Alternators not charging house battery

[Helmsman]

Source of the post Most isolators have a terminal for the alternator(s) input (to the isolator) and terminals for the battery connections (separate terminal for each battery or bank of batteries). The voltage regulator is built into your alternator.
If you find the make and model of your isolator, you should be able to locate a diagram.

Thanks. I have the manuals and the parts listing for my boat. When I get home I will look it up before I head to the boat.

[bud37]

I wouldn't worry about the galvanic isolator....that is part of the shore power system , nothing to do with battery charging.Hope you find it.

[Helmsman]

Source of the post I wouldn't worry about the galvanic isolator....that is part of the shore power system , nothing to do with battery charging.Hope you find it.

Thanks Bud. I figured that out today after looking at the wiring diagram for it.

[Helmsman]

OK. Here is what I found. I have a Sure Power model 3203 isolator. The wire leaving the isolator for the house battery goes up into the breaker box housing the bilge pumps, stereo memory and high water alarm. It then comes back out and and goes to the battery. The wire to the battery is a much larger wire than the one going in and the wires leaving the isolator for the two engine batteries.

I checked the batteries with no shore power, no generator, and without the engines on. The two engine batteries were at 13.4 (thought they should be lower) and the house showed 12.6. With the engines on the engine batteries showed 14.2 and the house was at 12.6. I then checked the circuit breakers. With the engines off, I found one between the isolator and the breaker box that was open. I reset it, and the house battery with the engines on now showed 13.6. So, I think that was all it was. Why and when it tripped I don’t know.

We will know for sure when I get it back out for a few hours without shore or generator power.

Thanks for all of the advice and help analyzing this with me. Even though it was only a breaker (I think) I learned a tremendous amount from you guys and then applying the knowledge.

[bud37]

Good stuff.....that 13.4 sounds like you may have just turned the charger off ( surface charge ) and 14.2 with engines is dead on what I see on our boat.It would be good to find out why the breaker opened though, hopefully just getting weak......

[tomschauer]

If it gives you a problem again, let us know what the breaker is labeled, and the amperage. Hopefully just an isolated incident.

[Helmsman]

Source of the post If it gives you a problem again, let us know what the breaker is labeled, and the amperage. Hopefully just an isolated incident.

It was a hi amp buss 80a waterproof cb185p-80 and was in line on the wire to the house battery (labeled accessories I think) before the wire Went into the breaker box.

[Keith S]

I suspect your charging system is similar to mine on a 38SS. The isolator is mounted to the bulkhead in front of the port engine. It has 2 inputs, one from each main engine alternator and 3 outputs, port engine battery, starboard engine battery and the house battery.
To test, with the engines off and the battery chargers off you should read battery voltage (12.6VDC) at the 3 output posts and zero volts at the 2 input posts. If you don't read battery voltage at the output posts, there is a breaker tripped or a wiring issue. When you run the port engine only the input post from the port alternator should read 14VDC, the starboard input post zero and the 3 output posts should read about 13.5 volt. When you run the starboard engine only, same results.
If the house battery post on the isolator does not rise above 12.6VDC with the engines running you probably have a bad diode.
The system allows the combined output of both alternators to charge the house battery faster.
Also if one alternator quits, both engine batteries can be charged by the other alternator.