Solar panel fuses - the functions and choosing tips

1. The importance of solar panel fuses

Unlike typical power distribution and applications with controllers, solar panel fuses will be subject to special conditions: long-term exposure to the environment can produce abnormal ambient temperatures, which in turn affects the performance of solar panel fuses, also the conductor and size selection.

Additionally, unlike conventional circuits that typically have a continuous load output, solar panel modules require additional considerations when sizing solar panel fuses if they are required to produce continuous current. Taking these conditions into account, this requires sizing the solar panel fuses in the kit before installing the system.

The structure of a solar panel system is basically as the figure below:

2. When is a fuse required and when is it not?

Solar panel fuses are used to protect cables and PV modules from line, line grounding, and mismatch faults. Its sole purpose is to prevent fire and safely open a faulty circuit in the event of an overcurrent.

However, there are certain situations where solar panel fuses are not required:

• Single series connection: No need for solar panel fuses
• Two wires in parallel: No need for solar panel fuses
• Three or more wires in parallel: Solar panel fuses needed

3. Choose the right fuse for your system components

Typically, in a complete solar power generation system, solar panel fuses can be added between different components, such as from the solar panel array to the charge controller, from the controller to the storage battery, and from the battery to the inverter.

The requirements for solar panel fuses may differ for each part of the devices, with the exact rating depending on the amperage of those device and wires.

• Fuses for the solar panel

Typically, those solar panels of 50 watts and above have 10 wires, which can handle current up to 30A. When you have more than 3 panels connected in parallel, each panel can draw up to 15A, and if one panel shorts out, the whole 40-60A will be directed to that shorted panel.

This would cause the wires leading to the panel to be well over 30A, creating a fire hazard. If solar panels are wired in parallel, each panel will need a 30A fuse. If your electrical panel is less than 50 watts and only uses 12 gauge wire, you will need a 20A fuse.

• Combiner box fuses in parallel systems

In a parallel system, a combiner box is used to secure the fuse/circuit breaker to each panel. When sizing this combination fuse, we must first determine the worst case current flow based on our particular panel. If we take a 195 watt 12 volt panel as an example and look at the short circuit current (Isc) we will see that it is rated at 12.23A.

In case of continuous load, add a factor of 25%, so the current increases to 15.28A per panel. If there were 4 panels in this parallel setup, the combined current could theoretically be as high as 61.15A.

Through experimentation, an 8 AWG wire set (minimum) from the combiner box to the charge controller is sufficient as it can handle 60A. In this case, a 60A fuse or circuit breaker should be used to protect the wire set. This is also consistent with the maximum capacity of the selected charge controller.

• Fuses from charge controller to battery

With a pulse width modulated (PWN) charge controller, the worst case scenario is that the current going in and out of the controller is the same, so the fuse and wire sizes can match. For example, a 60A fuse is recommended for a 60A PWM charge controller, placed between the unit and the battery pack.

• Battery fuse/circuit breaker to the inverter

Wiring and fusing from the battery to the inverter is critical as this is where the most current flows. Similar to the case with the charge controller, recommended wires and fuses should be obtained from the inverter manual.

It is recommended to prepare a fuse holder on its positive cable, which must be able to hold 50A. A typical 500 watt inverter 12V pure sign wave draws up to 50A continuously, in which case a 55-60A cable is required, at least a 6 AWG wire.

4. Safety design requirements for solar panel systems

• Some systems require complete control, inverting, monitoring, protection, and communication functions; some systems do not require monitoring and communication functions.
• High conversion efficiency, the efficiency of control - invert - output reaches over 92%, and whole series of TYCORUN inverter such as 2000w pure sine wave inverter and 3000w inverter can meet this requirement.
• Some systems require a high level of automation to achieve automatic start and stop, automatic metering, and automatic protection. You can operate the equipment with preliminary electrical knowledge.
• High manufacturing precision, pure sine wave output, voltage accuracy ≤±1.5%, frequency accuracy ≤±1.0%, and harmonics ≤±5%.
• Some systems require a high degree of digitalization, fully digital monitoring and output, and are equipped with RS232 and RS485 communication interfaces to achieve remote monitoring and operation.
• All systems require that the charge and discharge controller must have anti-reverse connection, anti-reverse charge, anti-over-discharge, anti-overcharge, anti-overload and short-circuit automatic protection functions.
• High execution reliability, the whole machine adopts unit design, the inverter unit is modularized, master-slave control, convenient for maintenance and replacement, and ensures that the system can operate normally during the inverter maintenance process.

5. Protection application of PPTC

PPTC, polymer positive coefficient temperature element, also known as resettable fuse or polyfuse, the characteristic of which is that it exhibits low resistance under normal current conditions, ranging from several milliohms to several ohms.

Under an overcurrent fault, the resistance rises sharply, thereby protecting the back-end circuit. Due to its excellent recoverability characteristics, when used for overcurrent protection, the circuit can automatically return to the conducting state after the fault is eliminated, eliminating the inconvenience of replacing the traditional fuse after it blows.

The main applications of PPTC in solar panel systems are as the following:

• For communication interfaces protection: Some systems require remote monitoring and remote control, so they have RS232 or RS485 communication interfaces. The input or output ports of the communication interface can be protected against short circuit or overload by PPTC, as well as lightning protection with TVS.
• For solar panels protection: Solar panels must charge the LFP battery through a conversion circuit. If the charging circuit of this conversion circuit is short-circuited, not only the purpose of charging will not be achieved , the battery will supply power in reverse direction, damaging the solar panel and charging conversion circuit. At this time, the solar panel fuses PPTC components can be used for circuit protection.
• For anti-reverse connection protection: When the solar panel or battery is connected reversely, it means that the photovoltaic battery and the battery are discharged in series, which will generate a strong current, which will not only damage the solar panel, but also damage the battery, and may also burn out the charging conversion circuit. At this time, the solar panel fuses PPTC can be used for protection.
• For short-circuit protection of the battery load: When the battery load is short-circuited, dozens or even hundreds of times of current will be generated, thus damaging the battery. At this time, the solar panel fuses PPTC can be used for timely and effective protection.
• For overload protection of the inverter: When the load of the inverter is overloaded or short-circuited, it may damage the inverter or cause the battery to over-discharge, which not only damages the circuit, but also greatly shortens the service life of the battery. The solar panel fuses PPTC can be used for protection. For the best inverters, you can check top 10 solar inverters.
• For small system circuits protection: Some small systems use wind power generation with photovoltaic power generation to charge the battery at the same time. Similarly, there are situations where reverse circuit connection or short circuit will damage the wind turbine and battery, at this time, the solar panel fuses PPTC can be used for effective protection.

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