What size Victron inverter you need comes down to three numbers on Victron’s datasheets: continuous watts, peak watts and the temperature the rating applies to. Victron’s names use VA, which confuses a lot of buyers. A “1200VA” or “3000VA” model does not deliver 1,200 or 3,000 watts continuously. This guide shows how to read the ratings and size a Phoenix or MultiPlus for your loads.
What Size Victron Inverter: VA vs Watts
| Model (120V) | Name rating | Continuous at 25°C | Continuous at 40°C | Peak |
|---|---|---|---|---|
| Phoenix VE.Direct 12/800 | 800VA class | 800W | 650W | 1,200W for 15s |
| Phoenix VE.Direct 12/1200 | 1200VA class | 1,200W | 1,100W | 1,600W for 15s |
| Phoenix VE.Direct 12/1600 | 1600VA class | 1,500W | 1,350W | 2,100W for 15s |
| MultiPlus-II 12/3000/120 | 3000VA | 2,400W | 2,200W | 5,500W |
| MultiPlus-II 24/5000/120 | 5000VA | 4,000W | 3,700W | 9,000W |
Source: Victron Phoenix Inverter VE.Direct 120V and MultiPlus-II 120V datasheets.
Notice the derating: every model delivers less continuous power at 40°C (104°F) than at 25°C (77°F). In a hot van or engine bay, size for the 40°C number.
Step 1: Add Up Running Watts
List everything you might run at the same time and add the watts. A coffee maker and microwave together is the usual worst case.
Step 2: Check Surge
Motors and compressors (fridges, pumps, air conditioners) briefly pull several times their running watts when they start. The peak rating covers that, but only for seconds. Check your appliance’s starting draw.
Step 3: Consider Idle Draw
A bigger inverter usually costs more watts just sitting on. The Phoenix VE.Direct 12/1200 lists 11W at no load on 12V, while the MultiPlus-II 12/3000 lists 13W (3W in Search mode). Over 24 hours that’s roughly 264Wh versus 312Wh. Estimate based on Victron’s zero-load figures.
Step 4: Battery Voltage
For large inverters, higher battery voltage reduces current and cable size. At 12V, a 2,400W load draws roughly 200A or more from the battery before losses. Estimate: 2,400W ÷ 12V = 200A.
Quick Picks (Estimates)
- Laptops, TV, Starlink, small appliances: Phoenix 12/500 to 12/800.
- Blender, small microwave, power tools: Phoenix 12/1200 to 12/1600.
- Microwave + coffee maker, RV air conditioner, shore power charging: MultiPlus-II 3000VA or larger.
Official pages: Victron Phoenix Inverter, Victron MultiPlus-II
VA vs Watts in Plain Terms
VA (volt-amps) is the apparent power an inverter can supply; watts are the real power that does work. For resistive loads such as kettles and heaters, the two are the same. For loads with motors or electronic power supplies, the power factor means they draw more VA than watts. Victron’s model names use VA, while the datasheet tables give continuous watts, which is the number to size against.
Worked Example: A Kitchen Corner in a Van
| Appliance | Running watts (est.) | Starting surge (est.) |
|---|---|---|
| Microwave (1,000W input) | 1,000W | Minimal |
| Coffee maker | 900W | Minimal |
| Blender | 400W | ≈ 800–1,200W briefly |
| 12V fridge on AC adapter | 60W | ≈ 300W briefly |
Estimates based on common appliance ratings. If you only ever run one cooking appliance at a time, the largest running load is about 1,000W, and the Phoenix VE.Direct 12/1200 covers it at 25°C. If the microwave and coffee maker might run together, that’s 1,900W, which points to the MultiPlus-II 12/3000 at 2,400W continuous.
Worked Example: Power Tools on a Job Site Trailer
A circular saw (1,400W running) can briefly draw two to three times that at start-up (estimate). The Phoenix 12/1600’s 2,100W for 15 seconds may handle a soft-start saw, while the MultiPlus-II 12/3000’s 5,500W peak handles it with plenty of room. For tool use, size by peak first, then by continuous watts.
Worked Example: Hot-Climate Derating
A van in summer where the inverter compartment reaches 40°C. The Phoenix VE.Direct 12/1200 drops from 1,200W to 1,100W continuous, and the 12/800 from 800W to 650W. If your biggest load is 1,000W, the 12/1200 still fits at 40°C, but with less margin. Ventilating the compartment keeps the inverter closer to its 25°C rating.
DC Current and Cable Sizing
| Continuous load | 12V current (est.) | 24V current (est.) |
|---|---|---|
| 800W | ≈ 74A | ≈ 37A |
| 1,200W | ≈ 111A | ≈ 56A |
| 2,400W | ≈ 222A | ≈ 111A |
| 4,000W | ≈ 370A | ≈ 185A |
Estimates using 90% efficiency. Size cables and fuses to the inverter’s manual, and keep the battery-to-inverter run short.
Inverter or Inverter-Charger?
A Phoenix is the simpler, smaller choice when you only need AC from the battery. A MultiPlus-II adds a battery charger and an automatic transfer switch, so it powers your outlets from shore or a generator when connected and switches to the battery when not. For RVs and boats that plug in regularly, that makes the MultiPlus-II the more complete choice.
A Simple Sizing Rule
Add up the loads you’ll run together, add about 20–25% headroom, and pick the inverter whose continuous rating at your expected temperature covers that figure. Then check that its peak rating covers the largest motor start.
Low-Draw Options for Light Loads
If your AC use is mostly a laptop, phone chargers and a TV, the smaller Phoenix VE.Direct models keep idle draw low, and ECO mode cuts it further when nothing is running. Many builders pair a small Phoenix for everyday light loads with a larger inverter that’s switched on only for cooking or tools.
FAQ
Is 1200VA the same as 1200W?
For the Phoenix VE.Direct 120V 12/1200, Victron lists 1,200W continuous at 25°C. For larger models such as the MultiPlus-II 3000VA, the continuous rating is lower: 2,400W.
Can a Victron inverter run a microwave?
Usually from about 1,200W upward, depending on the microwave’s input watts (not its cooking watts).
Do I need an inverter or an inverter-charger?
If you plug into shore power or a generator, an inverter-charger (MultiPlus) adds charging and automatic switchover.
Is a bigger inverter always better?
Not necessarily. A larger inverter costs more, takes more space and usually has higher idle draw, so match it to the loads you’ll really run.
Can I run a hair dryer?
Many hair dryers draw 1,200–1,800W on high. Check the label; a 12/1600 or a MultiPlus-II 3000VA covers most models.
Sources: Victron datasheets for Phoenix Inverter VE.Direct 250W–1600W 120V and MultiPlus-II 120V (victronenergy.com); EXPLORIST life, “Every Victron Inverter/Charger COMPARED!”; Broken Signal, “Are Expensive Inverters Actually Better?”.
Related: ALLWEI 1500W Pure Sine Wave Inverter Review, Pro Chaser 400W Car Power Inverter Review, EcoFlow Delta 3 Max Microwave Guide, plus the Victron Energy Guide