Hi i have a Mecer Axpert originally installed 18 months ago together with 2.8kW of pv modules and 2x2.4kWh of pylontech batteries. It generally runs nicely but every few days it randomly trips with a 08 error, usually around 2 or 3am when the only load is the security lights and the fridge cycling on and off. 

I've had it replaced three times as my contractor thought it was a dodgy batch and has suggested changing it for an Axpert King. 

Does anyone know what could be causing the problem and will upgrading to the Axpert King fix it or is there an easier way.

Thanks in advance for any help provided although please use non electrical engineering language as I'm a beginner at this.

12 hours ago, Justin W said:

It generally runs nicely but every few days it randomly trips with a 08 error, usually around 2 or 3am when the only load is the security lights and the fridge cycling on and off. 

I'm guessing that you have one of the higher voltage solar charge controller models (you didn't say what model Mecer Axpert, there are several). There is an issue with leakage to ground rectifying and causing the bus voltage to increase. For whatever reason, it mostly shows up at night, with low loads.

The work around is to automatically disconnect your panels at night, as in this post. You might be able to find the source of the leakage and fix it, but that sounds very difficult. For more background, see earlier discussion here.