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[bevedfelker]

Attached is the file I received from Thor describing the operation of the BIRD & Trombetta. In reading the description of the Trombetta's isolation function I had interpreted that when a battery was isolated from the other battery only one battery bank at a time was charging. That was I incorrect.

If I would have paid more attention to the BIRD "How It Works" I would have seen it specifically says the batteries are paralleled charging both. Here is the complete description:

How It Works
The BIRD operates in conjunction with a continuous duty solenoid to provide the isolator/battery charging functions of a motor home. It senses voltage on the coach and chassis batteries. If the voltage on either one is above 13.1 volts, indicating the battery is being charged, it closes the isolator relay, paralleling the batteries, charging both. It operates in two directions, charging the batteries from the engine alternator and charging the batteries from the converter. These functions are similar but operate at different thresholds.

Engine Alternator Charging Batteries
When the ignition switch is turned on and the engine is running, the system senses the level of voltage on the chassis 12 volt system. When this voltage goes 13.1 volts for approximately 2.5 minutes, as happens when the engine is running normally (normal alternator output voltage of a cold engine is approximately 14.4 volts), it will close the isolator relay providing charging current to the battery. This delay allows a cold engine an opportunity to start and warm up before having the heavy load of a discharged coach battery placed on it. If the voltage should fall 12 volts for more than about 1 minute, the relay will drop out to feed all the alternators available output to the chassis battery to keep the engine running. This might happen when the alternator is not able to supply sufficient current to all of the loads and charge the coach battery at the same time. When the chassis voltage goes 13.1volts again, the relay will again close in about 2.5 minutes to retry to charge the battery. The resultant flickering of lights would alert the driver of the system overload.

Converter Charging the Batteries
When the coach is plugged into shore power and the ignition is off, the unit senses the voltage on the coach batteries. When this voltage goes 13.1 volts for approximately 2.5 minutes, as happens when the converter isn't heavily loaded, it will close the isolator relay providing charging current to the battery. If the voltage should fall 12.6 volts for more than about 1 minute, the relay will drop out to prevent the coach loads from discharging the chassis battery. This might happen when the converter is heavily loaded by coach loads. When the coach battery voltage goes 13.1 volts again, the relay will again close in about 2.5 minutes to retry to charge the battery.