13 of 20 - Intro to Backup Power and Installing the Autotransformer

The Solis Energy Storage Inverter is capable of supporting a Backup (Critical) Loads Panel. The inverter generates 240V AC power with no neutral. If your supported loads accept 240V then you will be fine with no autotransformer. However, most people are going to want 120V/120V split phase with a neutral in order to energize a small sub-panel. In this case, a Solis Autotransformer is required.

! Important: Backup Mode can be turned on or off independently of Self Consumption, Time Charging, and Off Grid Modes.

The purpose of the backup mode is to energize the backup loads panel. If anything is connected to the AC-Backup terminals then in order to energize it (on grid or off grid) the Backup Mode will need to be turned ON.

To access the Backup Mode, go to Advanced Settings > Backup Control and then from there it can be turned on or off. The settings are also found there. The voltage should remain 240V and the frequency should stay at 60 Hz.

Once Backup is turned ON - the AC-Backup terminals will be energized by 240 Vac so take caution. 

The maximum that the system can produce is up to 6000W of AC backup power at 30A but the system can surge to 7000W for one minute before going back to 6000W. 

This guide will proceed under the assumption that a Solis Autotransformer and a backup loads panel are both on site.

The full Solis Autotransformer User Manual is attached at the bottom of this article.


How to install the Solis Autotransformer (ATR):

  • Mount the bracket for the ATR and follow the Installation Space Requirements below
  • Caution: the ATR is rather heavy (53 lbs) so use proper lifting techniques when handling it to avoid injuries
  • Bring the ATR in at a 15 degree or less angle and then rotate the ATR down so the hooks catch on the bracket
  • Secure the ATR with the four M4 screws provided - tighten them to 7.3-9 N.m

  • Take the cover off by loosening the six screws with a Phillips screwdriver
  • Then remove one of the plastic plugs from the bottom of the ATR

Solis ATR Specifications:


Michael is the author of this solution article.

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