Sunsynk CT Coil Wrong Readings: Troubleshooting Load and Export

Key Takeaways

• Incorrect load or export readings on your Sunsynk inverter often point to an issue with the CT (Current Transformer) coil installation.
• The first check for incorrect readings is the CT clamp's polarity and its placement on the incoming live supply.
• For three-phase systems, incorrect phase rotation can cause the load to appear to increase when the system is exporting power.
• Work involving the main incoming electrical supply and CT clamp installation requires a registered electrical person in South Africa, and a Certificate of Compliance (CoC).

Why Your Sunsynk Inverter Shows Wrong Load or Export

If your Sunsynk inverter displays load readings that do not make sense, shows export when there is none, or feeds power to the grid when it should not, the issue is often with the CT (Current Transformer) coil. The CT coil is crucial for the inverter to accurately measure the flow of electricity between your property and the grid. When it is incorrectly installed or configured, the inverter receives false data, leading to incorrect readings and behaviour.

How a CT Coil Works with Your Inverter

A CT coil is a device that measures the current flowing through a wire without making direct electrical contact. It clamps around the live incoming electrical cable to your property. As electricity flows through this cable, the CT coil senses the magnetic field created by the current and sends a proportional signal to your Sunsynk inverter.

The inverter uses this signal to understand how much power your property is importing from the grid or exporting to it. This information allows the inverter to manage your solar generation, battery charging, and grid interaction according to its programmed settings, such as zero export or selling first.

Common Sunsynk CT Coil Reading Problems and Solutions

Here are common issues with Sunsynk CT coils and how to address them:

Verifying Your CT Coil Installation

Accurate CT coil installation is critical for your Sunsynk inverter's performance.

CT Clamp Placement and Orientation

1. Placement: The CT clamp must always be placed on the live incomer cable of your property. This means it should be positioned before any Henley blocks — the connector or splitter blocks ahead of the board — or the distribution board itself, so it measures the total power entering or leaving your premises.
2. Clearance: If other CTs are nearby (e.g., for EV chargers or solar diverters), ensure they are placed at least 12 inches (30cm) apart to avoid interference.
3. Cable Routing: CT cables should not be coiled and must be kept as far as possible from any other live cables or data cables, which can cause interference or block the signal.

Connecting the CT Coil to Your Inverter

The CT coil connects to specific pins on your Sunsynk inverter:

• Single-phase inverters: The white tail of the CT clamp should be connected to pin 3, and the black tail to pin 4.
• Three-phase inverters:
• • Phase 1 CT tails connect to pin 3 and pin 4.
  • Phase 2 CT tails connect to pin 5 and pin 6.
  • Phase 3 CT tails connect to pin 7 and pin 8.

CT Ratio Settings

Your inverter needs to know the ratio of the CT coil to interpret its signal correctly.

• For standard Sunsynk CTs rated 100A / 50mA, the CT ratio is 2000:1.
• For High Voltage series inverters using 300A / 5A CTs, the CT ratio is 6000:1 (with a x100 multiplier). The CT ratio can be set in the inverter under 'Advanced Settings'.

CT Cable Length and Extension

Ideally, the cable length between the inverter and the CT clamp should be no more than 10 metres, though it can be extended up to 15 metres in some circumstances. If you need to extend the CT tails, the cable used must be made of copper and be of an equal or thicker gauge than the existing CT cables. If using CAT5/6 cable, a twisted pair should be used to reduce resistance and protect against interference. Mixing solid colour cores with colour/white cores in CAT-6 cable can cause interference, potentially doubling the perceived load.

When to Use an External Energy Meter

If you experience persistent issues with CT coil readings, or if the CT cable needs to be extended beyond 15 metres, an external energy meter can provide a more robust solution. Sunsynk inverters are compatible with several external meters, including models from Eastron and Owen Brothers.

Compatible External Meters

• Single-phase inverters: Eastron SDM120CT (120A / 40mA CT Coil), Eastron SDM230-Modbus, Owen Brothers OB115 Meter.
• Three-phase inverters: Eastron SDM630MCT, Eastron SDM630MCT v2, Eastron SDM630MCT-MV (these can also be configured for single-phase inverters).

Connecting an External Meter

External meters connect to the inverter via an RS485 connection.

1. Wiring: Follow the specific wiring instructions for your chosen meter model. For example, an Eastron SDM120CT series meter typically wires Live into port 4 and Neutral into port 3, with the CT coil (black to port 2, white to port 1). RS485 wiring connects solid blue to RS485-B (port 9) and blue/white to RS485-A (port 10) on the meter side.
2. Inverter Settings: Once connected, you must enable 'Ex_Meter_for_CT' in the inverter's 'Advanced Settings' and select the matching meter type in 'Meter Select'.
3. Cable Length: An RS485 signal can be carried up to 1200 metres with specialist data cable, or up to 100 metres with Cat5/6 cable.

What You Can Check Yourself, and What You Cannot

You can safely check the inverter's display for negative readings, verify the CT clamp's visible direction, and check the inverter's settings for the CT ratio or external meter selection.

However, any work that involves physically interacting with the CT clamp on the main incoming electrical supply, connecting or disconnecting wires to the inverter's terminals, or working inside the inverter's enclosure, must be performed by a registered electrical person. In South Africa, such work requires a qualified installer and must be accompanied by a Certificate of Compliance (CoC) to ensure safety and adherence to electrical regulations. Attempting to work on live AC tails or the main supply without proper qualifications is extremely dangerous.

What the published sources do not tell you

While Sunsynk provides extensive guidance, there are some limitations in the publicly available documentation:

• CT Orientation Contradiction: Sunsynk's documentation contains conflicting advice on the CT clamp's arrow direction. One document states the arrow should point towards the inverter, while another states it should point away from the grid towards the inverter. In practice, verifying the reading (e.g., ensuring positive load readings) is more reliable than relying solely on the arrow.
• Detailed Three-Phase CT Verification: While issues like incorrect phase rotation are covered, a comprehensive step-by-step verification process for three-phase CTs, similar to the single-phase guide, is not explicitly detailed.
• Inverter Model-Specific Pin-out Configurations: While general pin-outs are provided, the documentation often refers to checking the specific inverter manual for exact pin configurations, which are not universally available in the provided support articles.
• Quantified CT Interference Impact: The documents mention interference can cause incorrect readings but do not quantify the potential error or provide specific diagnostic steps to confirm interference beyond physical separation.