Charge controllers play a vital functional role in regulating the current and voltage between the solar panels and the batteries. They essentially ensure that batteries aren’t overcharged and thus prevent damage and extend their performance and lifespan.
There are four different types of charge controllers: PWM (Pulse Width Modulation), MPPT ( Maximum Power Point), the shunt regulator, and the series regulator, and each works slightly differently. The PWM and MPPT charge controllers are the most common.
We’ll be looking at the four different types of charge controllers and how they differ in their operation.
- The shunt charge controller
- The series charge controller
- The MPPT charge controller
- The PWM charge controller
The series and shunt controllers have similar functionality, while the MPPT and PWM operate differently from each other and to the shunt and series controllers.
How Does The Shunt Charge Controller Work?
The shunt controller is essentially an on/off the system, whereby the battery receives either the full charge or nothing from the array. When full, the controller shorts the panels to stop current flow.
Using a shunt controller will charge the battery until the disconnect voltage is achieved, at which point the array is shorted and shut off to prevent overcharging.
As the batteries deplete, they will reach the reconnect voltage level, at which point the short is removed, and the current flow from the panels resumes to recharge.
The shunt controller cannot regulate current flow to batteries as the PWM controller does or regulate the current to match the battery voltage like the MPPT controller.
How The Series Charge Controller Works
Like the shunt controller, the series controller is also an on/off system. The battery gets all the current or nothing except the series controller open circuits the array rather than short-circuiting it.
When the battery reaches the disconnect voltage, the charge controller opens the circuit to stop the current flow, and when the battery requires charging, the circuit is closed to allow recharging.
Using transistors that can be placed on either the positive or negative lines, these transistors open and close the circuit and control the current flow during recharging cycles.
Range of Pulses
As with the shunt controller, there is no voltage analysis, but the regulation of current is controlled through pulses which can range from a few seconds to a few hours depending on the level of discharge of the batteries.
Series controllers can also be connected to multiple relays and operate at different set points using different transistors. Series controllers also run cooler than shunt controllers, and these are best utilized in large arrays.
How Does The MPPT Charge Controller Work?
The Maximum Power Point or MPPT controller analyses the battery voltage against the panel voltage and ensures that the voltage to the battery is matched from the array.
This is because solar panels generate different voltage and current levels according to weather conditions. So at peak generation times, the solar panel can generate more than 16V, while the battery may only be operating between 12V and 14.4 V.
The MPPT controller optimizes the current to the battery and allows the solar array to deliver maximum power under all conditions. This facilitates more efficient and consistent charging as well as overall performance.
In most cases, the array voltage is higher than the battery voltage. The MPPT controller can determine the exact level of voltage the battery needs at any given point. Whether the array produces maximum generation capacity or less than maximum, the MPPT always delivers an optimized current for recharging.
MPPT controllers ensure the battery gets its precise voltage requirements, and they are more efficient than PWM modules, but they are also more expensive.
MPPT controllers are very common and utilized because they provide greater efficiency and consistency in regulating both voltage and current.
How Does The PWM Charge Controller Work?
The PWM or Pulse Width Modulation Controller delivers controlled pulses of voltage to the batteries with varying intervals and current intensity based on the status of the batteries.
The PWM analyses the battery requirements and determines how much current the battery needs from the array. It then sends a series of pulses with the longer pulses that carry more current when depleting the battery.
The pulses get progressively shorter as the charge levels of the batteries increase. Although the PWM controller accesses the full current available, it restricts the current into percentages of on and off cycles supplied to the battery.
For example, it may start with an 80% on and 20% off cycle when the battery charge is low and gradually reconstitute that as the charge levels increase, eventually ending with a 0% flow when the maximum charge state is reached.
As the batteries are used and start to lose charge, the PWM will assess the status and then open the transistors to restart the charging process at the required pulse level.
PWM controllers are similar to series controllers, but they use transistors instead of relays to open and close the array.
It should be noted that both MPPT controllers and PWM controllers are solid-state, and as such, they emit heat, and dissipation can be a problem in larger arrays.
Why Do You Need A Charge Controller?
A charge controller is recommended for any PV system as they prevent the batteries from overcharging, resulting in irreparable damage, battery failure, or diminished lifespan.
Smaller systems such as portable PV units may not require a charge controller as their voltage outputs are smaller than larger arrays. Still, even a small wattage panel can overcharge a battery if left unmonitored.
With larger solar arrays, the charge controller is an essential component. The voltages and current levels here are far greater, and overcharging a battery bank could lead to an explosion or rupture, which would NOT be a good idea.
When looking at charge controllers, you should always find one that has a slightly higher rating than the maximum voltage and current produced by the array, and this is pure as a safety precaution so that should the array deliver that little bit more, your controller and battery can handle it without risk.