Field Impact Notice- DC|DC Defects

Summary
A manufacturing process gap from one of EG4’s tier 1 semi-conductor manufacturers was discovered in July of 2025 on the DC-DC boards used in EG4’s line of Hybrid inverters. Due to the gap involving a manual process, only a fraction of units manufactured during the affected period were impacted.

After discovering the process error, EG4 quarantined, re-tested, reworked and age-tested all potentially affected units in inventory, though some units were released into the field prior to intervention. Due to the time required to retest and rework impact units, the inventory position of FlexBOSS units became backordered, delaying RMA fulfillment. This inventory impact has since been resolved.

To date, the total RMA rate on sold FlexBOSS units from a DC-DC failure is 1.17%, and we do not expect this rate to go up any further.

Customer Impact
Upon a failure of the DC-DC board, the inverter will throw a W027: Battery open fault that does not recover on its own. While in this failed state, the inverter will still allow power to pass through (grid to load) and will allow PV production to continue, however will not be able to charge or discharge the batteries.

Customers who have experienced a DC-DC board failure due to this manufacturing defect (see verification process below) will receive an advanced RMA of their affected inverter.

NOTE: Issues unrelated to the DC-DC board manufacturing defect can lead to a W027: Battery Open fault. Please reach out to EG4 to pursue additional troubleshooting.

Resolution
To confirm a DC-DC failure, the following steps can be taken –

Use a voltmeter to test voltage at the battery terminals and voltage at the inverter's battery input terminals. If voltage of battery is between 48-56v and above the SOC/Volt cut-off, check to see that vBus2, located on the EG4 monitoring site under the Data - Chart tab, is 6 times the voltage present on the battery terminals.

For example, if voltage at battery terminals is measured at 52V, vBus2 should read ~306V. A reading less than 100V indicates a DCDC failure.

Upon confirmation of a DC-DC failure contact EG4 support at [email protected] or call at 903-609-1988 for a Return Material Authorization (RMA). To expedite the process, please have your Inverter Serial Number available.

While awaiting a replacement unit, grid tied units allowed to export excess PV can continue to operate in PV only mode. To program the system to PV only the following steps should be taken –

Change the setting “Battery Type” to “No Battery” and the setting “No Batteries” should be set to “Enabled”