Although a charge controller is probably not the first thing that comes to mind when designing your solar system for your campervan, it is an essential one. A charge controller basically regulates the power that comes from your solar panels and goes to your leisure battery.
In a previous blog post, we already showed where to place your solar charger in your system. In a future blog post we will show how we have actually installed the entire electrical setup in our van.
Here we will shortly explain the importance of a charge controller and provide some background on two different types of solar chargers.
Why you should install a charge controller
The use of a charge controller has many advantages for the well-being of your system, but also for its efficiency. Here we have summarized the advantages of using a charge controller:
- Prevents reverse current flow: Electricity flows from high to low voltage. During the night, for example, the voltage of the solar panels is lower than that of your battery bank. A charge controller prevents electricity from flowing back to your solar panels in situations like these.
- Protects your battery from deep discharging: Many charge controllers have the option to directly connect your 12V appliances to them. When the voltage of the battery becomes too low – which can permanently damage your battery – the charge controller automatically disconnects your load and hence protects your batteries from deep discharging.
- Protects against overcharging: prolonged overcharging of your battery can cause damage. A charge controller monitors the voltage of your battery and adapts the current accordingly.
- Keeps your batteries topped off: When the battery is almost full, the charge controller switches to something called trickle charge. In this so-called ‘float’ stage, the current trickles in at the same rate as the natural discharge of your battery. It keeps your battery topped off while not damaging it.
- Protects against possible overvoltage: The voltage of your solar panels does not always equal that of your battery. A charge controller can convert the incoming voltage to that of your leisure batteries. This also allows you to install your solar panels in series instead of parallel when using an MPPT charge controller.
- Ensures rapid recharging: Charge controllers are known to increase the efficiency of your solar system by up to 40% compared to systems lacking one.
- Provides extra utilities: Some charge controllers also provide multiple additional utilities, such as a voltmeter, information on the charge status of your solar panels, ethernet connection to view the status online, and etcetera.
In short, a charge controller helps you protect your battery from damaging aspects like overcharging and overvoltage. In the long run, this will extend the life of your leisure batteries. Additionally, it will help you get the most out of your solar panels by increasing the efficiency. Who doesn’t want that?
PWM Vs MPPT
Generally, two types of charge controllers exist. We do not want to delve into the nitty gritty technical details of how both operate and such too much. We mainly want to highlight the general and most important characteristics and differences of both. If you really want to learn all the ins and outs, Victron has offers quite a nice and detailed explanation.
The first and less expensive option is the pulse width modulation (PWM) charge controller. It basically acts a monitor. It monitors the voltage of your battery and adapts the charging current and the voltage accordingly. As your battery reaches its capacity, the charge controller will reduce the current.
By doing so, a PWM controller protects your battery from all damaging aspects mentioned in our enumeration above.
The second and more expensive option is the maximum power point tracking (MPPT) charge controller. These do the same as PWM charge controllers – protecting your battery from damaging factors – but come with some additional benefits.
Utilization of higher voltage systems
Both the PWM and MPPT controllers will prevent overvoltage – converting the incoming voltage to match that of your batteries. However, only the MPPT type can fully utilize upon higher voltage solar panels.
This all has to do with the basic formula: watts = amps x volts. For an explanation about these terms click here.
Both types reduce the volts of the solar panel to match that of your battery. But as can be seen from the equation, a lower voltage results in a lower wattage provided to your battery.
Let’s take a 24V 280 watt solar panel charging your battery during optimal conditions with 9.39 amps at 31 volts as an example. A PWM controller will reduce the current from the solar panel to match that of your battery, say 13V. This panel would then provide you with: 13 x 9.39 = 122.07 watts. Nowhere near the rated 280 watts.
Now, what the MPPT charge controller does, is convert the excess volts into amps. The controller increases the amps by the ratio obtained when dividing the voltage of your solar system by that of your battery. In our example this would thus be: 31V/13V = 2.385.
When the same solar panel is connected to an MPPT charge controller, it will provide you with: 13 x (9.03 x 2.385) = 280, which equals the rating of the solar panels.
MPPT charge controllers are thus able to fully utilize higher voltage panels. This makes MPPT controllers ideal when installing solar panels in series, as then the voltage of the solar panels is added up.
Increased efficiency in sub-optimal weather conditions.
The second major benefit of using an MPPT charge controller is the fact that their efficiency is higher. Similar to what we explained above, all solar panels operate at a slightly higher voltage than that of your battery, around 18 volts. Both types of charge controllers change this to match that of your battery. However, again, the MPPT charge controller is able to convert this ‘loss’ in voltage to an increase in amps. As a result, the efficiency of the charging is increased even for solar panels rated as 12V.
The MPPT outperforms the PWM, especially in sub-optimal conditions. You can think for example of shade, and low solar radiation levels. But also with temperature extremes, such as cold winters. It has been found that the MPPT charge controller can outperform a PWM by up to 40% depending on weather conditions.
A PWM charge controller is thus mainly useful for lower wattage systems where the voltage of the solar panels matches that of the battery. For higher wattage systems, especially when installed in series (which can save you quite some wires), the investment of an MPPT will certainly be worth it.
We often see people take 100 watts solar systems as a rule of thumb as the maximum setup in which to use PWM charge controllers. Since we will have 400 watts of solar, we have invested in an MPPT charge controller ourselves.
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