I am experiencing a synchronization issue between my Victron Quattro 48V/5000VA/70A inverter/charger and my generator.
This setup has been running flawlessly since July 2021, but starting this autumn — when the PV input has become insufficient and generator charging is again needed — a new problem has appeared.
Problem description
The inverter no longer synchronizes properly with the generator, and as a result, battery charging from the generator never starts.
Here is what happens step-by-step:
The Victron system starts the generator automatically.
The generator runs unloaded for about 10–15 seconds.
The inverter switches to charging mode and starts to load the generator.
Immediately (within about 1 second) after the inverter engages the charging mode, the generator overload protection trips, cutting off the load before charging can begin. The generator then continues to run idle without load.
This problem did not exist before — the same setup and configuration worked perfectly for over three years. All inverter and assistant settings are exactly the same as before. (I have attached screenshots of the relevant settings.)
Note 1: If I switch the inverter to “Charger Only” mode manually, synchronization succeeds and charging starts normally.
→ The issue only occurs when the inverter switch is in the normal “On” position.
Note 2: If I reduce the generator input current limit in the settings to 6 A, synchronization works and charging starts.
After charging begins, I can manually increase the current limit to 10 A and charging continues normally.
However, if I try to start charging immediately with a higher current limit (above 6 A), the generator overload protection always trips.
My questions
Could the inverter be producing a momentary current surge at the instant of synchronization, which overloads the generator?
Could this indicate a technical fault or hardware issue in the inverter?
Is there a possibility of a firmware update or configuration change that would make the Quattro start charging gradually, for example ramping up load from 6 A → 8 A → 10 A, instead of applying full load instantly?
It seems that in earlier firmware versions the inverter ramped up charging power more smoothly, but this gradual start-up behavior no longer occurs.
I would greatly appreciate your help and any recommendations for resolving this issue.
Take a look at the input current limitation wizard.
This is often used for the warm-up phase of generators.
Generator cold… low current… Generator warm… maximum current
However, you will then need a temperature switch on the generator itself… e.g., oil pan or housing.
Since you have performed a FW update for the Quattro, wizards, virtual switches, and parameters have also been changed or deleted.
What is the power rating of your generator and what type of battery do you have?
have a look at the ip protection log on the grid tab of the VE Configure program. This may give you the reason the generator won’t sync at the higher current rating. This may be due to either low voltage or under frequency with the higher current start.
Thank you for your reply!
For time being I have been testing the system carefully.
It has become evident that synchronization between the inverter and the generator fails due to the AC-in (generator input) and AC-out being linked via the Transfer Switch in the VE.Configure 3 Grid tab.
When the Transfer Switch is manually disabled (so that the generator input is used solely for battery charging and does not participate in the power pass-through to the household loads — thereby removing the need to synchronize the inverter’s AC-out with the generator’s AC phase, frequency, and voltage), the inverter and generator synchronization always completes successfully.
The same flawless synchronization also occurs when the inverter is set to Charger Only mode.
Therefore, my question is: would it be possible to implement automatic control of the Transfer Switch — meaning it would be temporarily disabled during generator synchronization (once the system detects AC input from the generator) and automatically re-enabled immediately after synchronization has been completed?
Could this feature request please be forwarded to the Victron development team for consideration?
Thank you! All these settings, Weak AC, Dynamic limiter and Max current have been set earlier.
For time being I have been testing the system carefully.
It has become evident that synchronization between the inverter and the generator fails due to the AC-in (generator input) and AC-out being linked via the Transfer Switch in the VE.Configure 3 Grid tab.
When the Transfer Switch is manually disabled (so that the generator input is used solely for battery charging and does not participate in the power pass-through to the household loads — thereby removing the need to synchronize the inverter’s AC-out with the generator’s AC phase, frequency, and voltage), the inverter and generator synchronization always completes successfully.
The same flawless synchronization also occurs when the inverter is set to Charger Only mode.
Therefore, my question is: would it be possible to implement automatic control of the Transfer Switch — meaning it would be temporarily disabled during generator synchronization (once the system detects AC input from the generator) and automatically re-enabled immediately after synchronization has been completed?
Thank you for your early reply. In my case suggested generato settings are not relevant.
For time being I have been testing the system carefully.
It has become evident that synchronization between the inverter and the generator fails due to the AC-in (generator input) and AC-out being linked via the Transfer Switch in the VE.Configure 3 Grid tab.
When the Transfer Switch is manually disabled (so that the generator input is used solely for battery charging and does not participate in the power pass-through to the household loads — thereby removing the need to synchronize the inverter’s AC-out with the generator’s AC phase, frequency, and voltage), the inverter and generator synchronization always completes successfully.
The same flawless synchronization also occurs when the inverter is set to Charger Only mode.
Therefore, my question is: would it be possible to implement automatic control of the Transfer Switch — meaning it would be temporarily disabled during generator synchronization (once the system detects AC input from the generator) and automatically re-enabled immediately after synchronization has been completed?
Via careful reseach and testing, it has become evident that synchronization between the inverter and the generator fails due to the AC-in (generator input) and AC-out being linked via the Transfer Switch in the VE.Configure 3 Grid tab.
When the Transfer Switch is manually disabled (so that the generator input is used solely for battery charging and does not participate in the power pass-through to the household loads — thereby removing the need to synchronize the inverter’s AC-out with the generator’s AC phase, frequency, and voltage), the inverter and generator synchronization always completes successfully.
The same flawless synchronization also occurs when the inverter is set to Charger Only mode.
Therefore, my question is: would it be possible to implement automatic control of the Transfer Switch — meaning it would be temporarily disabled during generator synchronization (once the system detects AC input from the generator) and automatically re-enabled immediately after synchronization has been completed?
Lol. Usually that is switched on when there are troubles with generators.
Yours must be a good one if it can synchronise without that being enabled.
By the way you can leave it unchecked in your base program for normal operation.
I am aware. Also no AI generated or derived answers please. It is against community guidlines.
The wide frequency is documented for use onky with troublesome generators. If you aren’t having trouble then you don’t need the feature.
By the way it is not deactivating the transfer switch when you disable wide frequency, it is just changing how the inverter reacts.
This is the main input relay and is the clicking sound you hear on generator connect. So there would be no transfer from in to put without it. The AI is incorrect.
See the block diagram in the appendix of your physical manual
Apologies — it was simply easier for me to explain the idea this way.
What truly matters is what works reliably in practice and can be verified.
In my system, once the Transfer Switch is disabled, the generator no longer participates in the complex synchronization process — a process that has recently always failed and required my manual intervention each time.
Now, the generator is used solely for charging the battery bank, and in this configuration, synchronization always completes flawlessly.
The inverter alone supplies the household loads directly from the batteries, with the generator excluded from that process.
Since the generator operates only temporarily, this setup is generally acceptable. However, I would prefer a system design that prevents the generator from being repeatedly disconnected — especially in cases where the generator is not particularly robust and cannot easily handle such fluctuations.
Also when a Multiplus switches over from Invert to charge mode (when AC in appears, NOT the physical switch) There is a brief moment when the Multiplus connects the AC in NEUTRAL with Earth. IF the quatro behaves in a similar manner, and your generator has an RCCB as part of it’s output protection, then this could be the reason that the gen is tripping. I would not expect any “Large Reactive” current spike during the transfer, as if the Quatro is properly synchronised both Voltage and Phase will be matched. The quatro will then ramp down the inverter, transferring the load onto the generator over a period of a few seconds.
The transfer relay has to close to accept the generator if it is passing through or charging. So disabling it will not solve your problem.
So what is more likely is either the generator protection that is tripping has developed a problem (switchgear does age and can be affected by temperatures) or the wiring inbtween has an issues or an earth neutral bond has changed.
Check your wiring and connections.
MikeD also has also made some interesting points.
Thank you very much for your previous recommendations.
I disassembled the generator and thoroughly checked all wiring, connectors, and connections. Additionally, I treated all connectors with a specialized contact cleaner designed for electrical connectors.
Visually, the entire wiring system is in perfect condition with no visible defects. I also inspected the wiring and wire terminations inside the electrical panels — all screw and bolt connections were properly tightened, as originally done by a certified electrician.
Regarding the generator’s overload protection — access to it is not possible, as it is located within the generator control module, which is encapsulated in resin by the manufacturer. Therefore, the overload unit is not accessible.
All connectors of the control module have been serviced and checked.
Further testing confirmed that the AC relay in the system’s Transfer Switch remains connected regardless of whether the Transfer Switch option is checked or unchecked in VE.Configure 3 – Grid tab. Therefore, unchecking the Transfer Switch option did not resolve the synchronization issue between the Quattro and the generator when the Quattro is in the ON mode.
Important fact: When the Quattro is switched to Charger Only mode, synchronization is always successful — 100% of the time. I have not observed a single instance of synchronization failure in Charger Only mode.
For context, this is a fully off-grid system, with the generator connected to AC Input 1 and AC Input 2 left unused.
I have also tested synchronization under zero household load conditions (no external consumption, 0 W). Even in that case, synchronization in Inverter ON mode is not consistently successful — sometimes it works, but in most cases it fails. Therefore, I have not found any correlation between household load and synchronization success.
All device firmwares are up to date.
I would therefore like to ask two questions:
Why is there a synchronization difference in Inverter ON mode that leads to failure, while synchronization always succeeds in Charger Only mode where the AC-out is factually off?
Alternatively, is it possible to configure the system so that synchronization after generator start is performed in Charger Only mode, or in a state that mimics Charger Only operation, in order to avoid interruption of the household power supply — preventing repeated internet disconnections and forced shutdowns of all household appliances? If so, how can this be set up?
You have done some pretty extensive searching for the problem.
This is not what is happening when you uncheck wide frequency.
The transfer switch is the primary relay. What you are doing is changing what conditions the transfer switch connects or disconnects.
In charger only mode it does no synchronise to my knowlege.
The difference between inverter On and charger only is the inverter does not have to build its sine wave internally to follow along with the generator one. The transfer contactor closes for both operations to be successful.
This is find interesting as the recent firmwares there has been extensive effort toward improvements to generator synchronisation mechanisms.
Maybe a rollback could be considered if it was working before and is no doing so now.
Not with how things work i don’t think.
Do you manually start your generator or is it started by the system? If it is started from the system a simple node red flow based on the relay state to swap automatically between the two states is possible.
LX: Do you manually start your generator or is it started by the system?
Aleko: It is started automatically by the system. In Charger Only mode, as soon as charging begins (in 20sec after start), I quickly switch to Inverter ON mode — and in this case, there is no synchronization issue at all.
