Maximizing Alternator Output Current

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This topic contains 1 reply, has 2 voices, and was last updated by  Chuck Truthan 7 months, 2 weeks ago.

  • Author
  • #8767

    John Reynolds

    If you have a single switch that disconnects the battery from both engines, your alternator charging system is not optimized for maximum output current.

    After burning up a bunch of small case Balmar/Electromaax alternators in an attempt to shorten the charge time for the battery while cruising, I decided to install heavy duty Delco Remy 24SI alternators. After the installation was completed, I learned a few additional things that may be worth passing on.

    Major Points
    1. Connect each alternator/engine directly to the battery using a dedicated battery disconnect switch for each engine.
    2. Use a fused remote sense wire from each regulator to the battery. If using an external regulator, connect the regulator ground lead directly to the battery negative terminal.

    As built, the alternator/engine connections on Easy (now Balena) were wired as shown in the attached Figure 1, using 1/0 cable. The cables from the port engine were routed towards the aft end of the engine room, over to the starboard engine where they were crimped together with starboard engine cables. The starboard engine cables are routed towards the aft end of the engine room, over to the forward end of the battery box.

    This configuration combines the outputs of both alternators into a single 1/0 cable and a single battery disconnect switch. Due to the high alternator output currents, the cable and the switch were overloaded. In addition, this configuration tends to decrease the charging current into the battery, regardless of the alternator size, due to increased voltage drops in the cables.

    The power cables were separated at the starboard engine, another battery disconnect switch was installed, and each engine was connected to the battery through a dedicated power and ground cable as shown in Figure 2. This configuration eliminated the overloaded cable and switch and increased the current output from each alternator.

    Regardless of the connection configuration, Figure 1 or Figure 2, voltage drop will occur in the connection cables between the alternator and the battery, which always tends to reduce the available charging current. To compensate for the cable voltage drop, many regulators are equipped with a remote sense capability. Figure 3 is taken directly from the Delco Remy web site. As shown in Figure 3, a dedicated wire is connected from the remote sense terminal on the alternator directly to the battery. This wire allows the regulator to sense the actual battery voltage, instead of sensing the battery voltage plus the cable voltage drop. When connected in this configuration, the voltage regulator increases the alternator output voltage to compensate for the cable voltage drop, which increases the charging current leading to reduced charging time.

    If an external regulator is being used, the ground connections for the regulators should also be made directly to the battery, instead of connected to the engine as is usually done.

    To avoid interference, keep the remote sense wire(s) away from the cables that carry the alternator output current.

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  • #8818

    Chuck Truthan

    FIRST thing to do in our electrical systems is to CHECK EVERY CRIMP CONNECTION!
    On Insandity, we had to replace every battery cable crimp connection because the crimps were substandard and every connection could be wiggled out by hand 10 years after production (2006), including grounds to the engines.
    I talked to the factory and they say that they have replaced their crimping tool “a few years ago”.

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