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2x 5Kva Axpert inverters in parallel, one not charging - now strange behaviour


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These Axperts are connected to 2 PylonTech 3000US batteries and managed with Raspberry Pi with ICC dashboard.  Today I discovered the slave inverter is not charging.  I check to see if the batteries supply DC to this inverter as well as the pannels and both measurements was correct.  It is suspected that the MPPT card of this inverter is blown.  

Tonight I discovered that the inverters have switched to grid long before the percentage (40%) that is set for them to switch back to grid.  The current SOC stands on 77%.  I don't understand what is going on.

The only explanation I can get to,  is that the working inverter (remember the slave is currently not working due to the dysfunctional MPPT) switch to grid when the SOC dropped to 40% and has not reached the set 80% to switch back to solar/batteries (it stands currently on 77%).   And this is al due to the fact that there is now only 1 MPPT and 6 pannels (6/inverter) charging and couldn't get the SOC to above 77% (Also cloudy the whole day).

Does my thinking make sense?

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Now after 34 minutes both inverters have switched to battery, no longer grid. And that on an even lower SOC namely 72%.  

And the slave inverter, which this afternoon stayed on grid while the master was supplying power from battery and solar, has now joined in and is happily donating its share from the Pylontechs.  This is not normal, I remember when the inverters switched on for the first time after I installed the Pylons I heard something like relays clicking.  Do they have relays and is it possible that one got stuck.  Anyway I will know tomorrow finally when the solar pannels start delivering charging power if the MPPT is still alive on the slave.

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15 hours ago, Cassie said:

These Axperts are connected to 2 PylonTech 3000US batteries

Are the two Pylontechs paralleled with each other, both feeding both inverters? You can't have separate batteries to two inverters if the inverters are paralleled.

 

15 hours ago, Cassie said:

The only explanation I can get to,  is that the working inverter (remember the slave is currently not working due to the dysfunctional MPPT)...

If they are paralleled, then it should not matter whether the MPPT (Solar Charge Controller) is working or not. They should still work together sharing the load. Or have you switched one off, or isolated its output?

15 hours ago, Cassie said:

Tonight I discovered that the inverters have switched to grid long before the percentage (40%) that is set for them to switch back to grid.

What is your setting 12 (back to grid battery voltage)? When ICC is in control, it is my understanding that you need to set settings 12 and 29 very low, so that the inverters don't switch prematurely. Setting 29 (low DC cutoff battery voltage) has an undocumented effect on the switch to grid voltage; see FAQ #1.

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On 2021/03/08 at 12:26 PM, Coulomb said:

Are the two Pylontechs paralleled with each other, both feeding both inverters?

Yes they are paralleled feeding both inverters together.

Back to grid

On 2021/03/08 at 12:26 PM, Coulomb said:

setting 12 (back to grid battery voltage)?

Back to grid voltage is 47.0v  and battery cut-off voltage is 46v

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11 hours ago, Cassie said:

Back to grid voltage is 47.0v  and battery cut-off voltage is 46v

Perhaps try lowering the battery cut-off voltage to 45V, so that the effective back to grid voltage is 47V (presuming factory firmware). 

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  • 2 weeks later...

I have set my battery cut-off (29) at 42V, the back to utility (12) at 47V. The battery data sheet says the BMS cuts off at 40.5V, corresponding to 0% SOC.

Lately after 3 rainy days and during load shedding at night the system shut down completely although I thought to have some 20% SOC left.  I had to restart it from scratch when power was back. Therefor I increased the back to battery (13) from 49V to 50V. This way I get more battery charge before it switches back to battery mode.

Edited by Beat
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