Current Fuse, Car Fuse Box Wiring Harness Kit assembly

Fuse box & fuse holder wiring harness Kit assembly: fuse block, fuse adapter, relay, ls swap, fuse bypass switch, current collector, fuse relay wiring harness.

Before discussing how to design a fuse box, let’s first talk about the matching of wires and fuses. This will also help us better understand the fuse box problem later.
First, we need to determine the capacity of the fuse based on the current characteristics of the load and the working environment of the fuse, and then calculate the required wire diameter based on the load characteristics and the environment of the wiring harness. For circuits protected by fuses, it is necessary to confirm the matching between the wiring harness and the fuse before determining the wire diameter.
The calculation of fuse capacity is actually the calculation of rated operating current. However, if the load contains inrush current, the inrush current needs to be calculated. After the capacity is initially determined, the life of the fuse is checked for the inrush current until its capacity is finally determined.

Current Fuse, Car Fuse Box Wiring Harness Kit assembly

Rough selection can be divided into:
a. Fuse capacity > working current of electrical appliance or motor stall current (generally < 70% of fuse capacity)
b. Wire capacity > fuse capacityelectrical appliance (generally <85% of capacity at wire grade temperature)
c. Switching capacity > fuse capacityelectrical appliances (generally <85% of switching capacity)
d. Relay capacity > fuse capacity electrical appliances (generally < 85% of relay capacity)
e. Connector terminal > fuse capacityelectrical appliance (generally <85% of terminal capacity)
The calculation of wire diameter starts with the calculation of the rated current, which needs to consider the load characteristics, the ambient temperature of the wire harness, and the number of power loops in the same branch wire harness. For circuits protected by fuses, a matching calculation is required to ensure that the time it takes for the conductor to start smoking is greater than the time it takes for the fuse to blow. Finally, check the short-circuit current to ensure that the short-circuit current is enough to cause the fuse to blow in time when a fault occurs.

Current Fuse harness Kit assembly

Fuse selection:
In electrical circuits, the main function of fuses is to protect wires. If there is a current flowing through it, it will reach its fusing temperature within a period of time and interrupt the circuit.
The time it takes for a fuse to blow is related to its own temperature rise, which depends on the ratio of rated current/rated power (I/IF): the larger this value, the faster the fuse will blow.
The characteristics of a fuse are composed of two curves, and there are relevant standards (DIN, ISO, JASO)

Let’s give an example to illustrate how this curve is represented:
For 30A current, this fuse will blow in 0.15s to 5s.
For 90A current, this fuse will blow in 0.02s to 0.10s.
According to the speed of fusing time, they can be divided into fast-blow fuses and slow-blow fuses.

fuse relay wiring harness Kit assembly

Choice of wire type:
The wire type used in wire harness design focuses on the environment and function of the wire harness. For example: the ambient temperature around the engine is high, and there are a lot of corrosive gases and liquids. Therefore, be sure to use high-temperature-resistant, oil-resistant, vibration-resistant, and friction-resistant wires. The wires on the trunk lid must maintain their elasticity at low temperatures, so cold elastic wires must be used to ensure their normal operation. The wires on the automatic transmission must be resistant to high temperatures and hydraulic oil, and their temperature stability must be good. Weak signal sensors should use shielded wires, such as knock sensors, crankshaft position sensors, ABS wheel speed sensors, etc. The door inner wire has high bending resistance requirements.

The ambient temperature of the car plays a vital role in the selection of wires. Each area on the vehicle has its own ambient temperature, typically 85°C for the cabin area and 105°C for the engine compartment. But each car manufacturer has its own ambient temperature standards.
The wires commonly used in automobile wiring harnesses usually use multi-stranded copper wires, and the insulation is PVC insulation material. The wires used in wiring harnesses must be temperature-resistant, oil-resistant, wear-resistant, waterproof, anti-corrosion, anti-oxidation, and flame-retardant.
Commonly used wire types in automotive wiring harnesses include Japanese standards (AVSS, etc.), national standards (QVR), German standards (FLRY), American standards and other series. AVSS (AVS) wires are characterized by thin insulation and good flexibility. QVR is characterized by thick insulation, relatively soft and good ductility. German standard wire insulation is thinner and more flexible. American standard wire insulation is generally made of thermoplastic or thermosetting elastomer, and some are processed by irradiation technology. Appropriate types of wires can be selected according to user needs and different working environments.

Calculation of wire diameter
After determining the capacity of the fuse, you can calculate and select the wire diameter. First determine the material of the wire according to the ambient temperature of the wiring harness and then calculate the required wire diameter. Generally divided into two situations: no fuse protection and fuse protection. Circuits without fuse protection are generally non-power supply circuits such as signal connections. When designing, it is necessary to consider the rated operating current, the voltage drop due to line impedance, and the temperature rise of the pulse current.
For lines protected by fuses, in addition to the above calculations, it is also necessary to check the matching of the wiring harness and the fuse and check the short-circuit current. The algorithm is as follows.
The general approach is to make the fusing characteristic curve of the fuse based on the wire smoke characteristic curve. If the abscissa is current and the ordinate is time, the heating characteristic curve of the wire should be above the fusing characteristic curve of the fuse without crossing. That is, the heating time of the wire under any heating current must be greater than the fusing time of the fuse.
In fact, for ordinary vehicle low-voltage fuses and wiring harnesses, to meet the above conditions, you only need to ensure that the maximum current of the wire without smoke is greater than the minimum melting current of the fuse.
The minimum melting current of a fuse is generally calculated as 135% of the rated current of the fuse.
For the verification of short-circuit current, calculate the impedance of the wire according to the length of the wire, plus the impedance of the node, which is the total impedance of the loop, and then calculate the short-circuit current from this. To ensure that the fuse can be completely disconnected in the event of a short circuit, the general short-circuit current value should be greater than 350% of the fuse’s rated current. If the value is lower than this value, test verification or re-selection of wires is required.