question

This is the boring, and obvious answer from the manufacturer side;

Deliberately running the inverter outside of the listed specifications will likely lead to unintended behaviour including possible damage, which may not be covered under warranty.

I have to smile a little bit though - this user wants the voltage window to be lower, and you would like it to be (much) higher.

Victron has a very wide operating voltage range already, and yet there is no shortage of new batteries that want to operate outside of the norms that were set by lead acid 100 years ago.

The DC input voltage range for all products is listed on the data sheets here.

The larger Pheonix inverter models list their maximum at 66V. But I am sorry to say that I think 72V is VERY far too much and will certainly see over-voltage shutdown protection activated, and maybe worse.

If you can't find another inverter that is actually intended to operate in that range, then a seperate volt meter and isolation switch should be enough to manage it.

As a somewhat useful anecdote. Before I worked for Victron, one day I absentmindedly, accidentally connected a 24V multi with a maximum DC input voltage limit of 33V, to a 48V battery bank at 52V.

I knew the moment I saw the comically large arc flash from the connection that I had made a terrible mistake. My blood ran cold that I had just destroyed $1000 of dollars of equipment in a dumb moment.

Holding my breath, I reconnected it to a 24V battery and the unit happily started up, none the worse for it's moment at nearly twice the rating.

I still consider myself lucky and I would not recommend the experience to anyone.

Great answer, cheers mate. Looking into the larger Phoenixs and how far down I'll have to bring the battery in order for the little fellas to work.