Inverter names and data plates often use volt-amps (VA), while appliances are commonly described in watts. Understanding the difference helps prevent an inverter from being sized from the model name alone.
Volts and amps
Voltage is electrical potential and current is measured in amps. In a simple DC calculation, volts multiplied by amps gives watts. AC loads may also involve power factor, so apparent power in VA and real power in watts are not always equal.
VA versus watts
VA describes apparent power. Watts describe real power consumed or delivered. Some inverter model names use a VA rating, and the continuous real-power rating may be lower. The original Tech Tip uses the example that a 3,000 VA inverter may provide about 2,400 watts of continuous real power under specified conditions.
That relationship is not universal. Check the current data sheet for the exact inverter model, output voltage, ambient temperature, and duration.
Continuous and peak ratings
Continuous output is the load the inverter can support under its stated test conditions. Peak or surge output is available only for a limited time and is intended to help start compatible loads. A large peak number does not mean the inverter can supply that power continuously.
Load type matters
Motors, compressors, transformers, and some electronic loads can have starting current, reactive power, or waveform sensitivity that a simple wattage label does not reveal. Use measured data or manufacturer specifications for the appliance whenever possible.
Do not forget the DC side
A larger AC load requires substantial battery current. Battery-bank capability, DC cable size, fuse and breaker ratings, voltage drop, state of charge, temperature, and inverter efficiency all affect performance.
Size an inverter from the complete load profile and the exact product data sheet—not from VA, watts, or peak output alone.
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