Sunsynk Diesel Generator Auto-Start and Frequency Synchronisation Guide

Key Takeaways

• Sunsynk Classic, Elite, and Acure inverters can manage generator auto-start and charging.
• The generator must have an 'Auto' or 'Standby' mode selected for auto-start to function.
• Generators with built-in RCDs must connect to the inverter's GRID terminals, not the GEN terminals.
• Adjusting generator voltage/frequency limits in grid settings is for off-grid systems only; do not change if connected to the utility grid.

Configuring Your Sunsynk Inverter for Generator Auto-Start

Sunsynk Classic, Elite, and Acure inverters can automatically start a connected generator based on battery state of charge (SOC) or other conditions. This functionality relies on specific wiring and inverter settings. The generator itself must have an ‘Auto’ or ‘Standby’ selection option within its Control Panel, and this option must be selected for the auto-start function to be operational.

Understanding Generator Connection Points

Your Sunsynk inverter offers flexibility in how a generator can be connected. The generator can be connected to either the inverter's GEN connection or the inverter's GRID connection, depending on your system's specific requirements.

In most cases, it is advised to use the GEN connection. However, if the GEN connection is already being used for another function (such as an auxiliary output or a string inverter input), or if your generator has built-in earth leakage detection (an RCD), then the connection method changes.

If your generator has a built-in RCD, it is not possible to use the GEN input terminals on the inverter. Instead, the generator must be connected to the GRID input terminals. In this scenario, the 'Gen connect to grid’ setting must be enabled in the inverter settings. If the generator is connected to the GEN connection, this setting should not be enabled.

For systems that use both the utility grid and a generator, the inverter cannot accept both grid and generator power simultaneously. If grid power is detected by the inverter on the GRID connections, the generator relay will open, and generator power will not be accepted.

Generator Connection and Earth-Neutral Bonding

For off-grid systems where a generator is connected to the GRID terminals, an earth-neutral (E-N) bond needs to be created at the generator itself, which should also be earthed using a local earth rod. Many generators have a built-in E-N bond; check your generator's documentation. On the load side, an E-N bond should be created in the distribution board connected to the load terminals using an NC or NO relay. Both the generator and load side earth rods should be commoned to each other to share a reference to earth.

When the 'grid' (in this case, the generator on the grid terminals) is active, it will use the E-N bond at the generator and keep the load side one isolated. When the 'grid' is lost, the relay will close/open to connect to the temporary E-N bond in the load side distribution board. When the 'grid' returns and the grid relay closes, this will disconnect the relay to the temporary E-N bond, ensuring that only one of them is in use at any time.

Wiring the Dry Contact Auto-Start Relay

To enable the auto-start function, you must connect the generator's auto-start input to specific pins on your Sunsynk inverter.

Auto-Start Connection Pins

Use the connection pins on your inverter labelled G-S or G-Start. Please note that on some single-phase low voltage inverters, the signal may instead operate on G-V or G-Valve. The 'Gen Signal' is a normally open relay that closes when the Gen Start signal state is active.

Testing the Auto-Start Trigger

To test if your generator's auto-start function is working correctly, you can perform a manual trigger test:

1. Remove the ATS ‘Trigger’ Cable from the G-S or G-V pins of the inverter.
2. Short the two wires together to close the loop.
3. Observe if the generator starts up. It may take up to 30 seconds for the generator to auto-start.

Inverter Settings for Generator Control

Several settings within your Sunsynk inverter control how it interacts with a connected generator. These settings are typically found in the Battery Settings and Aux Load menus.

Generator Auto-Start Logic (Classic/Elite/Acure)

The inverter's auto-start logic depends on whether the system timer is enabled:

• With the system timer disabled: The generator auto-start will trigger when the battery SOC% falls below the 'Gen Load ON Batt' percentage. The batteries will then charge until the SOC% reaches the 'GEN Load OFF Batt' percentage.
• With the system timer enabled: The generator auto-start will trigger when the battery SOC% falls below the 'Gen Load ON Batt' percentage. The batteries will charge until the timer target SOC% is reached, but only during the time periods when 'GEN charge' is ticked in the timer settings. The highest SOC that can be obtained from generator charging is fixed at 95%. For more details on timers, refer to our guide on sunsynk-system-mode-and-timer-settings.

Generator Charging Current Limits

The 'Gen Amps' setting determines the power used to charge the batteries from the generator. This current is based on the DC voltage, following the formula Power = Current x Voltage. You can adjust this value to control the charging rate and ensure it is appropriate for your battery bank and generator capacity. For more information on charge rates, see our guide on sunsynk-battery-charge-discharge-rates.

Off-Grid Frequency Synchronisation

In off-grid scenarios, the Sunsynk inverter needs to synchronise with the generator's output. If the generator voltage or frequency falls outside the default range of the inverter, the upper and lower limits for voltage and frequency can be adjusted in the grid settings.

Important Safety Note: If your system is also connected to the utility grid (Eskom or municipality), these grid settings must not be changed, as they apply to both the generator and the grid connection. Changing them could violate your connection agreement or compromise grid stability. This adjustment is primarily for dedicated off-grid systems.

What you can change yourself, and what you cannot

As a system owner, you can safely adjust settings like 'On Batt', 'Gen Start', 'Gen Charge', 'Generator Peak Shaving Power', 'Gen Amps', 'Gen Force', 'GEN MAX RUN TIME', and 'GEN DOWN TIME' to optimise your generator's operation and battery charging strategy. These settings primarily affect the performance and efficiency of your system during load-shedding or off-grid use.

However, settings related to 'Gen connect to grid' and any adjustments to generator voltage/frequency parameters in the grid settings should ideally be configured by a registered person. Incorrectly altering these can affect grid protection, earthing, and compliance with local electrical standards like national grid connection standards. Any work involving physical wiring of the generator to the inverter, especially for systems connected to the utility grid, requires a qualified electrician and may necessitate an updated Certificate of Compliance (CoC).

What the published sources do not tell you

While Sunsynk provides comprehensive guidance on generator integration, some specifics are not detailed in the general support articles. For instance, detailed wiring diagrams for connecting a generator's auto-start relay to the G-S, G-Start, G-V, or G-Valve pins are not explicitly provided, often deferring to the inverter manual. Specific default frequency ranges for Sunsynk inverters are also not explicitly stated, although the ability to adjust them is mentioned. Furthermore, while the formula "Power = Current x Voltage" is given for calculating 'Gen Amps', concrete examples or typical DC voltages for this calculation are not provided, meaning you will need to apply this formula based on your specific battery bank's voltage.