Stay Amped: Demystifying Battery Chargers and Controllers

Stay Amped: Demystifying Battery Chargers and Controllers

by Stephan Edwards

An inescapable fact of modern overland life is that we use a lot of electricity. From running fridges to keep our beverages cool, to inflating our tires with on-board or portable air compressors, to simply lighting up our camp at night and charging laptops, tablets, and camera batteries, the amount of electrons flying around our rigs at any given time is staggering.

Patrick already wrote a comprehensive guide to power distribution for the Notebook - it covers the many variables you should consider when building out electrical systems in your rig. One area that is worth covering more in depth is battery chargers and controllers.

A charge controller sits at the heart of any power distribution system. It is a device that can be as simple or as sophisticated as you want it to be based on your particular needs. One way or the other, a controller is essential to the efficiency of the system and the long-term health of your batteries. This is particularly true as both the complexity and the different types of batteries on the market has grown in recent years. For the purposes of our discussion, let’s assume you are planning for a stand-alone auxiliary or house battery to feed your hunger for current.

What is a Battery Charger?

Just like it sounds, a battery charger is any device that replenishes the power of your battery (most commonly measured in amp hours) as you deplete its stores through your electrical components or devices.

On a vehicle, the most basic battery charger is simply your engine’s alternator. The same way the alternator maintains a full charge (measured in volts) for your main, or starter, battery, you can employ it also to keep the charge topped up in your house battery. Other charging sources can include solar panels (as Garrett discussed in the Notebook here), or even input from any normal 120 volt alternating current outlet you may find in your home.

However, you can’t just go throwing electrons at your battery without some kind of way to manage how that current is distributed. Enter the charge controller. There are three types that are commonly used by overlanders in their vehicles: isolators, DC/DC charge controllers, and AC/DC portable battery chargers.

Battery Isolators

Borrowed from the world of sailboats, the solenoid battery isolator is old, but time tested and proven technology. The benefit lies in its simplicity. These devices are small, rugged, waterproof, and essentially consist of only one moving part. The isolator works as the charge distribution point in any “split charge” or dual battery system that is connected to your vehicle’s alternator. In its most basic form, the isolator has an internal voltage monitor that “reads” the state of charge in your starter battery.

When the isolator senses that your main battery is operating at a healthy voltage (usually above 13 volts), it trips a solenoid switch that diverts the charge from your alternator away from your main battery and into your house battery. The main battery remains protected from excessive discharge, while the auxiliary battery gets the juice it needs as you drive.

Their diminutive size means isolators can be installed nearly anywhere in your vehicle. More advanced modern versions, like Redarc’s Dual Sensing isolators, feature microprocessors that not only manage current from your alternator, but can also detect charge coming in from other sources, such as a solar panel or a plug-in wall charger, and distribute that charge to the house battery, and even to your main battery should it run low.

If your power needs are simple and your charging sources relatively few, a heavy duty battery isolator is a no brainer for your set-up. It’s cost-effective, plug-and-play, requires almost no maintenance, and works so transparently you’ll hardly notice it’s there. 

There are a handful of drawbacks to old-school battery isolators. In the absence of any other charging sources, the solenoid isolator is only going to help charge your house battery when the engine is running. In addition, isolators work best with traditional flooded lead-acid batteries and some gel cell lead batteries. If you’re planning on AGM, LiPo4, or other lithium batteries, these require more careful management of current to prevent possible damage. Finally, most new trucks on the market today have “smart” alternators, which are controlled by the vehicle’s ECU, rather than a simple internal voltage regulator found in traditional alternators. Some solenoid isolators can struggle to manage voltage levels, or flat out not work at all, with these types of alternators.

DC/DC Charge Controllers

If you are planning a much more sophisticated electrical system for your overland build, you should be looking to the DC/DC charge controller. While a battery isolator can work well for power circuits with one or two charging inputs, when you start adding hundreds of watts of solar power, or AC shore power, for example, things get a little more intricate. Employing a battery isolator in this context is going to require adding multiple new parallel systems to your design, which increases its complexity. As Patrick noted earlier, the fewer connections, controllers, and devices you can use in your electrical system, the better. 

The DC/DC charge controller, through cutting edge microprocessors and algorithms, does the job of several charge management components all at once. It operates as a traditional battery isolator in concert with the vehicle’s alternator, and simultaneously as a solar charge controller, and most can accept multiple charging inputs, including from AC/DC converters, and even direct from AC shore power. All of your charging inputs can be connected into one device, saving you extra wiring, connections, and components, which reduces the risk of failures or short circuits in your electrical system. 

DC/DC controllers also offer a level of current management that far outstrips the traditional solenoid isolator. Their programming allows for the correct level of charging for advanced battery technologies like AGM and lithium, and they work seamlessly with today’s “smart alternators”. Some models, like Redarc’s BCDC 25, feature “Green Power Priority” charging, which, when detecting solar power input, will charge your auxiliary battery with the solar panels even while driving to save stress on your alternator.

In addition, some of these charge controllers (we can even refer to some of the more advanced models as “battery management systems”, like the BMS 1230S2-NA from Redarc) offer technologies that can monitor not only battery charge and health, but also battery draw from any number of your system’s components, and feature parameters that can be set by the individual user. Bluetooth connectivity and smartphone apps, such as RedArc’s RedVision, are just cherries on the cake. 

Of course all of this technology comes at a price - DC/DC charge controllers generally run more than twice the cost of high quality solenoid isolators, and in some cases much more than that. However, there are efficiencies to be had by investing in one of these amazing multi-taskers. Because they do the job of many devices, you can dispense with plenty of extra wiring, as well as the stand-alone isolators, solar charge controllers, and converters you would need without it.  

Some final considerations with the DC/DC charge controller are its size and its componentry. While generally quite tough and weather resistant, their sensitive electronics do best in an environment free from dust, moisture, and as much vibration as possible. They are also much larger than a traditional battery isolator, so you will need to plan carefully for its installation location.

Plug-In Battery Chargers

The last of our battery charging technologies is the AC/DC battery charger. These devices plug in to any regular household outlet, converting your home’s 120 volt AC current to 12 volts of direct current. In the past, older 12 volt chargers would simply hold a fixed charging voltage, which crammed current into your battery until it was fully charged, or overcharged. Left unattended, as heat and resistance in the battery rose over time, these chargers could even boil off a flooded lead acid battery - a dangerous situation to say the least.

Thankfully, today’s plug-in chargers feature microprocessors that monitor the charging state of your battery, and adjust the voltage necessary to meet its condition without overcharging or damaging the battery. They can be programmed to charge all kinds of batteries from lead-acid, flooded or gel, to AGM, to the new generation of lithium batteries. Many are sophisticated enough to “repair” batteries that have been discharged below their recommended thresholds. 

They are especially useful if your dedicated overland rig doesn’t see daily driver duty, and thus your auxiliary batteries don’t receive a regular charge. In “float” mode, plug-in chargers can safely and correctly maintain your battery’s full charge while in storage. That way you can be confident that when you hop in your vehicle, your batteries will be ready to go at the turn of the key. 

Which equipment do you use regularly that is a serious drain on your battery power? Let us know in the comments below! Hit us up with questions on how to design your own electrical system.


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