Fuse Selection
Choose a fuse rating from continuous load current, ambient temperature, and surge I²t; check derating, melting integral, and voltage rating to avoid nuisance blowing.
Key points
Fuse Selection: Choose a fuse rating from continuous load current, ambient temperature, and surge I²t; check derating, melting integral, and voltage rating to avoid nuisance blowing. Formula: In ≥ Iload/(derating × temperature factor) | I²t_fuse ≥ 2 × I_inrush²·t_inrush. Enter parameters on the DD-CAT IDE online tool page to get results instantly, with a calculation-model diagram that updates with the inputs. A fuse rating is not the operating current; apply continuous-current derating (often 75% for UL) and the ambient-temperature factor. Check capacitive-load and motor-start surges by I²t: fuse I²t should exceed surge I²t with at least 2× margin, otherwise it blows at power-up.
Inputs
In ≥ Iload/(derating × temperature factor) | I²t_fuse ≥ 2 × I_inrush²·t_inrushCalculation model (updates with parameters)
| Ambient-temperature derating factor | 95 % | 按 25°C 为 100% 的近似曲线 |
| Combined derating factor | 71 % | 75% 持续Derating × Temperature系数 |
| Required minimum current rating | 2.807 A | Iload / Combined derating factor |
| Recommended fuse rating In | 3.15 A | 按常用额定current档向上取整 |
| Actual load ratio | 63 % | 建议 ≤75~80%，当前 2 A / 3.15 A |
| Surge I²t (actual) | 0.500 A²·s | I_inrush² × t |
| Required fuse I²t (with margin) | 1.000 A²·s | 按 2× 浪涌 I²t 估算 |
| Selected I²t check | 未填额定Value | 填入手册 I²t 可自动校核 |
| Voltage rating check | 通过 ✓ | 32 V ≥ 24 V |
Engineering notes
- A fuse rating is not the operating current; apply continuous-current derating (often 75% for UL) and the ambient-temperature factor.
- Check capacitive-load and motor-start surges by I²t: fuse I²t should exceed surge I²t with at least 2× margin, otherwise it blows at power-up.
- Use DC-rated fuses for high-voltage DC; breaking capacity must exceed the prospective short-circuit current, with TVS / MOV coordination if needed.
FAQ
- What is Fuse Selection for?
- Choose a fuse rating from continuous load current, ambient temperature, and surge I²t; check derating, melting integral, and voltage rating to avoid nuisance blowing.
- What is the formula for Fuse Selection?
- Core formula: In ≥ Iload/(derating × temperature factor) | I²t_fuse ≥ 2 × I_inrush²·t_inrush. The tool returns results instantly using this formula and the selected parameters.
- What engineering notes should I keep in mind when using Fuse Selection?
- A fuse rating is not the operating current; apply continuous-current derating (often 75% for UL) and the ambient-temperature factor. Check capacitive-load and motor-start surges by I²t: fuse I²t should exceed surge I²t with at least 2× margin, otherwise it blows at power-up. Use DC-rated fuses for high-voltage DC; breaking capacity must exceed the prospective short-circuit current, with TVS / MOV coordination if needed.