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Axpert MAX 48V 7200W - low DC cut-off voltage patch


George.H
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Hello guys,

    at home I'm currently running setup of AXPERT MKS 48V 5kW + Batrium BMS + 6x Tesla battery modules (48V, cca 30kwh). I'm pretty happy with it. As I would like to upgrade my inverter (because I need to have higher power output), I'm looking into options like Axpert Max or Victron Quattro. Victron is fine choice however double in price to Axpert. Before I spend fortune on Victron, I would like to ask if anybody have the know-how about patching the Axpert firmwares. I would need just to change low DC cut-off voltage to the lower value than original firmware allows.

    I need this because Tesla modules are 12S (two in series), so my cut-off voltage needs to be around 38V. My Axpert gives me 40V, which is tolerable, Axpert Max has the 42V minimum - that is too high for me.

    I'm a developer, I know the assembler, however I know how time consuming would be to dive in firmware without any experience how it is structured. Does anybody have a hint? I know it's probably doable, I have seen that somebody here already did much more complex stuff to the firmware than this.

    Many thanks. George

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2 hours ago, George.H said:

 I'm a developer, I know the assembler,

We're a rare breed it seems, George.

2 hours ago, George.H said:

Does anybody have a hint? I know it's probably doable,

I could help you with this effort if you are serious. But the first problem is obtaining an image of the existing firmware, as a starting point for analysis and ultimately patching. Since the appearance of the clones back in about 2015, the firmware update files (which contain the firmware in the clear) have been difficult to obtain. I've not seen any for the Max at all. So that's the first hurdle.

As to what's involved: lots of disassembling, reading and understanding. I know my way around the various firmwares pretty well now (though I can't pretend to understand more than a small fraction of what is happening). When changing a limit, if you ever want to parallel the machine with another (maybe not so important with a 7.2 kW model), you also have to change the CAN packets relating to that limit, and that gets tricky. Otherwise, the patch could be as simple as changing a handful of immediate operands in instructions, possibly only one or two. Once you know what to change, you just edit a copy of dsp.hex, fix the checksums in the affected lines of the hex file using a spreadsheet, and reflash the firmware.

Of course, every change has consequences. To get full power from a reduced battery voltage, the inverter will have to draw more battery current. You may have to be careful to stay away from full power, to prevent overtaxing the battery side of the main DC-DC converter. So perhaps you should consider some extra patches to make yours a 38/42 x 7.2 = 6.5 kW max model. Not impossible, but more work.

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3 hours ago, Coulomb said:

Of course, every change has consequences. To get full power from a reduced battery voltage, the inverter will have to draw more battery current. You may have to be careful to stay away from full power, to prevent overtaxing the battery side of the main DC-DC converter. So perhaps you should consider some extra patches to make yours a 38/42 x 7.2 = 6.5 kW max model. Not impossible, but more work.

Thank you Coulomb for dragging me into reality :)

I didn't think about a risk that DC converter could be a limiting factor in such change. With that in mind, trying to stay within DC currents limits for lower voltages will make the Axpert Max not so sexy choice for me .... too much effort for 1.5kw gain from the model I have now.

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