Inverters can generally be divided into two types: sine wave and square wave. Some engineers also prefer to categorize quasi-sine waves separately, resulting in three classifications: sine wave, quasi-sine wave, and square wave.

1. Sine Wave: Its output waveform resembles that of standard utility power, but with superior quality. Therefore, this type is suitable for all electrical appliances. However, they come at a higher price point—a 300W model typically costs over 800 yuan. They are commonly used in high-precision equipment, detection, R&D, military applications, and similar fields. For household appliances, such high-specification units are unnecessary, making pure sine wave inverters less common in the market. They are often custom-ordered by buyers.

2. Quasi-Sine Wave: This is a mainstream product offering better conversion efficiency and cost-effectiveness than pure sine wave inverters. While its load compatibility is inferior to pure sine wave models, it performs comparably for household appliances like televisions, computers, audio systems, and motors under 1000W. Its lower price makes it the dominant choice in low-power inverter applications.

3. Square Wave: This type outputs a square waveform. It has poor load-bearing capacity and generates significant harmonic components with inductive loads, resulting in considerable noise when powering motors or televisions. These products were historically built using utility-frequency transformers and are now obsolete.

The above analyzes the waveforms of three different inverters. While understanding these is beneficial, buyers primarily seek to determine if an inverter suits their needs.

Therefore, before purchasing an inverter:

1. Confirm the power rating of your electrical appliances.

2. Determine their peak power requirements.

3. Verify input voltage, current, and frequency.

Points 1 and 3 are typically labeled on the appliance. The most challenging factor to determine is peak power, yet it is the most critical consideration when purchasing an inverter. Even if your inverter has sufficient rated power, it will fail to start if the peak power is inadequate.

What is peak power? Peak power refers to the power required to start an appliance the instant it is turned on. For example, when you switch on a TV or or a power drill, you'll hear a loud noise and notice voltage spikes when switching them on—these are the surge phenomena occurring at startup. Therefore, peak power differs from rated power. Generally, resistive loads like light bulbs don't have peak power issues, but inductive or capacitive appliances typically have peaks 3 to 5 times higher. This is why we must pay attention when purchasing inverters, as they are rated for double the peak power. For example, a TV rated at 75W nominal power has a peak of 5 times that, meaning its peak power is 350W. A 100W inverter won't power it because it only handles 200W peak. You need a 300W inverter with 600W peak capacity to handle it.

Regarding appliance peak power: - Light bulbs have no peak power; a 100W inverter can power a 100W bulb. - TVs have 3-5x peak power; a 75W TV requires over 300W to start. - Drills have 3x peak power. - Computer monitors typically have 6x or higher peak power. Thus, a 300W inverter struggles to start them. For laptops, typically 70W, a 150W inverter can handle them since they usually have a 3x peak (210W peak). For phone chargers, cameras, and other digital devices, a 100W inverter is generally sufficient.

Numerous inverter brands exist on the market, but a significant portion are private-label products. Among these private-label units, some are marketed as “high-power”—for instance, a 300W unit labeled as 500W, or a 500W unit labeled as 1000W. How can we verify their true specifications? Generally, you can determine this by examining its size, weight, and peak power rating. Since 99% of commercially available inverters share the same design principles, if an inverter of the same rated power is unusually compact, lightweight, or lacks sufficient peak power, it can be considered overrated.

Regarding inverter runtime, I'm referring to how to determine a battery's operational duration under a fixed load. First, let me clarify: battery capacity is standardized in ampere-hours (AH). An ampere-hour represents the maximum discharge current a battery can deliver over one hour. For example, a battery rated at 100AH can sustainably output a maximum current of 100A for one hour. Therefore, we can use this value to calculate how long a battery will power a load.

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Battery capacity × current