AVR unit for a generator with auto-start: a complete guide to selection and connection

Power outages are a headache for owners of private homes, summer cottages and small businesses. Even a short-term blackout can cause heating boilers, refrigeration equipment or servers to malfunction. Solution to the problem - ATS unit (automatic transfer switch) paired with a generator equipped with an autostart system. This combination guarantees uninterrupted power supply: if the network fails, the generator starts automatically, and the ATS unit switches the load without human intervention.

However, not all ATS units are equally effective, and connection errors can lead to failure of both the generator and the connected devices. In this article, we will look at how to choose the right ATS unit for a generator with auto-start, what connection diagrams exist, and what to pay attention to when setting it up. We will pay special attention popular models (for example, Fubag ATS, Genmac ATS-100, Vevor 100A) and typical mistakes made during installation.

What is an AVR unit and how does it work with a generator?

The ATS unit (Automatic Transfer Switch) is a device that automatically switches power between the main network and the backup source (generator) in the event of a power failure. In the case of a generator equipped with autostart, the process looks like this:

1. Network interruption: the ATS unit detects a lack of voltage in the main line.
2. Launch command: The ATS sends a signal to the generator via dry circuit contacts or according to protocol RS-232/RS-485.
3. Warm-up and stabilization: the generator starts and reaches operating speed (usually 1–3 minutes).
4. Load switching: The ATS unit disconnects the main network and connects consumers to the generator.
5. Return to main network: When power is restored, the ATS switches back and turns off the generator.

The key difference between AVR units for generators with automatic start is the presence control contacts (for example, START, STOP, FAULT), which interact with the generator controller. Without them, automatic starting is impossible.

Types of AVR units: which one is suitable for a generator with autostart

Not all ATS units are compatible with generators that have an autostart function. Main selection criteria:

• 🔌 Control type: must support dry contacts (relay) or digital protocols (Modbus, CAN).
• ⚡ Rated current: 40–63A is enough for a house, 100A and higher for a cottage or workshop.
• ⏱️ Switching delay: optimally 5–15 seconds (protects against false alarms).
• 🔄 Possibility of manual control: Useful for testing or emergency situations.

By design, AVR blocks are divided into:

ATS type	Benefits	Disadvantages	Model example
Electromechanical	Simplicity, reliability, low price	Slow switching (up to 10 sec), contact wear	Fubag ATS 63A
Electronic (thyristor)	Instant switching (0.1–0.5 sec), no moving parts	High price, sensitivity to interference	Genmac ATS-100
Hybrid	Combines the speed of electronic and reliability of mechanical	Difficulty setting up, high cost	Vevor 100A Hybrid

For generators with automatic start, it is better to choose electronic or hybrid units — they react faster to network failure and more accurately control the launch. Mechanical ones are suitable only for budget solutions where switching speed is not critical.

Connection diagrams for the AVR unit to the generator

There are three main connection schemes, each suitable for different conditions:

1. Single-line diagram (for single-phase networks)

The simplest option for your home or garden. The AVR unit is installed between the meter and the distribution board. The generator is connected to the ATS via reserve input, and the main network - to main entrance.

220V network → Meter → ATS unit → Consumers
↓
Generator (autostart)

2. Three-phase circuit with load balancing

Relevant for cottages with three-phase input. Here the AVR unit must support uniform load distribution in phases, otherwise the generator will be overloaded.

380V network → Meter → ATS unit (3-phase) → Consumers
↓
Generator (3-phase, autostart)

3. Circuit with bypass (bypass switch)

Used for critical systems (for example, servers or medical equipment). Allows you to manually switch to the generator, bypassing the automatic transfer switch, if the automation fails.

Network → Meter → [Bypass] → ATS unit → Consumers
↓
Generator (autostart)

For generators with autostart It is necessary to have a connection between the ATS unit and the generator controller. This is usually implemented via:

• 🔌 Dry contacts (relay START/STOP)
• 📡 Digital protocol (Modbus RTU, CANopen)
• 🔌 Analog signal (for example, 0–10V for voltage control)

What happens if you connect an ATS without communication with the generator?

The ATS unit will switch the load to the generator, but it will not start automatically. As a result, consumers will be left without power and the generator will be idle. In addition, when the network is restored, the ATS will return the load back, but the generator will continue to run idle, which can lead to overheating or failure.

Step-by-step instructions for connecting the AVR unit

Installation of the AVR unit requires knowledge in electrical engineering. If you are not confident in your abilities, it is better to consult a specialist. Below are basic instructions for a single-phase network.

1. Preparation of tools and materials

Screwdrivers (Phillips, flat-head)|Multimeter|Terminal blocks|Cables with a cross-section of 4–10 mm²|Insulating tape/heat shrink|Soldering iron (optional)|Drill for attaching AVR-->

Select the cable cross-section based on the generator power:

• 🔌 Up to 5 kW – 4 mm²
• 🔌 5–10 kW – 6 mm²
• 🔌 Over 10 kW - 10 mm² and above

2. Installation of the ATS unit

Install the ATS unit in a dry, ventilated place, next to the distribution board. The optimal height is 1.5–1.8 m from the floor. Mount the housing to a wall or DIN rail (depending on model).

3. Main network connection

Turn off the power to the input circuit breaker. Connect phase (L) and zero (N) from the meter to the terminals MAIN IN on the AVR block. Grounding (PE) connect directly to the ground bus.

4. Generator connection

Connect the generator output to the terminals GEN IN on the AVR block. Be sure to observe polarity: phase to L, zero to N. For generators with auto-start, additionally connect:

• 🔌 Contacts START and STOP to the corresponding terminals on the generator controller.
• 📡 Signal FAULT (error) - if the ATS unit supports diagnostics.

5. Load connection

ATS block output (LOAD OUT) connect to the distribution board. Make sure that the total power of consumers does not exceed the power of the generator.

6. Setting parameters

Using the display or DIP switches on the ATS unit, set:

• ⏱️ Generator start delay (usually 3–10 seconds).
• ⏱️ Generator warm-up time (1–3 min).
• ⏱️ Network return delay (1–5 min).
• ⚡ Operation threshold (eg 180V for shutdown, 210V for return).

Common connection mistakes and how to avoid them

Even experienced electricians sometimes make mistakes that lead to incorrect operation of the system. Here are the most common:

⚠️ Attention: Never connect the generator to the home network through an outlet! This will lead to neutral burnout in a substation transformer and will pose a threat to the lives of repair crews. Use only an ATS unit or a manual changeover switch.

Error 1: Incorrect cable cross-section

If the cables from the generator to the ATS are too thin, they will heat up, which will lead to a loss of voltage and tripping of the protection. For example, for a 7 kW generator, the minimum cross-section is 6 mm² (copper).

Error 2: No generator grounding

The generator must have separate ground loop, not connected to the grounding of the house. Otherwise, when switching to reserve, damage to the electronics may occur.

Mistake 3: Ignoring network return delay

If the ATS unit switches back to the mains immediately after it appears, the generator will often turn on/off when the voltage is unstable. This reduces the life of the starter and engine.

Error 4: Connecting a three-phase generator to a single-phase network without balancing

If the generator is three-phase and the load is single-phase, one of the phases will be overloaded. This will lead to phase imbalance and generator failure. The solution is to use balun transformer or AVR unit with balancing.

Error 5: Incorrect polarity when connecting control contacts

If you confuse START and STOP, the generator will start when the network is restored and stop when it is lost. Always check the wiring diagram in the generator manual.

Review of popular models of ATS units for generators

The choice of ATS unit depends on the power of the generator, the type of network (single-phase/three-phase) and budget. Let's look at a few proven models:

Model	Type	Max. current	Autorun support	Price (approximate)
Fubag ATS 63A	Electromechanical	63A (14 kW)	Dry contacts	12 000–15 000 ₽
Genmac ATS-100	Electronic	100A (22 kW)	Modbus, dry contacts	25 000–30 000 ₽
Vevor 100A Hybrid	Hybrid	100A (22 kW)	CANopen, dry contacts	35 000–40 000 ₽
Bison AVR-40	Electromechanical	40A (8.8 kW)	Dry contacts	8 000–10 000 ₽

Fubag ATS 63A — the optimal choice for the home due to its simplicity and reliability. Genmac ATS-100 suitable for cottages with three-phase input, and Vevor 100A Hybrid - for critical systems where high switching speed is required.

When choosing, pay attention to:

• 🔌 Generator Controller Compatible (for example, DeepSea, ComAp).
• ⚡ Availability of protection from overvoltage, short circuit, overheating.
• 📡 Remote control capability (via GSM or Wi-Fi).

Maintenance of the ATS unit and generator

In order for the system to operate without failures, regular maintenance is necessary:

1. Checking the ATS unit

Every 6 months:

• 🔍 Inspect the terminals for oxidation or burning.
• 🔧 Tighten the screw connections.
• 📊 Test switching in manual mode.

2. Generator maintenance

For generators with autostart it is critical:

• 🛢️ Oil change every 50–100 operating hours (or once a year).
• ⛽ Fuel level monitoring — when left idle for a long time, gasoline loses its octane number.
• 🔋 Battery check — charge it with an external charger once every 3 months.
• 🔥 Cleaning the spark plugs (for gasoline generators).

3. System testing

Once a quarter, simulate a network outage to check:

• ⏱️ Response time of the AVR unit.
• 🔊 Correct starting of the generator.
• ⚡ Output voltage stability.

⚠️ Attention: If the generator does not start during the test, check:

• Battery condition (voltage must be at least 12.4V).
• Integrity of wires between the ATS and the generator controller.
• Delay settings in the ATS unit (perhaps the warm-up time is too short).

FAQ: Frequently asked questions about ATS units for generators

Is it possible to connect the AVR unit to the generator without autostart?

Yes, but in this case the generator will have to be started manually. The ATS unit will only be able to switch the load, but will not send a start command. For full automation you need a generator with built-in autorun controller (for example, Honda EU70is, Fubag BS 6600 A ES).

Which AVR unit should I choose for a 15 kW diesel generator?

Suitable for a three-phase diesel generator with a power of 15 kW Genmac ATS-100 or Vevor 100A Hybrid. Both units support current up to 100A and have an interface for autostart control. If the generator is single-phase, it is enough Fubag ATS 63A.

What to do if the ATS unit does not switch to the generator?

The reasons may be the following:

1. The voltage sensor in the ATS unit is faulty (check the input voltage with a multimeter).
2. Insufficient voltage on the generator battery (less than 12V).
3. Open circuit in the control contact circuit (START/STOP).
4. Incorrect delay settings in the ATS unit (set 5–10 sec).

Start by checking the power and connections, then test the ATS unit manually.

Is it necessary to install an RCD in front of the ATS unit?

Yes, RCD (residual current device) It is recommended to install both at the input from the network and on the line from the generator. This will protect against current leaks that may occur during switching or generator failure. Select the rating of the RCD one step higher than that of the input circuit breaker (for example, 63A for a 50A circuit breaker).

Is it possible to use the AVR unit to connect solar panels?

No, the AVR unit is intended only for switching between mains power and generator. For solar panels you need hybrid inverter with redundancy function (for example, Victron MultiPlus or Huawei SUN2000). Such an inverter can operate in parallel with the network and generator, providing uninterrupted power supply.