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Optimising the alternator's charging profile without an expensive 'smart' charger

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What is the issue?
The typical modern alternator and regulator charging system found on boats comes from the automobile trade and hasn't changed much in over 40 years. The alternator, such as pictured above, produces electricity to recharge the battery. A typically integrated regulator sits between the two systems deciding the power output from the alternator to optimize the battery charging. It refreshes the battery with a tapered charging process that is the default charging mechanism of a standard alternator. The taper causes the battery to charge rapidly at first and then slow down as it reaches full charge. This eliminates the risk of overcharging and battery damage.

The standard system works well refreshing a single vehicle battery that it is designed for. However the default alternator taper is highly conservative, i.e. it drops down the charge output too quickly, in the context of refreshing a well-used boat battery in a short amount of time. The performance shortcoming is dramatic when refreshing a bank of batteries. Although the default charge setting will charge a vessels batteries in time, the alternators taper drops the output so as to make it unnecessarily inefficient.

Why address this?
This results in an irony where we are running the engine to charge the batteries whilst the regulator is dropping the charge and unnecessarily choking off the charge potential. Hence the engine is being running longer, adding engine time, consuming unnecessary fuel and increasing the length the engine noise has to be endured in the cabin.

How to address this?
Reduce the suboptimal regulator taper to address your exact battery requirements so that the alternator performance is optimised. Please read care and maintenance of batteries Experience for contextual understanding.

There are two broad approaches to this, an automated system or a manual.

  • • A "smart" chip-controlled charger - There are many smart microprocessor driven battery charging systems that provide sophisticated and optimised charging. These units measure the condition of each battery and automatically regulate the charge according to an optimised charging curve. They typically have multiple charging steps and a digital screen that both monitors the charging process and allows real-time battery capacity readings. Smart regulators can also be programmed to cater to alternative battery types such as deep cycle and Gel. These smart charging systems are simply excellent but are expensive and complex to install. But the installation of a "smart" chip-controlled charger will optimise both battery performance and battery life and will pay for itself over the long haul.

  • • Install a manual charging setting - If however, a "smart" chip-controlled charge cannot be afforded a much more cost-effective approach is to add a manual over-ride step to the alternator's regulator to provide a fixed high-charge setting.

This is what we did during our circumnavigation with the aid of Gurd an excellent electrician in New Zealand. As we had no Gel cells, and a large 4 x battery to alternator capacity ratio, the over-ride high setting was 14.2 Volts. Once the override switch was turned off it fell back to the standard alternator taper charge that typically dictated a continuous-preservation charge of 13.2 volts following the overide.

The problem with this system is that you could accidentally leave it on a high charge setting and boil the batteries. Human control, even devoting full attention to the process, is going to be less than perfect. However, when you live aboard and are cautious it is unlikely that you will boil your batteries.

Gurd calculated that we should switch over after the first 4 hours of high charge which provided a lot of time on a high charge. We also placed a conspicuous flashing red LED that blinked at us when the high charge was engaged. You could also add a light ping to this to make certain it is not overlooked. Typically we ran it for an hour or two at the most when the batteries were low and we found the performance differential to be enormous.

There is one note of caution. Installation of an upgraded regulator can cause problems with electric tachometers. As this is an important engine instrument it is recommended that you check the planned upgrade with the tachometer manufacturer. If there are issues you may still procede by installing a mechanical tachometer but this is an additional cost that has to be factored into the cost equation.

With thanks to:
Michael Harpur, with thanks to Gurd of Bay Marine Electronics New Zealand.
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