Coulomb

You can parallel non-VM models of Axpert inverters to increase their power output. For example, two 5 kW inverters can act as a single 10 kW inverter. But to do that, you need some extra wiring and a another breaker, and two "paralleling kits": If you already have these boards and cables (two sets are required), then it's probably worth considering the slight extra cost of paralleling them. But if not, just ignore this option, unless you find that you need more inverter power later on,

Using a whole inverter just for solar charging seems a waste. Why not just use a stand alone Solar Charge Controller? To answer your question, it relies on the voltage of the battery. Since the battery is LFP, it won't know how full it is until it's nearly full; then the battery voltage will suddenly shoot up. So the external charger is useful for pouring energy into the battery while it's not full. I used to do this before I had two inverters in parallel. I set the bulk/absorb battery voltage setting of the external charger just a little under than of the main inverter. That way they don't get confused near the end of the charge. The battery can't charge at high current at the end anyway, so it doesn't matter than only the main inverter charges the battery the last few percent. Being plus models, you might add paralleling boards so that the inverters talk to each other. Plus/King models can do that; straight OG models can't (they're Axpert VM models). But if you're not using the output, it might get confused, and I don't see the point of the added expense. There is CAN bus messaging going on between paralleled inverters; I think that one of the things that they communicate is their battery voltage. Possibly also State of Charge. But I don't know if they use this information to improve the charging process.

I would normally offer suggestions on firmware versions, but the VM III series is so chaotic that I have no idea what's going on. I might be able to research this topic, but it will be very time consuming, and other projects are far more urgent at present. I don't even have a single 71.xx firmware for a VM III, other than 71.03 itself. It's from March 2024.

From the appearance and specifications, it seems that this is a "work alike" based on an Axpert MKS 5K-48, PF0.8 version. It possibly uses Voltronic firmware, either under license or illegally. I have a partial (≈80% complete) schematic trace of a Voltronic 60 A (predecessor of the Voltronic 80 A) Solar Charge Controller here. Interleaved SCC block diagram here. Heh. Those are automotive relays; they are rated at 70 A at 14 V, but only 40 A at 27 V. They get away with them because they should always be switching at zero amps. Can you give an idea what part of the circuit this was from? Power supply, gate driver, comms, .... ? Good luck with it.

See FAQ #2.

Is the problem triggered by the relatively rare commands of more than 5 characters? With 2 CRCs and a carriage return, that makes more than 8 bytes per command, and with Python library functions (and possibly others), you have to split longer commands into two that are both 8 bytes or less. Even USB comms goes through opto isolators (at neck breaking 2400 bps!), and these do degrade with time. Perhaps whatever cooked the RS-232 port damaged or "wounded" the optos. Part number COSMO1010 comes to mind. I believe that these optos and the rest of the comms circuitry are inside with the display drivers in models with the round display. Or they might be separate from the display.

Check the gate driver. If it's not being driven properly, then it can be in a resistive state, where it will draw a lot of power. This is a common problem. It takes a lot of current to start the DC->AC converter. It may be that your power supply isn't up to it. I'd try a 3 A limit if it can do it, and at least 54 V if it can do that (assuming it's a 48 V model, as it presumably has to be for a 5 kW model).

We've been talking about at least two sets of capacitors. For fault code 08 and 51, it seems that the ceramic capacitors in series with the MOSFET gate transformers go low in value. These are 10μF 50 V SMD capacitors; it may be hard to find them in SMD form. They are not through-hole components, so I cant show them to you on your photo. On the PIP-4048MS traced schematic, these are C74 and C31, see this post for other parts that should be checked. The transformers are small, usually near the MOSFET heatsinks. Look for large SMD capacitors near the transistor end of these transformers. Possibly bottom left of your photo. The driver transistors look like tall TO-92 through-hole parts. This post confirms the value of C31 and C74 as 10μF. It's unusually high for an SMD part. All these links are findable from the repair and hardware modifications index. The other capacitors that cause big problems are the power supply capacitors; see this post and scroll down.

My apologies; I do have a more recent one (from May 2024). It is available from a Google Drive; link in this post:

What is the low DC cut-off voltage set to? These inverters have lead-acid logic from decades ago still active.

Duplicate post. Answered here.

I believe that it does, yes. No, it works for three power levels: 6.0kW, 4.0kW, and 1.5kW. Not for 4.2 or 6.2 kW. This firmware is from January 2024 (per the date stamp on the hex file). Versions 60.87 (Feb 2024) and 60.10 (June 2024) are later.

Please post in English on this forum. The latest I know of in the 56.xx series is 56.11, available here. [ Edit: But see 3 posts down. ]

This is factory firmware version 72.08 for the Axpert Max E 8kW '28066 non-Twin. Do not use with any other model or version. Use at your own risk. The hex file is dated 23/10/2024. As of this post, it is the most recent firmware for this model, but it does not have the "presumed good" MPPT logic. As a result, low light performance may be poor. For better MPPT performance in low light, consider factory firmware version 72.75, or patched firmware version 272.66. Firmware upload instructions for models with a removable display. This firmware processes the QDOP command, so with suitably recent display firmware, it should support SoC% for settings 12,13, and 29 when connected to a suitable battery's BMS. MAX_8K_72.08.7z

That's quite old; about 3 years old now. Fault code 55 is "over DC voltage in the AC output", which does not sound like it might not be fixed by firmware. But it's free, so you may as well try it. The latest 72.xx firmware for Axpert Max E 8kW '28066 non-Twin is 72.08. But it does not have the "presumed good" MPPT logic. So you might like to try 72.75, which does have this logic (so low light PV production should be OK), and it even has the QDOP command for SoC% values for three settings (mainly for other readers). If you need the absolute best performance in low light conditions (cloud etc), then consider patched firmware version 272.66. Not to toot my horn too much, but the best way is to post on this forum with your existing firmware version (as you have, thanks!), and hope that I see and respond to your post. I collect all the Axpert firmwares that I can find, and explore their internals to a limited degree. So I can figure out what is the latest downloadable firmware for a given model (series, type of display, power rating, chipset, whether Twin, Duplex or neither) with particular features (e.g. good MPPT logic), search for it, and post a link to it.

I would only attempt this firmware in models that come with main (U1) firmware version 28.xx. Good to know that this work might help several people.

These would be alternatives. VM III and VM IV firmwares are a big mess. It seems to be possible to intermix VM III and VM IV firmwares, though I'm suspicious about that. There are also 56.xx, 60.xx, and 70.xx firmwares, just for the Twin models. The latest in the 56.xx series is 56.72, available here. The latest in the 60.xx series is actually 60.10, which may have fixed the "stuck at 60V" issue, according to this post.

Many crazy measurements usually means a problem with the -12 V power supply. That causes problems for the op-amps used in nearly all measurements.

No, all 5 kW. Sorry.

I have one and only one 28.xx VM II Twin firmware, so I hope that this works. This is patched firmware version 428.13, based on factory firmware version 28.13 for the Axpert VM II 5.6kW '28066 Twin. Do not use with any other model, not even 24 V models running 28.xx. The original hex file is dated 28/07/2023. This firmware ONLY forces 48V operation, and changes the reported version number to 428.13. The removable display will continue to show version U1 28 13. Use at your own risk; I cannot test this firmware as I do not own an Axpert VM II. It has been "sanity checked" by disassembling the firmware and confirming that the intended changes are present. Firmware upload instructions for models with the old-style display. dsp_428.13_patched Forced 48V VMII 5.6kW.zip

I'm out of ideas. Perhaps someone who uses a Restar battery, or at least a battery using the LIB protocol, could comment.

Has the firmware been changed / updated? The firmware on these models operates on both 48 V and 24 V hardware. Sometimes also on 12 V hardware. The firmware reads the voltage on an I/O pin at start-up, and depending on what it reads, it sets the assumed voltage variable to 4, 2, or 1 (for the number of 12 V modules expected, even if it's actually a set of lithium cells). Yours is assuming 2, when it should be 4. What firmware version is it? There is a small chance that I have a compatible firmware that I can patch to always assume 48 V.

Assuming that the Restar BMS talks the same protocol that your inverter is (selected by the Battery Type setting, e.g. PYL, LIB), then it seems to me that your battery is simply badly unbalanced. Is there more than one battery module? If so, are they the same age, and have they always been connected to each other? Does the problem seem to be slowly getting better? For example, warning code 69 at 50% one day, then at 52% the next day, 53% the day after?

I have no knowledge of these new-fangled batteries with built-in BMSs. But I would imaging that the cables between battery modules run a proprietary protocol, so you'd have to stick with Pylontech. It seems to be hard enough to get new Pylontechs to talk to old Pylontechs, let alone changing brands. But others may know for sure.

No, sorry. It's fairly old now (Nov 2023). Don't be tempted to update to 12.17 (Jan 2025), as this is for the Ultra models, which have a very different (graphical) display.