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Tuong Lee avatar image
Tuong Lee asked

Multiplus II 2x 120v - Won't power on after firmware downgrade

I recently downgraded the firmware on my multiplus and following the downgrade when I reconnect my multiplus to my cerbo gx, it would fault and toggle back between the inverter on (geren light) and Float (yellow light) and 3 yellow lights for charger (bulk, aborbtion, float). I would have no AC power from the invter. DC power is fine. when I turn the inverter off and back on, it would not power on. The only way I was able to get the inverter to turn back on is if I took the vebus cable that was connecting the multiplus to the cerbo gx and plug it into my laptop via the mk3 usb interface. When connected, inverter appears to be functioning, i get AC power in my trailer, but if I run a big load like my microwave, i get the low power warning.

Has anyone seen this error with the toggle of the lights? what was your fix?img-6084.png img-6085.png

I upgraded the firmware back to the latest version and experience the same issues.


A bit of history:

This started with me setting up my Multiplus II 12v 3000w in my trailer. I have an 888 AH lifepo4 battery bank (3 x 12v batteries in parallel. I have a cerbo-gx and a victron smart shunt (but the smart shunt was not yet connected to the cerbo-gx. (as I didn't have a ve direct cable long enough) Everything was working fine, ran heavy ac loads like the air conditioner and air fryer which was drawing 2000+w off battery and ran these loads using grid power and everything worked as expected. It was the original factory firmware from when i purchased the multiplus in July 2023 so am guessing it was version 504 or 505 firmware. I then did a firmware update to the latest which was v510. I saved my veconfigure settings and After the firmware upgrade, i restored my ve configure settings for the multiplus. I started to get low battery and low voltage warnings and the inverter would shut off (even though my smart shunt was reading the battery as near full.


I thought it was because my smart shunt was not yet connected to the cerbo-gx so it wasn't getting accurate voltage readings So i purchased a ve-direct cable that was long enough and connected the smart shunt to my cerbo-gx (initially it wasn't reading it, turns out I had one of the serial #'s where there is a known problem, long story short, i swapped it for a more current one and everything read fine). I updated the firmware of the smart shunt to the latest firmware.

Even after connecting the smart shunt was still getting the same low voltage / low battery warning, inverter would shut off, and then restart itself after a few seconds. Even though the cerbo gx was reading the correct voltage the entire time (and battery was near full).


I verified the settings in my multiplus are set correctly so shouldn't have triggered the low voltage warnings. (also they were the same settings from before the firmware upgrade where everything is working was working fine. I played around with the low voltage warning and alarms, and was still getting the trigger and the inverter would shut off.


I decided to downgrade my firmware for my multiplus and that is where I'm getting the issue that I described at the beginning of this post. tried a few older versions of the firmware, and tried upgrading to the latest and still not able to get the inverter to turn on after a reset and plugging the inverter back into the cerbo-gx.


any suggestions or help would be greatly appreciated


Multiplus-II
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2 Answers
Matthias Lange - DE avatar image
Matthias Lange - DE answered ·

Use the Victron Toolkit App to identify the error code.

Check the VE.Bus wiring. Did you use the correct ports on the Cerbo?

What happens if you disconnect the VE.Bus cable?

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Tuong Lee avatar image Tuong Lee commented ·

Thanks @Matthias Lange - DE I used the toolkit app and followed the recommended steps. Changing the UPS state in VEConfigure to force the push of all config settings and reboot of the multiplus seemed to have worked.

Now Multiplus stays on, but am getting the low voltage error whenever there is a load.

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pwfarnell avatar image
pwfarnell answered ·

You say the SmartShunt gives the SOC as nearly full. If your SmartShunt is not set up right it can read full when the batteries are empty. Have you checked the SOC via battery voltage (not easy for lithium I know) or SOC on the batteries if they have Bluetooth. Post a screenshot of your SmartShunt settings and we can advise.

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Tuong Lee avatar image Tuong Lee commented ·

I charged the batteries over night just to be sure and am still getting the low voltage error whenever I put a load on and the multiplus will shut off and then reboot itself after a few seconds.


Here are screenshots of my settings. img-6094.png

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pwfarnell avatar image pwfarnell Tuong Lee commented ·

@Tuong Lee your SmartShunt settings are OK and should not give you false high readings, it was worth checking because we see a lot of cases where the battery is empty even though thevshunt says full because of wrong settings.

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Tuong Lee avatar image Tuong Lee commented ·

Also, here is the voltage drop when I turned on my AC in the trailer, there is a drop but certainly not enough to set off the low voltage alarm which is set to 11.2V and showdown set to 12.0V


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Tuong Lee avatar image Tuong Lee commented ·

So continuing to troubleshoot and decided to leave the dc input low pre-alarm at the default 10.9V and the low-input shutdown at 9.3v


This time when I turned on the Air conditioner, the low battery and overload alarm triggered during the starting but then disappeared. And the Air conditioner ran for another 3 minutes before it the low battery alarmed again and this time the flashing red light stayed on but the inverter didn’t shut down.

It’s about 20” of cabling from the battery bank to the inverter. The shunt is connected at the battery bank. I did recently swap out my 1 AWG cable for 2/0 cable. But wouldn’t think this is due to voltage drop could it?


AC has been running straight for 8 minutes now without inverter failing.

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Tuong Lee avatar image Tuong Lee Tuong Lee commented ·

On my Cerbo I do have dvcc enabled.

So when I access the multiplied through the Cerbo gx menu, it does pick up the voltage from the smart shunt. But low battery alarm still goes on. Also look at the descrepancy between the battery voltage from the smart shunt vs the mppt and the air conditioner is running

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pwfarnell avatar image pwfarnell Tuong Lee commented ·

@Tuong Lee as your MPPT is displaying a much lower battery voltage than your SmartShunt You may have a poor connection somewhere in your system. The SmartShunt is connected directly to the battery -ve and the sense lead directly to the battery positive so it gets good readings. I then assume you have some isolators, fuses and a busbar in the +ve and a busbar in the -ve and the MPPT is connected to the busbars. Therefore you are getting 1.7V drop between the location where the MPPT connects and the battery. This could be poorly crimped terminals, bolts not tightened up, poor quality isolators or loose fuses. Check to see if anything is getting warm and use your multimeter when the ac is running to measure voltages at all locations.

A common problem is using low quality isolators, use quality items like Blue Sea 500A rated isolation.

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