Xantrex XW6048 - fault F49 - DC over voltage

In my earlier response about battery size, I forgot about the ripple current the AC sinewave inverter puts on the battery.  The ripple current from inverter sinewave power profile will put ripple current on battery at twice the AC line frequency rate.

The net charge to battery may be zero due to PV charge controller supplied power but for high inverter output AC power push, the ripple current that is impressed on batteries can be quite large.

With a solar charge controller tied to batteries, the PV output is mostly a smooth continuous PV illumination based current push to batteries and inverter DC input.  The batteries act as large filter capacitor to smooth the inverter's AC power profile ripple current.  

This means the battery size must be large enough to take the large ripple current even though the average power taken from battery is zero.

If your application is to primarily provide AC power supplementation with only occasional grid power outage you are better off to use PV grid tie battery-less inverter to supplement AC power.  Using an XW with DC coupled PV power puts a large continuous ripple current on batteries that will wear them out. 

You could use an AC coupling arrangement, but I would probably keep GT inverter directly on grid mains most of time to avoid the issues with reverse power surge push into XW output when grid is down.  GT PV inverter power output control with frequency shifting by XW is slow reacting. 

With no grid power, battery backup operation, during high PV production, if you switch off a large house load there is a sudden overproduction that must be sucked up by XW inverter until it does the frequency shifting, GT inverter recognizes it and backs down its production.  This can also happen when grid drops out eliminating ability for PV power grid push.  This can take up to a couple of seconds to correct during which the XW is getting hit with the large back surge current from PV GT inverter.

There is no battery charge current regulation for AC coupling back surge, other than inverter shutting down for DC input voltage over high end limit.  Generated power always has to go somewhere.

Brock said:

What is an open loop charge/discharge?  I do have the xantrex set to only 25 amps charge if needed in the middle of the night.  Each 48v 100a battery has its own 100amp BMS so I really have 400 amps at 48 (54) volts with 800 amps surge, which I hope to never need.  Most of the time I am pulling under 1000w or about 20 amps from the bank or 5 amps per pack. 

Open loop would be the XW or it's chargers not actively managing charge/ discharge from  BMS data. You will not get Soc data on the SCP or Insight devices out to the Cloud. The BMS in closed loop would actively monitor the xanbus network. You probably are fine with a 400AH bank.

 A 100AH bank could be damaged by XW in a big surge or charging from a large source if it were open loop.

 The homes below with the green 100  (in bat Soc) are closed loop systems that get Soc out to the cloud or your phone.