How Charge Controllers Work (detailed)

While you can connect a solar panel to a battery directly and have it charge, the problem is that the panel will continually send current to the battery, resulting in the battery sustaining damage.

A charge controller is used to regulate and control the voltage and current from the solar panels to the batteries in the system. This is critical to ensure safe and efficient charging of the batteries as the controller can shut down the flow of electricity to the batteries and prevent overcharging.

TO understand more fully what the charge controller does, we need to look at the following elements:

  • When do you need a charge controller for your system
  • The different types of charge controllers
  • How are charge controllers rated

Understanding how charge controllers work and why they are a critical element of any PV system will help you keep your PV system performing at optimum or allow you to choose the right type for your PV set up.

Charge controller and solar panel

Does Every PV System Require A Charge Controller?

Not every system needs a charge controller, as using a solar panel to charge golf cart batteries would not require one. But where the solar panels are above 140W or more, the charge controller is essential.

The controller is needed because solar panels do not emit a consistent and steady voltage. The voltage and current can fluctuate with atmospheric conditions with the larger wattage panels of 120-140W and over.

If there were no charge controller, the batteries would receive varying volts and amperages, leading to overcharging, battery damage, and even potential fire hazards!

Think of the charge controller as a police officer directing traffic, controlling the number of cars and speed moving through an intersection when the traffic lights are down.

Without that control, it’s chaos!

The same would apply to your solar panel array and batteries. The current and voltage flows would be chaotic and unsafe, so the charge controller becomes the traffic policeman in your array.

What Kind Of Charge Controllers Do You Get?

There are several types of charge controllers, with the most common being the MPPT and PWM control modules, and they each work slightly differently.

See also: What A Solar Charge Controller Does (Explained)

How Does The PWM Charge Controller Work?

PWN is an abbreviation for Pulse Width Modulation, and this controller works to maintain the voltage flow to the batteries during the charging process. Solar panels generally have higher voltages than batteries.

The average battery is around 12.4 V while lithium-io can be around 14.4 V. A solar panel can deliver more than 16V, and while this is good when the battery charge is low, it’s not good when the batteries approach full charge.

The PWM controller determines how much voltage the battery needs and uses a series of varying pulses to control the voltage sent from the panels. A shorter pulse for a lower duration has less voltage and current, and a longer pulse has greater voltage and current.

The shorter pulses are used when the battery is closer to fully charged, while the longer ones would be used when the battery has been discharged or at low charge. The PWM charge controllers are cheaper than the MPPT controllers, but they can also be expensive at the higher end.

How Do MPPT Charge Controllers Work?

MPPT stands for Maximum PowerPoint, and these are far more efficient than the PWM controller, but they are also more expensive. MPPT charge controllers look at the voltage of the solar panel compared to the battery’s voltage.

It then optimizes the solar panel voltage to provide maximum charging power to the batteries. This is especially effective in colder or adverse weather climates where the MPPT can extract the maximum charge from the panels and provide more efficient charging.

The MPPT charge controller thus delivers optimum charging efficiency at all times, and they are 20% -30% more efficient, even though they cost more.

Where Are Charge Controllers Connected In The System?

The charge controller is installed between the panels and the batteries and has a positive and negative output that runs to the battery and the load in some cases. Some charge controllers may also have a USB and DC output.

Remember that traffic policeman example? The charge controller directs current between the panels and the batteries, preventing reverse current leakage that could lose charge from the battery array at night.

How Are Charge Controllers Rated?

All controllers are rated based on their output current and their input and output voltages.

Most charge controllers can accommodate between 12V-24V for battery voltages, and the larger, more expensive controllers can extend that to 72V. Solar panel input voltages can range from 24V to 250V depending on the array size and connected panels.

Based on the size of the PV system you require, your charge controller should always safely deal with the current, so when consulting with a supplier, they will advise you on the best option for the charge controller.

For a 200W solar panel that can deliver between 10A and 12A during peak generation periods, using a charge controller rated at 15A makes sense to give you that little extra room to wiggle on the current.

What Happens If You Overcharge Your Battery?

Overcharging your battery will reduce its lifespan by around 50%, and there is a risk of explosion.

Overcharging leads to damage of the battery’s internal structure and the electrolyte plates, and once this happens, it cannot be easy to repair. The batteries will need to be replaced in most cases, as fixing them is often not an option.

While lead-acid batteries are cheap, they are not that cheap to simply throw them away if they suffer from overcharging, and in this case, prevention is far better than cure! A PV system is an investment, and having a charge controller protects your power source and will deliver optimum performance and longevity.

Why Is It Important To Have A Charge Controller?

Even with small systems, leaving the panel connected to the battery can result in overcharging, which will damage the battery, in which case you may end up replacing it!

Why waste money and go through the inconvenience of poor battery performance and degeneration when you can avoid it by using a charge controller. If your system is small, you don’t need to spend a lot of money on one, but having one is always a good idea.

Even a small 10W solar panel generating about 0.7A can overcharge a battery if it’s left unattended.


Photo of author
Elliot has 20+ years of experience in renewable technology, from conservation to efficient living. His passion is to help others achieve independent off-grid living.

SolVoltaics is an affiliate and an Amazon Associate, we earn from qualifying purchases - at no extra cost to you.