The Advantages of Dual Alternators

by Daniel R. Mueller
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Using dual alternators in a motor vehicle typically serves one of a handful of engineering design purposes. In vehicles likely to function for long periods of time without maintenance or vehicles likely to sustain heavy damage during the course of regular use, a second alternator can serve as a backup power generation system in the event that the primary system fails. Dual alternators can also be used to compensate for vehicles with exceptionally high drain devices, such as recreational vehicles or police reconnaissance vans.

Dual Alternators as a Redundancy Feature

Dual alternators are a helpful feature for military vehicles, allowing them to function even in the event of battle damage to a primary alternator. Mechanics working on dual alternator vehicles should note whether the dual alternators are in place because of a shared output need or if they include a redundancy switch and are each capable of supporting the vehicle's electrical power needs. A redundancy switch is a sensor that detects when voltage drops below a critical threshold from one alternator, deactivating the damaged alternator and switching to a secondary backup.

Dual Alternators for High-Power Drain Applications

Alternators are particularly helpful for high-drain vehicle power applications where the vehicle needs to have sustained power output without the engine running, without sacrificing the vehicle's ability to turn over. Vehicle engineers can approach this from two separate design approaches. The first is to connect both alternators to a large battery bank shared among the starter, spark plugs and other vehicle systems. A shared system offers the advantage of inexpensive simplicity; however, extended use without running the motor runs a real risk of draining the batteries to the point where the engine will not turn over. The second design philosophy approach sets up two separate power systems, one for critical systems and another for secondary optional devices. A dual independent power system approach prevents the vehicle from getting stuck due to draining too much power from the batteries but adds significant expense. The dual power system design works well with vehicles like RVs or police surveillance vehicles. Two alternators can also serve as a jerry-rigged replacement for larger alternators by combining two in series to reach the same level of power output, which is particularly helpful in improvised repair situations.

Pairing Two Alternators of Different Sizes

Occasionally, system additions to a vehicle will stress the alternator beyond its output capacity, forcing mechanics to make a critical decision about either upgrading the size of the primary alternator or adding a secondary smaller alternator to meet electrical needs. Two different sized alternators are ideal for this scenario due to the fact that adding a second alternator the same size may be unnecessary and add additional expense. Adding a secondary smaller alternator to complement a systems upgrade can help upgrade projects on budget.

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