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TECHNICAL NOTE: Sunny Boy US-41: Secure Power Supply Operation with TS4-R-O

Posted by SMA America LLC on


This notice provides instructions for installing the Secure Power Supply for a Sunny Boy PV system outfitted with SMA TS4-R-O devices.


  • Sunny Boy 3.0 / 3.8 / 5.0 / 6.0 / 7.0 / 7.7-US-41
  • Type designation: SBx.x-1SP-US-41
  • Firmware software package version: 3.01.06.R or higher


The TS4-R-O devices have built-in rapid shutdown functionality in accordance with NEC 2017 Article 690.12. The rapid shutdown functionality is designed to be triggered when either the DC or the AC power connection to the inverter is switched off. Therefore, when a grid outage occurs, the inverter signals the TS4-R-O devices to enter a rapid shutdown condition which reduces the DC voltage inside of the PV array boundary to less than 80 Volts within 30 seconds in accordance with NEC 2017 Article 690.12(B)(2)(2). 80 Vdc would normally be less than the Sunny Boy inverter’s starting voltage and therefore would be insufficient to power the Secure Power Supply during a grid outage, even if there was sufficient sunlight available.

To overcome this situation, the inverter must release the TS4-R-O devices from their rapid shutdown condition. This can be achieved if the following conditions are met:

1.The inverter model is SBx.x-1SP-US-41 with a firmware package of 3.01.06.R or higher.

2.There are two 9-Volt batteries connected in series (18-Volts in total) connected to the high voltageside of the Secure Power Supply Switch (as shown in Figs. 1 and 2)

3.The user manually activates the Secure Power Supply switchUnder these conditions, when the utility grid is disconnected, the 9-Volt batteries energize the rooftop gateway, which releases the TS4-R-O devices from their rapid shutdown condition and therefore allows the inverter to commence operation from the DC inputs, assuming there is sufficient sunlight available.

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