Alternators

Rules of thumb concerning horsepower drain and charging
It’s easy to regard the alternator as a free source of electrical power,

just whirring away as your engine runs. But, in fact, it absorbs a lot of engine power, which you pay for in increased fuel consumption.The rule of thumb is that the horsepower drain on the engine is twice the number of kilowatts produced. For example, if a 100-amp alternator is charging a 12-volt system at full capacity, it’s producing 1,200 watts, or 1.2 kilowatts. Therefore, it steals 2.4 horsepower from the engine.Another rule of thumb concerns charging capacity. It states that the alternator should have a charging capacity in amps of 25 to 40 percent of the total amp-hour capacity of your batteries. This assumes you’re using a modern multistage regulator that won’t allow overcharging, particularly when the batteries become warm.If you don’t have a multistage regulator, the rule of thumb for long battery life is to limit the charging rate in amps to 10 percent of available amp-hours. For example, if you have two batteries with capacities of about 100 amp-hours each, your alternator shouldn’t have a constant charge rate of more than 20 amps when it’s charging the two together.Because charging at such a low rate takes so long, many boaters ignore the rule, preferring to charge at 20 to 25 percent and to buy new batteries more frequently as a consequence.See also Smart Regulators.

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alternators	motorcycle alternators