Coulomb

It could be that the two inverters are seeing different battery voltages. That could be because of poor battery wiring (e.g. daisy chained battery connection), or because the battery measurement of one or both inverters is poorly calibrated. With low load and low charge, do the two inverters read the same (± 0.1 V, you can always get one Least Significant Digit differing by one) battery voltage measurement? If not, see Calibrating your inverter's battery voltage reading .

That's true. But to me the dangerous situation is when there is high PV power, then suddenly there is a large decrease in load that the PV was supplying, either in whole or in large part. Now as the control system tries to "turn off the tap", that very VI curve means that as the power is reduced, the voltage is increasing. So if the bus voltage is getting dangerously high, then the only option to lower it is to dump some of the energy presently stored in the bus capacitors into the battery. [ Edit: Not quite; see next post. ] I have no idea how models with no battery cope with this. Maybe that's why they want a lowered battery charge limit when the PV voltage is high, so that they always have the option of exceeding their self-imposed limit without exceeding the limit set by the customer. If we allow full current at high PV voltage, then that option is no longer there; to make the bus voltage safe, the firmware would have to exceed the customer set limit, which might damage the battery. The effect of exceeding the limit whenever a large load turned off would be pretty small, I think, and would have negligible effect on battery life. That's the big question. Did they limit the current because they rushed the firmware, or because there is an important safety / reliability / other reason? Unfortunately, I don't know the answer. If you watch your bus voltage in the inverter with the disabled derating after a drop in load and the battery current surge isn't excessive, then it seems to me that it's safe. But there may be other scenarios that I haven't thought of. I still want to go through some other firmwares to see how common this derating limit is. I haven't gotten around to that yet.

I expect the problem would be with overshoots on the DC bus, i.e. going over 500 V. Axpert control loops are notorious for overshoots.

Yes, DC bus voltage regulation. The PV voltage is boosted and becomes the bus voltage. It may be that if you allow a lot of PV power at high PV voltage, the firmware may not be able to keep the bus voltage inside safe limits. Can you monitor the bus voltage on yours? It's available via the QPIGS command, which only works for the inverter that the monitoring software is connected to. Solar Assistant and others probably use the QPGS command, which can get information about all paralleled inverters, but does not have the bus voltage (per the documentation I looked up quickly; it could well be inaccurate).

Most especially in the case of the high PV voltage transfirnerless models, you must not parallel PV inputs. This type of inverter is by far the most common these days.

If it's stopping at different times, then any firmware update will fail the same. It's either the USB to RS-232 adapter, or the cable needs a resistor (see the files section, link in the post linked below), or it's slow opto couplers inside the inverter or its display. You could also try the USB drive via a USB On The Go cable. That bypasses the serial electronics. See the Firmware Upload Instructions for details.

I can certainly port cuba.cz's changes to 2708.07, or even make a 278.08. But first I'd want to know that the changes are safe under all conditions.

The 71.xx and 72.xx King 1 firmwares are for the 5kW models only. The 51.xx and 52.xx are for the 3kW Kings. Possibly 52.01 uses the same firmware source code as 72.01, but compiled for the 3kW model, just using slightly different #define statements.

Yes, it has not updated. The other way to update requires a Windows PC, a compatible USB to serial adapter, and the grey D9 to RJ-45 cable that should have come with your inverter.

No, just interested in firmware, and South Africa for some unknown reason uses a lot of inverters 🤔 Also, I inherited a Dutch surname, but born in Australia.

I don't know the King II models specifically, but they all use much the same main power supply circuit, and that does have basically battery positive at one end of the load/start switch. So yes, that's expected. Alas, this means that plugging that into the wrong place could cause damage.

What exact firmware did you try to update it to? Have you tried the techniques in If you think your inverter is bricked?

I think it's a UPS: https://www.rctzone.co.za/power-solutions/power-solutions/line-interactive-ups/rct-850vas

My understanding, without owning a Max model, is that this should work. This is based on me reading the firmware; as far as I know, "mks2.hex" is not mentioned in any Voltronic documentation. So this is pure theory. So far, I'm not aware of anyone saying "hey, this does not work". Please report your results, good or bad.

If you are successfully running 78.xx firmware then you have a '28066 DSP. I'm 99% sure that recent EASuns are genuine Voltronic models, largely if not completely made in the Voltronic factory. Back in 2021, it may have been a different story. Large genuine Voltronic reseller MPPSolar accused EASun and others of being clone makers, and warning prospective buyers not to buy them. That web page is still there, but perhaps no longer easily findable: https://www.mppsolar.com/v3/fake/ I have a theory that Voltronic actually sues some clone makers, or threatens them with legal action unless they convert to becoming a genuine reseller. That appears to have happened with EASun and possibly a few others. In any case, I regard all EASun firmwares as genuine now, and as far as I know, they are completely compatible and interchangeable.

Answered in your other post here.

Please post in English on this forum. The needed cable wiring depends on the inverter as well as the battery. They probably provided a cable to suit a Deye or other common inverter. To fix that, we need to know the pinout at the battery end, or if the Pylontech compatibility includes the communications connector. There are usually several RJ-45 connectors on the battery, most of them 8-pin, so you also have to plug into the correct one. Hopefully you got a user manual with the battery, or at least there is a web site to download it from. Also, your display firmware, which handles communication with the battery's BMS, is fairly old. It might be worth updating it to version 12.28 or 12.29. Edit: They drop the leading "1" digit with recent display firmware, so recent 12.xx are compatible with older 112.xx display firmwares.

Yes, I can't see why not.

Please post in English on this forum. I don't have 82.07, but there is 82.06 in this thead; don't bother downloading the tmp (temporary) files, as these are automatically generated. https://powerforum.co.za/topic/24190-new-firmware-for-axpert-max-ii-10kw/#findComment-187125 I actually doubt that the differences between 82.02 and 82.07 would prevent paralleling; it's probably some other issue (e.g. cabling). What fault code comes up when you try to parallel? Edit: If you have trouble with the "stuck at 90 V" issue, you are probably better off updating both inverters to firmware version 82.63, which has the "presumed good" MPPT logic, and is 6 months later than 82.06. For whatever reason, 10 kW firmwares are more rare than others.

I assume you mean that the display that replaced the one that failed has version 38.08. I believe that you have an Axpert Max E 11kW Duplex model, so you need a Duplex removable display firmware. The only one I have is version 62.03. As far as I know, all the displays are hardware compatible with each other, as long as they are both removable or both round/colour, and have the same number of buttons (some have 4 touch buttons, others have 6 physical buttons). So this should work, but I can't guarantee it. You will need a Windows computer and a USB to RS-232 cable, as well as the cable that came with your inverter. This is factory display (MCU) firmware version 62.03 for the Axpert Max Duplex models. Do not use with any other model or version, not even a Twin model. Use at your own risk. The hex file is dated 23/11/2023. Firmware upload instructions for models with a removable display. Remote Panel_Reflash_MCU(62.03).rar

I'm not aware of places to buy just the cables. As far as I know, the cables are just straight through, i.e. pin 1 to pin 1, pin 15 to pin 15 and so on. I do hear of the parallel boards failing at times; I had one of my own take out a transistor due to nearby lightning. If you don't do electronic repairs, it might be worth buying a whole kit anyway. One of the old boards might be still working, so you can keep it as a spare.

Someone mentioned derating; it seems that it can derate charging power for four reasons. The reasons were high internal temperature, high PV voltage, low utility voltage, and I forget the fourth one. I was shocked to see a manual extract indicating that if PV voltage is over 360V, the charge current would be derated to a maximum of 90A. I suspect that there would be a ramp based on PV voltage, not a sudden drop of 33% as implied. That gives me a promising avenue to continue searching, if and when I find the time.

I usually do. In this case, fault code 90 is designed to "catch out" clone makers use Voltronic firmware without paying for it. I don't want to help clone makers in any way, if at all possible. In this unusual case, no patching was required, just updating to the latest firmware.

This is a complex issue. I've put a few hours into it with no bug found yet that might cause this, but I have to move onto other things. Please remind me again if I forget to get back to this.

Do you mean that the firmware failed to update, or it updated and there is no change, or now the inverter appears to be "bricked"?