Mercury 8.1S Horizon, Product Applications Manual

Page: 130 / 163

Electrical System
90-863758060 AUGUST 2006 Page 8A-11
EFI Electronic Control Module (ECM): The ECM requires a stable voltage source. During
multiple engine operation, an onboard electrical device may cause a sudden drain of
voltage at the engine's battery. The voltage may go below the ECM's minimum required
voltage. Also, the alternator on the other engine may now start charging. This could cause
a voltage spike in the engine's electrical system.
In either case, the ECM could shut off. When the voltage returns to the range that the ECM
requires, the ECM will reset itself. The engine will now run normally. This ECM shut down
usually happens so fast that the engine just appears to have an ignition miss.
Recommendations
Batteries: Boats with multi-engine EFI power packages require each engine be connected
to its own battery. This ensures that the engine's electronic control module (ECM) has a
stable voltage source.
Battery Switches: Battery switches should always be positioned so each engine is running
off its own battery. DO NOT operate engines with switches in BOTH or ALL position. In an
emergency, another engine's battery can be used to start an engine with a dead battery.
Battery Isolators: Isolators can be used to charge an auxiliary battery used for powering
accessories in the boat. They should not be used to charge the battery of another engine
in the boat unless the type of isolator is specifically designed for this purpose.
NOTE: Sure Power Industries Inc., Model 32023A meets this design specification.
1. The boat may have 2 engines connected to a single Model 32023A battery isolator.
2. The Model 32023A battery isolator is connected to 2 banks of batteries.
3. Each bank contains 2 batteries with the cranking battery for 1 engine in each bank.
4. The second battery in each bank is connected in parallel to the cranking battery.
5. The Model 32023A battery isolator is designed for this type of use; 2 battery banks, 2
charging sources, 120 amps (maximum alternator output).
6. When the engines are running, either engine's alternator could be charging either bank
of batteries through the Model 32023A battery isolator.
Any other manufacturer's battery isolator that is the same type as the Sure Power Inc.,
Model 32023A could also be used.
Generators: The generator's battery should be considered another engine's battery.
Battery Switch
!
WARNING
When designing and installing the electrical system, adhere to all applicable marine
regulations (United States Coast Guard [USCG], European Union–Recreational Craft
Directive [EU-RCD], etc.) and the standards they reference (American Boat and Yacht
Council [ABYC], Society of Automotive Engineers [SAE], International Standards
Organization [ISO], etc.) for the market in which the boat will be sold.
A battery switch may be desirable to allow the power to be turned off when the boat is not
in use and to allow switching between batteries in multiple battery applications. Certain
industry standard and regulations require the use of a battery switch and should be
consulted for requirements.
•
The intermittent rating of the switch shall not be less than the maximum cranking current
of the largest engine cranking motor that it serves.
• The minimum continuous rating of the switch shall be the total of the ampacities of the
main overcurrent protection devices connected to the battery switch or the ampacity of
the feeder cable to the switch, whichever is less (ABYC Standard).