Charging on Alternator

[vickyb]

From the Boat schematics, I see that all 3 charging systems go to the charger unit: Alternator, Generator and Shore Power. From there it seems to distribute it to the batteries.

When I have the Shore power connected: Batteries are at 13V
With Generator: 13V
With Alternator: 12V and steadily drops to 11.5 no matter what the engine RPM. All DC house systems are turned off, especially the refrigerator

I checked the breakers on the Port Side aft wall (where the orange wires come in from the alternators and they are good. Checked the output from the Alternators with the engines running and it is 14.2V.

Really confused with this. Is this normal?

All batteries replaced last week.

[bud37]

Have you put a multimeter on the batteries to double check the voltages ? Where are you seeing these voltage numbers you have mentioned ?

I will double check but I remember ( foggy at best ) some switches on the breaker panel in our old boat and the battery switch position changed things at the helm readouts.

[vickyb]

These numbers are on the gauges on the bridge. The batteries are brand new.

[km1125]

On shore power or generator, the Battery Charger is supplying power to all your batteries and keeping them "up to snuff". When your engines are running, there needs to be a separate path to your house batteries to keep them charged, or you'll just be depleting them. You should have charging isolators or voltage-sensitive-relays (VSRs) connected between your engine/start batteries and the house batteries so that either engine can charge the house batteries. Either you don't have those or there is something wrong in those circuits, like a popped breaker.

Also sounds like your house batteries are probably weak. How long does it take for them to drop to 11.5V and what do you have running on them at the time?

[km1125]

Oops.. just saw that comment about the "batteries are brand new". Does that include the house batteries too, or just the engine/start and generator batteries?

[vickyb]

My main concern are the two engine batteries that drop in power. House and Generator batteries are fine when alternator is on. The two engine batteries (also brand new) are the problem.. they drop to 11.5 volts (port) and 11.8 (STB) in about 2 hours of running. As indicated on the dashboard panel on the bridge

[Viper]

If the alternator outputs are leaving the engines and connecting elsewhere other than the engine, you likely have a battery isolator. I would check there first. Check for input voltage which should be the alternator output voltage, then check the isolator output which should be equal to or slightly less than alternator output (less than 1 volt difference) depending on the isolator type.

QR_BBPOST.... With Alternator: 12V and steadily drops to 11.5 no matter what the engine RPM. All DC house systems are turned off, especially the refrigerator....

I assume this is with no shore power hooked up or generator running (charger non-operational)?

[vickyb]

That is correct. No shore or generator power.

I will troubleshoot as per your suggestion above. Thank you

[km1125]

OK, first post was confusing. Didn't realize it was the engine batteries that were low. I agree with Viper's comments, especially if the house battery is over 12.8 while the engines are running. That means it's getting some kind of a charge from one or both alternators.

[bud37]

QR_BBPOST My main concern are the two engine batteries that drop in power. House and Generator batteries are fine when alternator is on. The two engine batteries (also brand new) are the problem.. they drop to 11.5 volts (port) and 11.8 (STB) in about 2 hours of running. As indicated on the dashboard panel on the bridge

That is why I asked if you had checked the voltage directly on the sets of battery terminals themselves with the engines running.....