Automatic transfer of a reserve (ATS) for a generator with auto-start is not just convenience, but a guarantee of uninterrupted power supply in conditions of frequent outages. Unlike manual starting, the ATS system independently detects a power failure, activates the generator and switches the load without human intervention. However, an incorrectly assembled circuit can lead to equipment breakdown, short circuit or even fire.

In this article we will analyze three proven AVR schemes (for single-phase and three-phase networks), we will dwell in detail on the selection of components - from the controller to contactors, and also reveal critical nuances of setting start and stop delays that 90% of masters miss. The material is aimed at owners of private homes, workshops and small businesses, where the reliability of backup power comes to the fore.

1. What is an automatic transfer system and why the usual autostart of the generator is not enough

Many people confuse AVR (automatic reserve entry) with simple generator autostart. The difference is fundamental:

  • 🔌 Autostart — the generator starts when the network goes out, but does not switch load automatically. You will have to manually throw the switch or wait for the main equipment to burn out.
  • ⚡ AVR - a complete system that not only starts the generator, but also instantly switches consumers to a backup source, and after the network is restored, returns everything back.

Without an ATS, even the most expensive generator with autostart (for example, Honda EU70is or Fubag BS 6600) becomes useless in a critical situation. Imagine: the lights are turned off at night, the generator starts, but the refrigerator, boiler and server continue to operate from a dead UPS battery. After 10 minutes - complete collapse.

Key tasks of ABP:

  • 🔄 Instant load switching (delay no more than 0.5–2 seconds).
  • 🛑 Monitoring the stop of the generator after the network is restored (so that it does not run idle).
  • ⚠️ Protection from reverse current (when the generator begins to power the neighbors' network).
📊 What generator do you have installed?
Single phase (220V)
Three-phase (380V)
Haven't chosen yet
Other

2. Three ATS schemes: from simple to professional

The choice of scheme depends on load power, type of network (220V or 380V) and budget. Let's consider three options - from the most affordable to the most reliable.

Scheme 1: ATS on a voltage relay (for low-power systems up to 5 kW)

Suitable for cottages, small houses or workshops with a load of up to 3–5 kW. Uses voltage control relay (for example, RKN-1-15-08) and starter (contactor).

Benefits:

  • ✅ Minimum cost (from RUB 3,000 for components).
  • ✅ Easy to install (can be assembled in 2-3 hours).

Disadvantages:

  • ❌ There is no control of generator battery charging.
  • ❌ Switching delay up to 5–10 seconds.

Connection diagram:



220V network → Relay RKN → Contactor KM1 → Load


↓


Generator → Contactor KM2 → /
Detailed diagram with symbols

Download a PDF diagram with exact pin designations and fuse ratings: [link to file].

Scheme 2: ATS based on a controller (optimal option)

Uses specialized AVR controller (for example, ComAp InteliLite AMF 25 or Deep Sea DSE7320). Suitable for power generators 5–50 kW.

Benefits:

  • ✅ Fine-tuning start/stop delays.
  • ✅ Monitoring fuel level, temperature, battery charging.
  • ✅ Possibility of integration with GSM module for remote control.

Typical scheme:



Network 220/380V → ATS controller → Main contactor → Load


↓


Generator → Reserve contactor → /

Scheme 3: Industrial ATS with bypass (for 380V and power from 30 kW)

Used in enterprises where it is required zero downtime. Includes bypass switch, allowing you to switch manually if the automation fails.

Features:

  • 🔧 Used contactors with mechanical interlocking (for example, ABB ES90-30).
  • 📊 Installation required ammeter and voltmeter on every line.
Scheme Max. power Component cost Difficulty of installation
On the voltage relay up to 5 kW 3,000–8,000 rub. Low
With controller 5–50 kW 15,000–40,000 rub. Average
Industrial with bypass from 30 kW 50,000+ rub. High
💡

For three-phase generators, be sure to use a controller that supports 380V and phase control (for example, ComAp InteliLite AMF 25).

3. AVR components: what to buy and what not to save on

The quality of the components directly affects system reliability. Here is the minimum set for a circuit with a controller:

  • 🔌 ATS controller: Deep Sea DSE7320 (for generators up to 30 kW) or ComAp InteliLite AMF 25 (for three-phase systems).
  • ⚡ Contactors: ABB ESB20-20 (for 220V) or Schneider LC1D32 (for 380V).
  • 📊 Phase control relay: Eaton DILM32 (protects against phase imbalance).
  • 🔋 Uninterruptible Power Supply (UPS) for the controller (for example, APC Back-UPS 600).
  • 🛠️ Circuit breakers: on 20–32 A for single-phase and 16–25 A for three-phase lines.

What you shouldn't save on:

  • ❌ Cheap Chinese controllers (for example, unnamed ones from AliExpress) - often malfunction during power surges.
  • ❌ Contactors without mechanical interlocking — can simultaneously short-circuit the network and the generator, which will lead to an accident.

Average cost of a generator kit 10 kW:

Component Budget option The best option
AVR controller 5,000 rub. (no-name) 20,000 rub. (Deep Sea)
Contactors (2 pcs.) 3,000 rub. (IEK) 8,000 rub. (ABB)
Phase control relay 1,500 rub. 5,000 rub. (Eaton)
💡

Before purchasing a controller, check whether it supports Modbus protocol - this will allow you to integrate the ATS into the smart home system (for example, through Home Assistant).

4. Step-by-step installation of ATS: from marking to commissioning

Installation of ATS requires strict adherence to sequence. Errors at the connection stage can lead to burnout of contacts or generator damage.

Step 1: Preparing the Shield and Components

Install metal shield (for example, Schneider Electric Kaedra no less than 500×400×200 mm). Place the components so that:

  • 🔥 Between the contactors and the controller there was a distance of at least 50 mm (for cooling).
  • 📏 The wires did not cross or touch sharp edges.

Step 2: Connecting the power section

Use copper cable cross section:

  • 🔌 For 220V: 4–6 mm² (load up to 7 kW).
  • ⚡ For 380V: 10–16 mm² (load up to 30 kW).

Contactor connection diagram:



L1 (network) → Contactor KM1 (normally closed) → Load


L1 (generator) → Contactor KM2 (normally open) → /

Step 3: Controller Setup

Set the following parameters in the controller (for example Deep Sea DSE7320):

  • 🕒 Generator start delay: 5–10 sec (to avoid false positives).
  • ⏱️ Generator warm-up time: 10–20 sec (depending on the model).
  • 🔄 Network return delay: 3–5 min (so that the generator cools down).

Ensure generator is fueled|Check oil and coolant levels|Disconnect all non-critical loads|Set breaker to "Test" position|Connect UPS to controller-->

⚠️ Attention: Never connect inductive loads (for example, pumps or compressors) directly to the AVR without soft starter. A current surge during switching can burn out the contacts.

5. Typical mistakes when assembling ATS and how to avoid them

Even experienced electricians make mistakes that negate all the benefits of an ATS. Here are the most common:

  1. No contactor interlocking

    If both contactors (mains and generator) close at the same time, short circuit or generator damage. Solution: Use contactors with mechanical locking or add interlock relay.

  2. Incorrect delay settings

    Start delay too short (<3 sec) will lead to false positives in case of short-term network failures. Too long (>20 sec) - to UPS battery drain.

  3. Ignoring phase control

    In three-phase systems phase imbalance or zero break may damage the equipment. Solution: install phase control relay (Eaton DILM32).

Another critical error - connecting ATS without grounding. In this case, if there is a current leak (for example, due to damaged generator insulation), the system will not work, and a person may receive an electric shock.

⚠️ Attention: If your generator is equipped electronic voltage regulator (AVR), make sure that the ATS controller supports working with such models. Otherwise possible voltage surges up to 260V, which will damage sensitive electronics (such as boiler or server).

6. Testing and commissioning: how to test the automatic transfer switch without risk

Before the first launch necessarily perform manual testing. Here is a step-by-step algorithm:

  1. Mechanical check

    Make sure that switches and contactors switch without sticking. Check mechanical locking — when the mains contactor is switched on, the generator contactor must be blocked.

  2. No load test

    Disable all consumers. Simulate a network outage (for example, turn off the input machine). The generator should start and the controller should show status "Backup power".

  3. Test under load

    Connect non-critical load (for example, an incandescent lamp 100 W). Make sure that the switching occurs without the light blinking.

If during testing you observe:

  • 🔥 Sparking contacts - check alignment of contact groups and tightening the screws.
  • ⚡ Power surges - configure voltage stabilizer or replace the generator with a model with AVR.

To fix parameters use oscilloscope or multimeter with recording function (for example, Fluke 179). Normal indicators:

Parameter Norm Deviation
Switching voltage 220V ±5% More than ±10% is critical
Switching time <2 sec >5 sec – setup required
Generator starting current No more than 2×In More than 3×IN - check the battery

7. ATS maintenance: inspection schedule and prevention

AVR is not “set it and forget it.” To ensure that the system works flawlessly, carry out routine checks:

  • 📅 Monthly:
    • Checking the fuel and oil levels in the generator.
    • Test launch of ATS in manual mode.
  • 📅 Once every 6 months:
    • Cleaning contactor contacts (use contact lubricant, for example, Kontakt 60).
    • Checking the charge of the generator battery (the voltage should be 12.6V–13.2V).
  • 📅 Once a year:
    • Replacing the generator air filter.
    • Checking cable insulation with a megohmmeter (resistance >1 MOhm).

Pay special attention generator battery. If the voltage drops below 11.8V, the ATS controller may not start the generator. Solution:

  • 🔋 Install buffer charger (for example, Ctek MXS 5.0).
  • 🔄 Set your controller to weekly recharge (if the generator is not used).
⚠️ Attention: If your generator is running on diesel fuel, drain the sediment from the fuel tank every 3 months. Water in fuel is the main cause of failure of diesel generators during an emergency start.

FAQ: Answers to frequently asked questions

Is it possible to assemble an ATS without a controller, only with a relay?

Technically yes, but such a scheme will have critical disadvantages:

  • ❌ There is no control of generator battery charging.
  • ❌ The switching delay will be 5–15 sec (critical for boilers and servers).
  • ❌ High risk false positives in case of short-term network failures.

We recommend using the controller even for low-power systems.

Which generator is better to choose for AVR: gasoline or diesel?

The choice depends on load and battery life:

Parameter Gasoline Diesel
Power Up to 10 kW From 5 kW
Operating time without refueling 4–8 hours 10–24 hours
Cost 20–30% lower Taller but more durable

For ATS in a house with a load of up to 5 kW A gasoline generator is suitable (for example, Fubag TI 6000). For a cottage or workshop with a load 10+ kW - diesel only (SDMO HX 6000).

What happens if the ATS switches while the pumping station is running?

If the pumping station is connected directly (without soft starter or frequency converter), then when switching the ATS the following will happen:

  1. Sudden voltage drop (due to pump starting current).
  2. Possibly protection triggered generator or contactors.
  3. In the worst case - pump winding burnout.

Solution: connect the pump via soft starter (SCP) or use a generator with high starting current (for example, Huter DY6500L).

Is it necessary to legalize AVR in energy supervision?

The legislation of the Russian Federation does not require mandatory approval AVR for private houses and non-commercial objects power up to 15 kW. However:

  • 📝 If the generator power exceeds 15 kW, will be required power supply project and agreement with Rostekhnadzor.
  • ⚡ For three-phase systems (380V) installation required reverse power relayto exclude external power supply from your generator.

In any case, we recommend notifying the local grid company about the availability of a backup generator - this will help avoid conflicts in the event of an emergency.

How to integrate ATS with a smart home system?

Modern AVR controllers (for example, ComAp InteliLite) support protocols Modbus RTU or CAN. For integration with Home Assistant, MajorDoMo or IoT systems you will need:

  1. Modbus gateway (for example, USR-TCP232).
  2. Survey script (you can write to Python with library pymodbus).

Example commands for status polling:



# Read generator voltage (Modbus address 0x0100)


client.read_holding_registers(0x0100, 1, unit=1)



# Reading the ATS status (0 - network, 1 - generator)


client.read_holding_registers(0x0200, 1, unit=1)

This will allow you to receive notifications about the activation of the ATS in Telegram or by email.