Nothing in cart
Review of Caravans Plus Service
Quick response with no problems and well done Caravansplus
3rd order by Darelle from NSW
Caravan & Campers Guide to Battery Chargers
Article by Rob Smith Sep 2022 - Caravans PlusRead Time: 7 mins
Contents
The continual advancements made in the renewable energy sector have been responsible for a vast improvement in the affordability of high quality lithium batteries. Being smaller, lighter and more powerful they are perfect for the RV industry and are providing new opportunities to remain off-grid comfortably for longer.
Once you have invested in a quality battery it is important to be able to safely and efficiently maintain your system for optimum performance and longevity. Due to this need, there have also been great advancements in the performance of battery chargers in both the DC to DC and AC to DC categories.
DC to DC chargers (sometimes referred to as Voltage Booster Charger) use power from your vehicle's alternator to charge your battery when you are driving, while AC Chargers require a 240V input from either mains power or a generator. A comprehensive RV setup will utilise both styles of charges for maximum flexibility and the ability to travel to different environments.
No matter whether you are looking at a DC to DC or AC to DC Battery Charger there is a large range available at a variety of price points. For Caravan, RV and 4x4 installations a good multi stage charger which covers your battery chemistry profile (e.g. Lithium) is generally recommended for overall performance. This style of charger continually monitors your battery's condition and adjusts the power output, providing the most efficient charging without the risk of damaging your battery.
Multi Stage Battery Chargers
The 3 main stages of modern battery chargers are known as Bulk, Absorption and Float. Other terminology you might come across when dealing with Lithium Batteries are:
Constant Current (CC) which refers to the Bulk Stage.
Constant Voltage (CV) which refers to the Absorption Stage
A typical Lead Acid Battery utilizes a three stage charging process while Lithium Batteries only require the first two stages with the Floating Charge being removed as it can damage Lithium Battery due to their low self-discharge level. Another key difference between charging Lead Acid Batteries and Lithium Batteries is the State of Charge (SoC) achieved in the Bulk Stage. Lead Acid Batteries require the Absorption Stage at around 80% SoC while with Lithium it is 90-95% SoC. It is for these 2 main reasons that it is highly recommended to use a Battery Charger with a Lithium Profile on Lithium Batteries.
Lead Acid Charging Profile
Bulk Charge - This applies the highest safe voltage and amperage and will run until battery level reaches approx 80%
Absorption Charge - This stage slows the charging to allow the cells to equalize, as the battery reaches 80% capacity the voltage level remains constant but the amperage is reduced. The lower current is needed to ensure the battery does not overheat as the battery is brought closer to full charge.
Float Charge - This is the final stage at around 95% capacity, the voltage is dropped and held at a constant safe level until the battery reaches 100% where it is maintained with a trickle charge indefinitely.
Lithium Charging Profile
Stage 1: The CC Charge is the bulk stage and can be applied safely to lithium batteries to achieve a 90-95% State of Charge (SoC).
Stage 2: The CV Charge is the absorption stage which allows the cells in the battery to equalise or balance.
After stage 2 is completed the charging process is stopped and the battery voltage is monitored until it drops to a predetermined level at which point the bulk stage begins again.
AC to DC Battery Chargers
When reviewing AC to DC battery chargers there are a lot more options than DC Chargers as there is a larger variety of applications. There are smaller (5A) portable units to service your car, bike or boat batteries ranging up to larger (100A) charges which are permanently mounted and wired to your battery setup in your Caravans or RV.
When determining what AC Battery Charger best suits your needs the first step is to make sure it has a charging profile for your battery chemistry. While most of the chargers offered on our site include a Lithium profile not all chargers do. The next step is to select the appropriate Amperage Output, this is based on your battery size / capabilities. While your battery will have a specified max input rating, this is generally only for a short period. Charging at a higher rate for an extended period will damage your battery and shorten this life span.
As an example Enerdrive recommends using an AC Charger with an output of around 30-40% of the battery capacity on their Lithium B-Tec Range. This translates to a 40A Charger on 125A battery being preferred for longevity. This means that spending more on a larger charger has the potential to damage your battery. To overcome this, higher quality chargers will have an adjustable output setting allowing you to correctly match your existing setup while enabling you to expand it at a later date.
As with all Battery Chargers when installing it is crucial to be positioned as close as possible to the battery, and that you connect using the appropriate size cabling. The reason for this seems simple but is often overlooked - batteries require precise voltage for effective charging. Too low and nothing happens, too high and you damage your battery, the chargers calculate the correct voltage and output at the optimal level. At this point any voltage drop will greatly impact the charges efficiency, and the main cause of voltage loss is cable size and length.
The table below illustrates Enerdrive's recommended cable sizes to be able to handle the amperage required while minimizing the Voltage Loss based on mounting position.
DC to DC Battery Charges
As mentioned earlier, voltage is the key factor when it comes to effectively charging a battery. At the most basic level a DC to DC battery charger accepts power (generally at a lower voltage) from your vehicle's primary battery(alternator) and converts it to a higher and stable voltage for more effective charging. This process also makes it possible to achieve a full state of charge on your auxiliary battery as opposed to traditional direct alternator charging which is limited to around 80% state of charge. Finally DC to DC chargers are the only reliable option if your vehicle has a smart alternator. The voltage output of smart alternators is highly variable and controlled by the ECU for fuel efficiency, this makes them unsuitable for Voltage Sensitive Relays (VSR) and Direct Charging.
When choosing a DC battery charger there are a few factors to consider, the most obvious being the output required. This is generally based on the size of the battery you are charging, some models have a variable output allowing you to lower the amperage to suit smaller battery capacities.
Some chargers also include a solar input allowing you to connect your solar panels directly without the need for a regulator. If solar input is an important part of your setup, take the time to review the chargers specifications. Some models may only have basic Solar Regulator while others have a high output MPPT Controller. Some models allow blending of both sources simultaneously to achieve maximum input.
To get the most out of your DC Charger you need to ensure it is receiving the required Voltage Input which generally comes back to selecting the correct size cabling. The mounting position of the charger (ie. the distance from the main battery) will determine the gauge of wire required. The further away the greater the potential for voltage loss and thus larger Heavy Duty Cable is required, this becomes noticeable when installation is in the middle of your caravan vs in the rear of your 4x4.
The team at Enerdrive performed a simple real world example of this replicating a caravan installation. They lined up three 10m lengths of different size cable 6mm, 10mm & 16mm. One by one they hooked them up to an idling 4x4 and the Enerdrive 40A DC2DC Charger and measured its output, as you will see the smaller under capacity cable almost halved the output.
Disclaimer - The information contained in these articles is provided in good faith and we do our best to ensure that it is accurate and up to date, however, we cannot be held responsible for any damage or loss arising from the use or mis-use of this information or from any errors or omissions. The installer is ultimately responsible for the safety of the system so if you are in any doubt, please consult a qualified electrician.
0 Comments