Disconnecting/Reconnecting PV input while the inverter is working?

[Luk88]

I'm not sure if this should go into AIO forum of off-grid forum, but I'm leaning towards AIO as this inverter has grid support, grid charging etc. I'm talking about ESUN smh-ii-7k and MPS-VIII ECO 4.2KW (very similar devices) and other similar ones

I never saw anything about it in the respective units manuals, but it was mentioned in few places on the forum you shouldn't connect the PV input while the inverter is powered on. You should switch it off, connect the PV input, then power the unit back on.

This is contrary to how I'm hoping to use my unit. So I'm starting this thread to learn what is this advice based on? Just overabundance of caution? Or some technical reason that will cause the device to blow up the first time the rule is broken?

I have an grid-tied inverter with a PV string. I would like to set up an automated way to disconnect this PV string from the grid-tie inverter and connect it to a the AIO inverter in an extended grid-down situation. As at the time the AIO inverter will be powering my entire house from the battery I definitely do not want to be swithing it off to connect PV. What do you think? Can it be done?

Also, this is a high voltage unit, up to 450V VOC, and my string can be up to 400V in cold temperature.

 

[SeaGal]

I'm not familiar with those inverters. However, the general rule is that you mustn't connect or disconnect MC4 PV connectors whilst there is a current flowing through them. Connecting or disconnecting PV input via a suitably rated DC isolator is OK - in fact my Solis inverters have those built-in. It would be ideal to first stop PV current before isolating the connection in that manner, but not essential.

In your case, I do not see an issue. If the grid is down, your (non-hybrid) grid-tied inverter will have powered down, so it will be drawing no PV current. And the AIO/hybrid will be starting with no PV input, so safe to connect PV to that inverter IMHO.

 

[wpns]

I’m with SeaGal, the real rule is don’t connect/disconnect while current is flowing.

But you want an automated solution? Does this scenario happen enough that it can’t be manual?

If you connect PV to your AIO will it start using the solar? Maybe that ambiguity is the reason for the power-cycle recommendation

 

[Luk88]

Thanks. Initially it will be manual, but eventually I'd like to automate it with a delay. For example if the grid is down 10 minutes switch the PV to the AIO.

I'll definitely use the devices rated for the current/voltage.

Regarding if the AIO starts using the panels. I think it will, but there is only one way to find out...

 

[SeaGal]

Regarding if the AIO starts using the panels. I think it will, but there is only one way to find out

Hopefully OK - my Solis starts using it just fine in that situation. Don't see there is much difference to the sun coming up in the morning

 

[wpns]

Hopefully OK - my Solis starts using it just fine in that situation. Don't see there is much difference to the sun coming up in the morning

Depends on the firmware, if it checks for panels on power-up or (as would make more sense) constantly/occasionally and starts using them as soon as {they are connected, the sun comes up}. Probably the power-cycle instructions are based on the worst case.

But yeah, try it. Just use a proper switch or sacrificial MC4 connector in case there's a precharge spark. The SCC won't (shouldn't(?), firmware again) start drawing power from the panels until a few minutes has gone by and the input power is stable...