Alternator charge controller

External charge regulator or DC/DC charger: what is the difference?

An external charge regulator takes over the regulation of the alternator. With a regulator such as the Mastervolt Alpha Pro III charge regulator, the alternator itself is adjusted for optimal charging. The full power of the alternator remains available and the regulator charges the batteries in several stages. This way you get the most out of your alternator and prevent damage to the starter battery or other consumers. The Alpha Pro III works on 12 and 24 volt and fits alternators with a standard Bosch connection.

A DC/DC charger is placed between the alternator and the batteries. The charger determines how much current passes through and can be set to a maximum output current or output voltage. The alternator itself is not modified. Need more charging current? Then you connect several chargers in parallel.

Which one do you choose?

• Choose an external charge regulator if you want to get the maximum power out of your existing alternator, for example with a large battery bank and few engine hours. Prefer to replace everything at once? Then choose the upgrade set charge regulator plus alternator.
• Choose a DC/DC charger if you need flexibility, for example with multiple battery banks or different battery types. Because the charger limits the current, the alternator is not overloaded and each battery gets the charging profile that suits it. This extends the lifespan of your batteries.

Why a standard alternator does not charge lithium batteries properly

Charging lithium batteries with a standard alternator requires smart regulation. Without additional protection, an alternator can become overloaded or charge the batteries incorrectly under heavy load. Overheating can also occur at high temperatures in the engine room or during prolonged use at idle speed. How this works and what to look out for when connecting, you can read in our article charging a lithium battery with an alternator.

How many amps do you need?

The DC/DC chargers in this category deliver from 10 to 100 amps. As a rule of thumb, choose a charger of 20 to 40 percent of the capacity of your battery bank: with 200 Ah that is 40 to 80 A. Also check what your alternator can spare. The charger should not demand more than the alternator still delivers next to the engine and the starter battery, otherwise the alternator gets too hot.

12, 24 or 48 volt, isolated or not

With a DC/DC charger, the first number stands for the input and the second for the output. A 12/24 charger therefore charges a 24 volt battery bank from a 12 volt alternator. The Victron Orion-Tr Smart chargers are isolated: input and output are galvanically separated, so the negative of the starting system and that of the house battery do not have to be connected. The Mastervolt Mac Plus chargers connect to a CZone network.

What is a normal charging voltage of an alternator?

An alternator in a 12 volt system charges at around 14 volt, in a 24 volt system at around 28 volt. According to Mastervolt, that voltage often drops to 13.5 or 26.5 volt in a warm engine room, and then a battery does not get beyond 60 to 70 percent of its capacity. An external charge regulator or DC/DC charger solves that. If your alternator does not charge at all anymore, the internal regulator is often defective. You can find those under voltage regulators for the alternator.

Help with your choice

We do not install, but we are happy to think along. Send a photo of the type plate of your alternator and your batteries via WhatsApp, or call +31 514 745 007. In stock and ordered today means delivered tomorrow in the Netherlands.