Hi

I encounters some problems with my two axpert max wired in parrallel mode (no grid input0

, see my other topic about that).

One of the two inverters get in faut mode with error 61 (firmware mismatch). The two inverters have the same display firmware and same MCU firmware (46.82). The axperts are old MCU ones.

This is compleltely random (the error could occur at startup or after few days).

The firmware in one of them is corrupted ?

Should i must downgrade firmware ?

Nice to hear from you soon

Best Regards

On 2026/04/08 at 7:00 PM, fhocorp said:

One of the two inverters get in faut mode with error 61 (firmware mismatch). The two inverters have the same display firmware and same MCU firmware (46.82).

I think you mean fault code 71. If it's really warning (not fault) code 61, then that's a problem with communications with the battery's BMS.

On 2026/04/08 at 7:00 PM, fhocorp said:

This is completely random (the error could occur at start-up or after few days).

The firmware in one of them is corrupted ?

I would not think that it's corrupted firmware. The fault code is raised when a particular CAN bus message arrives with the wrong "paralleling constant" (my term). This should happen in the first minute after start-up, so I'd say that the firmwares are fine. If flash memory is not reading correctly, considering that the DSP is executing millions of instructions per second, it would probably crash anywhere, not consistently just the part that fetches the instruction with the paralleling constant. It may not be the actual data stream that is corrupted; it may be one of the several "control" lines that are wire-ORd together. If one of those is asserting when the other machines are not expecting it, it could conceivably trigger an unrelated fault code.

Far more likely, something is going silly with the paralleling boards. It may be that the opto couplers are losing speed and/or current transfer ratio (CTR) as they age, or lightning (partially) damaged a transistor. I had a transistor completely fail due to nearby lightning. More distant lightning might induce a sort of "non-fatal wounding" causing an intermittent fault like you are seeing. Of course, electrolytic capacitors in the power supply are always popular candidates for weird problems.

If you have spares, try swapping paralleling boards first. Or just replace the power supply capacitors as it's a good idea after 5 years of operation anyway.

30 minutes ago, Coulomb said:

I think you mean fault code 71. If it's really warning (not fault) code 61, then that's a problem with communications with the battery's BMS.

I would not think that it's corrupted firmware. The fault code is raised when a particular CAN bus message arrives with the wrong "paralleling constant" (my term). This should happen in the first minute after start-up, so I'd say that the firmwares are fine. If flash memory is not reading correctly, considering that the DSP is executing millions of instructions per second, it would probably crash anywhere, not consistently just the part that fetches the instruction with the paralleling constant. It may not be the actual data stream that is corrupted; it may be one of the several "control" lines that are wire-ORd together. If one of those is asserting when the other machines are not expecting it, it could conceivably trigger an unrelated fault code.

Far more likely, something is going silly with the paralleling boards. It may be that the opto couplers are losing speed and/or current transfer ratio (CTR) as they age, or lightning (partially) damaged a transistor. I had a transistor completely fail due to nearby lightning. More distant lightning might induce a sort of "non-fatal wounding" causing an intermittent fault like you are seeing. Of course, electrolytic capacitors in the power supply are always popular candidates for weird problems.

If you have spares, try swapping paralleling boards first. Or just replace the power supply capacitors as it's a good idea after 5 years of operation anyway.

@Coulomb Thanks ! I will try this 👍

The error where show early in the morning, when the battery where near empty.

When the master battery of my second pylontech rack goes out of energy, it sends a shutdown signal to the inverter that also shutdown, even if the master battery of the first rack is working with a 50% of SoC. A feature to disable this shutdown signal could be useful as my batteries racks have sometimes different SoC.

Best Regards