What’s a PWM Solar Charge Controller? Explore Working, Disadvantages, and Comparison with MPPT Controllers

A PWM solar charge controller, also known as a Pulse Width Modulation controller, is an electronic device that regulates the flow of electricity from solar panels to batteries. It protects batteries from overcharging or damage by switching the panel-to-battery connection on and off many times per second. These controllers were very popular in the 90s, but have been replaced by MPPT solar charge controllers, especially in solar energy systems. 

One of the biggest disadvantages of a PWM solar charge controller is that it forces the solar panel voltage to drop down to the battery’s voltage. As a result, the extra energy that the panels could have supplied is lost. This energy loss is the main reason why MPPT solar panel charge controllers have replaced PWM solar charge controllers in most hybrid and off-grid solar systems. 

Today, most solar panel charge controllers use MPPT (Maximum Power Point Tracking) technology. An MPPT solar charge controller ensures that the solar panels operate at their most efficient voltage and current, allowing for the maximum power to be drawn and safely sent to charge the batteries.  

Instead of wasting the extra output from the panels, as PWM controllers, an MPPT controller converts that extra voltage into additional charging current. This makes MPPT controllers up to 30% more efficient than PWM solar charge controllers.

PWM charge controllers are sometimes used in small setups, such as RVs and boats, where cost is a factor, but they’re hardly used in residential or commercial solar installations, as MPPTs offer significantly higher efficiency. 

In this blog, we will explain what a PWM solar charge controller is, how it works, its key features, and the primary disadvantages that led to its replacement by MPPT controllers in battery-based solar systems.

We will also reveal whether you need a solar panel charge controller with on-grid rooftop solar panel systems for homes and housing societies, and why choosing an  on-grid solar system is preferable to off-grid and hybrid solar systems for residential and commercial rooftop systems.

TL;DR Summary Box: Can a PWM Controller Overcharge a Battery?

A properly working PWM solar charge controller will not overcharge or damage a battery. Its main job is to prevent that from happening. PWM controllers regulate charging in the following three stages, ensuring the batteries do not suffer from damage due to overcharging:

• Bulk stage: In this stage, the controller sends maximum current until the battery reaches a set voltage.
• Absorption stage: During this stage, the PWM controller’s role is to maintain the battery at the set voltage it attained during the bulk charging stage. After that, the controller reduces the charging current slowly. 
• Float stage: In this stage, the controller reduces the charging voltage further to maintain the battery at a safe level without overcharging.

However, incorrect settings, mismatched battery types, and faulty or inexpensive PWM controllers can result in battery damage and overcharging, as these issues prevent the controller from regulating the voltage properly. 

Simply put, a properly configured PWM solar charge controller will not overcharge a battery, because it regulates charging in three stages to keep voltage within safe limits. However, improper configuration or a cheap-quality PWM controller can lead to battery damage due to overcharging.

Here are the main topics covered in this blog in detail:

What is a PWM Controller?

A PWM solar charge controller is a simple electronic device that uses the Pulse Width Modulation (PWM) algorithm to regulate voltage and current flow from solar panels to batteries through rapid electronic switching. Pulse Width Modulation technique ensures that the current can be turned on and off multiple times in seconds to charge the batteries safely, without overheating them. 

It’s important in PWM solar charge controllers that the solar panel’s nominal voltage matches the battery bank’s voltage. If the battery’s voltage is extremely lower than that of the solar panel’s output, solar electricity being generated by the panel will be wasted because the PWM controller will bring down the panel’s voltage to the level of the battery’s voltage. 

Here are the key characteristics of a PWM solar charge controller and how it really works:

• Voltage matching: The controller operates at the battery voltage level. Hence, the panel’s nominal voltage must match the battery voltage.
• Switching technology: It uses rapid on-off switching to control the flow of current, minimizing energy wastage as heat.
• Current control: The PWM solar charge controller adjusts the pulse width duration based on battery charging requirements.
• Protection functions: The primary role of this controller is to prevent overcharging, even if that means reducing the output from the panels.

PWM Solar Charge Controller Full Form

The full form of PWM is Pulse Width Modulation. It is the algorithm that PWM charge controllers use to charge a battery safely. The controller sends very fast on-off bursts of power from the solar panel to the battery. 

It’s called a Pulse Width Modulation controller because it modifies the width of the pulse. It means the controller decides for how long the current will be sent to the battery, and it switches the flow of current on and off multiple times per second.

• It sends quick pulses of current to the battery: The controller switches the panel-to-battery connection on and off many times every second. The controller can switch the current on and off at rates ranging from 100 times per second to tens of thousands of times per second.
• It changes how long each pulse lasts: If the on time is longer, the battery receives more current. If the on time is shorter, the battery receives less current. This is how the controller regulates the flow of current during battery charging.
• It controls current smoothly: By varying the on time, the controller delivers a steady current instead of rough bursts. This maintains stable charging and reduces stress on the battery.
• It maintains the optimal voltage for your battery: The controller closely monitors the battery’s voltage and temperature. Based on that, it ensures the battery always receives the correct voltage for its type and charging stage. This way, the battery gets fully charged without the risk of being overcharged.

How Does a PWM Solar Charge Controller Work?

A PWM solar charge controller works by directly linking the solar panel and the battery. Then, it controls how the DC electricity from the panels flows to the batteries. Instead of changing the panel’s voltage like an MPPT controller does, a PWM controller uses a rapid on-and-off switching method to regulate the charging process. 

While the switching ensures the battery is charged safely without damage, it also forces the panel’s voltage down to match the battery’s voltage, resulting in energy wastage and reduced efficiency. 

Here’s the step-by-step breakdown of how a PWM solar charge controller works:

• Step 1 – Solar panels produce DC power when sunlight falls on them: The solar panels convert sunlight into direct current (DC) power. The voltage of this power is usually higher than the voltage of the battery bank.
• Step 2 – The PWM controller connects the panel directly to the battery: Instead of adjusting the voltage like an MPPT controller, a PWM controller connects the solar panel output directly to the battery whenever charging is needed.
• Step 3 – The controller rapidly switches the connection on and off: The Pulse Width Modulation (PWM) algorithm causes the controller to turn the panel-to-battery connection on and off many times per second. By controlling the duration of current flowing into the battery during each cycle, the PWM controller regulates the average charging current flowing into the battery. This on-and-off method is crucial to PWM’s functioning, as it prevents battery damage.
• Step 4 – Battery voltage pulls panel voltage down: When the connection is made, the solar panel voltage is forced to drop to a level close to the battery’s voltage. This keeps the battery safe from overcharging. However, it also means that any extra voltage the panel might be producing is lost instead of being converted into usable current.
• Step 5 – The controller manages charging in stages: A PWM controller does not send the same current to the battery at all times. It follows a series of charging stages to ensure the battery’s safety. The three stages are the bulk stage, the absorption stage, and the float stage. 
• Step 6 – Battery receives safe but less efficient charging: The battery receives the necessary voltage and current for safe charging, but the solar panel is not operating at its most efficient point. This results in greater energy loss compared to MPPT controllers, particularly when the panel voltage is significantly higher than the battery voltage.

A PWM solar charge controller works by linking the solar panel and the battery directly. Then, it controls how the DC electricity from the panels flows to the batteries. Instead of changing the panel’s voltage like an MPPT controller does, a PWM controller uses a rapid on-and-off switching method to regulate charging. 

While the switching makes sure the battery is charged safely without getting damaged, it also forces the panel’s voltage down to match the battery’s voltage, resulting in energy wastage and reduced efficiency. 

What Are the Three Charging Stages a PWM Solar Charge Controller Uses to Charge Solar Batteries Safely?

The three-stage charging method is designed to make charging faster, safer, and healthier for the battery. Without these stages, the battery could either be overcharged, undercharged, or stressed in a way that shortens its life. 

By splitting the process into bulk, absorption, and float stages, the PWM solar charge controller ensures that the battery is charged efficiently and maintained at a safe level once it is full.

• Bulk stage battery charging: In the bulk stage, the PWM controller allows the maximum current to flow from the panels into the battery. This stage continues until the battery reaches a set voltage, which is usually close to 80-90% percent of full charge capacity. Bulk charging is the fastest stage and is responsible for charging most of the battery’s energy.
• Absorption stage battery charging: Once the battery has reached the set voltage, the controller shifts into the absorption stage. Here, it keeps the voltage steady while slowly reducing the charging current. This stage prevents the battery from overheating or becoming stressed as it approaches full capacity. The absorption stage is crucial because it safely charges the battery to nearly 100% without damaging it.
• Float stage battery charging: After the battery is fully charged, the controller enters the float stage. In this stage, it lowers the voltage and sends only a tiny amount of current to the battery. The goal here is not to keep charging, but to maintain the battery at full charge. This prevents overcharging while making sure the battery is ready for use. 

Features of a PWM Solar Charge Controller

The most important features of a PWM solar charge controller include multi-stage charging to extend battery life, settings for different battery types, built-in protection features that prevent battery damage, and display screens that show real-time system performance.

Let’s check out all the critical features in detail:

• Multi-stage charging: The PWM solar charge controller charges batteries in three stages, known as bulk, absorption, and float. The battery charges very quickly at first, then the charging rate slows down as it nears full during the absorption stage, and finally, it is maintained at a safe level to prevent overcharging.
• Battery selection option: Users can choose from various battery types, including lead-acid, gel, AGM, and lithium-ion. Then, based on the chosen battery type, the controller uses charging levels that match the battery’s chemistry.
• Temperature sensor to adjust for hot and cold weather: Batteries need different charging levels in summer and winter. With a temperature sensor, the PWM solar charge controller automatically adjusts the charging and ensures the battery is protected in all seasons.
• LCD screen: PWM controllers have a display screen that shows battery voltage, charging current, power, the current charging step, and any errors. 
• Overcharge protection: When the solar rechargeable battery is full, the controller reduces or stops charging. This protects the battery and helps it last longer.
• Over-discharge protection: If the battery level drops too low, the controller disconnects the load. This prevents damage that can permanently reduce battery capacity.
• Short-circuit protection: If a short circuit occurs, the controller shuts down. This protects the wiring and the devices in your system.
• Reverse polarity protection: If someone connects the panel or battery incorrectly, the controller blocks the current flow to prevent damage.

Which is Better, PWM or MPPT?

MPPT is superior to PWM solar charge controllers for solar systems because it extracts more usable power from the panels and can be up to 30% more efficient.

The biggest strength of PWM solar charger controllers that made them so popular in the 90s was that they prevented batteries from overcharging. However, this strength started backfiring very quickly, as the PWM controllers protected batteries from overcharging even if that meant reducing the output from the solar panel. When that happens, the extra energy the panel could have supplied is not used and is wasted.

This energy loss pushed researchers to find a more efficient option, which led to the widespread adoption of MPPT solar charge controllers. Unlike PWM, an MPPT controller allows the panels to operate at their maximum power point (MPP) and then converts the excess voltage into additional charging current. An MPPT controller can be up to 30% more efficient than a PWM controller.

PWM controllers are still used in small boats and RVs where cost is a concern and the panel voltage is close to the battery voltage. For most residential and commercial battery-based solar systems, MPPT solar charge controllers have replaced PWM because they deliver more usable energy.

Here’s a tabulated snapshot of the key differences between PWM and MPPT solar charge controllers:

What Are the Disadvantages of a PWM Solar Charge Controller?

The biggest disadvantage that led MPPT to replace PWM solar charge controllers is their lower efficiency, which is ~65%. PWM controllers lower the panel’s output to match their voltage to the battery’s voltage. For example, if your solar panel produces 18V but your battery is at 12V, the PWM controller reduces the panel’s voltage to 12V, discarding the 6V difference. This is the biggest disadvantage of PWM controllers. 

Let’s check out all the disadvantages that eventually led to their replacement in battery-based solar systems:

• They are less efficient than MPPT solar charge controllers: PWM controllers are up to 65% efficient, which is way less than the 95% efficiency rate of MPPT controllers. 
• Needs panel and battery voltages to match: A PWM controller works best when the panel voltage is close to the battery voltage. This limits panel choices, making the system design less flexible.
• Bigger losses in cold weather: Solar panels generate a higher voltage in cold conditions. A PWM controller cannot use that extra voltage. The gap between the panel voltage and the battery voltage increases, resulting in more energy being left unused.
• Not a good fit for high-voltage panels: Many modern high-wattage solar panels run at much higher voltages. A PWM controller cannot make good use of that voltage.
• No tracking of the best power point: A PWM controller does not search for the point at which the panel produces maximum power. When sunlight, shading, or temperature changes occur, it misses chances to draw more power.
• Weaker performance in low light: Early morning, late evening, and cloudy periods keep the panel voltage well above the battery voltage. A PWM controller still pulls it down and loses more energy at those times.
• Harder to expand later: If you add panels that do not match the voltage of your existing ones, the system may not play well with a PWM controller. You may need to change the controller instead of just adding panels.

Is a Solar Panel Charge Controller Required With On-Grid Solar Systems?

A solar panel charge controller is not required with on-grid solar systems because on-grid PV systems do not need batteries in the first place. That’s also the primary reason why on-grid solar systems are more affordable than off-grid and hybrid solar systems. 

Battery-based solar systems usually require lithium batteries, which are expensive to install. Additionally, they must be periodically replaced once their lifespan has ended. Simply put, battery-based solar systems are not only expensive to install but also expensive to maintain. 

On the other hand, on-grid rooftop solar systems are cost-effective, do not require lithium batteries, and make homeowners and housing societies eligible to receive a subsidy, making solar installation even more affordable. 

Let’s check out the multiple reasons why on-grid rooftop solar systems for housing societies and homes are better in places with a reliable grid:

• They do not require batteries to function: Battery-based solar systems use lithium batteries to store excess solar energy generated by the panels during the daytime. This requirement is nullified in on-grid solar systems since they send the excess energy generated during the daytime to the grid. At night or when solar output is low, these systems draw power from the grid to maintain the load. 
• They are eligible for a subsidy: Homeowners and housing societies can claim a subsidy under the PM Surya Ghar Muft Bijli Yojana only for installing an on-grid rooftop solar system. This financial assistance will not be offered for off-grid solar systems, ground-mounted solar systems, or commercial rooftop systems.
• They lower electricity bills by 90% or more: Appropriately-sized on-grid rooftop solar systems can reduce your reliance on the grid to such a huge extent that your bills will be reduced by at least 90%. Since the panels will provide free electricity for 25 years, you will save tens of lakhs of rupees you would have otherwise had to spend on electricity bills, sans a solar system. 

Here’s a comparison table between the cost of installing a 5 kW on-grid rooftop solar system in India vs the solar savings it offers in its 25-year lifespan:

*Please note: The 5 kW solar panel price in India with subsidy mentioned above is indicative as of 29th September 2025 for the SolarSquare Blue 6ft variant. The actual solar plate price depends on your DISCOM charges, city, product variant opted for, panel type, inverter type, mounting structure height, type of after-sales service, savings guarantee, roof height, etc. Prices are subject to change. Additionally, when calculating savings, we have considered an annual tariff escalation of 3% and an annual degradation of 1%. The actual final savings from a 5 kW solar system depends on the types of solar panels you’ve installed and their efficiency, intensity of sunlight your rooftop receives, orientation of the panels and tilt angle, the pollution level and weather conditions in your city, the temperature, shadow on the roof, impact of dirt/dust, and how well you maintain your panels after installation.

Use SolarSquare’s free solar power estimator calculator to estimate the cost of installing a rooftop solar system in your city, as well as the savings this system will offer over its 25-year lifespan. 

Conclusion

A PWM solar charge controller uses a Pulse Width Modulation (PWM) algorithm to prevent battery damage from overcharging. However, in its quest to prevent battery damage, a PWM controller reduces the output from the panels to the battery’s voltage. This results in massive losses. Hence, an MPPT solar charge controller, up to 30% more efficient than PWM controllers, is used in battery-based solar systems nowadays.

You will not require any solar charge controller for on-grid solar systems, which makes them very affordable. For any further queries regarding rooftop solar, you can book a free solar consultation call with SolarSquare today.

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FAQs

Q1. Can I use MPPT and PWM together?

Ans. Technically, you can, but it is highly recommended not to do so. Mixing them on the same panels usually causes problems because they use different operating principles and charging algorithms.

Q2. What is the lifespan of a PWM solar charge controller?

Ans. A PWM solar charge controller can last from 5 years to 10 years, depending on the controller’s quality and how well it is protected from heat, dust, and moisture.

Q3. Which type of battery works with a PWM solar charge controller?

Ans. As long as it has the right settings for the chosen battery type, a PWM controller can work with lead-acid, AGM, gel, and some lithium batteries.

Q4. What is the purpose of a PWM controller?

Ans. The primary purpose of a PWM solar charge controller is to regulate the charging process while ensuring the battery charges safely and does not get overcharged or damaged.

Q5. How does a solar charge controller work?

Ans. A solar charge controller works as a connection between the solar panels and the battery. It monitors the battery voltage and controls the flow of power, ensuring the battery charges steadily, does not overcharge, and remains healthy for a longer period.

Q6. Can I use a PWM solar controller for lithium batteries?

Ans. Yes, you can, but only if the PWM controller has a lithium setting or adjustable charging parameters. Otherwise, it may not charge the battery correctly or safely.