by Kerry Green
Many passengers ask about Birdswood’s electric power system
Many passengers ask about Birdswood’s electric power system Birdswood is powered by lead-acid wet cell batteries. These are made up of individual 2V cells contained in two tanks located at the rear of the passenger compartment either side of the galley doors. You may not have noticed these as they make very convenient tables for the souvenirs! The battery, comprised of the combination of cells and tanks, provides 48V with 860Ah capacity and is enough to run the boat for about six return trips to Leewood pumphouse. The batteries are connected to a motor controller which changes the DC (direct current) into 3 phase AC (alternating current). The voltage is transformed from 48V DC to 32V AC. This then powers a low voltage 32V AC motor which is maintenance free. The motor controller runs the motor at a speed determined by the position of the speed wheel which is a brass wheel just in front of the boat master when he is at the helm. The speed wheel pushes a cable which moves a lever and turns a potentiometer, the same type of device you would find as a volume control on an old radio. The motor controller is a state of the art device which means it’s very efficient as it chops up the DC power at ten thousand times a second. The electric motor then drives a hydraulic pump which is connected by pipes to a hydraulic motor in the rudder. The pump pushes oil through the hydraulic pipes which then turns the hydraulic motor to which the propeller is attached. You can see the black hydraulic hoses coming out of the rear of the boat and disappearing into the water next to the rudder. If the boat is to be reversed then a brass lever opposite the speed wheel is moved which pulls a cable which changes a hydraulic valve which reverses the flow of oil to the hydraulic motor and so reverses the propeller. Birdswood also has a battery-monitoring device which measures the power going into and out of the batteries. This communicates to the motor controller which then sends the information to the dashboard so we always know how much power is in the batteries, just the same as a fuel gauge on your car. Another device called a DC to DC converter connects to the 48V battery and converts it to 12V to charge a small 12V car battery which is used to power the cabin lights, PA system and water pumps.