On 27 Jul 2006 07:14:27 -0700, "Achilles Keel"
wrote:

The unit works fine when the boat is disconnected from shore power. It
converts the 12 volts DC from four 100 amp gel batteries into 120 volt
60 cycle AC. When I connect to shore power (30 Amp 120vac), the
inverter switches into a battery charger and sends the ac thru to the
boat. (I think thru an isolation transformer). When that switch is
made (a few seconds after connection) the ac power and battery charger
goes out. After a bit (4 or 5 minutes), the ac and charger reset and
come on for another short period (4 or 5 minutes), and the cycle
continues. I tried disconnecting various loads to eliminate bad
appliances, but still have the problem.

There is no isolation transformer, only a transfer switch (relay)
which activates to divert incoming AC around the inverter when hooked
to shore power or a generator. The transfer switch is supposed to be
activated by the controller board when it senses incoming AC of the
correct voltage and frequency.

My guess is that you either have a defective controller board or
possibly the transfer switch itself. Either way you are going to need
a qualified service technician.