Magic smoke protection is a key feature for solar installations. The image shows a fault when a charge controller failed and blew the inverter.
What happened?
A failure of the charge controller fed PV voltage to the system, where the charge controller was connected to the bus bars along with the battery and inverter. The BMS saved the battery, however not all systems would have a BMS, such as lead acid batteries. However the voltage into the 12v inverter was at 79v causing this electrical fault.
What failed?
Inside a solar charge controller is basically a switch, well a group of switches. These turn off and on to regulate the voltage, there are a few parts that make this work, a controller, a resistor, and the switch, which is usually a device called a mosfet, some have IGBT if they are high power.
The gate (switch) is held open and closed by the resistor and this is controlled by a controller IC.
The controller IC (Integrated Circuit) reads the input and output voltages and current in order to determine the amount of switching that needs to be done.
Any failure in these three parts will lead to problems. but the big problem is when the gate is closed and this means that the full source voltage is fed into the output. And a fuse wont save you!
Protection of your electrical systems can come in the form of a fuse/breaker which will protect you for current issues (amps) but to protect your system for a voltage issue you need something a little more robust, this is a SSR ( solid state relay) they come in various sizes but have to have a control circuit in order to work.
How much is this going to cost?
Lower voltage systems have higher currents and therefore the bigger your protection and costs will be.
If you do not have a BMS then you will need two units to protect the battery and the inverter. You would select the SSR based on known working loads. and have some margins, you would not want a 80 amp SSR when your loads are 80 amps as its NOT a fuse or breaker.
lets say you have this 80 amp SSR, your load would be 65amps, on a 24v system that’s going to a 1500w inverter.
A 6KW inverter with a 48v system voltage will have 125amp load therefore a 150a SSR will protect the system battery. You are looking around £120 for protection of the battery
Protection from the solar controller.
A lower cost solution here is due to the solar output current when the system is working.
To work out the protection that you need, you would use power factoring calculations.
(PV voltage / Battery voltage) X PV Current (isc) = Output current.
Here you are looking at around £45.00
How do I buy one?
Contact us as we will make these on commission basis if they are not in our shop
You can buy SSR from the shop if you intend to make your own.
Need a smart one?
If you would like a SSR to protect your system but have “added features” such as those in our smart solar controllers and combiners, you can request this feature. – Have MQTT data sent showing the PV current and Voltage to your home assistance for monitoring and alarms.
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