Why Inverter kVA Divided by 48 V Is Not DC Input Current
By Highidea Power · 22 October 2026 · 3 min read
Estimate steady DC input current from real AC output power, total efficiency at that condition and the voltage actually present at the inverter's DC terminals: I ≈ Pout/(η × Vdc). A kVA label divided by nominal bus voltage omits power factor, losses and voltage variation. The estimate prepares design inputs; it does not select cable size, a fuse or a protective setting.
Highidea's H inverter family includes different DC-input routes for station and telecom applications. Defining the actual source and load helps compare a suitable configuration before the electrical designer approves its feeder.
Establish the power balance
Watts and VA describe different output quantities. Use measured or documented real watts for energy conversion. The load must also meet the inverter's VA and transient limits; the formula does not remove those checks.
Define efficiency as total AC output power divided by total DC input power under the stated condition. Then DC input power is Pout/η. If this efficiency already includes the inverter's internal consumption, adding a separate no-load wattage would count some loss twice.
A different model may explicitly separate conversion-stage losses and fixed consumption. Use that model consistently, including its applicable conditions. Do not combine its terms with an unrelated catalogue maximum efficiency.
Work a voltage sensitivity example
For an illustrative steady-load calculation, assume 900 W AC output, total efficiency 90% at each comparison condition, and no other source of energy. The assumed DC input power is 900/0.90 = 1,000 W.
Assumed DC terminal voltage | Estimated steady DC current |
|---|---|
54 V | 1,000/54 ≈ 18.52 A. |
48 V | 1,000/48 ≈ 20.83 A. |
42 V | 1,000/42 ≈ 23.81 A. |
The same output requires more current at a lower terminal voltage under these assumptions. These voltages and efficiency are invented comparison inputs, not Highidea operating limits or an approved discharge range. Actual efficiency may change with voltage and load.
Keep the terminal boundary explicit
Source voltage and inverter-terminal voltage can differ because of the distribution path. Give the designer the source range, approved path information, equipment maximum input data and the intended operating states. The source and feeder review must address their interaction without assuming that nominal voltage is available everywhere.
Victron's Inverter Smart specification provides an example of input ranges, continuous W/VA, maximum efficiency and no-load consumption listed separately. Its values apply to its own models; the useful lesson is the need for separate, condition-aware inputs.
Add events and operating states
Startup, load changes, protection behavior and recovery may not be represented by a steady estimate. Manufacturer data and a qualified design review must establish the required short-event current and relevant constraints.
Where a product has alternate input paths, name the state being reviewed. Do not assume the DC source supplies all AC demand in every mode, or that a mode transition has the same current as steady operation.
No trial short circuit, undersized lead or deliberate production undervoltage is needed to use this worksheet. Electrical measurements require the approved equipment and safe procedure.
Deliver a feeder-design input package
Record the exact inverter, output W/VA and transient profile, terminal-voltage envelope, efficiency/model basis, manufacturer input limits, operating modes, environmental conditions and unresolved assumptions. Have the responsible electrical designer select conductors, protection and verification against the complete applicable design.
Send Highidea the source/load profile and required DC-to-AC task. We can discuss the suitable product route and the model information the project needs.
Manufacturer example
FAQ
Frequently asked questions
Can maximum efficiency be used for every load?
Only if its applicability is established. A maximum is not automatically the efficiency at the project's actual operating point.
Does this current estimate establish battery runtime?
No. Runtime also depends on usable stored energy, the changing task and the complete configuration conditions.
Is source nominal voltage sufficient for the calculation?
No. Identify the applicable terminal-voltage condition for each operating case and retain the manufacturer’s limits. An estimate based on nominal voltage can understate current at a lower operating voltage. It also cannot establish transient demand, voltage drop, conductor suitability or the source’s ability to support that case.
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