Low Voltage Warning

[Wagonhound]

I was running my boat for about an hour today an then I got a low voltage warning 11.5 volts, boat still ran fine. Cranking battery is at 13.6 volts, house battery is 14.6, and alternator is producing 16ish.

[chpthril]

Was the alarm with engine on or off?

[Wagonhound]

Was the alarm with engine on or off?

I was running about 30mph across the lake when it came on. We docked for lunch, then idled through no wake zone with no alarm, then alarm came on when I throttled back up.

[lee]

Might have been because alternator was putting out 16 volts.

[Wagonhound]

Cranking battery has a bad cell, lost 2 volts overnight. I switched all cables over to the AUX battery and it ran fine. Also explained why the stereo kept fading out after 10 minutes with the key in ACC mode.

[ericinmich]

If your alternator is really putting out 16 volts it could of cooked the battery. I'd check that ASAP.

[chpthril]

Cranking battery has a bad cell, lost 2 volts overnight.

Was it connected or disconnected? If connected, could have a drain that would explain the voltage loss. If it does have a bad cell, a battery will only reach a little over 10V after a period of charging. Would know its bad without waiting over night. Just make sure that that 2v drop wasnt the surface charge thats there right after taking off the charger and the actual static charge after the surface charger dissipates. The fading stereo still puzzles me, as it runs off that house battery anyway.

[Wagonhound]

So on the water when the engine was running with the cranking battery connected, I was getting 11.5 volts with my meter at the battery and the "low voltage" warning alarm on the console was also reading 11.5 volts. When I switched everything over to the HOUSE battery it was showing 13.5 volts on the console. I checked the CRANKING battery this morning after being disconnected and it is showing 12.3+ volts (seems normal) and the HOUSE battery is at 12.7 volts.

Before I get too carried away with the battery issue, I should question if all the battery connections are correct. The PRIMARY ISOLATOR (+) and the SECONDARY ISOLATOR (+) are both connected to the HOUSE battery, this does not seem right? Should the PRIMARY ISOLATOR (+) be connected to the CRANKING battery? The only thing connected to CRANKING battery is the PRIMARY GROUND (-) and the PRIMARY SWITCH (+) leads, and another small 16a wire connected to a 3 amp fuse.

The next step would then be to double check the alternator output. I would think if it were in fact putting out over 16 volts it would overcharge the battery? However, I ran the engine for a good 2-3 hrs yesterday just on the HOUSE battery and it's still 12.7 volts. I would probably need to remove the alternator to do an accurate load test at the shop to check it, but with only 220 hours on the engine I wouldn't think it would have a bad regulator already?

[chpthril]

So on the water when the engine was running with the cranking battery connected, I was getting 11.5 volts with my meter at the battery and the "low voltage" warning alarm on the console was also reading 11.5 volts.

Thats an alternator or cable issue.

Before I get too carried away with the battery issue, I should question if all the battery connections are correct. The PRIMARY ISOLATOR (+) and the SECONDARY ISOLATOR (+) are both connected to the HOUSE battery, this does not seem right? Should the PRIMARY ISOLATOR (+) be connected to the CRANKING battery?

Need to know year, engine and main battery switch style just to be sure, but no, does not sound correct. There should be a cable from from what ever ISO you have, going to each battery B+ post.

When I switched everything over to the HOUSE battery it was showing 13.5 volts on the console
The next step would then be to double check the alternator output.

Yes, but that fact the house battery is supplied by the same battery and showed 13+, id say the alternator is good.

[Wagonhound]

I checked my voltage at what I assume is called the isolator switch (see pic). I connected the PRIMARY ISOLATOR cable back to the CRANKING battery an it was reading 12.16V on the left terminal and 12.78V on right terminal of the isolator switch. Turned on engine and I was getting 13.58V on the left pole, 14.47 on the center pole (I would assume this is the alternator feed) and 13.6 on the right pole. This should solve my problem.
Isolator.jpg

[chpthril]

That should do it.