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Solar system trip when battery voltage is low


Francois du Rand
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I have a solar system consisting of:

1. 18 x 330 W solar panels

2. 3 x 5 kW Axpert inverters

3. ! x 10 kW Dyness Li-on battery

As I have started of with 2 x 5 kW inverters, my solar panels provide power through these two panels and the 3 rd inverter gets power from the grid and battery.

My problem now is that in the case I draw about 9 kW from the system and the battery voltage came down to 47 V the whole system trips out (goes dead) and have to reboot.

At night time with less of a load on the system and the battery comes down to 47 V, the system elegantly switches over to the grid until the battery reaches "back to battery" voltage.

My question is why the system elegantly switches to the grid when the load is low and trips out (without switching to the grid) when the system is under load?

I have added the third inverter to overcome this challenge, but sadly it made no difference.

 

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5 hours ago, Francois du Rand said:

3. ! x 10 kW Dyness Li-on battery

I assume that you mean 1 x 10 kWh Dyness Li-ion battery.

5 hours ago, Francois du Rand said:

My question is why the system elegantly switches to the grid when the load is low and trips out (without switching to the grid) when the system is under load?

I think that 10 kWh is too small a battery for a 9 kW load. That's an 0.9C load. Yes, you'd want the utility to take over for that load, but I think that when that sort of load comes on suddenly, the battery voltage sags too low too quickly, and the power supply (or something else) inside the inverters can't cope with the sudden dip in battery voltage, and the inverters' computers "faint from lack of oxygen to the brain", so to speak.

Yes, it's poor and should not happen. There is possibly a hardware fault causing it, though you'd expect at least one of them to keep running, certainly the most recently added one. But maybe you just have too much resistance in the battery cables, or possibly an isolating switch or fuse? Check for voltage drops with a multimeter when there is a moderately large load, like a water kettle. There should be no more than 0.1 V drop from battery positive to any inverter battery terminal positive, and same for the negatives, preferably half that.

Final thought: are all three inverters running identical firmware?

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19 hours ago, Coulomb said:

I assume that you mean 1 x 10 kWh Dyness Li-ion battery.

I think that 10 kWh is too small a battery for a 9 kW load. That's an 0.9C load. Yes, you'd want the utility to take over for that load, but I think that when that sort of load comes on suddenly, the battery voltage sags too low too quickly, and the power supply (or something else) inside the inverters can't cope with the sudden dip in battery voltage, and the inverters' computers "faint from lack of oxygen to the brain", so to speak.

Yes, it's poor and should not happen. There is possibly a hardware fault causing it, though you'd expect at least one of them to keep running, certainly the most recently added one. But maybe you just have too much resistance in the battery cables, or possibly an isolating switch or fuse? Check for voltage drops with a multimeter when there is a moderately large load, like a water kettle. There should be no more than 0.1 V drop from battery positive to any inverter battery terminal positive, and same for the negatives, preferably half that.

Final thought: are all three inverters running identical firmware?

What are the chances that because its pulling close to 1c, the battery BMS is kicking in and shutting off the battery and throwing it into protection.
That would explain why all the inverters are switching off considering the inverters need a battery connected to run.

The Dyness 9.6kw battery has a maximum output of 4.8kw

image.png.15dca8a36d18318330ca9f1672a7d9b4.png

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