Windrunner
Member
Hello,
I have a question about fuses and how to calculate their required size. I understand that determining the appropriate fuse size isn't always as simple as multiplication. It often involves considering various factors such as the type of load, ambient temperature, fuse type, and inrush currents, which can complicate calculations.
But let's assume we have the most basic, simple case. From what I have found so far, these are the basic steps:
1.) Determine the Normal Operating Current (In): This is the maximum current that your load is expected to draw under normal operating conditions. You can usually find this information in the device's specifications or by measuring the current using a clamp meter.
2.) Select a Safety Factor (SF): To ensure reliable protection, it's common to apply a safety factor to the normal operating current. A typical safety factor is 1.25, but it can vary depending on the application and standards.
3.) Calculate the Required Fuse Current (If): Multiply the normal operating current (In) by the safety factor (SF). This gives you the required fuse current, ensuring that the fuse won't blow under normal operating conditions but provides adequate protection against overcurrent conditions.
4.) Select the Nearest Standard Fuse Rating: Once you have the required fuse current, you'll need to select the nearest standard fuse rating that is equal to or greater than the calculated value. Fuse ratings are typically available in standard increments, so choose the next higher rating to ensure sufficient protection.
Here is a practical example:
Power supply unit: S8VK-C24024
Power ratings: 240 W
Efficiency (Typical): 230 Vac input: 87%
Voltage: 100 to 240 VAC
Current (Typical): 230 VAC input: 1.3A
Power factor (Typical): 0.92
Calculation 1:
240W/0.87 = 275.86W
275.86W/100V = 2.76A
2.76A/0.92 = 3A
3A*1.25 = 3.75
Fuse size: 4A
Calculation 2:
240W/100V = 2.4A
2.4A*1.25 = 3A
Fuse size: 4A
Calculation 3:
240W/240V = 2.4A
1A*1.25 = 1.25A
Fuse size: 2A
Are these calculations accurate, if so which one? Or am I overthinking it? Have I interpreted the factors and efficiency ratings incorrectly?
The last question is about finding the main fuse size. If I have three circuit branches, do I just add up the sizes of their fuses and multiply by the safety factor (1.25)?
Thank you.
I have a question about fuses and how to calculate their required size. I understand that determining the appropriate fuse size isn't always as simple as multiplication. It often involves considering various factors such as the type of load, ambient temperature, fuse type, and inrush currents, which can complicate calculations.
But let's assume we have the most basic, simple case. From what I have found so far, these are the basic steps:
1.) Determine the Normal Operating Current (In): This is the maximum current that your load is expected to draw under normal operating conditions. You can usually find this information in the device's specifications or by measuring the current using a clamp meter.
2.) Select a Safety Factor (SF): To ensure reliable protection, it's common to apply a safety factor to the normal operating current. A typical safety factor is 1.25, but it can vary depending on the application and standards.
3.) Calculate the Required Fuse Current (If): Multiply the normal operating current (In) by the safety factor (SF). This gives you the required fuse current, ensuring that the fuse won't blow under normal operating conditions but provides adequate protection against overcurrent conditions.
4.) Select the Nearest Standard Fuse Rating: Once you have the required fuse current, you'll need to select the nearest standard fuse rating that is equal to or greater than the calculated value. Fuse ratings are typically available in standard increments, so choose the next higher rating to ensure sufficient protection.
Here is a practical example:
Power supply unit: S8VK-C24024
Power ratings: 240 W
Efficiency (Typical): 230 Vac input: 87%
Voltage: 100 to 240 VAC
Current (Typical): 230 VAC input: 1.3A
Power factor (Typical): 0.92
Calculation 1:
240W/0.87 = 275.86W
275.86W/100V = 2.76A
2.76A/0.92 = 3A
3A*1.25 = 3.75
Fuse size: 4A
Calculation 2:
240W/100V = 2.4A
2.4A*1.25 = 3A
Fuse size: 4A
Calculation 3:
240W/240V = 2.4A
1A*1.25 = 1.25A
Fuse size: 2A
Are these calculations accurate, if so which one? Or am I overthinking it? Have I interpreted the factors and efficiency ratings incorrectly?
The last question is about finding the main fuse size. If I have three circuit branches, do I just add up the sizes of their fuses and multiply by the safety factor (1.25)?
Thank you.
