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Axpert King not Using Solar correctly


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52 minutes ago, Calvin said:

My data so far indicates that I never get PV drop-outs on the 2S5P inverter, but quite often on the 3S4P ones (always both together)

Thanks so much for doing that.

53 minutes ago, Calvin said:

the 3S make the SCC run very hot (30C hotter than the 2S,

I know that converters are more efficient when the "turns ratio" (ratio of output voltage to input voltage) is closer to unity. But I didn't think it would be that dramatic! I guess that explains why some installations with voltage near but not actually exceeding the limit are still causing dips; it's limiting due to temperature.

57 minutes ago, Calvin said:

I have however seen no disadvantages to 2S,

From the inverter's point of view, no. But there is no escaping that 2S is more expensive to wire compared to 3S or even 4S in a few cases, and that's presumably what drives people to keep trying it.

Thanks for the vindication 😎

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@pierre.  Thanks for the link back, I can confirm that after firmware upgrades my system started behaving much better. 

 

Main inverter software version - 71.92  https://powerforum.co.za/files/file/52-axpert-king-main-firmware-version/

Controller / Display software version - 02.49 https://powerforum.co.za/files/file/53-axpert-king-remote-display-firmware/

 

My system should technically be able to give me 6480 watts, if I work on the % given by Coulomb earlier in the post than I am spot on with my solar production.

Reaching almost 5400 watts the other day at around 11 already. 

 

I am not sure if summer will bring through much change, might reach the 5400 watts much earlier than expected.

 

Factors to take into consideration:

Roof angle very flat compared to most roof structures

Being on a hill and winter the sun tracks low across the horizon each day

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54 minutes ago, Blowdart18 said:

@pierre.  Thanks for the link back, I can confirm that after firmware upgrades my system started behaving much better. 

 

Main inverter software version - 71.92  https://powerforum.co.za/files/file/52-axpert-king-main-firmware-version/

Controller / Display software version - 02.49 https://powerforum.co.za/files/file/53-axpert-king-remote-display-firmware/

@Blowdart18

I have upgraded to the same firmware for 2 Kings in Parallel but are now experiencing issues with the "Max charging current" jumping around. Are you seeing this?


Discussed in detail HERE

 

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21 hours ago, Calvin said:

My data so far indicates that I never get PV drop-outs on the 2S5P inverter, but quite often on the 3S4P ones (always both together),

After looking at my log files in more detail I need to make a correction.  It is NOT always both together.  Sometimes only one of the 3S SCCs trip.

I have had a good look at a few other incident and what they all have in common:

  1. Inverter (always wired 3S) has spare PV, so the MPPT voltage has been raised to reduce power output.  Typically around 135V
  2. Sun suddenly pops out behind a cloud.
  3. Voltage goes up to over 145V. SCC trips. 
  4. Takes between 3 and 15 minutes to restart.

Below is an extract from by database - in this case both the 3S inverters tripped. The column PVm show independently measured solar power, calibrated to correspond to what my system can produce.  It clearly shows the sun popping out from behind a cloud.

  I1PvWatts I1PvVolts I1AcWatts I2PvWatts I2PvVolts I2AcWatts I3PvWatts I3PvVolts I3AcWatts PVm BatteryWatts
2020-08-11 11:06:12 1733 133 708 1275 88.2 762 1259 136.4 745 5770 1786
2020-08-11 11:06:12 1874 133 708 1362 88.2 762 1259 136.4 745 6110 1873
2020-08-11 11:06:13 1874 133.2 824 1362 88.6 806 1259 136.7 867 6720 1873
2020-08-11 11:06:14 2025 133.2 824 1512 88.6 806 1505 136.7 867 7420 1837
2020-08-11 11:06:15 2025 137.3 890 1512 88.6 806 1505 138.7 917 7990 1837
2020-08-11 11:06:16 2035 137.3 890 1512 88.6 806 1374 138.7 917 8830 448
2020-08-11 11:06:17 2035 137.3 890 1512 88.6 806 1374 138.7 917 9060 448
2020-08-11 11:06:18 2035 137.3 890 1512 88.6 806 0 138.7 917 9440 -1558
2020-08-11 11:06:19 2035 145.8 983 1512 92.2 938 0 146.4 1024 9750 -1558
2020-08-11 11:06:20 2035 145.8 983 1512 92.2 938 0 146.4 1024 9750 -1558
2020-08-11 11:06:20 0 145.8 983 1619 92.2 938 0 146.4 1024 9310 -1845
2020-08-11 11:06:21 0 146.9 1084 1619 92.4 1057 0 146.4 1091 8930 -1845
2020-08-11 11:06:22 0 146.9 1084 1666 92.4 1057 0 146.4 1091 7600 -2163

It is interesting that I have only started seeing this since changing my charging paradigm from "get to 100% SOC asap" to "get to 100% SOC as slow as you can".  Under the former the SCC was always at full power until the batteries were full, which means MPPT voltage is around 114V, which means no tripping even when the sun pops out behind a cloud.  Once the batteries were full it made very little difference if some SCCs tripped - one is normally enough to supply my loads.  Under the new paradigm the SCC rarely operates at full power (due to the restricted charging currents) so the MPPT voltage generally hovers in the mid 130s.

Lesson from this: Either live with these drop-our, or do not wire 72 cell panels 3 in series.

 

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22 hours ago, Coulomb said:

Thanks for the vindication 😎

Final confirmation, if it was needed.

I took 1 string away from my one 3S inverters, and added 2 of the panels to the 2S inverter.  Now my configuration is: 

  • Inverter 1: 3S3P
  • Inverter 2: 2S6P
  • Inverter 3: 3S4P

Good testing weather today, sun is continuously in and out from behind the clouds.

What I saw:

  • Inverters 1 and 3 still drop PV when sun pops out.  Inverter 2 does not, despite now also having 12 panels.
  • Inverter 1 & 3 still run much higher MPPT temperatures than inverter 2, this despite inverter 1 having less PV on it than inverter 2.

Off I go to buy some more cables...🤣

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3 hours ago, Calvin said:

Lesson from this: Either live with these drop-our, or do not wire 72 cell panels 3 in series.

@Calvin, you've come to the right conclusion. But for other readers, I'd like to point out that:

  • 145 V is not the start of PV power throttling, it's the end, and the point where the hardware could blow up.
  • The start of PV power throttling is 130 V (undocumented).
  • The upper end of "MPPT range" in the specifications is 115 V.
  • These Solar Charge Controllers, at least the ones in the MKS models that I'm familiar with, have no way of disconnecting from the PV input. When the PV "drops out", this isn't some "fail safe" condition. The two relays on the SCCs disconnect the output of the SCC from the battery, not the PV terminals from the buck converter input.
  • All this is worse at colder temperatures, since panel voltage increases with decreasing temperature. So while the SCC might shrug off a few 146 V situations in the middle of the day, one cold morning with unusual weather conditions it might encounter 152 V and blow up, possibly taking other parts of the inverter with it. In fact, just recently Weber had to visit a remote client whose inverter failed (LC Display comes on only briefly, then off for a time, and repeats). It has a 3S 72-cell configuration, and there is evidence that it disconnected PV the day before. It was unusually cold and windy weather. He's now preparing a replacement inverter, and will recommend that the client gets the array rewired to 2S.

So to me the lesson to be learned is: do not wire 72 cell panels 3 in series, or risk blowing up your inverter. This of course only applies to models with the 145 V (absolute!) max PV voltage.

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7 hours ago, Blowdart18 said:

I am not sure if summer will bring through much change, might reach the 5400 watts much earlier than expected.

@Blowdart18 This table from geyserwise is pretty good as a reference for how much difference there is between the months.  Don't mind what the actual value is in this table, just calculate the percentage relative to the best summer month, then do the math to predict what you will get in that month based on what you currently get.

https://www.geyserwise.com/wp-content/uploads/2016/03/0207_PV-system-installation-manual_web.2016March09.pdf

image.thumb.png.2c2f007d38847e1152918499d3741da3.png

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1 hour ago, pierre. said:

This table from geyserwise is pretty good as a reference for how much difference there is between the months

One really important thing that they don't point out: This is per square metre of horizontal surface.

If you tilt your panels the figures change dramatically.  At about 40% from horizontal, facing North, the difference becomes very much smaller.

Below the output for Stellenbosch for panels at 0%.  Note how the daily output numbers are close to the Cape Town ones from Geyserwise.

1764351390_Angle0.jpg.4098755d028b441e8249c43e4c38d674.jpg

And here is the output at 40 degrees tilt.

882709535_Angle40.jpg.934f8082f757d451561b9d06f2507d62.jpg

As you can see, at 40 degrees tilt the difference between the months is much less.

Edited by Calvin
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