Generator kVA · AC Input Current Limit · Loading % · PowerAssist Boost
A generator that is too small overloads the moment the charger activates. A generator that is too large runs at 30% load, destroying rings through wet stacking and diesel fuel dilution. This calculator finds the correct generator kVA for your hybrid off-grid system, calculates the precise AC input current limit to set in your inverter-charger, and shows you exactly what happens at each setting — including the PowerAssist boost window. Built for Victron Multiplus-II, Deye, Growatt, and generic inverter-chargers running in Nigeria and West Africa.
How to use this calculator
Step 01
Enter your AC load
Input the peak AC load that will be running when the generator starts. This is the load your inverter-charger must serve simultaneously while charging the battery bank. Do not use average load — use the simultaneous peak.
Step 02
Select your inverter-charger
Choose your Victron Multiplus-II, Deye, or Growatt model from the list, or enter custom charger specs. The calculator extracts the DC charger current rating and computes the maximum AC demand the charger can place on the generator.
Step 03
Review loading scenarios
The results table shows your generator loading percentage at every common AC input current limit setting (4A to 20A). The recommended setting is highlighted — it keeps loading within the 80% safe operating envelope.
Step 04
Configure your inverter
Take the recommended AC input current limit value directly into VEConfigure (Victron) or the equivalent parameter in your inverter-charger settings. Verify with a clamp meter under combined load before signing off.
Off-Grid Generator Sizing Calculator
Generator kVA · AC input limit · Loading % · PowerAssist boost window
Eneronix
Your Energy, Our Precision
1 Generator Sizing
2 AC Input Limit Guide
Step 1 — System loads & parameters
80%
Step 2 — Inverter-charger
Generator Sizing Result
AC input limit scenarios
Engineering summary
The AC input current limit is the single most important parameter to configure correctly when integrating a generator with an inverter-charger. It caps the total current the inverter-charger draws from the generator — for both the connected AC loads and the battery charger simultaneously. Misconfiguring it is the root cause of the majority of generator integration failures in the field.
// Step 2: AC load current I_load = P_AC_load / V_AC
// Step 3: available for charging I_AC_limit = I_safe − I_load → round down to nearest integer
Where to set it — by inverter brand
Victron Multiplus-II
VEConfigure → Charger tab → AC input current limit Also: Cerbo GX → Device List → Multiplus → AC Input Current Limit
Victron Quattro
VEConfigure → AC1 / AC2 input current limits separately
Deye / Sunsynk
Inverter settings → Grid/Generator → Max charge current from AC
Growatt
ShinePhone app or LCD menu → AC Charge Current
The two ways this gets misconfigured
Mistake 1 — Not setting it at all: The inverter-charger draws its maximum rated charger current from the generator simultaneously with the AC load. A 5kVA generator with a 70A DC charger (Multiplus-II 48/5000) and a 2kW AC load will attempt to draw 2,000W + (70A × 48V / 0.94) = 5,574W — 111% of the generator’s rated output within seconds of paralleling. Generator collapses within 2 minutes.
Mistake 2 — Setting it to the generator’s rated output current: A 5kVA / 230V generator has a rated output current of 21.7A. Setting the AC input limit to 21A still produces combined demand of 2,000W + (21A × 230V) = 6,830W — 136% of rated output. The limit must be set to the safe operating current minus the AC load current, not to the generator’s rated current.
How PowerAssist changes the equation
When the AC load momentarily exceeds the AC input current limit, PowerAssist activates. The inverter supplements the generator output by drawing from the battery bank, allowing the total effective load to reach I_AC_limit × boost_factor × V_AC watts without exceeding the generator’s current limit. This is not free power — the battery discharges during the peak and recharges when the load drops back below the limit. At the default Victron boost factor of 2×, a generator with an 8A AC input limit can momentarily serve up to 8A × 2 × 230V = 3,680W of effective load without the generator seeing more than 8A.
A generator should never be loaded above 80% of its rated output for continuous operation. Above this threshold, the AVR struggles to maintain stable voltage under load transients, the engine governor hunts, and exhaust temperatures rise into the thermal damage range. The 80% rule is not conservative — it is the boundary between controlled and uncontrolled degradation.
Why combined demand matters
The inverter-charger places two demands on the generator simultaneously: the connected AC load and the battery charger. Most installers calculate only the AC load. The charger demand at full current on a 48V system with a 70A charger is 3,574W — nearly matching a 2kW AC load. The combined demand is what the generator actually sees, and the combined demand is what must stay within 80% of rated output.
Wet stacking and minimum load
Diesel generators loaded below 30% of rated output build up unburned fuel deposits on the cylinder walls, turbocharger, and exhaust system — a condition called wet stacking. Over time this causes blue-white smoke, power loss, and premature engine failure. The AC input current limit is also your tool for ensuring the charger keeps the generator above 30% minimum load at all times.
Voltage regulation under load
Generator output voltage sags under combined load, especially on budget units with brush AVR designs. The Victron Multiplus-II has a lower AC input acceptance threshold of 180V. A generator showing 231V at no-load that sags to 187V under combined load sits only 7V above the rejection threshold. The inverter will accept the generator but may drop the AC input after 60–90 seconds if the sustained low-voltage triggers its internal quality monitoring. Measure voltage at the inverter terminals under full combined load — not at the generator output terminals.
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