VA vs Watts in Victron Inverters: What's the Difference?
VA (Volt-Amperes) and Watts measure different aspects of electrical power in Victron inverters. While Watts indicate real power consumption, VA represents apparent power — and this difference is crucial when sizing your inverter for motor-driven appliances.
What's the difference between VA and Watts?
Watts (W) measure real power — the portion of electrical effort your appliances turn into useful work like heat, motion, or light. This is what shows up on your power bill and what your batteries actually have to supply.
VA (volt-amperes) measure apparent power — the total electrical effort the inverter's switching stage has to deliver, whether or not it ends up doing useful work. For purely resistive loads like a kettle, a heater, or an incandescent bulb, every volt-amp becomes a watt and the two numbers are equal. For loads with motors or transformers — fridges, pumps, microwaves, power tools — some of the effort is shuffled in and out of windings rather than doing work, so the watt figure ends up below the VA figure.
Power factor links the two
Power factor (PF) is the ratio between real power (W) and apparent power (VA):
Watts = VA × Power Factor
A resistive load has a PF of 1.0 — VA and W are the same number. A typical mixed household load sits around 0.8, which is exactly the assumption Victron uses when publishing the continuous W rating alongside the VA rating (3000 VA × 0.8 = 2400 W). That's the gap you see in the specs.
One nuance worth knowing: most modern laptops, phone chargers, and LED drivers sold in NZ now have built-in power factor correction and run close to PF 1.0. The gap matters most for fridges, freezers, pumps, microwaves, induction cooktops, and motorised tools.
Why Victron rates in VA
VA is the honest engineering number. It describes what the inverter's switching stage can deliver regardless of what you plug in. If a manufacturer rates an inverter only in watts, they've quietly chosen an assumed power factor — and different manufacturers pick different ones, which makes head-to-head comparison unreliable. Victron sidesteps the assumption by publishing both: the VA rating, and the continuous watts at three temperature points.
The second reason your "3000" may not give you 3000 watts: heat
Inverter electronics get less efficient as they warm up, so continuous wattage falls with ambient temperature. The Phoenix Smart 48/3000, for example:
- 2400 W continuous at 25°C
- 2200 W continuous at 40°C
- 1700 W continuous at 65°C
If your inverter lives in a sealed compartment, a vehicle in summer, or an unventilated cupboard, plan for the warmer numbers.
When does the VA–Watt gap matter most?
The gap becomes important when you're running:
- Motor-driven appliances: fridges, freezers, fans, pumps, power tools, air-con compressors
- Transformer-based gear: some battery chargers, older audio equipment, welders
- Older or unbranded switch-mode power supplies without active power factor correction
For purely resistive loads — kettles, heaters, hot-water elements, incandescent lights — you can read the watt rating straight off the appliance and the VA rating barely matters.
Startup surges are usually the real sizing driver
Motors can draw 3–7× their running wattage for a fraction of a second when they kick in. A 150 W fridge can briefly pull 1000 W. Victron inverters tolerate a short peak well above their continuous rating (see the "peak power" figure on each datasheet — but note that figure is a brief pulse measured in milliseconds, not a sustained capacity). For systems with multiple motor loads that could start simultaneously, headroom over your running total matters more than the PF gap does.
How to size an inverter
- Add up the running watts of everything you might run at once. Use the nameplate W rating on each appliance.
- Check for startup surges. List anything with a motor and make sure your inverter's continuous rating, plus its peak surge capability, comfortably covers a worst-case moment where one (or two) of those motor loads start while everything else is still running.
- Match against continuous W at the right temperature — not the VA on the box, and not the 25°C figure if your inverter will actually live somewhere that runs at 40°C.
Worked example: small off-grid cabin
A small cabin running LED lighting, a 230 V bar fridge, a laptop, and the occasional cordless tool on charge:
| Load | Running W | Notes |
|---|---|---|
| LED lighting | 60 W | Resistive — no PF gap |
| Laptop charger | 90 W | Modern PFC — close to PF 1.0 |
| Bar fridge (running) | 100 W | Brief startup surge around 600 W |
| Cordless tool charger | 60 W | — |
| Running total | 310 W |
The running load is well under 500 W. But the moment the fridge cycles on, total demand momentarily jumps past 800 W. A Phoenix 12/1200 (1200 VA, 1000 W continuous at 25°C, with a peak rating of 2200 W) handles that comfortably. Step up to a 24/2000 or 24/3000 once you add a microwave, induction hob, or any kind of pump.
A few models from the current Victron range
- Phoenix 12/375: 375 VA / 300 W continuous at 25°C
- Phoenix 12/800: 800 VA / 650 W continuous at 25°C
- Phoenix 12/1200: 1200 VA / 1000 W continuous at 25°C
- Phoenix Smart 48/3000: 3000 VA / 2400 W continuous at 25°C
The continuous W rating is always lower than the VA rating across the range — that's the 20% power factor allowance built in. Specific figures vary between the Phoenix VE.Direct, Phoenix Smart, MultiPlus, and Quattro ranges, so the spec sheet on each product page is the source of truth.
Want help sizing your system?
If you'd rather not work this out by hand, the AnyKit Solar Design Tool sizes your inverter alongside your panels and batteries, using NZ conditions and realistic power factors. Or send us a list of the appliances you want to run — with brand and model where you have them, and how often they'd run together — and we'll spec it for you.