What Is PWM and How Does It Work in a 12V Setup?

When it comes to off-grid power, you’ve probably come across the acronym “PWM” – especially when researching solar charge controllers. But what exactly is PWM, how does it work, and is it the right choice for your setup? In this article, we’ll break it down in simple terms so you can make informed decisions for your 12V system.

What Does PWM Stand For?

PWM stands for Pulse Width Modulation. It’s a technology used in many electrical systems, but in the world of 12V and solar power, PWM most commonly refers to a type of solar charge controller. Its job is to manage the flow of power from your solar panels into your battery – protecting it from overcharging, helping to maintain a healthy voltage level, and extending its lifespan.

How PWM Works

PWM charge controllers work by rapidly switching the connection between the solar panel and battery on and off, many times per second. By adjusting how long the “on” pulse lasts compared to the “off” pulse, it controls the amount of current sent to the battery.

• When the battery is low, the PWM controller allows a longer “on” time, pushing more current through.
• As the battery approaches full charge, the controller shortens the pulse duration, delivering less current to prevent overcharging.

This pulsing action is where “pulse width modulation” gets its name. It’s like tapping your foot on a hose – a quick tap lets out a little water, a long press lets out more. It’s simple, effective, and helps regulate charge in real-time.

PWM vs MPPT: What’s the Difference?

PWM (Pulse Width Modulation) and MPPT (Maximum Power Point Tracking) are the two main types of solar charge controllers – and they work quite differently.

A PWM controller sends energy from your solar panel to your battery by rapidly switching the power on and off. It’s simple, cost-effective, and works best when the solar panel voltage is close to your battery voltage (for example, a 12V panel with a 12V battery).

An MPPT controller, on the other hand, is more advanced. It constantly tracks the “maximum power point” of your solar panel to convert excess voltage into usable current. This means it can pull more power from your panels – especially useful in cloudy conditions, colder weather, or when you're using higher-voltage solar panels.

Here’s a quick comparison in plain terms:

• Technology: PWM is simpler and uses rapid pulsing to regulate charge. MPPT actively converts power to improve efficiency.
• Efficiency: PWM offers decent efficiency (up to ~75%), while MPPT can reach up to ~98%.
• Solar Panel Compatibility: PWM requires your panel voltage to closely match your battery voltage. MPPT can work with much higher panel voltages.
• Cost: PWM controllers are generally cheaper. MPPT controllers are more expensive but often worth it for larger or more complex systems.
• Best Use Case: PWM is ideal for small, budget-friendly setups. MPPT is better suited to larger systems or anyone looking to maximise solar performance.

In short, if you’re after simplicity and value, PWM is a solid choice. But if you're chasing maximum solar efficiency or working with higher-voltage panels, MPPT might be the better fit.

When Is PWM a Good Choice?

PWM solar controllers are ideal in the following scenarios:

• You’re running a small 12V setup, such as a single AGM or lithium battery.
• Your solar panel’s rated voltage is close to your battery’s voltage (e.g., 12V panel with 12V battery).
• You want a budget-friendly, reliable solution for basic off-grid camping or caravan use.
• You’re happy with slightly lower charging efficiency in exchange for simplicity.

For many off-grid travellers, a quality PWM controller is more than enough to keep your batteries topped up and your essentials running – especially when paired with a well-matched solar panel.

Pros of Using a PWM Charge Controller

• Cost-Effective – Great for entry-level or budget-conscious setups
• Reliable & Durable – Fewer moving parts and simpler circuitry mean fewer things can go wrong
• Easy to Use – Plug it in, set your battery type, and you’re good to go
• Works Well With AGM & Lithium – Modern PWM controllers like ours are fully compatible with KickAss lithium and AGM batteries

Cons of Using a PWM Charge Controller

• Lower Efficiency – Especially noticeable if you’re using high-voltage panels or charging in low light
• Requires Voltage Matching – Your panel must closely match your battery voltage (e.g., 12V panel with 12V battery)
• Not Ideal for Larger Systems – If you’re running multiple panels or large battery banks, MPPT is usually the better option

How to Get the Most Out of Your PWM Setup

If you’re using a PWM controller, there are a few tips to keep things running at peak performance:

1. Match your solar panel voltage to your battery voltage.
2. Use quality cabling with the correct gauge to minimise voltage drop.
3. Position your panels well to maximise sun exposure.
4. Keep your panel clean – even a bit of dust can affect charging efficiency.
5. Choose a reliable PWM controller with features like battery type selection, temperature sensors, and built-in safety protections.

Final Thoughts

PWM may not be the flashiest tech on the market, but it’s a reliable, affordable, and effective solution for many off-grid power users. If your solar and battery voltages are well matched and you don’t need the extra bells and whistles of an MPPT, PWM can be the perfect choice for weekend getaways, caravanning, or basic off-grid camping setups.

Still unsure which solar controller is right for your setup? Get in touch with our expert team – we’re here to help you build the ultimate 12V system for your adventures.