S/V Barbara Ann 

Portsmouth, NH (11/03/01) - No ship's system on the Barbara Ann has received closer scrutiny than the electric power generation system.  The watermaker, air conditioning and refrigeration, washer/dryer and dishwasher - all require 120VAC for their operation and have high startup surges.  We wanted the boat to be independent of shore power but able to utilize a shore connection when available.

Most inverter installations bypass the inverter when shore power is available.  This works if the shore connection is sufficient to handle the boat's peak consumption.  However in our cruising waters, you might be lucky in some places to get a long extension cord to an outlet in a shed.

The heart of the Barbara Ann's electrical system is a Trace dual SW2512D power panel which provides 5KW of continuous power and can handle startup loads of up to 10KW. The inverter monitors battery level and drain and controls the operation of a Fischer Panda mini-8 generator provides 8KW of power.  Rather than operate the generator all the time (as is the case on larger vessels) or whenever AC power is turned on (as is the case on many smaller vessels), the Trace turns on the generator whenever the power consumption is greater than a set level or whenever the house battery bank is drained more than 10%. Based on the Electrical Power Load Analysis, the generator will be typically be operated four to six hours per day.  Heavy air conditioner loads in the tropics can increase this to as much as 19 hours per day.

Onboard power generation is augmented by solar panels and by a separate charger for shore power connections.  Using a separate charger solves several problems.  Since it is only connected to the battery with a DC connection, there is no need for either a heavy and expensive 10KW isolation transformer or galvanic isolator.  This approach is also easily adapted for handling any quantity or quality of shore power available (120VAC, 220VAC, 240VAC 50 or 60Hz) since the charger is simply providing DC for the battery directly and is not part of the ship's AC power system.

The house battery bank consists of the largest and most robust lead acid batteries we could fit on the boat.  We use three four-volt Rolls-Surette 4KS25 batteries in series.  These batteries have thicker plates than higher voltage batteries and provide an amazing 4290Ahr of reserve capacity.  Separate AGM batteries are provided as starter batteries for the engine and genset.  For extra isolation from electrical failures and to provide additional redundancy, there are no electrical connections or switches between the various battery banks, nor are they charged by the same chargers.