Batteries
The battery bank in the STI system is analogous to a fuel tank. It can receive electrical input from a variety of sources: dockside AC via a battery charger, the DC generator, regeneration from the freewheeling prop, even solar photovoltaic cells and wind turbines. The battery bank provides power to the drive motor(s) and auxiliary systems through a common buss – the Safety, Power Management and Distribution box. The standard installation has twelve 12V batteries wired in series to provide a 144 VDC power source.
STI systems employ Lifeline Absorbed Glass Mat (AGM) 12 volt batteries.
Left: Batteries in box constructed to hold them in catamaran hull, with motor beyond.
AGM batteries have conventional lead-acid chemistry. But their construction is very different from the standard automobile flooded cell battery, where liquid sulfuric acid is simply poured into the cells. In AGM batteries, the acid electrolyte is absorbed in a fiberglass mat, which is packed tightly within the lead plates. The electrolyte can’t spill, and plate separation is greatly reduced, which decreases internal resistance. These completely sealed, leak-proof, maintenance-free batteries function in all positions, even upside down. No venting is required because byproduct gases are recombined.
An independent review published in the June 1997 Cruising World found that AGM batteries outperform flooded and gel cell batteries. Compared to flooded and gel batteries, AGMs recharge faster, discharge slower and have better cranking performance, reserve capacity, depth of cycle and cycle life. AGM batteries exceed U.S. Coast Guard and U.S. Military performance standards.
House Batteries
It is highly recommended that you have one or two separate batteries supplying 12 volt house power requirements. These house batteries can be charged from the main battery bank with an optional 144 VDC to 12 VDC cross charger (DC-DC converter).
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