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I had an alarm yesterday for the Solis to say no battery was connected, a quick check revealed the 50Amp NH fuse link had blown, at the time I assumed this had been caused by an in rush of maximum current to charge the batteries back up from 18%SoC to 20% Soc in line with maintaining the battery until solar charging weather arrived.

I checked the breaker was otherwise ok and swapped out the NH link for a new spare and reset the system and all was well, I then went in to the Solis control and set the charge to 1000W max rather than the 3.6kW max the system can charge at to avoid in rush of current.

Ten minutes ago the same link had again blown, the holder was warm to the touch - I've isolated the system and will go in tomorrow (if the weather is dry) and take off the covers and check that all the connections are still torqued up correctly but other than a loose connection is there anything else that could be causing the problem ?

Moxi

Doesn't sound great - good job you've got a fuse there. Did you get any data from the inverter to show what was happening at the time?

Also made me think - I assume the fuse is between the inverter and the battery.

My system doesn't have any fuses, or even an isolator between battery and inverter. Each battery just has it's own on/off switch.
It was installed by a solar company and signed off as MCS accredited. Seems a bit strange to me

Yes it is between the inverter and batteries, weather forecast is dry tomorrow so I can get in the shed to take a better look see at the terminals on the breaker unit and on the batteries and the inverter.

At the time of failing the battery was charging and at 23 % SoC

My money is on a loose connection on that leg but will know more tomorrow.

Moxi

If that is a 48V system and you have limited the max charge rate from the Solis to 1000W, that would be slightly over 20A so blowing a 50A fuse seems, to me at least, that maybe the battery is delivering >50A to something n the Solis when it is charging. Does that make any sense?

The fuse carries current both ways, charge and discharge. 50A is too small for a 3.6kW inverter. If the inverter is supplying a house load at its full capacity - 3.6kW then it will be drawing 70A from the battery and through the fuse, 1.5 times its rated current. The fuse will survive quite a long time but will eventually blow. Replace with 100A fuses. They are there to protect the wiring and in the event of a short circuit - hence the NH type fuse which can reliably disconnect several kA of current. The BMS and inverter will normally limit the current.

Just limiting the charge current to 1000A would not stop the inverter drawing 70A from the battery if the load demanded it.

Hi Marshman,

I have just taken a look at the inverter trace and I think you maybe right, the inverter was clearly putting 3.4kW in to the battery before failure of the fuse. I have checked the setting and it’s still set to charge from grid at 1kW but I am wondering if that setting was for forced charge and that the bms asking for a low SoC charge still takes it at maximum ie 3.6kW.

Now we are chatting about it I do seem to recall Nowty or someone saying that 50 Amp seemed small for the kit but as it was supplied.

Ive ordered some 100A replacements ready.

Moxi

Yes, setting the charge current on the time of use page only sets the charge current for those times you want it to charge. Force charging has its own setting for SOC to start and max grid power (i.e. charge current). I think you have been lucky the fuse survived this long. It probably has not gone when the inverter has been supplying full load to the house as it would tend to only be short duration, where as charging is at a continuous high current.

SoC to start was what I set at 18% the default before that was 15% on mine and forced charge was definitely 1kW so maybe it didn’t get saved and uploaded as by then I had been checking quite a few settings from my phone and clearly the battery was charging at 3.4kW

It’s all off and isolated at the minute so I will update you tomorrow but thanks again for your inputs, it’s always good to canvas learned opinions.

Moxi