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Essential Guide to Alternators: "Smart" vs "Dumb"

What does the alternator do?

The engine of a 4WD produces mechanical energy, however, it doesn’t generate electricity, that task belongs to the alternator. The 4WD charging system consists of a battery, a voltage regulator, and an alternator. The alternator converts mechanical energy to electrical energy with an alternating current.

When the 4WD engine is running, it turns a drive belt that rests on a pulley attached to the alternator. The pulley rotates the alternator's rotor shaft, which spins a set of magnets around a coil. These spinning magnets generate alternating current (AC) around the coil, which is then channelled to the alternator's rectifier. Then the alternating current (AC) is transformed into a direct current (DC). A voltage regulator sends the power from the alternator to the battery and controls the amount of energy provided to allow a steady flow of power to the battery.   

Hema 4WD alternator

"Dumb" Alternator

A traditional alternator, or “dumb” as we are calling it, has been in use since World War Two when they were installed on vehicles to power radio equipment. They used to be called a generator as they work the same as one, the 4WD engine spins wheels under the bonnet that crank a wheel on the alternator which produces electricity. 

The issues with a “dumb” alternator are that it only offers a single voltage target, and that target is often not even correct. The typical target of the “dumb” alternator is between 13.6V and 14.2V, which is too low for an absorption phase and too high for a floating stage. What this means is that the battery may not fully charge and in the long term it may overcharge the battery, in turn, damaging it. 

With a secondary battery setup, an intelligent battery management system or a DCDC charger is not required, a simple battery isolator or voltage sensitive relay (VSR) will do. A DCDC charger or intelligent battery management system, however, will look after the second battery better. 

What is a "Smart" Alternator?

Smart alternators, also known as variable voltage alternators, control the output voltage and current produced by the alternator based on the 4WD operating condition. In doing so the smart alternator is more efficient and helps the engine reduce emissions by reducing the voltage supplied to the battery when the 4WD is driving. Unlike a “dumb” alternator, which supplies a constant voltage of between 13.6V and 14.4V when the engine is running, a smart alternator’s voltage is variable. 

A smart alternator is unable to charge a secondary battery system due to the variable voltage, which can range between 12.3V and 15V making them ineffective to charge a second battery effectively. A VSR won’t work with a smart alternator, however, DCDC chargers or intelligent battery management systems, such as the Redarc Manager 30 or an Enerdrive Power System have the smarts to charge and maintain a secondary battery setup to 100%.

Next steps

Check out our new Mid North Coast New South Wales Map that includes a comprehensive map of the Barrington Tops National Park. This is available at all good outdoor retailers or you can purchase directly from Hema Maps at this link.

At Hema Maps, we strive to provide the most comprehensive and accurate maps and guides for outdoor enthusiasts looking to explore Australia's natural wonders.

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  • Graeme Munro: May 17, 2023


  • lenard herron: May 17, 2023

    Hi , from past experience, I have used both and found the old system sheds than the smart charge system .Having had 2 isuzu’s, the 2021 model caused me more headaches than I needed. 1- battery under sized for the job it is supposed to do. having to replace it (at my cost ) with a more powerful battery, under 2 years old, because of the way the smart charging system works. I am not the only one who has this problem. But you can’t push/ clutch an automatic. I learnt that when I was a mechanic ,in my past life .5 minutes listening to the radio and guess what, flat bettery. cheers Len.

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