Read the manual thoroughly and understand all of the instructions, cautions, and warnings before using this equipment. If any section of the manual is not understood, contact your nearest authorized dealer, or contact Generac Customer Service at 1-888-436-3722 (1-888-GENERAC), or www.generac.com with any questions or concerns. 

Understanding the home standby generator's charging system

This article explains the home standby generator charging system, and how the charger adjusts voltage based on temperature and connects to a 120 VAC source. It describes the charger's behavior during utility failures and regular operations and emphasizes that the battery charger powers the controller during standard operation. 

Environment

This article applies to Generac air-cooled Guardian Series 10-26 kW generators.

What does the home standby generator charging system do?

The charging system of the home standby generator is crucial for keeping the battery in optimal condition, ensuring it is ready to power the generator whenever needed. This system intelligently adjusts the charging voltage based on the ambient temperature to maintain battery health and efficiency.
 

Charging voltage levels
 

• High Temperature: at high ambient temperatures, the system charges the battery at 13.5 VDC to prevent overcharging.
• Normal Temperature: Under typical conditions, a 14.1 VDC setting is used, ideal for maintaining a full charge.
• Low Temperature: In colder environments, the voltage is increased to 14.6 VDC to ensure the battery receives enough charge.

Power source and charging cycle

The battery charger is integrated into the home standby generator's controller. The charger provides current directly to the battery depending on temperature and is powered through a 120 VAC fused circuit from the transfer switch.
 

• During normal operation (with utility power present), the battery charger supplies all the power to the generator's controller; the generator battery is not used to supply power. 

• During a utility failure, the charger will momentarily be turned off until a load is applied.

• If there is a utility outage and the generator is turned off, the battery charger is powering nothing, as no electricity is being produced.

18-hour charge cycle

The charging cycle is initiated when the battery voltage drops below 12.6V. It then supplies power based on temperature, engaging in an 18-hour charge cycle. If the battery’s charge current is too high or the voltage too low at the end of this cycle, an “inspect battery” [Nexus] or “charge warning” [Evolution] is triggered.

For more information on battery alarms, see: Troubleshooting home standby battery alarms and error codes

Note: If at any point during the battery’s 18-hour charge cycle, the generator's engine cranks the 18-hour charge cycle timer is reset.

Temperature considerations

At the end of the 18-hour charge period, the charge does one of two things depending on ambient environmental temperature considerations.

After the 18-hour cycle:

• Below 40 Degrees F: The charger continues at 14.1V, suitable for cold conditions.

• Above 40 Degrees F: The cycle stops to prevent overcharging.