Hello KK38,

This is not an uncommon occurrence with todays modern alternator regulators. Particularly when they are combined with the secondary battery charging systems that are often found on board today's vessels.

When a 12 volt battery system overcharge condition is detected, most modern regulators have the capability to shut off, or lower to almost nothing, the field current to the alternator. When this happens, the alternator stops charging and you see and hear a voltage alarm. When the alternator is shut off completely, the AC tachometer signal from the alternator also disappears and the tachometer stops reading. Due to the high state of battery charge, your measured system voltage can still be quite high as shown on panel gauges.

Typically, this happens when the engine is running and the alternator is charging batteries in conjunction with a charge output from solar and/or wind. After the batteries get a high state of charge, the regulator for the alternator detects the charge current from the solar and/or wind sources and senses a high voltage overcharge situation. The regulator then shuts off the alternator. This makes warning lights come on and the tachometer needle stop reading. Many 'smart' regulators have a 3 step charging scheme that raises and lowers charge voltage based on a timer sequence. This may explain why the alarms are coming and going 'over time' rather than occurring continuously.

There are numerous combinations of different regulators, batteries and solar/wind chargers in use today. It is not easy to explain how all of these different combinations can interact. Therefore, it is our simple recommendation that you disconnect all ancillary charging systems, I.E., Solar, wind, shore power, generator, while the propulsion engine is running and the alternator or smart regulator is trying to do its job of maintaining the battery bank charge. This disconnect can be accomplished with simple manual switches or simple and inexpensive automatic relays that open when the engine is running. Feel free to contact us directly to discuss a disconnect system for your particular installation.

Like many, I have a Balmar smart regulator controlling charging of the house bank by the alternator on my Beta 38 (plus a Balmar Duo Charge to charge the starting battery from the house bank, but doubt that matters here). Plus, perhaps like KK38, I have a solar panel through a solar charge controller attached to the house bank in parallel to the alternator/regulator connection. So I would like to, as you suggest, disconnect the solar from the batteries when the engine is running to avoid fooling the regulator into slowing/stopping charging too early. I could route the solar through a manual switch but my physical layout isn't great for that. Can you suggest a proven automatic disconnect that (a) doesn't drain current when nothing is running, and (b) doesn't create a voltage drop for the charge power running through it? Thanks!