Everything You Should Know about a PWM Solar Charge Controller

A Pulse Width Modulation charge controller aka the PWM solar charge controller used to be a very popular type of solar charge controller in the 90s. 

But first things first: PWM is an algorithm; not a device. When this algo is embedded in a solar charge controller, that controller is known as the PWM solar charge controller.   

The purpose of a PWM charge controller, or any solar charge controller for that matter, is to bring the voltage of the solar power system down to correspond with the voltage of the load. 

The PWM charge controller modifies the input waveform to create a specific kind of waveform that is required for the output. 

In this way, PWM is utilised to regulate the formation of output waves, which subsequently regulates the load automatically. 

Although not very popular nowadays, PWM solar charge controllers did have their fair share of benefits and limitations! Let’s find out everything in detail.

Working of a PWM Solar Charge Controller 

Charging a solar-powered battery at the right level is significant. A PWM solar charge controller helped with this. 

Whenever the voltage of the batteries used to come to the set point of regulation, the PWM controller algorithm steadily lessened the charging current. It helped to prevent the battery from overheating and gassing. 

Notably, there are three stages of charging in a PWM solar charge controller – the Bulk Charging stage, the Absorption Charging stage, and the Float Charging stage.

The Technical Functioning

A PWM controller works by switching the frequency levels. This frequency modulation is done to modify the output. That is how this charge controller calibrates the output. 

The sine waveform’s switching frequency is 50. That means the PWM controller will observe 50 ups and downs within each second. 

The significant task of a PWM controller is to adjust the frequency to 36 or 40 or anything else per the requirement. 

How does the PWM Solar Controller change the waveform?

It comprises some specific circuitries, including an inductor choke that functions to modulate the waveform. We should control (on/off) the inductor choke. This can be done by the modulation in the current waveform.

There are 3 major types of PWM charge controllers, namely: 

• Single pulse PWM 
• Multiple PWM
• Sinusoidal PWM – this one is used specifically for household appliances 

Features of A PWM Solar Charge Controller 

Now, let us understand the features of this controller —

• Higher Reserve of Battery Capacity: A PWM Solar Charge Controller facilitates the maintenance of 90 – 95%, unlike the on-off regulated charge controllers that offer 55 – 60% capacity. 

• Prevention of Heating & Gasification: It prevents the battery and the load from overheating. Also, it controls the voltage rises and effects of high temperatures in a solar system. 

• Suitability to Smaller Applications: The PWM solar charge controller used to be the most suitable option for small solar systems during the 90s.

Price of PWM Solar Charge Controller

One of the most important factors that is considered while purchasing any equipment is its price, PWM solar charge controller was no different when it was in use. 

The price of a decent PWM solar charge controller used to be around INR 1500 to 2000, at a max power input of 500 W, which was costlier in the 90s.

Their high cost was one of the reasons that they were replaced by the MPPT solar charge controllers in the first place. 

MPPT v/s PWM Solar Charge Controllers    

One of the most commonly asked questions is how MPPT and PWM solar technologies differ from each other. Well, here’s how!

A PWM charge controller is used to connect a solar system right away with the battery bank. The PWM modulates the sinusoidal waves required by certain loads in a way that they meet the requirement of the load. Remarkably, it shapes the waveform.

Whereas, an MPPT solar charge controller weighs up the VMP input voltage of the solar panel and modifies the PV voltage to correlate with the load voltage.  

Hence, it brings down the high voltage coming from the solar panel to suit the lower voltage required by the load. It optimises the output and does not have any concern with the waveform. 

Before we give out the verdict on which of the two is better, we’d like to elaborate on their differences. 

Here are the major differences between a PWM Solar Charge Controller and an MPPT Solar Charge Controller.

Productiveness

• The utmost productiveness of the MPPT controllers is around 96%. These are highly productive.

• The utmost productiveness of PWM controllers used to be around 68-70%. Hence, they were relatively very less productive.

Size 

• MPPT controllers are larger as they are specifically designed for bigger solar panels.

• PWM controllers were smaller in size. They had a maximum capacity of 60 amps.

Market Presence

• PWM solar controllers aren’t very commonly used now. Their lower productivity made them costly. Which is why they were eventually replaced.  
• MPPT controllers are relatively new. They have many benefits. Hence, they have been trending in the market lately.

Price Aspect

• The price of an MPPT solar charge controller is high. But their productivity justifies every single penny.

• The PWM charge controller’s price was expensive in the 90s and its productivity was low.  

Applicability

• MPPT charge controllers are ideal for professional use.

• PWM charge controllers used to offer good performance in small applications only.

Limitations

• MPPT solar charge controller is a highly rewarding device. The sole limitation is the high upfront cost.

• You cannot use PWM controllers with a large number of solar panels (greater than ten panels). In fact, they’re obsolete now.

How does a PWM Solar Charge Controller Work in a System of Batteries?

When installing an off-grid solar system with a system of batteries, you significantly need a solar charge controller for that system. The controller assesses the voltage and controls the battery charging accordingly.

Your solar power system and battery bank are both required to have equal voltages for deploying a PWM solar charge controller. 

When the battery becomes dead, it needs charging. When the battery needs charging, the PWM controllers start functioning in a way that they can change the waveform as per the waveform requirement of the battery.

Once the battery is fully charged, the PWM controllers sustain a trickling state, i.e., constantly supplying a little amount to keep the battery loaded.

In a system of batteries, a PWM charge controller was used to limit the current supplied by the solar PV modules to the battery or drawn by the loads. 

Conclusion 

A PWM solar charge controller was the most sought-after solar charge controller for small off-grid solar systems in the 90s. 

However, they had many flaws, including low productivity and high cost. Hence, they were gradually replaced. It’s mostly an MPPT solar charge controller that’s used nowadays.

FAQs

Q. Should I need an MPPT or PWM solar controller?

Since PWM solar charge controllers are now almost replaced by MPPT solar charge controllers, you need MPPT solar controllers. 

Q. Who should deploy a PWM Solar Charge Controller?

The PWM charge controller was intended for smaller solar systems. 

It was suitable for installations where the solar cell temperature used to be moderate to high, i.e., 45°C to 75°C range.

Q. What used to be the rate of productivity in PWM Solar Charge Controllers?

A PWM solar charge controller had a basic charging feature – they worked to cut down the voltage coming from the panel to charge the batteries. 

Their productivity ranged from 68-70%.