Engine not charging batteries very well

Don S/V ILLusion · Sep 20, 2015

Charge rate is a function of battery state of charge, not alternator/charger capacity.

If your batteries were fully charged, you should expect to see the voltages mentioned considering the inaccuracies of most on-board voltmeters.

That is not to say your batteries or the charge system are problematic especially if the batteries are, as you implied, 10 years old.

Maine Sail · Sep 20, 2015

VelaFella said:
The engine is not charging the batteries (two 4D's) very well, as opposed to not-at-all. After tightening the alternator belt, I motored for about 4 hours on the Chesapeake Bay (no wind and was in a hurry), the voltmeter only read 12.4 volts at the end of the trip. It had risen to that level from 12.0 volts at the beginning of the trip. Later, after connecting to shore power, the charge went up to 12.8 volts (Xantrex Freedom 20 inverter/charger). The generator will also raise the charge to 12.8 volts. So, any thoughts as to poor performance when using engine only (in contrast to a situation where there is zero performance)? Volt regulator? Alternator? Connections? Etc. All equipment is 10 years old.
Thanks in advance.

A few probable issues:

#1 You are discharging your batteries far too deeply, don't let them drop below 12.0V!

#2 You could have a battery with a dead short sucking the bank down

#3 You have a bad connection somewhere causing serious voltage drop

#4 You have an erroneous volt meter

#5 You have a diode battery isolator creating excessive voltage drops plus you are overly discharging your bank.

#6 You have two bad charge sources simultaneously. (quite unlikely)

Under normal average house loads (+/- 7-10A), on a 40+/- footer, you should not allow your bank voltage to go below 12.0V when discharging.

The more info you can give us the better. Beg borrow or steal a DC clamp meter and physically measure the alternator output and charger output in amps as well as measuring for voltage drop. Course if you have a battery monitor that would give you the info too.

Ralph Johnstone · Sep 20, 2015

VelaFella said:
Later, after connecting to shore power, the charge went up to 12.8 volts (Xantrex Freedom 20 inverter/charger).

Just as a quicky, no cost test, charge your batteries as much as possible with the Xantrex and then shut off the charger and remove all DC loads i.e. shut off your AC and CD breakers. Leave the batteries for 24 hours or longer and then check the battery voltage. If the voltage is way down, this gives a lot of weight to Maine's statement that "You have a battery with a dead short sucking the bank down".

You can get fancy after that and charge the batteries again (as best you can with the Xantrex) and then physically remove all cables from the battery posts and see what comes out in the wash after 24 hrs. using a voltmeter. Somehow, I don't think you're going to like the outcome ($$$).

KZW · Sep 20, 2015

Suggest you buy a clamp voltmeter. Either Amazon or Harbor Freight have reasonable units for reasonable prices. Be sure to read the specs and get one that reads DC Amps. Not all of them do. You really want one of these on your boat!

Last month I destroyed my two year old and three year old Interstate 4D batteries with the OEM Charleston 20 Amp charger on my boat. It is not good to have non-working batteries on the boat (no bilge pump) when living on the Gulf Coast in Hurricane season. I check the water on the first of each month. They were fine on 1 August. Two weeks later the first had four dry cells and a week later the other had three dry cells. I am on the boat at least weekly and check the battery voltage first thing up opening up. I ended up replacing the 4Ds with four GC2 Duracell golf cart batteries from Sam's and replaced the charger with a Promariner computer charger.
Good Luck!

Benny17441 · Sep 21, 2015

You do not seem to be complaining about not having adequate power to operate the boat so over the long run chances are your batteries, alternator and inboard charger are working adequately if not properly. It may be likely that your doubts stem from incorrect readings or incorrect assumptions drawn from the boat's voltmeter. Before trusting a voltmeter it has to be verified correct and then the readings need to be interpreted according to what is currently taking place within the system. In essence it takes time and observation to learn how to read useful results from a volt meter. if you are convinced something is afoul I would recommend you have the batteries tested at a retail center as they have the equipment to ascertain their condition as well as their state of charge. Then after certifying the good condition of the batteries you can move unto diagnosing fault in the alternator, regulator and wiring. For future readings use a trusted digital multi-meter and measure across the battery terminals. At deep discharge both battery charger and alternator will display near maximum output but when batteries are close to being fully charged the charger may display a low voltage trickle charge and the alternator may be cutting on and off.

bananabender56 · Sep 21, 2015

VelaFella said:
The engine is not charging the batteries (two 4D's) very well, as opposed to not-at-all. After tightening the alternator belt, I motored for about 4 hours on the Chesapeake Bay (no wind and was in a hurry), the voltmeter only read 12.4 volts at the end of the trip. It had risen to that level from 12.0 volts at the beginning of the trip. Later, after connecting to shore power, the charge went up to 12.8 volts (Xantrex Freedom 20 inverter/charger). The generator will also raise the charge to 12.8 volts. So, any thoughts as to poor performance when using engine only (in contrast to a situation where there is zero performance)? Volt regulator? Alternator? Connections? Etc. All equipment is 10 years old. Thanks in advance.

I presume the generator is also charging thru the Xantrex inverter/charger, the same as shore power. Do you have a separate alternator charge controller?
I have 3x4D's being fed by a Xantrex 3012 - the voltage usually sits around 13.2. So, as others have said the batteries need checking, even though they are newish. What batteries did you replace - lead acid with lead acid. Maybe also check the battery selection on the Xantrex remote.

Don Lucas · Sep 25, 2015

Have you measured the voltage at the alternator and at the battery while running the engine? Are they the same?

What is the size of your alternator?

What type of regulator do you have?

Where is the voltage sense wire for the regulator attached (at the alternator or at the batteries)?

I bet you are maxing out the alternator and are getting enough voltage drop and that the regulator is sensing voltage at the alternator and thinks it is putting out a higher voltage than the batteries are seeing.