the shore charger side, and probably not your batteries. If the batteries aren't charged its looking more like batteries - though they shouldn't have gone "bad" within one charge cycle (barring a catastrophic event like a high voltage overcharge). Also, depending on the type of batteries, how's the water level in them?

Assuming they charge ok from shore power, and check out with a multimeter after resting, I'd first start the motor and check the voltage coming off the alternator at the back - maybe deplete the batteries a bit if they're charged fully so the alternator will start with a 14.x voltage charge at the beginning. If the alternator isn't putting out the expected voltage there's the likely problem. If it is putting out the expected voltage, check your regulator (if you have one) to ensure its in the right charging mode (e.g. not float if the batteries are at 75%), and if that's fine, then check the difference between your alternator voltage and voltage at the batteries when it should be charging. If there's a large difference then its down likely to wiring/connections, so trace all that and make sure there's no corrosion or loose connections.
 

Dil

.
Jul 13, 2020
38
Hunter 30T Neptune
I'm at the boat the batteries are charged i picked up a volt meter now I have the engine covers off and exposed at first glance I think the belt to the alternator is just to loose going to tighten then check after that to see volt readings hoping that is all it is but it is definitely on the motor side of the charging system
 
  • Like
Likes: tfox2069
Sep 25, 2008
6,315
Alden 50 Sarasota, Florida
Wow... how do you know the batteries are charged? If you haven’t allowed them to reach a ‘resting’ state, you may be seeing a misleading indication.

Unless the belt is so loose as to squeal and not turn the alternator, that’s not the problem
 
Jul 7, 2004
8,020
Hunter 30T Cheney, KS
I think you should be able to turn your charger off, run the engine and check the alternator output at the battery bank. Or at the selector switch if you are wired that way.
 

Dil

.
Jul 13, 2020
38
Hunter 30T Neptune
I am wired that way the belt was loose enough that when I turned the alternator wheel by hand it slipped on the belt. in looking at the house indicator im seeing 12.85 v + .3 amps - 0 amp hrs and led indicators show all bars of charge and also seeing the voltage steadily climbing while writing is come up to 13 volts
 

Dil

.
Jul 13, 2020
38
Hunter 30T Neptune
it also seems and i could be wrong this is my first experience with a boat but im having to learn as fast as I can that if I have many dc items on at one time the alternator does not keep up with the draw such as fridge and freshwater pump, freshwater pump seems to pull 1.2extra amps the alternator can compensate for does that seem normal?
 
May 17, 2004
3,483
Beneteau Oceanis 37 LE Havre de Grace
Is there much belt dust around the engine, or did you hear any squeaking indicating it was slipping? How much does the belt deflect when you push on it?

When a charge source is present the voltage should be well over 13 volts. When not charging and left at rest for a while they should settle to around 12.7 volts. When you saw 12.85V and +.3 amps was a charging source connected? If so you should have seen either many more amps (like 20+) or more volts (like 13.5).

An alternator should be able to keep up with a fresh water pump and fridge pretty easily.
 
Aug 1, 2011
3,959
Catalina 270 255 Wabamun. Welcome to the marina
Something to think about based on that last post, a battery is not something you want to drain past a certain point. Beyond that, all the charge in the world wont bring ‘em back. So think about that when the fridge is on all day.
 

Dil

.
Jul 13, 2020
38
Hunter 30T Neptune
I have the motor running shore power charger turned off belt is tight now some dust but not tons alternator is in such a tight spot not sure how to safely get a tester to the leads
 
Jul 7, 2004
8,020
Hunter 30T Cheney, KS
I have the same fridge. When it comes on, and that's not often, it's about the equivalent of a 65w lightbulb. The water pump is not on much either when it cycles. Alternator should be sufficient if it's working properly. How many batteries do you have?
 

Dil

.
Jul 13, 2020
38
Hunter 30T Neptune
I have 2 house batteries one motor i think what I'm seeing now that the batteries are fully charged is a momentary draw till the voltage regulator notices it and compensate s for it. I have turned off all DC items and have been turning them on one at a time and watching the house panel indicator. now my im very interested to know if anyone knows where the DC voltage regulator would be located on a 1991 Hunter 30T or if there is one I assume there is but really don't know. I was at anchor last weekend and had a lot of thing on and not paying it much attention and in tightening the belt I think that solved the problem but it is a situation that reminds me I need to lean more about boats
 
May 24, 2004
6,796
CC 30 South Florida
Oh, a 91' h30, have no clue how yours is wired. If your engine is a Yanmar and your alternator a Hitachi it is likely that it has an internal regulator.
 
Last edited:
May 17, 2004
3,483
Beneteau Oceanis 37 LE Havre de Grace
+1 for the regulator likely being internal to the alternator. To test the voltage you can start by just connecting the meter leads to the battery posts. It won’t tell the whole story but is a good starting point without having your hands around the running alternator.

Nigel Calder’s book isn’t a bad place to start for learning a lot of what you’ll need to know. $32 for the kindle edition, $54 for the dead tree edition. Not a bad investment.