How to Choose the Right Generator for Your Workshop, Business or Farm in Ireland

A power cut can mean much more than losing the lights. For a workshop, farm, warehouse or production business, it can stop machinery, pumps, compressors, computers, heating systems and other equipment that may be essential to everyday operations.

However, choosing a generator is not simply a case of buying the model with the highest power rating.

The right generator depends on what you need to power, how much electricity the equipment requires, whether it has high starting loads, how long the generator will operate and whether your electrical system is single-phase or three-phase.

This guide explains the main points to consider when choosing a generator for a workshop, business or farm in Ireland.

What Will the Generator Need to Power?

The first step is to make a complete list of everything you expect the generator to run.

For a small workshop this could include:

• lighting;
• power tools;
• a compressor;
• a bandsaw or drilling machine;
• computers and office equipment.

A farm may need to maintain power to pumps, motors, refrigeration, lighting or other agricultural equipment.

A larger engineering or manufacturing facility may have substantially greater requirements, including three-phase machinery, extraction systems, compressors and production equipment.

This is why two businesses operating from buildings of a similar size can require completely different generators.

Why You Shouldn’t Choose a Generator Based on Building Size Alone

A common question is:

“What size generator do I need for my workshop or warehouse?”

Floor area alone cannot provide an accurate answer.

A 500 m² warehouse primarily using lighting and basic electrical equipment can require considerably less power than a much smaller engineering workshop operating motors, saws, compressors and machine tools.

Generator sizing should therefore be based primarily on electrical demand rather than the physical size of the building.

Running Watts vs Starting Watts

This is one of the most important things to understand before choosing a generator.

Electrical equipment can have two different power requirements:

Running wattage is the power an item needs once it is operating normally.

Starting wattage is the short-term additional power that certain equipment requires when it first starts.

Motors, pumps, compressors and many workshop machines can require considerably more power during startup than during normal operation.

This means simply adding together the normal running wattage of your equipment may result in an undersized generator.

The technical information supplied with the equipment should be checked wherever possible. We recommend checking the manufacturer’s documentation or consulting a professional electrician for accurate requirements.

How to Calculate What Size Generator You Need

A useful starting process is:

1. List all equipment

Record every machine, tool, pump, light, computer or electrical system that may need to operate from the generator.

Consider what will realistically need to operate at the same time, rather than simply listing everything connected to the building.

2. Check the power requirement

Check the identification plate, technical manual or manufacturer specification for each item.

Record both:

• normal running power;
• starting or peak power where applicable.

This is particularly important for electric motors, compressors, pumps and other machinery with higher startup demand.

3. Calculate the simultaneous load

Add together the running load of the equipment that is likely to operate simultaneously.

Then consider whether one of those items has a substantial starting requirement.

A generator may be capable of operating several machines once they are running but still struggle when a large motor or compressor starts.

4. Allow additional capacity

It is normally sensible not to select a generator that will need to operate permanently at its absolute maximum rating.

Some additional capacity can help accommodate:

• starting loads;
• temporary demand increases;
• additional equipment;
• future expansion.

A margin of around 20–30% is sometimes used as a general planning guideline, although the appropriate capacity depends on the application and should not be treated as a universal rule.

5. Get professional advice for complex installations

For larger workshops, farms and industrial facilities, actual electrical demand may need to be measured.

A qualified electrician can assess peak loads, starting currents, phase requirements and the proposed connection method.

Generator selection should be based on the real requirements of the site rather than estimates alone.

kVA vs kW: What Is the Difference?

Generator specifications frequently use both kVA and kW, which can make comparing models confusing.

A simple way to understand the difference is to think about a pint of beer.

The entire glass represents kVA — the apparent or total electrical power.

The beer itself represents kW — the real power that is available to perform useful work, such as operating machinery, tools, lighting or other equipment.

The relationship between the two is determined by the power factor.

In simple terms:

kVA = apparent power

kW = real usable power

This is particularly important in commercial and industrial applications because motors, compressors, pumps and machinery can have different electrical characteristics.

A common mistake is to compare the kW requirement of a machine directly with the kVA rating of a generator without considering power factor and starting demand.

Single-Phase or Three-Phase Generator?

Another important consideration is the electrical supply required by your equipment.

A single-phase generator may be suitable where the main loads are lighting, portable tools, computers and other standard single-phase equipment.

A three-phase generator may be required when powering industrial machinery, larger motors, pumps or other three-phase equipment.

Workshops and production facilities often contain a combination of different electrical loads, so this needs to be checked before selecting the generator.

Do not assume that a larger three-phase generator is automatically the better choice. The generator should match the equipment and electrical installation it will actually supply.

Petrol, Diesel or Inverter Generator?

Different generator types suit different operating requirements.

Petrol Generators

Petrol generators are commonly chosen for portable and occasional power requirements.

They can be a practical option for smaller workshops, site work and situations where the generator will be required periodically rather than operating for extended continuous periods.

Diesel Generators

Diesel generators are often considered for higher-demand and longer-duration applications.

For businesses, farms and larger facilities where backup power may need to operate substantial loads or run for extended periods, diesel can offer a more suitable solution.

Inverter Generators

An inverter generator can be particularly useful when portability, lower noise and the quality of the electrical output are important.

They are commonly considered when powering sensitive electronic equipment alongside more conventional electrical loads.

Portable Generators

Where power needs to move between different areas of a site, farm, workshop or construction environment, portability can be an important consideration.

PTO Generators

For agricultural businesses already operating suitable tractors, a PTO generator can provide another practical source of electrical power.

Common Generator Buying Mistakes

Many problems can be avoided by considering the application before purchasing.

Choosing only by price

A lower-priced generator is not necessarily better value if it cannot reliably start or operate the equipment you need.

Looking only at running power

Ignoring starting current is one of the easiest ways to undersize a generator.

Buying far more power than required

Oversizing also has disadvantages. Generator capacity influences purchase cost, size and operating requirements, so the objective should be to select an appropriately sized solution.

Ignoring single-phase and three-phase requirements

Generator output needs to match the electrical equipment being supplied.

Forgetting future requirements

If additional machinery or equipment is likely to be installed, this should form part of the planning process.

Ignoring service and spare parts

A generator is an engine-driven machine and requires maintenance.

Oil, filters and other service components may need replacement over its working life. Maintenance requirements should therefore be considered when comparing equipment, not only the initial purchase price.

Where Should a Generator Be Installed?

Safety and ventilation are critical.

Combustion-engine generators produce exhaust gases and must not simply be operated inside a workshop, warehouse, office or other enclosed occupied space.

The location should be planned according to the generator manufacturer’s instructions and the requirements of the electrical installation.

Manual or Automatic Backup Power?

Another question for businesses is what should happen when mains power fails.

For some applications, manually starting a generator may be perfectly acceptable.

For operations where interruption needs to be minimised, an appropriate automatic changeover arrangement may be considered.

The electrical connection between the generator and the building should be designed and installed correctly. For fixed backup systems in particular, professional electrical advice is important.

What Features Should You Consider?

Depending on the model and application, useful generator features can include:

• electric or manual starting;
• suitable sockets and connections;
• voltage and frequency monitoring;
• hour meters;
• appropriate voltage regulation;
• sufficient fuel capacity;
• transport frames or wheels;
• provision for automatic backup systems on suitable models.

An hour meter can be particularly useful for commercial users because operating hours can be used to plan servicing and routine maintenance.

Generator Maintenance and Spare Parts

Generator reliability depends not only on choosing the correct model but also on maintaining it properly.

Routine maintenance can include items such as oil and filter replacement according to the manufacturer’s recommended service schedule. The supplied source similarly identifies oil and filter changes as part of generator maintenance.

This is another reason to consider parts availability and after-sales support before purchasing.

Millennium Machinery stocks a range of generator spare parts and service components in Ireland, including selected filters, switches and replacement parts, helping customers maintain equipment and replace components when required.

Choosing a Generator for a Workshop

For an engineering workshop, pay particular attention to:

• compressors;
• motors;
• saws;
• drilling and milling equipment;
• extraction systems;
  
• starting currents;
  

The machine with the highest kW rating is not necessarily the only factor that determines the generator size — startup behaviour and the combination of equipment operating together are equally important.

Choosing a Generator for a Farm

Agricultural applications can present a different set of requirements.

The required generator therefore depends on what must remain operational during a power interruption and for how long.

For suitable agricultural applications, both conventional generators and PTO generators may be worth considering.

Choosing a Generator for a Business

For offices, warehouses and commercial facilities, the priority may be keeping essential systems operating rather than powering every electrical load in the building.

Identify which systems are genuinely critical.

Separating essential loads from non-essential loads can significantly change the generator capacity required.

Need Help Choosing the Right Generator?

There is no single generator that is right for every workshop, farm or business.

The correct choice depends on the required power, starting loads, operating time, phase requirements, equipment being supplied and how the generator will be used.

At Millennium Machinery, we supply a range of Unicraft generators in Ireland, including inverter, portable, petrol, diesel and PTO generator options.

Our team can help you compare suitable models based on your application and power requirements.

Selected generators can also be viewed at our showroom in Ballymahon, Co. Longford, with demonstrations available where applicable.

With generators, spare parts and after-sales support available through Millennium Machinery, customers have a local point of contact both before and after purchase.

Explore our range of generators or contact Millennium Machinery to discuss the best option for your workshop, business or farm.