Battery charging

[Huntington41ds]

I have been on a mooring for 2 days after motoring for 8 hours. Running just the fridge, elec toilet, radio and a few lights in the eve.

Battery ran down. Ran motor for 2 hours and does note seem to add to charge. Have motor on now and got lots of green lights on the xantrax, - dc volts 12, dc amps <10, incoming breaker amps 15. When I shut down, I get 11.5 volts in orange. Seems like it is not charging.

Any ideas? House batteries are brand new.

Thanks!

 

[Don S/V ILLusion]

Empirically, you probably used over 100 amps through two days based on your description; maybe more. Since I assume you know the capacity of your battery bank, you can figure out how discharged they should be (assuming they were fully charged before you picked up the mooring).

The stock alternator in the 41 should produce 35 amps or more running at high RPM. If you are trying to recharge with the engine idling, it will take forever! Simple enough to calculate time to recharge at a rate of 35 amps/hr.

Check voltage AT the battery bank while the engine is running to ensure the V is high enough to accept a charge.

 

[captainpat]

If you are going to spend a lot of time on the hook you will probably need to make some changes. Assuming your batteries are good (you said new) and if you have a 40 amp alternator, you might consider upgrading to a hi output - 100 amp or so. Spending time on the hook will require a lot of engine time to bring the batteries up while at the same time you are using amps running your DC loads - and the batteries still wont be fully charged.

Same thing at the dock. Most stock chargers are 40 amp. Not enough for your boat. The charger propably runs all of the time; especially with the fridge running. Upgrade to an 80 or 100 amp charger. If your boat has a genset you can charge through the battery charger at about a quart of diesel per hour and will not have to run the engine at about a gallon + per hour.

 

[heritage]

New batteries need to cycle a few times before they reach their rated capacities.

Also, when checking the voltage, make sure all of the DC loads have been off for several minutes.

 

[Bill1565]

You don't say what size your batteries are, but whatever size the two are you are in the neighborhood of 200 Amp Hours total capacity till they are dead. In two days you could have run them down nearly completely. It will take 5-8 hours at cruising rpm to recharge them with a 35-40 amp alternator as:
1. You need to put in more than you took out.
2. As the batteries get above 70% charged, they will accept less than the altenator is capable of.

You desperately need a DIGITAL BATERY MONITOR. I use a Victron because I have bad feelings about Xantrex. Ample power and others also have digital battery monitors.

MainSail's forum on this site is a goldmine of electrical and other wisdom

 

[Blitz]

Check water in batteries also!