Outback FX-R Series Technical Note on Input Modes

Application Note

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cycle life. So for three strings of OutBack 200RE batteries about 1500 W minimum AC

load, or 30 Adc is best.

2. Be sure the RE kWh exceeds the load kWh or the batteries may be chronically

undercharged as the batteries compete with the loads for power to recharge themselves.

The RE kWh minus the load kWh must equal enough charging current during the RE

period to properly charge the batteries.

3. The RE kWh must be more than the load kWh, but not so much that the maximum

battery bank charging current is exceeded. For example, a 4kW Radian/FXR inverter

with a 4kW PV array into an FM80 charge controller will produce a maximum current of

80 Adc. If the DoD Amps is set to 7 Aac, this would result in a 32 Adc draw from the DC

bus (minimum suggested per guideline #1), which leaves 48 Adc for charging the battery

bank. This is too much for a single string of OutBack 200RE batteries, and a little on the

high side. It is all right for two strings, and just about right for three strings. If a larger

array is going to be used, then Li Ion batteries would be a good choice as they can be

charged and discharged rapidly with very little consequence.

Mini Grid Mode

The normal operation of Mini Grid is for the inverter and loads to be disconnected from the grid

and power the loads with PV power and/or stored energy from the battery. Unlike Grid Zero, the

rate of discharge from the battery is not controlled. Grid power is not blended with PV power

unless it’s in Offset mode while charging the batteries. However, similar to Grid Zero, the Mini

Grid mode works best when there is more PV power kWh than load demand kWh as it only

connects to the grid when the battery hits a user selectable low-battery setting. As long as there

is adequate active PV power and stored PV power in the batteries to power the loads, then Mini

Grid will never connect to the grid. If the low battery setting is reached for the delay period

specified, then the Radian/FXR connects to the grid and it will power the loads. If the

Radian/FXR charger is turned on, then the batteries will complete a full charge cycle from the

grid (a partial charge cycle can also be specified). The inverter will not disconnect from the grid

until adequate PV power is available, or achieves one of the three DC voltage targets (see

Offset application note). If the Radian/FXR charger is turned off, then the grid will power the

loads on reaching the low-battery setting, but will not charge the batteries from the grid. The

Radian/FXR will not disconnect from the grid and start powering loads with PV power until

adequate PV power is available for charging the batteries and powering the loads. Follow the

same battery sizing guidelines listed above under Grid Zero.