How to Stop Solar Batteries Discharging to an EV Charger: Sunsynk & Deye

As electric vehicles (EVs) become increasingly widespread in South Africa, homeowners frequently integrate dedicated Level 2 (standard single-phase or three-phase) EV chargers into their existing hybrid solar systems. However, an unexpected operational conflict frequently emerges: when the electric vehicle is plugged in, the hybrid inverter detects the substantial charging current as an ordinary household load and rapidly drains the home stationary battery bank to support it.

This interaction is highly inefficient—it amounts to discharging an expensive stationary battery to charge a vehicular battery, exhausting critical household backup reserves right before a scheduled load shedding window.

This engineering guide outlines two distinct manufacturer-approved methodologies to prevent storage batteries from discharging into an EV charger on Sunsynk and Deye hybrid inverters: software-based Time of Use (TOU) scheduling, and hardware-based physical metering isolation.

1. The Cross-Battery Discharging Conflict

In a conventional hybrid solar setup, the inverter utilizes an external current transformer (CT) clamp or smart energy meter placed at the main grid intake to measure net household import and export:

```
[ Utility Grid Meter ] ───────► [ Main Intake Tails ] ───────► [ External CT Clamp ]
│
▼
[ Main Distribution Board ]
(Includes EV Charger)
│
▼
[ Inverter Discharges Battery ]
```

When the vehicle starts charging:

• The EV charger draws continuous high current (typically 32A on single-phase connections).
• The external CT clamp detects this power draw flowing past the intake and signals the hybrid inverter to offset the import.
• The inverter discharges the stationary battery bank at its maximum rated output, depleting home storage reserves in a matter of hours.
• To avoid this undesirable behavior, installers can deploy either an inverter software schedule (Method 1) or a physical wiring modification (Method 2).

2. Method 1: Software Control via Time of Use (TOU) Settings

If physical rewiring of the distribution board is impractical, installers can utilize the inverter's internal System Mode timer scheduling.

```
+──────────────────────────────────────────────────────────────────────────+

+──────────────────────────────────────────────────────────────────────────+

+───────────────────────────+──────────────────────────────────────────────+

+───────────────────────────+──────────────────────────────────────────────+
```

Configuration Steps

In the inverter's System Mode or Time of Use (TOU) screen:

• For the scheduled time block when the vehicle is programmed to charge (such as overnight during off-peak municipal tariff hours), adjust the battery parameters.
• As detailed in manufacturer operating manuals, configure the battery soc to 100% or you can set the battery to charge in this window.
• Setting the target state of charge to 100% instructs the inverter control logic that the battery is already below or at its target threshold, immediately halting battery discharge.

Operational Trade-Off

While Method 1 requires zero electrical modifications, it has a notable operational limitation: locking the battery target to 100% stops the batteries from discharging to all property loads during that time window. If other household appliances (such as refrigeration or air conditioning) run overnight, they will draw power directly from the grid rather than the battery. If a customer desires to continue discharging battery power to ordinary household loads while isolating the EV charger, Method 2 must be implemented.

3. Method 2: Physical Hardware Isolation via Henley Block Splitter

Method 2 reconfigures the incoming distribution wiring to physically "hide" the EV charger from the inverter's current sensing electronics:

```
[ Main Grid Meter ]
│
▼
[ Henley Block Splitter ]
├──► [ Dedicated EV Sub-Distribution Board ] ──► [ EV Charger ] (Unmetered by CT)
│
└──► [ Inverter CT Clamp ] ──► [ Main Distribution Board ] ──► [ Inverter Essential Loads ]
```

Physical Wiring Architecture

As specified in official technical installation guides (where UK manuals use the term consumer unit for a distribution board, and a Henley block for an insulated splitter block):

Splitting the live tails coming from your meter using a henley block and connecting the ev charger to its own sub-consumer unit allows the inverter ct to be positioned in a way that the ev charger is hidden from the hybrid inverter and is no longer seen as a property load.

When wired in this configuration:

1. The meter tails emerging from the utility meter enter a double-pole insulated Henley block (splitter block).
2. One pair of tails feeds a dedicated mini-distribution board (what UK manuals call a sub-consumer unit) fitted with an appropriate Type B or Type A-EV RCD and circuit breaker strictly dedicated to the EV charger.
3. The second pair of tails continues toward the property's main distribution board.
4. The inverter's external CT clamp is installed on the live conductor downstream of the Henley block, placed exclusively on the feed entering the main consumer unit.

System Performance Benefits

By placing the EV charger upstream of the CT clamp:

• The electrical draw of the vehicle never passes through the CT sensor core.
• The sunsynk inverter will only see the loads from the main consumer unit therefore the batteries will cover these loads only (protecting the main property distribution board while isolating the vehicular load).
• The home batteries seamlessly power lights, refrigeration, and entertainment loads throughout the evening, while the EV charger draws directly from the grid without touching battery reserves.
• If solar generation during the day exceeds main household consumption, the inverter exports excess power past the CT clamp, where it can be naturally absorbed by the EV charger if the vehicle is charging during daylight hours.

4. Comparison of Methodologies

Summary Checklist

• Evaluated customer preference between software scheduling (TOU) and hardware isolation (Henley block splitter).
  
• If using Method 1, TOU target SOC configured to 100% during vehicle charging hours.
  
• If using Method 2, incoming meter tails split via certified insulated Henley block splitter.
  
• External CT clamp confirmed to be installed downstream of the EV feed, measuring main distribution board loads only.
  
• System tested under live charging conditions to verify zero battery discharge toward the vehicle.