House batteries not charging when engine running

[stackwalker]

I was taking my first shakedown passage on my Hunter 410. I noticed that under engine power my house batteries were reading 12.4 volts. My starting battery read almost 14. This told me that my house batteries weren’t charging. As the trip wore on battery voltage dropped to 12.2 or so and I decided to turn around. Back on shore power now and house batteries are over 13 volts again apparently charging.
Batteries never get over 12.4ish volts. No clue how old the house batteries are. Not sure this is just a bad battery situation or more to it? I assume alternator is ok as it’s charging the starting battery fine

 

[kappykaplan]

My gut tells me that the alternator output isn't getting to the house bank.

 

[CrispyCringle]

You need to put a volt meter on the house and start battery and see whats really happening. If the alternator is not getting power to the house battery determine where the connection is lost. But its concerning that you are only seeing 12.4 V maximum from your house batteries, even after being charged from shore power. Thats why I say you need to measure the voltage with a volt meter and see what you are really getting under shore power and alternator. Im assuming you have lead acid batteries. 12.1 volts is typical for 50% charge. You shouldn't let them get below that, if possible. And if they really wont get above 12.4 volts with a proper charge, they are done.

 

[Tally Ho]

I depends on how your alternator is wired to the batteries. My old system had the alternator output backfeeding to the Common post on the 1-2-Both-Off switch.

I recently switched the house bank to LiFePO4 and separated the house and starting circuits. The alternator is now feeding only my lead acid start battery (I don’t want the LFP BMS from shutting down and frying the alternator).

Or you may have an ACR or DC-DC charger in the circuit that is t working.

You need to start tracing how your batteries are and alternator are wired up.

Greg

 

[Davidasailor26]

If you’re seeing 13+ on the shore charger but decreasing voltage when the engine is running is means the alternator is not charging the house bank. You’re seeing 14 V on the start battery so the alternator is functioning. This all suggests you have a wiring or switching issue, not that a bad battery is the cause. You’ll need to trace wires to see how the alternator is intended to charge the house bank, whether that’s through a switch that’s in the wrong position, a battery isolator, or a bad wiring connection.

 

[Tally Ho]

You may also have some old, tired batteries since the voltage is dropping seemingly quickly when off a charging source…but that is a separate issue. My 5-year old 6-volt golf cart batteries were showing 13+ volts when I left the dock and while motoring, but the voltage dropped quickly after I shut down the engine. I replaced them with 2) 12v LiFeP04 and they stay at 12.8v or more while sailing.

A load on the batteries may drop the voltage, so you might want to charge them up at the dock, then turn off the charger and see where the batteries end up once they are at rest for a few hours.

Greg

 

[Don S/V ILLusion]

Start with the easy stuff first.

check the battery isolator or ACR relay.
if you have an isolator, what you see is normal given the inherent voltage drop.

 

[marcham]

Assumption: a) you have flooded/agm cells and not lithium b) the previous owner did not do "improvements" aka modifications...


1) Do you have the Hunter owner's manual for your boat? They usually have pretty good electrical diagrams that show how the DC system is wired, including the battery combination method.
2) Does it appear the previous owner modified anything ?
3) What does your start/house battery switching arrangement look like?
4) Can you take a look behind the battery switch panel and take a good photo?

Likely scenarios: There is an automatic relay, that either latches based on alternator output voltage or should latch automatically when the ignition is active. On my boat, there was a breaker that had to be toggled once the engine was running to latch the solenoid, combine and charge both banks after the engine started.

If marine electrical is all new to you, it might be worthwhile to pay a good marine electrician to survey the electrical of the boat from end to end.... usually takes about 3-4 hrs plus report writing time. That would give you a better understanding of how your boat is currently wired and what systems may need attention/maintenance.... There's no point to blindly start replacing stuff (like batteries), without understanding the state of the overall system...

Recommendation: install a battery monitor. Voltage isn't the whole story....

Example:

BMV-712 Smart | Victron Energy OR

SmartShunt | Victron Energy

The SmartShunt is an all-in-one battery monitor, only without a display. Your phone acts as the display. The SmartShunt connects via Bluetooth to the VictronConnect app on your phone (or tablet) and you can conveniently read out all monitored battery parameters, like state of charge, time to go...

www.victronenergy.com

They give you excellent tracking of the remaining capacity and state of charge of the house bank and also tracks start bank voltage....