MPPT VS PWM Comparison of Solar Charge Controllers

Learn what MPPT and PWM are.

Explore the key differences between MPPT and PWM.

Learn what to pay attention to when designing MPPT and PWM circuits.

When there are different ways to do the same job, these methods usually have their own advantages and disadvantages. But when specific job requirements and resources are carefully considered, one often stands out as the better choice.

The same goes for solar charge controllers. In this work, two common choices are MPPT vs. PWM. In this article, we discuss the differences between the two technologies, help you decide which is a better fit, and provide design recommendations for using both technologies.

What are MPPT and PWM?

MPPT (maximum power point tracking) and PWM (pulse width modulation) are both technologies that power solar charge controllers. PWM does this by varying the duty cycle of the connection to charge the battery from the solar panel.

PWM charging acts like a switch where a MOSFET is used to bridge the connection between the solar panel and the battery. Typically a microcontroller is used to control the charging phase by varying the duty cycle of the charging current. Normally, PWM charging goes through three stages: strong charging, equalizing charging, and floating charging.

The strong charging stage is when the charger allows a reasonably large amount of current to pass through to charge the battery. The next stage is equalization charging, allowing the battery voltage to stabilize before releasing a constant current. Finally, the float stage ensures that losses from battery self-discharge are compensated for through trickle charging.

MPPT chargers also go through these stages when charging batteries. However, it does this dynamically by regulating voltage and current simultaneously, allowing for maximum charging efficiency.

MPPT and PWM solar chargers

MPPT and PWM solar chargers differ in various aspects.

1►

run

The charging voltage and current produced by the MPPT charger are related to the maximum power on the solar panel's I-V curve. The charging process also takes into account the temperature, angle and exposure of the solar panels.

And the PWM charger behaves like a switch between the solar panel and the battery. It's not designed to track maximum power on the I-V curve, so it will run strictly no matter what.

2►

efficiency

MPPT chargers are much more efficient than PWM chargers. MPPT chargers can be as efficient as 99%, but PWM charging is only 50%-75% efficient. Let's explore why this happens.

A PWM charger behaves like a switch, so the solar panel will always charge at the voltage of the battery. A solar panel with an open circuit voltage of 24V, when connected to a PWM charger, will pull the voltage down to almost the same voltage as the battery's 12V. This reduces its charging efficiency by 50%.

On the other side, the MPPT adjusts the charging voltage and current to the maximum deliverable power. It behaves like a DC-DC transformer rather than a switch, which allows it to minimize charging losses.

3►

cost

PWM chargers are less expensive than MPPT chargers due to their simpler construction. A PWM charger typically costs less than $100, while an MPPT charger can cost up to several hundred dollars.

Design MPPT or PWM

Key considerations when charging

Whether designing around MPPT or PWM charging circuits, there are a few points to note. Both circuits utilize high-frequency switching, so care should be taken during design to reduce EMI emissions. Shorten trace lengths and place components close together to minimize loop inductance.

Both types of chargers can be designed to handle high charging currents from 1A to 60A. To do this, make sure the traces are wide enough to handle the maximum current. Otherwise, the traces may overheat or break when stressed.

Whether it is an MPPT or PWM charging circuit, it will be of great benefit to the design if it can be checked using efficient PCB design and analysis software. inspectAR software uses augmented reality (AR) to interactively evaluate and improve the PCB design process, making PCB inspection, debugging, rework and assembly easy and accurate.

The image above shows the inspection of AR stack-up fabrication in inspectAR software. Using AR technology, engineers or manufacturing technicians can compare individual devices, traces, subcircuits, or entire circuit boards with design specifications at any time during the manufacturing process, and view technical manuals and add comments and comments at any time.