Alternator Selection Overview Selecting the proper alternator/regulator combination for your application can make the difference between successful battery charging and endless frustration. In a perfect world, your engine, charging system, battery banks and electrical loads would all be considered simultaneously when designing a vessel's electrical system. Unfortunately, in the real world, most vessels are equipped with a very basic charging system that's designed to supply enough power to charge a starting battery. After standard house loads are included in the equation, the standard charging system becomes woefully strained. Add even more demand -- air conditioning, inverter loads, for example -- and the situation grows far worse. Balmar high-output alternators and smart, multi-stage voltage regulators provide the additional charging horsepower required to meet the additional demands created by onboard electronics and creature comforts. Selecting the appropriate alternator for your application depends on three primary components: engine type and mounting configuration, width of drive belt, and the capacity of your battery banks. Failure to follow the guidelines for alternator selection may result in poor performance, damage to the alternator, or damage to the engine or belt. Determining Alternator Mounting Configuration Balmar high-output alternators are available in five primary mounting configurations to match most engine models: 1" single foot (Motorola style), 2" single foot (Delco style), 3.15" ID saddle mount (import style), and 4" ID saddle mount (J-180 style). Identifying the proper mounting style for your engine requires that you inspect your engine's existing alternator mounting style and order the Balmar mounting style that best matches your engine's alternator mount. While most engine manufacturers use a consistent mounting style throughout their product lines, it's not uncommon to see mounts that have been modified by engine installers, or engine distributors -- or to see mountings change when an engine manufacturer introduces a new engine style. The following table will provide a rough guideline for alternator mounting based on engine type. Keep in mind that inclusion in this table is not a guarantee of proper fit out of the box. Some applications may require modification at one or more mounting points. Other applications may require an alternator other than the model listed, so, at the risk of sounding like a broken record (or a broken CD), inspect your existing alternator's mount and compare to our four standard mounting configurations before ordering

Alternator Output Limits Based On Drive Belts

Another key factor in determining the right alternator for your system is the width of the belt driving the alternator. Typically, most marine gas or diesel applications can be broken down into four groups:

1. Systems driven by a single v-belt measuring less than 1/2",
2. Systems driven by a single 1/2" v-belt,
3. Systems driven by dual or triple v-belts
4. Systems driven by multi-groove serpentine belts

V-Belts measuring less than 1/2" - Capable of driving alternators up to 80 amps (50A @ 24V)with horsepower demands up to three horsepower.

V-Belts measuring 1/2" - Capable of driving alternators up to 110 amps (65A @ 24V) with horsepower demands up to four horsepower.

Multiple V-Belts - Capable of driving alternators up to 300 amps (220A @ 24V) with horsepower demands up to 10 horsepower.

Multi-Groove Serpentine Belt - Capable of driving alternators up to 300 amps (220A @ 24V) with horsepower demands up to 10 horsepower.

Exceeding recommended output limits based on belt size will ultimately lead to belt slippage and premature belt failure, and potentially to resulting damage to the engine and alternator. DO NOT attempt to drive an alternator with an improperly-sized belt. In addition to potential system damage, use of a high output alternator with an undersized belt could result in voiding of both engine and alternator warranties. Don't take the chance.

High output alternators generate a substantially increased demand on drive belts over that created by standard OEM alternators. Balmar strongly recommends the use of premium belts, such as "Top Cog" by Dayco (http://www.daycoproducts.com) and "Green Stripe" by Gates Rubber (http://www.gates.com) for maximal performance and belt life.

Once installed, proper belt tensioning is essential for optimal performance. When installing a new belt, run your engine for 15 to 30 minutes after initial tensioning. Re-tension after shutting down. Repeat. Continue to inspect belt tension prior to engine start up each time you use the boat. Tension whenever your belt deflection exceeds engine manufacturer's specifications.

Alternator Output Requirements Based On Battery Capacity

A general "rule-of-thumb" that works quite well in determining the alternator that's best suited to your vessel is the "25%" rule. In most cases, if your alternator is rated at 25% of the rated capacity of your battery banks' output capacity, the alternator will be adequate to handle your battery demands. This is particularly true with flooded batteries, where the batteries are capable of accepting roughly 25% of their available capacity.

In cases where AGM or gel batteries are installed, the alternator will be better suited to the batteries if its rated output is closer to 35% of battery capacity.

Failing to properly match alternator output to battery capacity may result in longer charging times, greater wear on belts and decreased alternator life -- and may invalidate the alternator's warranty.

Ideally, when designing the charging system for any application, the system designer will start out by determining the maximum allowable alternator output based on the quantity and width of the alternator drive belt(s). Once the maximum alternator output capacity is determined (based on belt width and quantity), the maximum battery capacity can be calculated based on the maximum recommended alternator-to-battery ratio.