Sunsynk Inverters: Smart Energy Management for Your Home’s Power Needs

The clarification on EPS, UPS, and Aux/Gen, as well as the “pass-through” function of the inverter.

Sunsynk inverters are sophisticated hybrid devices designed to intelligently manage multiple power sources – the utility grid, solar panels, and battery storage – to provide reliable and efficient electricity to your home. Understanding their various outputs and how they handle power transfer, especially during grid outages, is key to appreciating their role in a modern energy system.

Understanding Sunsynk Inverter Outputs

A Sunsynk hybrid inverter typically features distinct output terminals, each with a specific purpose:

Grid Input/Output (Grid-tie): This is the primary connection point to your utility grid.
- Input: When grid power is available, the inverter uses this connection to draw power for your home, charge your batteries, or accept excess solar power from your panels.
- Output: This is where the inverter can export surplus solar energy back to the grid if you have a grid-tied agreement and also provides power to the home load via the AC connection (home of grid powered).
- NOT: This output is not designed to provide backup power to your entire house directly in the event of a grid failure. Its fundamental role is grid interaction.
Load (Essential Loads / EPS / UPS): This output is your designated lifeline for critical appliances and circuits.
- Function: This terminal supplies power to your Essential Loads, meaning those appliances and circuits you need to keep running constantly, particularly when the grid goes down. This serves as your Emergency Power Supply (EPS) and Uninterruptible Power Supply (UPS), ensuring power for crucial items when the grid fails.
- How it Works:
  - Grid Present: When the grid is active, power from the grid (or from solar/battery, depending on your inverter’s settings and current conditions) is supplied to this “Load” output.
  - Grid Failure (UPS/EPS Function): When the grid fails, the inverter executes a rapid, seamless transfer (typically within 10-20 milliseconds). This is achieved through internal relays:
    - An internal grid-isolation relay immediately opens, disconnecting the inverter and your essential loads from the failed grid. This is crucial for safety, preventing power from being fed back onto the grid during an outage (anti-islanding).
    - Simultaneously, an internal backup relay closes, connecting the inverter’s internal power generation (from your batteries and/or solar panels) to this “Load” output. This swift action ensures a virtually imperceptible transition for your connected critical loads.
- Usage: For homes operating entirely off-grid, the entire house load would typically be connected to this “Load” output, as the inverter becomes the sole power source.
Aux (Smart Port / Input or Output): This provides flexible control over specific circuits.
- Function: This “smart port” can be configured either as an input (e.g., for a generator ) or, more commonly, as a controllable output. As an output, it’s perfect for “smart loads” – appliances you want to switch on or off based on specific conditions, such as excess solar production, time of day, or battery levels. Examples include geysers, pool pumps, or electric vehicle chargers.
- Control: You have extensive programming options to automate this output. For instance, you could program it to activate only when your batteries are fully charged and there’s ample solar power, or to turn off if battery levels drop below a certain threshold.
- Backup: The “Aux” output can also be configured to receive power during a grid outage from your batteries and solar. However, it’s frequently used for non-essential loads that can be shed to conserve battery energy, unlike the “Load” (essential loads) output.
- NOT: This “Aux” port is not primarily designed for always-on, uninterrupted critical loads like the “Load” (essential loads) output, unless specifically programmed for that purpose and treated as an extension of essential loads or for additional inputs. – There are conditions here for input power types.

How the Inverter Functions When Wired to a House

When a Sunsynk inverter is integrated into your home’s electrical system, it acts as a central energy manager:

Grid Connection: The inverter is connected to your main electrical panel via its “Grid Input/Output.”
Load Separation: For effective backup and energy management, your home’s electrical circuits are typically divided:
- Essential Loads: These circuits (e.g., lights, fridge, Wi-Fi, critical medical equipment) are connected to the inverter’s “Load” (Essential Loads) output. This ensures they benefit from the UPS function.
- Non-Essential Loads: These typically remain connected directly to your main electrical panel, powered by the grid. If you want some of these to be controllable, they can be connected to the “Aux” (Smart Port) output.
Internal Relays and Switching: The Sunsynk inverter relies on internal relays to manage power flow:
- Grid Present & Stable: The inverter’s internal bypass relay is closed, allowing grid power to flow directly through the inverter to the “Load” (Essential Loads) output. At the same time, the inverter continuously monitors solar production and battery state, charging batteries or exporting excess solar to the grid as programmed.
- Grid Failure (UPS/EPS Activation): Upon detecting a grid failure, the internal grid-isolation relay opens instantly, disconnecting your essential loads from the faulty grid. Simultaneously, the internal backup relay closes, connecting the inverter’s internal power generation (from batteries and/or solar) to the “Load” (Essential Loads) output. This rapid, automatic switching is what defines the UPS/EPS function.
- NOT: The inverter does not rely on an external Automatic Transfer Switch (ATS) to manage this transfer for your essential loads because its internal relays provide the necessary high-speed isolation and transfer.
Grid Connected: Used for the flow of power too and from the inverter and grid, This can include to home loads where the inverter pushes power to the grid connection ( limited with a CT clamp) where the house loads are also accounted for in the production. This is a typical standard installation, and a Single wire install.

Why We Don’t Use an External ATS for the Whole Load

You typically do not install a separate, external Automatic Transfer Switch (ATS) to change the entire house load between the grid and a Sunsynk inverter for several practical reasons:

Integrated UPS Functionality: The Sunsynk inverter inherently provides the high-speed transfer capability for its “Load” (Essential Loads) output via its internal relays. This built-in UPS function negates the need for an external ATS for those critical circuits.
Grid-Tie Compliance & Safety: For grid-tied systems, the inverter must isolate from the grid during an outage to prevent back-feeding electricity (which could endanger utility workers). The inverter’s internal relays manage this crucial safety isolation. An external ATS would be redundant and could potentially complicate or interfere with the inverter’s safety protocols.
Optimal Load Management: Sunsynk inverters are designed for intelligent power management. Attempting to run the entire house load directly from the inverter can lead to frequent overloading if the inverter’s capacity is exceeded by large appliances. By separating loads into “essential” and “non-essential,” you ensure critical items remain powered during outages while conserving valuable battery energy for what truly matters.
Cost and Complexity: Adding an external ATS for the whole house introduces unnecessary complexity and additional cost without offering significant advantages over the inverter’s robust, integrated capabilities for typical residential applications.

The EPS/UPS Ensures Essential Loads Are Always On…

This refers directly to the “Load” (Essential Loads) output of the Sunsynk inverter. Any appliance or circuit connected to this output benefits from the Emergency Power Supply (EPS) and Uninterruptible Power Supply (UPS) function. This means that, as long as there is power available from your solar panels, batteries, or the grid, these essential loads will remain powered without interruption, even during grid failures.

The Load is Dropped When…

The inverter will intelligently shed or disconnect certain loads under specific conditions to protect itself, your batteries, or to adhere to programming:

Overload: If the total power drawn by the connected loads (on the “Load” or “Aux” outputs) exceeds the inverter’s maximum continuous output rating, the inverter will trip and disconnect the output to prevent internal damage.
Low Battery Voltage: If the battery voltage drops below a pre-set low-voltage cut-off point, the inverter will disconnect loads from the batteries. This protects the batteries from excessive deep discharge, which can drastically reduce their lifespan and performance. ( the smart port can be programmed separately)
Inverter Fault: In the unlikely event of an internal fault or critical error within the inverter, it will cease operation and drop all connected loads as a safety measure.
User Configuration (Aux / Smart Port): For loads connected to the “Aux” (Smart Port) output, you can program the inverter to drop these loads based on various conditions:
- Battery State of Charge: (e.g., turn off the pool pump if batteries drop below 50%).
- Time of Day: (e.g., don’t run the geyser during peak grid tariff hours).
- Lack of Solar Production: (e.g., don’t run heavy loads if there’s insufficient sunlight).

The Inverter Has a Pass-Through Which Provides Power Connected to the Grid and When…

The “pass-through” or “bypass” functionality is a key efficiency feature of Sunsynk inverters when operating with a grid connection.

How it Works: When the grid is present and stable, the inverter’s internal bypass relay closes. This allows grid power to flow directly through the inverter’s internal circuitry to the “Load” (Essential Loads) output without first being converted from AC to DC and then back to AC by the inverter’s internal power electronics.
Benefits:
- Efficiency: This bypass mode reduces energy losses that would occur during a double conversion process (AC-DC-AC), making the overall system more efficient when grid power is available.
- Capacity: It allows your essential loads to draw power directly from the grid, potentially exceeding the inverter’s continuous output rating (as long as your main circuit breaker and wiring can handle it).
When it Applies: This pass-through functionality applies when:
- The grid is present and stable.
- The inverter is not actively converting power from batteries or solar to supply the “Load” output (e.g., when batteries are fully charged, or solar production is low, and grid power is the primary source).
- NOT: The pass-through does not provide power from the grid during a grid outage. At that critical point, the inverter isolates from the grid and switches to using power from batteries and/or solar to supply the “Load” (Essential Loads) output.

By clearly understanding these distinct outputs, the precise role of internal relays, and the intelligent management capabilities, you can effectively utilize a Sunsynk inverter to create a resilient, efficient, and smart energy system tailored to your home’s unique power demands.

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if you are within 1 hour of Basingstoke we can carry out the work for you and take the headache away.
There are a few ways in which the inverter can be wired, it is why they are so popular. So you could wire these in a number of ways to get to the same result. you can also get it wrong. Remember the inverter is multi use, therefore you must consider all purposes of the inverter and have the logic of how and why to make this work.

Information is a table format:

Feature / Scenario	Grid Input/Output (Grid-tie)	Load (Essential Loads / EPS / UPS)	Aux (Smart Port)	Key Relay Actions
Ports & Purpose	Connection to the utility grid. For grid interaction (drawing/exporting power).	Designed for critical appliances/circuits that must remain powered. Provides Emergency Power Supply (EPS) & Uninterruptible Power Supply (UPS).	Flexible output for “smart loads” (e.g., geyser, pool pump) that can be controlled based on conditions. Can also be an input.
Normal Operation (Grid Present)	Grid connection active. Inverter draws power from/exports power to grid.	Primary Power Source: Grid (via bypass relay), then Solar, then Battery (based on settings). All essential loads are powered.	Primary Power Source: Grid (or Solar/Battery if configured). Controlled based on programming (time, battery %, solar surplus).	Bypass Relay: CLOSED (allowing grid power to flow directly to Load port).<br>Grid-Isolation Relay: CLOSED (connecting inverter to grid).
Grid Failure (UPS/EPS Activated)	Disconnected. Inverter isolates from the grid for safety.	Primary Power Source: Instantaneous switch to Battery & Solar. Seamless power for all essential loads.	Primary Power Source: Battery & Solar (if configured for backup). May be shed based on battery level settings.	Grid-Isolation Relay: OPENS immediately (disconnecting from grid).<br>Backup Relay: CLOSES immediately (connecting internal inverter power to Load port).
Overload Condition	N/A (assuming overload on output side)	Output Disconnected. Inverter trips to protect itself.	Output Disconnected. (if connected to this port).	Internal Output Relays: OPEN (to disconnect loads from inverter).
Low Battery Voltage	N/A	Output Disconnected. Inverter disconnects loads to protect batteries from deep discharge.	Output Disconnected. (if configured to shed on low battery).	Internal Battery Discharge Protection Relay: OPENS (disconnecting battery from inverter if critical low).<br>Output Relays: OPEN (to disconnect loads).
Pass-Through Function	Grid power available.	Grid power flows directly to this port via internal bypass, without DC-AC conversion by the inverter. Most efficient when grid is present.	N/A (Pass-through typically applies to the main “Load” output).	Bypass Relay: CLOSED (allowing direct grid power flow to Load port).
NOT:	NOT backup power.	NOT designed to run the entire house unless specifically sized and configured for off-grid.<br>NOT disconnected by an external ATS.	NOT primarily for always-on critical loads unless specifically configured.	NOT using an external ATS for whole house transfer (internal relays handle essential loads).