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Axpert King not Using Solar correctly


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Hi,

So I have this little problem with my Axpert King inverter i just installed.
Previously I had the MKS 4kw 5kva version and the Solar power i got average on a sunny is about 2.3kw per inverter, there are 3x3 330w panels on each inverter giving a total of 2970 or 5940w for both.

After i installed the Kings i noted that the PV utilization is shot to hell.

Whats strange is is that it seems that the PV utilization is somehow link to the total load in a way, the max utilization seems to be 1.7kw per inverter if under load.

I have tried changing multiple setting but cannot seem to get it to function correctly.

Please see attached screenshots of settings, load scenarios and log.

I look forward to your guys help!

INVERTER 3.PNG

Inverter Load.PNG

Inverter No Load.PNG

20200719142733.xls

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I see your "operation logic" is ECO Mode; I've never understood this fully, and the manual I have says where describing Bypass/ECO Mode: "* ECO mode disabled when in parallel mode". Maybe this is confusing the firmware somehow?

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So i set it to Online, Seems the battery is charging with all the available current now.

It seems that the Axpert king inverters are extremely bad at pv conversion as i still only get max 1.7kw

As a proof i will tonight connect the old MKS up to the one set of panels and at 12am tomorrow morning i will get my wife to take an image of both of the inverters PV conversion efficiency. 

This is extremely disappointing of the Axpert king.

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Hi Bain

For the King, choosing ECO mode diverts all solar power to the batteries and never to the load except if there is a mains fail then batteries will supply power to load. Once the batteries are full then the PV power generated drops to zero !

Your current CPU version 71.90 has a known bug that even if you selected in Question 16 the option of Udc (don't charge batteries from the grid) the grid still charged the batteries at a small current. This is much less than if you had the inverter in ECO mode but where the full PV power would charge the battery.

I upgraded to 71.92 (not for the faint hearted as one is so poep scared to brick the inverter...). This should have fixed the above Udc charging problem but the grid still charges the batteries albeit at a reduced current to before.

Their is another thread on the forum about flashing the CPU where @Coulomb has given lots of valuable advice. I used the USB OTG method. My additional advice to what has already been shared is to be patient while the upgrade is in progress (just wait the 10 minutes or so) when upgrading and don't interrupt it like i did. Then you get error 32.... and subsequent headache.

PS my 6.1  kWH battery is doing well 👍

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Hi Greenman,

Glad to hear you are pleased with my product.
After that video i upgraded to 71.92 on Sunday, results are the same. I have also selected solar for Load first option, also no success. no matter what setting i change or what combination i use i cannot get it to perform close to the efficiency of my old inverter.
Also regarding the charge on the batteries, the current is set to 50a so it should have anyway pushed allot more power to the batteries regardless as they were nowhere near full.
Also just to make sure, before i took the video i turned of my PV and turned the geyser on for 40min to drain the batteries even more.

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Looking at the correlation between the PV input power and the load input power it would appear that the PV input drops when the load drops.  This is due to your Solar balance being disabled, try enabling the solar balance option

temp settings.JPG

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Tried that as well, you can also see in one of the short videos i turn the inverter on. the 1.6 goes to 1.7kw. 
Also regarding the setting, its anyway faulty because why would it only be pushing in 1.6kw into the battery when the charge current is set to 50a (2688w @ 56v)?
Also tried setting to 120a, made no difference.
The inverter had the solar power balance on by default, i disabled it in an attempt to resolve this issue.

Everything about these inverters are buggy. really disappointing.

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2 hours ago, Bain Viljoen said:

Hi Greenman,

Glad to hear you are pleased with my product.
After that video i upgraded to 71.92 on Sunday, results are the same. I have also selected solar for Load first option, also no success. no matter what setting i change or what combination i use i cannot get it to perform close to the efficiency of my old inverter.
Also regarding the charge on the batteries, the current is set to 50a so it should have anyway pushed allot more power to the batteries regardless as they were nowhere near full.
Also just to make sure, before i took the video i turned of my PV and turned the geyser on for 40min to drain the batteries even more.

Hi Bain

Also in terms of overall efficiency, remember the King inverters operate (when not bypassed, obviously) in Online mode (in UPS speak). That is why you have zero transfer time to battery when there is a mains failure. This means that the inverter is always inverting and there is the inefficiencies of this as the DC is converted to AC.

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1 minute ago, GreenMan said:

Hi Bain

Also in terms of overall efficiency, remember the King inverters operate (when not bypassed, obviously) in Online mode (in UPS speak). That is why you have zero transfer time to battery when there is a mains failure. This means that the inverter is always inverting and there is the inefficiencies of this as the DC is converted to AC.

I don't understand what that has to do with the low PV efficiency? 

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3 minutes ago, Bain Viljoen said:

I don't understand what that has to do with the low PV efficiency? 

 

4 minutes ago, Bain Viljoen said:

I don't understand what that has to do with the low PV efficiency? 

Ah, i meant overall efficiency of the system and not purely PV efficiency. My guess is that the PV efficiency is dependant on the MPPT firmware and hardware ? Just guessing.

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1 minute ago, GreenMan said:

My guess is that the PV efficiency is dependant on the MPPT firmware and hardware ? Just guessing.

Usually, PV to battery efficiency is around 98%. I see no reason why the King MPPT would be much different from the MPPT in an MKS model (not MKS II or MKS III).

2 hours ago, GreenMan said:

For the King, choosing ECO mode diverts all solar power to the batteries and never to the load except if there is a mains fail

But it seems that ECO mode is disabled when units are paralleled. In the one video that I could download, it showed "SL" for slave, i.e. it's paralleled.

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1 minute ago, Coulomb said:

But it seems that ECO mode is disabled when units are paralleled. In the one video that I could download, it showed "SL" for slave, i.e. it's paralleled.

Correct. I run 2 inverters in parallel to power my entire house including geyser and stove. For the test sake i disconnected the salve and connected the cables to my MKS  for the test.
Even the master only gets 1.7kw, also connected to 2.97kw of panels.

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Hi All

First, Bain thanks for all the testing effort appreciate your effort . 

I have been following this thread with interest as I was really keen on getting a King. This feedback is very concerning as it really means that using the King in a Solar situation is very disadvantages. "I mean, only 1.7kw from 2970w panels... no man.. " is spot on this is a huge issue. 

Coulomb and Bain do you feel this is specif to your inverter or true for all Kings, certainly seems like it is not a specific issue ?

Does anybody have any recommendations on Inverters that give you the flexibility of the King but with better MPPT, or is there a design that anyone has that could improve this ? 

Cliff

 

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Hi, 

I installed a King two weeks ago. I'm just starting to build my system so have started with 3x275W panels in series. I also see something that does not compute. In a case where it shows PV @ 85V and around 9A its showing PV power of around 530W. Something is not right there. I am also measuring a lower PV input current on a clamp meter than what the unit reports. 

The PV power reported on the display shows as input power so efficiency should not come into it (???). The only way of really checking is to accurately measure PV power in and combined AC and DC output by external means. 

The problem I am finding is that this unit, like other Axpert/etc models is a branded voltronic unit and it very difficult to find a supplier that knows anything about it or has any line back to the manufacturer. 

I guess you get what you pay for. A Victron or Sunsync setup would cost almost double which for me means I would be waiting quite a while longer to cough up the cash. 

Rob

 

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4 hours ago, RobM said:

I installed a King two weeks ago. I'm just starting to build my system so have started with 3x275W panels in series. I also see something that does not compute. In a case where it shows PV @ 85V and around 9A its showing PV power of around 530W. Something is not right there. I am also measuring a lower PV input current on a clamp meter than what the unit reports.

I think the PV Amps shown is on the output of the MPPT, in other words at the voltage you're charging the batteries. 56V*9A is more or less 530W. 530W from 825W theoretical maximum is probably in the right ballpark.

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9 hours ago, gooseberry said:

I think the PV Amps shown is on the output of the MPPT, in other words at the voltage you're charging the batteries. 56V*9A is more or less 530W. 530W from 825W theoretical maximum is probably in the right ballpark.

Thanks for your thoughts @gooseberry. Hmm Something still not fitting with my logic... What the MPPPT controller should be doing is converting a higher voltage, lower current input to a lower voltage higher current output to the battery - or the DC bus at least, which feeds the inverter and the battery. If the display is showing PV voltage going in to the controller and current going out of the MPPT controller thats not very consistent but would explain the lower than expected power. To get a better idea of the efficiency I would then have to use the measured input current and not the displayed current to get an idea of the PV input power.  

It would be really helpful if these things had better documentation. Also, the people that sell them are not very clued up.

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Yeah it's the way MPPTs are rated. The voltage matters on the input side (how many panels you can connect in series) and the current on the output side (how fast you can charge your batteries) For example the Victron BlueSolar 150/70 has a 150V input voltage and a 70A max output current at 24V.

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On 2020/07/30 at 9:16 PM, gooseberry said:

530W from 825W theoretical maximum is probably in the right ballpark.

Apologies if I am starting to get painful: 530W from an 825W array seems rather inefficient to me. So: 

1. Its late July and the sun is not at its peak. I would expect higher power as summer comes on.

2. The MPPT controller has some losses. What is a typical figure for MPPT efficiency.

Lets eliminate 1 by trying to establish the actual incoming PV power. Typically at midday I get around 7-8A @ 85V - this is what I measure independently of what the inverter tells me. The inverter's voltage reading seems to tally closely. Lets assume the current the inverter shows is MPPT output so we disregard that and work with the measured incoming PV current. This means that the PV array is pushing between 595-680W. The inverter tells me PV power is between 530 and 560W. So somewhere I'm losing between 15-20% of the incoming PV power. If my logic is correct this means the MPPT controller is around 85% efficient at converting PV input into useful power. I would have expected better but... not being an expert in these matters this may be reasonable. 

Did I buy a lousy inverter? 

Perhaps there is some simple rule of thumb I am missing. Any thoughts anybody?? 

Rob

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On 2020/08/03 at 12:48 AM, RobM said:

What is a typical figure for MPPT efficiency.

The manual quotes "98% max". At these relatively low power levels, I'd expect at least 95%.
 

Axperts do have a fairly high self-consumption, of the order of 50 W for a 5 kVA model; Kings might be slightly higher with the extra AC-DC converter. So about 5% efficiency and some 10% from self consumption brings it to roughly 85% at that power level. But it's not clear to be whether self consumption would be counted against the PV production; it seems more likely that it would not.

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On 2020/07/29 at 12:05 PM, Cliff said:

do you feel this is specif to your inverter or true for all Kings, certainly seems like it is not a specific issue ?

I run 3 Kings in parallel (each with 12 x 365W) and I can say that one thing that works reasonably well is the SCC.  I regularly get production of about 3900W at mid-day - 90% of installed capacity.

One thing to note: the King clips the SCC output when the SCC temperature (parameter SCCPWMTemperature on Q1 query) gets to 87C.   For some reason this temperature is far higher when using 3S configuration than when using 2S.

 

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@Calvin Thanks for the insight that sounds much closer to what is claimed on paper. 

Would you mind sharing with us how you wire your panels, i.e. how many in series or parallel of the 12x365, and do you use anything like optimizer between panels ?

 

 

 

  

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3 minutes ago, Cliff said:

@Calvin Thanks for the insight that sounds much closer to what is claimed on paper. 

Would you mind sharing with us how you wire your panels, i.e. how many in series or parallel of the 12x365, and do you use anything like optimizer between panels ?  

After much reading about this, including many warnings by @Coulomb about using 72 cell panels in 3S, I decided to cover myself and do it both ways, in order to test for myself.

So,  I decided wired 2 inverters as 3S4P and one as 2S6P.  In theory anyway.  In transit somebody drove a fork-truck into the box containing the panels, so I ended up with only 34.  That meant the 2S6P became 2S5P, which has slightly undermined my intention of comparing performance.😂

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), for several minutes at a time. This happens not particularly when operating at high production or variable loads, but seems to be when it is partly cloudy (variable PV) and the MPPT is clipping.  It is not clear whether that is because of the higher voltage of 3P or because of the lower installed capacity, or even because the 3S4Ps are the slaves, but I suspect it is the voltage.

I need to install the extra 2 panels though before I can reach firm conclusions.  I have however seen no disadvantages to 2S, whilst the 3S make the SCC run very hot (30C hotter than the 2S, leading to clipping and a shorter life-span) and is probably the cause of the drop-outs.  I will probably convert all of them to 2S.  If I was starting out now I would do it as 2S.

I have no optimisers, but my panels are shade-free.

Hope this helps!

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