As energy demands grow for RVs, camper vans, marine vessels and other specialty vehicles, relying primarily on solar and traditional alternators can limit overall system capability.
High output secondary alternators offer a solution by providing significantly more charging power — crucial for large lithium battery banks and modern energy needs.
Orion XS 1400 DC/DC Charger now available for pre-order:
Secondary alternators are generally used in systems with large energy needs and limited space for solar.
Common applications include:
The primary alternator of a vehicle is generally not intended to support high energy demands.
Any added load will ultimately reduce the life span of the primary alternator. If the alternator fails, the starter battery will die and your vehicle won’t start, so we want to do our best to protect the alternator and not overload it.
While DC-DC chargers are acceptable, they must be sized properly and are limited in output compared to a secondary alternator.
The Orion XS 12/12/50A has a max output of 700W
Compare this to the Arco-A8000-48V at 7,383W at sustained cruising output.
DC-DC chargers are still an excellent option as a supplementary charge source, but secondary alternators can be primary power supplies, in some cases completely replacing traditional generators.
While secondary alternators have been commonplace in the marine industry for many years, they’ve only recently begun to explode in popularity for RVs and camper vans.
We strongly recommend that all secondary alternator installations be done by a qualified professional. Contact us if you’d like to be connected with a professional.
Check out our webinar for more specific industry experience.
A secondary alternator installation requires a number of components. Here we will primarily cover the install and necessary components for systems using Arco Zeus regulators. Specific parts may vary for different kits, but the overall SOP will remain the same.
Once you’ve identified the proper secondary alternator kit, review the following documentation:
Zeus Regulator installation guide:
https://cdn.shopify.com/s/files/1/0110/9521/2098/files/ARCO_Zeus_Installation_Guide_2025.pdf?v=1744399640
Zeus/Victron diagram:
https://www.victronenergy.com/upload/documents/Genless-monohull-with-Victron-MultiPlus-Lynx-Smart-BMS-NG-600Ah-NG-Li-HP-Alternator-Arco-Zeus-regulator.pdf
Zeus/Cerbo GX integration guide:
ARCO_Zeus_CerboGX_IntegrationGuide_R2-1.pdf
The above documents lay the foundation for a successful installation, but there are some important SOPs to consider to reduce risk of alternator damage.
If a secondary alternator has been installed, do NOT start the vehicle if:
In addition, you must confirm:
Key safety protocol:
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If a vehicle must be started before all of the above conditions have been met, just disconnect both harnesses from the regulator. Keep harnesses disconnected until installation is complete.
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Note: Before system testing, be sure to update the firmware on the Arco Zeus, Victron GX Device, Victron Lynx BMS or other batteries that have communications.
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It’s important to understand that most damage to secondary alternators is a result of the alternator outputting large amounts of power with nowhere for that power to go.
For example, if there’s a sudden BMS disconnect, or if the main system fuse blows, there could be thousands of watts suddenly back feeding into the alternator.
This risk can be mitigated with ‘closed loop’ communication, allowing for safer, faster and more accurate charging.
The Arco Zeus regulator is capable of communicating with various BMSes, including the Victron Lynx BMS. When integrated with the Lynx BMS, the Arco Zeus should be set to ‘Victron follower mode’, which will allow the regulator to dynamically direct alternator charge output based on data coming the the BMS and battery cell status (see Zeus/Cerbo GX Integration Guide in ‘Preparing for installation’ section).
Additionally, in the event of a BMS disconnect, the regulator will shut the alternator off before the main contactor between the batteries and the rest of the system opens. This ensures a safe shutdown with no excessive power spikes.
That said, in the event of a blown main fuse, it’s still always recommended to use an alternator protection module (APM).
We strongly advise using BMSes with communcations when integrating secondary alternators. This is by far the safest method.
If it is not possible to use a BMS with comms, basic batteries may be used, however there is another important safety consideration.
Earlier, in the ‘Preparing for Installation’ section we mentioned that the Batt V-sense cable must be installed on the ‘System’ side of the main disconnect switch. This is to ensure the regulator does not mistakingly think there’s a connection to the battery.
If, for example, the Batt V-sense was installed directly on the battery, and the disconnect switch were off, this would damage the alternator because it would be trying to send power with nowhere for that power to go.
In a system with a Lynx BMS, it’s sufficient to place the Batt V-sense cable on the System side of the disconnect switch (not on the switch itself, but instead located on the fuse stacked on the positive connection coming from the alternator).
However, there is the possibility that, even if the disconnect switch is off, the system may still be energized in the event there’s solar present. With the Lynx BMS, this isn’t of concern because when the main disconnect switch is off, the BMS does not allow charge. Without the Lynx BMS, there’s an additional safety measure that should be implemented.
To account for this, systems without communications between the BMS and regulator must use a Main Disconnect Switch that includes an Alternator Field Disconnect (AFD). This ensures that, anytime the main disconnect switch is turned off, the alternator is also off.
Arco has been making alternators for over 60 years, and their experience is evident when looking at the design choices and performance of their Zeus line of high output alternators.
All power electronics perform better when kept at cooler temps. Arco alternators stay cooler than other brands because of:
1. increased alternator surface area (see slides below)
2. alternator case design with ample space for air flow (see slides below)
3. native field/rotor voltage for better performance in 24V and 48V systems
All power electronics perform better when they’re cooler. ‘Cold’ alternator data is not an accurate representation of performance, as alternators shift from cold to hot within the first few minutes of run-time. For real-world applications, the ‘Hot’ curve is what really matters.
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