Why Use a Secondary Alternator?

In the last year or so, we’re seeing many more van builders including 400 to 600 amp hours (or more) of battery storage capacity in their rigs. Prior to that, a “large’ system was maybe 300 amp hours. These higher capacity systems are absolutely fantastic for powering your loads for long periods of time while boondocking off grid. Massive battery banks even open up the possibility of using an energy efficient 12-volt air conditioner overnight (check out our comparison of these).

However, there are three main problems with these large battery banks. First it’s bloody expensive. But, if you want top-quality batteries with intelligent CAN bus-enabled BMS systems like our Victron Energy or Lithionics examples, you’ll just have to bite that bullet. Secondly, it takes up a lot of space. Using fewer, higher density/higher capacity batteries, as we recommend in this post makes this much less problematic. Finally, with that much battery capacity – especially if you’re using a lot of it regularly – it becomes nearly impossible to adequately recharge with solar or DC-DC chargers. As your battery bank grows in size, so does your need for charging. We think adding a powerful secondary alternator is the best solution to this problem.

And here’s the thing about a camper van…. you’re going to drive it – that’s sort of the point, right? So, if you can power everything in your van from the engine while driving (or the fuel tank you already have), you are going to have an incredibly capable off-grid rig. Imagine this: fast and reliable battery charging from a secondary alternator, water heating from your engine coolant lines with a Isotemp water heater and perhaps a Webasoto gasoline or diesel heater sipping tiny bits of fuel from your van’s tank. In fact, in many ways, this system makes having solar panels superfluous which can free up roof space on your van for vent fans, air conditioners and rooftop decks!

But, What About Solar?

Solar panel charging is a great “bonus” charging source when conditions are “just right” but it’s not reliable like driving since conditions are often not optimal. Obviously, solar charging is only possible during the day and they have to be in the sun and, of course, you also have weather and seasons to contend with. We’ve seen some van builds that have their entire roof covered with solar panels so that they can generate enough power to run a residential-style “split” AC system which is a very complex installation by comparison to a rooftop unit and frankly, may not work correctly after bouncing down the road for thousands of miles. Think about this… they have to be parked in the hot sun during the day in order for this to work at all which is defeating to the goal because it will cause the the air conditioner run more which means that there is less energy available to charge the batteries which will be needed to run the air conditioner through the entire night.

In this example system we don’t have any solar panels but they could certainly be added in the same manner as we have them on our other example electrical system.

1. The Nations 280 Amp Secondary Alternator Kit

Our kit from Nations Alternator includes the powerful alternator itself which outputs an average of 200 amps and can surge up to 280 at high RPMs! When you compare that to a pair of 30 amp DC-DC chargers that are commonly used in a more “traditional” camper van electrical system, it’s nearly 3.5 times more charging capability. In our testing, we see anywhere between 120-150 amps of charging current at idle and around 200 amps or higher when driving (depending on vehicle and engine RPMs).

To put this into practical terms, without considering any solar charging, recharging a 640 amp hour battery bank at 30 amps while driving would take nearly an entire day (21 hours). If you used two Orion DC-DC chargers (which is fairly common), you’d still need to drive for over 10 hours to recharge. With this system, you can charge at an average of 200 amps which would take just over 3 hours of driving which is much more in line with real-world vanlife. You might spend two or three days at a campsite, off-grid, drawing down your battery, and then drive to your next destination. With this system, just a few hours of driving will restore your battery bank.

The Nations alternator kit comes with everything you need for the installation including a vehicle-specific mounting bracket, hardware, belts, etc. The installation is not difficult for anyone who has some experience working on cars. It’s also possible to hire your local mechanic to install the secondary alternator – something any qualified mechanic can help you with easily.

One important feature of the Nations alternator that wasn’t immediately obvious to us but was explained by our friends at Wakespeed is that it uses something called “avalanche diodes”. Why is that important? Imagine your secondary alternator system is up and running, charging away as you drive and something goes wrong such as the fuse connecting the alternator output to your 12 volt DC bus blowing or someone accidentally disconnecting the battery(s) from the system using the disconnect switch. That situation is referred to as an “uncontrolled disconnect”. When that happens the Wakespeed regulator (more on that below) can detect this and respond quickly with the alternator to dissipate the remaining electricity that now has no place to flow to (often referred to as a “load dump“). However, there is a brief period of time when voltage spikes significantly. If the alternator didn’t use avalanche diodes, this voltage spike would be up to 130 volts (!) going into a 12 volt system, which is as bad as it sounds. However, with the avalanche diodes, the voltage is moderated to about 30 volts, and, get this, apparently, 12 volt systems are designed to handle voltage spikes up to 45 volts. Those diodes just saved your van!

Nations Alternator Charging Capabilities Table

2. Wakespeed WS500 Regulator

The Wakespeed WS500 regulator is the brains of the operation and interfaces with the alternator and batteries to charge the batteries with the correct voltage, current, and temperature parameters. You can think of the regulator as the device that turns the alternator into an intelligent battery charger rather than just producing current. And, like all battery chargers, it must be configured/programmed to charge the specific batteries you’re using. The Wakespeed regulator is the most advanced regulator of its kind and is regarded by many in the marine/boat world as the very best and most reliable option.  It constantly monitors 5 parameters of charging and is highly configurable.

Want to learn more about the Wakespeed WS500? We have another post that is a technical deep dive on the Wakespeed including a 1.5 hour video with the founders! 

Another great feature of the Wakespeed WS500 is its ability to intelligently manage the charging current from the alternator so that it doesn’t exceed the maximum charging current of the battery. For example, if you only had one of the Lithionics batteries, the Wakespeed would be aware of this (via the CAN bus) and automatically limit the 200 amp output of the Nations alternator to the maximum recommended charge current for that battery which is 150 amps. Meanwhile any “remaining” current (50 amps in this case) can flow into your DC power system to power loads (air conditioners, refrigerators, inverter, etc.) while also maxing out the charging of the battery!

3. High Quality, CAN Bus Enabled Lithium Batteries

In a system this powerful, it’s essential that the batteries are up for the job! They must be reliable, robust and one of the brands/types that is officially supported by Wakespeed to work correctly and safely.

You can visit the “technical” tab on the Wakespeed product page to see which battery brands are qualified for safe and effective use. Each of the qualified battery types has a corresponding configuration file available. In order to be considered for qualification, the manufacturer must provide batteries to Wakespeed for testing and engage in “engineer-to-engineer” level conversations with the Wakespeed team. These measures are to ensure that installers can have the highest level of confidence in the functionality and safety of their systems.

We also highly recommend batteries that have CAN data connection to their BMS. CAN stands for “controller area network“. It is a highly reliable standard that uses messages to allow many “devices” inside a system to communicate with each other. CAN is used extensively in the automotive industry and has various implementations in the mobile world including RV-C for RVs and NMEA 2000 in the marine world. If you have lithium batteries that have a CAN connection that the Wakespeed can read (or a “language” that it can “translate”), the Wakespeed will use the data available digitally on the CAN bus such as voltage, current, and temperature to very accurately control charging. It can also monitor other messages from the batteries such as disconnect warnings to prevent situations like load dumps.

At Vanlife Outfitters, the CAN-enabled batteries we use in secondary alternator camper van electrical systems are Lithionics and Victron Energy Smart batteries (paired with a Lynx Smart BMS and Cerbo GX).

Links to example wiring diagrams can be found at the top of this post!

In addition to the compatibility, quality, and CAN bus, both the Lithionics and Victron batteries pack a lot of storage into a small space compared to most of the internal BMS batteries on the market which is, of course, a huge advantage in a camper van or RV!

Why This Is Awesome Example #1
Running a Mabru 12-volt Rooftop Air Conditioner Overnight with 600 Amp Hours of Battery Capacity

Let’s run a scenario where you run a Mabru 12,000 BTU air conditioner in your camper van overnight for 8 hours. Let’s assume it’s cycling on and off about half of the time such that the compressor is only operating for 4 hours during that 8-hour block of time. I’m choosing the Mabru unit in this example because of its extreme energy efficiency. If you take a look at our comparison spreadsheet, you’ll see that the Mabru uses about the same amount of power as the Dometic 2000 RTX while producing nearly twice the cooling capacity! The reason is that Alain Mabru has leveraged his decades of marine cooling experience to engineer an innovative “inverter” system for the compressor. This design provides substantial improvements in energy efficiency, quieter operation and longer longevity than traditional compressors.

Scenario #1, it’s freaking hot. So, you’re operating the unit on “high” with medium fan speed. That’s going to draw about 55 amps. Running for those four hours (50% duty cycle overnight) would consume around 220 amp hours from your battery bank. This means that, with no other loads,you have something like 380 remaining amp hours of capacity for other loads throughout your day and you could fully restore the energy consumed by the air conditioner by driving (or idling) for just over one hour!

Scenario #2, it’s hot but not freaking hot. In this case, you’re operating the unit in the “eco” mode drawing around 25 amps for the same 4 hours (50% duty cycle overnight). In this scenario, you would consume only around 100 amp hours from your battery bank which means that you have something like 500 remaining amp hours of capacity for other loads throughout your day and you could fully restore the energy consumed by the air conditioner by driving (or idling) for only around a half hour!

Fancy Monitoring with Victron Cerbo GX and GX Touch 50

Since this is such an amazingly capable electrical system, we decided to go all-in and “upgrade” from the “standard” Victron Energy BMV-712 battery monitor to a Cerbo GX with a GX Touch 50 screen. Honestly, this is pretty cool!

The Cerbo GX is the device that all the signals connect to for monitoring and the GX Touch 50 is a small, full-color, touch screen that you would typically locate with the rest of your monitors/switches/control panel and it allows you to control, monitor and interact with all the various devices from it’s slick (and responsive) touch-screen interface. The Cerbo GX has a super wide range of compatible inputs. In this example, the MultiPlus inverter/charger is connected to the Cerbo GX using the VE.Bus, the SmartShunt is connected via VE.Direct and, if you had a Victron SmartSolar MPPT charge controller it could also connect to the Cerbo GX with a VE.Direct connection. In addition, we show a “room temperature sensor” so you can monitor the room temperature. However, the same temp sensor could be used in other ways such as monitoring the refrigerator temperature and you could even get two of these sensors (about $25 each) and do both. There are even ways of using the Cerbo GX to monitor your tanks such as your fresh water or grey water tanks but that’s getting beyond the scope of this post and will be the topic of a future one!

Often vans with a Victron MultiPlus inverter/charger will use the remote control panel in order to easily turn it on/off or into charging-only mode. The remote panel also includes a handy dial used to adjust the maximum input current the MultiPlus will pull from the shore power connection. This is a great feature that allows you to literally “dial in” your current draw based on the capacity of the outlet you’re plugged into – typically either a 15amp or 30amp circuit. But, if you use this “fancy monitoring” approach with the Cerbo GX and GX Touch screen, it will override the setting on the MultiPlus essentially ignoring the dial on the remote panel. And, since you can also control the state of the MultiPlus from the touch screen, you don’t need the remote panel in this scenario.

Not Fancy Enough? Connect It To The Interwebs!
Want to get even fancier? Now that you have a “GX device” (The Cerbo GX), if your van has an internet connection (as most of us do), you can create an account on the Victron Remote Management (VRM) website and have your Cerbo GX send regular data updates from all the devices you’re monitoring on your GX Touch 50 screen to this online portal. This is a “free for life” monitoring solution that is really amazing for monitoring and troubleshooting and you can also set alarms for various things such as battery state of charge or other settings. For now, the full set of data (advanced data) is kept for 6 months but the basic data is kept for at least 5 years. The advanced data is primarily for troubleshooting and if you want to keep your own archive, you can download your data into .csv or Excel files. VRM even allows you to control the components remotely and update firmware on them if that is enabled on the GX device.

Track Your Van with GPS
If you add a USB GPS receiver to your Cerbo GX you can also monitor its GPS location and use the “geo fencing” feature to notify you if your van moves somewhere you think it shouldn’t which is a really great security feature. This video shows how this works.