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Alternator overheating is often a result of the one or more of the following conditions:
1. Belt mis-alignment.
2. Belt over or under tension.
3. Inadequate engine room cooling.
4. Loose or corroded battery cables or connectors.
ALTERNATOR TO BATTERY FUSING
The American Boat and Yacht Council (ABYC), in its standards for safer boating recommends that cable runs to your
battery banks be fused to protect the boat and owner against damage and injury. Circuit protection, as described by
ABYC standards can be accomplished by installing either a resettable circuit breaker or a fuse. The fuse or breaker
you choose will depend on both the amperage rating of the alternator and the size of cable used. The following con-
siderations can be used to determine fusing:
1. The largest available circuit protection device smaller than the amperage capacity of the cable being protected.
2. Larger than the maximum continuous current that will flow in the circuit.
We find that a circuit protection device sized at approximately 140% of your alternator’s rated amperage is typically
suitable for the circuit being protected. For more info about circuit fusing, see https://tinyurl.com/r8comkd
ALTERNATOR OUTPUT-TO-BATTERY CAPACITY RATIO
In order to achieve optimal performance from your charging system, it is essential to determine the capacity your
charging system is capable of supporting. In general, the size rating of the alternator should mirror the acceptance
rate of the batteries being charged. Differing battery technologies will vary in terms of their acceptance rates. For
example, a deep-cycle flooded battery is typically capable of accepting roughly 25 percent of its available capacity
during bulk charging. As a result, we want our alternator’s rated output to equal the acceptance rate of the battery
being charged when it reaches its full discharge rate.
In other words, a deeply discharged 400 amp hour deep cycle flooded battery would require an alternator rated at 25
percent of 400 amps, or 100 amps to support that bank. In simpler terms, a deep-cycle flooded battery bank will re-
quire 25 amps of alternator output for every 100 amp-hours of battery rating. Some newer battery technologies, such
as AGMs and spiral wound batteries can accept 40 percent or more of their available capacities.
Many LiFePO
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lithium batteries can accept 100% or more of the battery capacity. Therefore, alternator output should
be increased to reflect the optimal ratio between alternator and battery capacity. Failure to meet recommended alter-
nator-to-battery ratios will commonly result in slower charge times, increased alternator heat and wear, and reduced
alternator life.
