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GermanThe process of calculating inrush current involves three steps, critical for protecting electrical equipment from the high surge of current when switched on. Inrush current, typically 2 to 3 times the steady state current of a device, can spike up to 30 times in devices like electric motors or transformers. Despite modern circuit systems’ efficiency and lower impedance, inrush current remains a concern, often leading to equipment overheating. Inrush Current Limiters (ICLs) are essential for controlling this surge and maintaining equipment safety.
To select an appropriate ICL, one must understand various parameters, including maximum output power, input voltage, reset time, single or three-phase system, filter or link capacitor value, scope trace of inrush current, and ratings of fuse, circuit breaker, and diode bridge if applicable.
Step 1: Calculating Minimum Resistance
This calculator is used to determine the minimum resistance required in a circuit to limit the inrush current to a specified maximum value. It’s important for designing circuits that can handle initial high currents without damage.
Where Voltage Peak (VDC) = Voltage RMS × √2
Example Calculation:
Given:
Voltage VAC = 230 V
Max Allowable Inrush Current = 5 A
Calcualtion:
Calculate Voltage Peak (VDC): 230 V × √2 ≈ 325.22 V
Resistance = 325.22 / 5
Resistance ≈ 65.044 ohms
Step 2: Calculating Steady State Current
This calculator is used to determine the steady-state current in an electrical circuit, based on the power and voltage of the system, and considering the system’s efficiency.
Example Calculation:
Given:
Power = 500 W
Voltage = 220 V
Efficiency = 90%
Calculation:
Convert efficiency to a decimal: 90% = 0.9
Current = (500 / 220) × 0.9
Current = 2.2727 × 0.9
Current ≈ 2.0454 amperes
Step 3: Calculating Total Energy
This calculator determines the energy rating of an inrush current limiter. It’s particularly useful in electrical circuits to understand the energy dissipation characteristics of a limiter.
Example Calculation:
Given:
Voltage = 230 V
Capacitance = 50 μF
Calculation:
Convert capacitance to farads: 50 μF / 1,000,000 = 0.00005 F
Energy = ½ × 0.00005 × (230)2
Energy ≈ 1.3225 joules
Based on the above example calculations, we would have recommended either the Ametherm SL03 22102 or the Ametherm SL05 4R003. This ICL has a resistance of up to 220Ω (at 25°C), a maximum steady state current of 2A (up to +65°C) and a maximum total energy of 2J. If you would like to discuss any of your Inrush Current Limiter requirements, please contact one of our engineers today.
Popular manufacturers
The below table lists some of the inrush current limiter series available through us by Ametherm, along with their specifications:
| Ametherm SL Series | ||||
|---|---|---|---|---|
| Series | Maximum Steady State Current | Resistance at +25°C | Maximum Capacitance at 120VAC | Maximum Recommended Energy |
| SL03 | 1A to 2A | 10Ω to 220Ω | 100μF | 2J |
| SL05 | 0.25A to 3A | 4Ω to 120Ω | 200μF to 340μF | 3J to 12J |
| SL08 | 1.1A to 3A | 4Ω to 120Ω | 550μF to 697μF | 8J to 12J |
| SL10 | 1A to 5A | 10Ω to 30Ω | 700μF to 2000μF | 2J to 120J |
| SL12 | 1A to 10A | 1Ω to 220Ω | 1389μF to 2778μF | 10J to 60J |
| SL15 | 2A to 10A | 1Ω to 220Ω | 2778μF to 4167μF | 35J to 55J |
| SL18 | 3A to 12A | 0.7Ω to 47Ω | 4500μF to 8335μF | 65J to 120J |
| SL22 | 1A to 16A | 0.5Ω to 220Ω | 3473μF to 10000μF | 2J to 160J |
| SL32 | 15A to 36A | 0.25Ω to 10Ω | 6946μF to 20839μF | 100J to 300J |
| Ametherm MS Series | ||||
|---|---|---|---|---|
| Series | Maximum Steady State Current | Resistance at +25°C | Maximum Capacitance at 120VAC | Maximum Recommended Energy |
| MS12 | 2A to 2A | 150Ω to 150Ω | 7500μF to 7500μF | 110J to 110J |
| MS15 | 4.2A to 4.2A | 30Ω to 40Ω | 9300μF to 9300μF | 135J to 135J |
| MS22 | 2A to 8A | 0.5Ω to 220Ω | 5100μF to 16400μF | 75J to 240J |
| MS32 | 6A to 40A | 0.5Ω to 50Ω | 13500μF to 20700μF | 250J to 300J |
| MS35 | 10A to 50A | 0.5Ω to 20Ω | 34000μF to 62000μF | 500J to 800J |
| Ametherm AS Series | ||||
|---|---|---|---|---|
| Series | Maximum Steady State Current | Resistance at +25°C | Maximum Capacitance at 120VAC | Maximum Recommended Energy |
| AS32 | 6A to 36A | 0.5Ω to 50Ω | 17500µF to 20700µF | 250J to 300J |
| AS35 | 10A to 50A | 0.5Ω to 20Ω | – | 500J to 800J |
Users are hereby informed that Rhopoint accepts no responsibility for any inaccuracies or issues that may arise from the use of our online calculators. All data and results should be independently verified prior to their application in any projects or calculations.
