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Pulse Width Modulation Charge Controllers Explained

blue-light / 2011-08-09
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Overview of PWM Charge Controller

The technology behind Pulse Width Modulation (PWM) Charge Controllers is one of the most popular charge controller technologies on the market today. A time-tested technology that has been used for many years in solar photovoltaic (PV) systems with batteries; it is also needed for wind, hydro, fuel, or utility grid. PWM Charge Controllers are inexpensive (when compared o other variants such as MPPT or maximum power point tracker charge controller), available in several amperages, and highly durable. Newer model PWM Charge Controllers also come with significant advantages, making them a strong choice in many PV array installations. This article provides an overview of PWM charge controllers from the point of view of solar PV systems.


How does a Pulse Width Modulation Charge Controller Work?

The purpose of Charge Controller is to ensure efficient charging and discharging of system battery (or a bank of batteries). PWMs help to regulate the often inconsistent voltage put out by power sources (for example, solar panels) in order to protect the system batteries from overcharging. When a solar array has the PWM mode activated, the charge controller uniquely handles the job of battery charging by constantly checking the current battery state and self-adjusting accordingly to send only the right amount of charge to the battery.


In essence, this type of charge controller works by reducing the current from the power source according to the battery’s condition and recharging requirements, which is in contrast to on/off charge controllers which suddenly cut off power transfer to minimize battery overcharging. The PWM charge controller does this by checking the state of the battery to determine both how long (wide) the pulses should be as well as how fast they should come.


With that information, the PWM charge controller then self-adjusts and sends the appropriate pulse to charge the battery – it varies the length and speed of the pulses sent to the battery as needed (see Figure). This is essentially a rapid on and off switch. When the battery is nearly discharged, the pulses may be long and continuous, and as it becomes charged, the pulses become shorter or trickled off. This trickle or finish type charging mode is important for systems that can go days or weeks with excess energy during periods when very little of the solar energy is consumed.


This type of charge controller is idea for solar arrays where excess energy is a regular occurrence, and provide several key benefits: higher charging efficiency, rapid recharging, and healthier batteries that operate at full capacity.


Benefits of Using a PWM Charge Controller


Traditional systems for charging solar system batteries relied on on-off regulators to limit battery outgassing during periods of excess energy production, but this often resulted in early battery failures and increased load disconnects. With a PWM algorithm, the charge controller can slowly reduce the charging current to prevent problems like gassing and overheating of the battery.

The benefits of this type of system are significant – a PWM charge controller will increase charging efficiency, allow for rapid recharging, and maintain healthy battery life. In all, a PWM charge controller comes with the following advantages:


Battery Aging Adjustments: By automatically adjusting to the battery’s needs, a PWM charge controller will overcome traditional problems with charge acceptance seen in older batteries.


Battery Gassing and Heating Reductions: By recharging more quickly than other charge controllers, a PWM avoids problems with gassing and heating which damage the battery.


Charge Acceptance Increase: Charge acceptance is a necessity with solar system batteries, though this has typically been a problem in solar arrays. A PWM algorithm, however, increases the charge acceptance of the battery so that more of the energy generated by the array gets captured.


Drifting Battery Cell Equalization: Many PWM charge controllers hold battery cells in better balance through equalization, which evens out the acceptance of charge to avoid capacity deterioration.


High Battery Capacity Maintenance: The state-of-charge should remain high in order to maintain a healthy system and preserve the life of the battery. PWM algorithms provide better battery capacity maintenance due to the increased number of charge/discharge cycles.


• Lost Battery Recovery: Sulfation of lead-acid batteries in solar systems is a significant problem due to extended undercharging, which results in grid corrosion and sulfate crystal formation on the battery’s positive plates. PWM charge controllers have been shown to recover lost capacity over time by deterring sulfate deposit formation, and pushing through corrosion at the interface.


Self-Regulation with Drops in Voltage or Temperature: Older charge controllers can be negatively impacted by temperature effects or voltage drops, creating problems with the final charge of the battery. But a PWM charge controller will taper the charge to minimize these impacts.


Taken together, these PWM advantages can be very attractive to PV owners looking for a simpler way to manage their solar charge. One downside of PWM charge controllers should be noted, however. The sharp pulses created by the controller can create interference for the owner operating radios and TVs. Another disadvantage in pulse width modulation charge controllers is the limitations they create for system growth.


Standards and Warranties Associated with PWM Charge Controllers


Warranties for charge controllers can range depending on the brand and model in question. In general, PWM charge controller warranties range anywhere from two years to five years. Many PWM charge controllers are CE and RoHS listed, though some of the smaller units are not CE listed. Those that are not UL listed are generally not preferred by installers.


In summary, PWM type charge controllers are highly advantageous for solar arrays because of their ability to hold the voltage more constant than other technologies. By reducing the current gradually rather than having a straight on/off control, pulse width modulation charge controllers offer many benefits for battery life and system maintenance.


WELLSEE PWM charge controllers are with WS-C models, you canclick here to view the details. WELLSEE PWM solar controllers have LCD display which shows the charging status and battery status of the whole system.

User Comment

Anonymous user: give point ( 2012-09-22 18:12:49 )
I have a pwm controller, i noted that the middle light flashes YELLOW even when battery is flat from nights use.What's the yellow light mean, also the charging is only 7amps in full sunlight when i have seen 20amps.
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