FORTRESS Power 

If the customer cannot supply the load information, or assumptions cannot be made, the rule of thumb as an absolute minimum battery size is to match the power rating of the inverter in kW to the energy rating of the battery in kWh. If a single inverter is rated at 6.8 kW, meaning a minimum battery size of 6.8 kWh would be required. In that case an LFP-10, with an 80% discharge capacity of 8 kWh would be enough to meet the minimum battery size by this very basic calculation method. 

Setting up a Fortress Power Lithium Battery using Magnum Inverter/Charger 

Magnum MS4448PAE Inverter Battery Turn On/Off Levels Setting 

Low Battery The inverter will shut off whenever the battery voltage falls to the LBCO (Low Battery Cut Out) level to protect the batteries from being over-discharged. After the inverter has reached the LBCO level and turned off, the inverter will automatically restart after one of the following conditions:

1. AC Power is applied, and the inverter begins operating as a battery charger.

1. Battery voltage rises to the LBCI (Low Battery Cut In) level. 

*High battery voltage may be caused by excessive or unregulated voltage from solar panels or other external charging sources 

Magnum MS4448PAE Inverter/Charger Values 

• Shore Max This setting ensures the inverter AC loads receive the maximum current available from the utility or generator power. When the total current used to power the AC loads and charge the batteries begins to approach the Shore Max setting, the current that was used for charging the batteries will automatically be reduced. 
• 01 Search Watts This setting allows you to turn off the power-saving Search Mode circuitry or adjust the power level at which the inverter will "wake up" and start inverting. 
• 02 Low Battery Cut Out Voltage - This setting determines when the inverter will turn off based on low battery voltage. The inverter turns off automatically after the battery voltage has been below this setting for more than one minute. This protects the batteries from over-discharge and the AC loads from unregulated power (brownouts). 
• 03 Batt Amp Hrs. (see "Max Bulk and/or Discharge Current") - This setting allows the user to input the battery bank size in amp hours which tells the charger how long to charge the batteries in the Absorb charge stage. 
• 04 Battery Type - Sets the type of batteries being used in the system; this information tells the charger what voltage level to use to charge the batteries. 
• 05 Charge Rate This setting can be used to turn off the charger, limit the amount of current that the charger can use (leaving more current available to power loads); or to ensure small battery banks are not overheated because of a charge rate that is too high. 
• 06 VAC Dropout Sets the minimum AC voltage that must be present on the AC input before the unit transfers from Standby Mode to Inverter Mode. This protects the AC loads from utility outages and brown-outs. On MS-PAE models, when two inputs (leg 1 and leg 2) are used, the VAC Dropout voltage is determined by the sum of the two inputs ÷2. For example, if input 1=120VAC and input 2=110 VAC, the sum (230) ÷2=115. In this example, 115 VAC is what the inverter's AC input is sensing to determine when to stay connected or disconnect and start inverting. 

Charge Controller Settings 

In a DC coupled system, solar controller(s) must be used to regulate the PV power and charge the batteries. Please select the Charge controller which is compatible with Fortress Lithium batteries. We use MAGNUM PT-100 MPPT Charge Controller as an example here. 

Parameter Setting for PT-100 Charge Controller 

Please reassess capacity and charge/discharge current settings, when Fortress battery quantities change. 

How to Calculate the Max Charge Rate 

RULE: I Battery Max Charge > Charge Controller Max Charge + Inverter Max Charge 

Example: 1 MAGNUM PT-100 MPPT Charge Controller; 

1 MS4448PAE; 2 LFP-10 batteries 

Recommend setting : I Battery Max Charge = 80A per Battery; 

Total: 160A for 2 batteries 

Charge Controller Max Charge =100A (100%) per Charge Controller 

I Inverter Max Charge must be less than or =60A (160A-100A =60A) 

One MS4448PAE maximum output charge current is 60A. 

Therefore, the Max Charge Rate of the inverter will be set at 100% (60A / 60A =100%) 

Example: