Generator and battery for welding: sizing, noise and operation

What is a mobile power unit?

A mobile power unit is a suitcase-format battery-powered power plant: a lithium battery, an inverter delivering 230 V AC / 50 Hz in grid quality, and sockets or CEE outputs for the machines. The smallest ones handle approx. 2-4 kWh and 3-4 kW of continuous power with high peak power, while the large units range from 8-10 kWh and 10-11 kW of continuous power.

The difference from a generator is crucial on site: no exhaust fumes, no fuel, no starting procedure. The unit turns on, delivers smooth voltage and frequency, and makes less than 10 dB(A) of noise - by comparison, an alarm clock makes approx. 40 dB(A).

Why use a battery instead of a generator?

Grid quality power: a good inverter delivers stable voltage and frequency regardless of load. This matters for electrofusion control boxes and butt welding machines that calculate and document based on supply quality, and for electronics that can fail due to unstable generator power.

Noise and neighbourhood: the unit can be used indoors, in trenches near inhabited properties, at night and in areas with low-noise requirements - without exhaust gases that would otherwise need to be ventilated away from the trench.

No fuel logistics: no diesel or petrol on site, no fuel cans in the vehicle and no spill risk. Charging takes place via the domestic grid (230 V) or faster on three-phase (400 V), typically in 2-5 hours depending on charging power.

Maintenance and operation: no oil changes, no spark plugs, no cold starting. The unit stands charged and ready, even after extended periods of inactivity.

Generator: size according to starting current, not the rating plate

A generator must be able to deliver both the continuous power and the current surges generated by the heating element and hydraulics upon starting. Useful power drops when other equipment is running simultaneously, and at low temperatures and high loads it drops further.

Choose a generator with good regulation if it is to power a controlled machine or an electrofusion control box. Poor regulation causes voltage fluctuations that the controller interprets as faults, and the welding process is interrupted - often in the middle of the heating phase.

Never start large loads such as a compressor or hot-air tool simultaneously with a welding operation. It is better to sequence the work so that the load on the generator remains steady. If the machine keeps cutting out due to current issues, have it inspected - see service and maintenance.

A mobile power bank is a real alternative to the generator when the job does not require power all day: no engine noise, no exhaust on site and no idling consumption. Advantages, caveats and sizing are described in the section on mobile power banks below.

Generator requirements for butt welding: kW, kVA and AVR

Butt welding places different demands on the generator compared to electrofusion welding: here it is not a short current surge, but the heating element, trimmer and hydraulics running simultaneously for an extended period. The continuous power of the generator must therefore at least match the total rated power of the machine, and there must be a margin for the starting current when the trimmer and hydraulics start up.

Power increases with diameter. Machines typically range from approx. 2.65 kW in Ø160 to approx. 5.4 kW in Ø355 at 230 V, and from approx. 6.5 kW in Ø500 to 21-43 kW in the largest sizes at 400 V. As a rule of thumb, the generator should be able to deliver approx. 1.5 times the rated power of the machine, so that starting current and voltage drop do not cause faults in the middle of a joint.

kVA is obtained by dividing kW by the power factor, calculated here as 0.8: 3.65 kW corresponds to approx. 4.6 kVA, and 11.65 kW to approx. 14.6 kVA. The figures in the table are rounded upwards because the generator's useful power drops when it gets warm, and because there is rarely only one machine running on site.

Regulation is crucial when the machine features WeldControl or CNC. The control system monitors the supply voltage and stops if it fluctuates, so the generator must have AVR regulation or be an inverter generator with pure sine wave voltage. A generator without regulation may deliver enough power and still interrupt the welding process during the heating phase. For manual and mechanical machines, the requirements are milder, but stable voltage still provides a more consistent welding process.

The requirements for electrofusion welding are lower and can be found in generator requirements for electrofusion fittings, where you can also calculate the specific fitting dimension. If the machine is to run on a generator all day, also check the fuel, earthing and ensure the cable is fully unwound before plugging it in.

Mobile power banks: power without generator noise

A mobile power bank is a battery with a built-in inverter that supplies 230 V - and in larger versions also 400 V - to the welding machine. It replaces the generator at work sites where there is no mains power, and where there is no space or desire for an engine running all day.

The most noticeable advantage is the sound. A generator runs continuously, even when no welding is taking place, and on a quiet residential street, by a wastewater treatment plant or in a residential area, this is the noise that neighbours and inspectors notice. With a power bank, you can hear the birds chirping between joints, and you can talk normally with your colleagues or on the phone without having to shout. This also results in shorter working days, because communication and concentration are not worn down by noise.

Environmentally, there are two benefits: no exhaust gases at the work site and no idling consumption. A generator burns fuel whether welding is taking place or not, and the exhaust must be kept away from trenches, basements and enclosed spaces where carbon dioxide can accumulate. A power bank emits nothing during use and can be charged from the mains or from solar panels at depots and sheds.

Economically, the calculation must be made per job: a power bank costs more to purchase than a corresponding generator, but in return there are no fuel costs, no oil and filter changes, and far less service. On recurring jobs in the city where a generator would otherwise idle most of the day, the difference is often quickly recovered. If large diameters are to be welded all day, a generator or fixed supply is still the cheapest per kWh.

Practically, you must size according to two things: the power requirements of the machine (see tables above) and the energy per joint, i.e. how many welds you need to make on a single charge. Furthermore, check that the output provides a stable sine wave voltage - WeldControl and CNC monitor the supply voltage and stop in the event of fluctuations - and that the power bank can deliver the starting current for the trimmer and hydraulics. Capacity drops in freezing weather, so do not leave it cold overnight.

A combination often works best: power bank for small and medium-sized tasks in the city, and generator or fixed 400 V connection for large diameters and jobs lasting all day. Ask us if you want to calculate what makes sense for your typical task.

What can be welded on battery power?

Electrofusion welding: the obvious application. An electrofusion control box typically draws less than 1 kW, and power consumption is determined mainly by the diameter of the fitting: the larger the fitting and the shorter the welding time, the more power is used per joint. A small unit of 2-3 kWh therefore forms the basis for many fittings and a full day's work. The battery keeps the voltage stable all the way out into the trench, even on the last fitting.

Butt welding: machines for smaller pipes (typically up to Ø160-Ø200) draw 1.5-3.5 kW and can typically be powered by a medium-sized power unit. Remember to check the recommended power source for the machine: some machines require 3-phase power, in which case the unit must have a 400 V output (CEE 16/5) - the smallest units only supply single-phase 230 V.

Tools and auxiliary equipment: charging batteries, motor-driven scraping tools, pumps, lighting and laptops - everything that would otherwise draw power from the generator can be connected to the sockets. Large units typically feature CEE 16/3 (230 V), CEE 16/5 (400 V) as well as sockets for parallel connection of two identical units if power needs to be doubled.

How to find the right size

Calculate power (kW) first: the sum of the equipment that needs to run simultaneously must be below the continuous power of the unit. Electrical peak loads (starting the heating element, compressor or motor) can be many times the nominal current, so check that the peak power is also sufficient.

Then calculate energy (kWh): the machine's power multiplied by the total welding time. Example: a butt welding machine with 2 kW average and 4 hours of work uses approx. 8 kWh. Also maintain a safety margin - a cold, damp tent and long heating periods can increase consumption, and the battery should never be completely discharged.

Charging and logistics: look at charging power and time. With 4.4 kW charging, an 8-9 kWh unit is fully charged in approx. 2 hours on three-phase power and approx. 5 hours on 230 V. Wheel sets and handles are invaluable on site, and a parallel cable between two identical units is a flexible way to obtain extra output when the task requires it.

Power bank in practice: charging, temperature and connection

Charging time is part of the planning. A compact 230 V unit is charged from a standard socket and is ready again after a few hours, while a 230/400 V unit can typically be charged in approx. 8 hours at 230 V and in a couple of hours at 400 V. If it can be charged from a solar microinverter at the depot, you save mains electricity and are ready in the morning.

Temperature sets limits. Most units can be discharged down to around -10 to -15 °C, but charging typically requires frost-free temperatures, and capacity drops in the cold. Therefore, do not leave the unit cold overnight, and bring it indoors when charging.

If the task is to last longer than a single charge, two units can often be connected in parallel to provide both higher power and greater capacity. This is a flexible way to scale up with tasks without buying a generator.

Safety is built-in: battery management monitors the cells, and the units feature protection against over- and undertemperature, overload and insulation faults, as well as emergency stop. Nevertheless, check the enclosure class if the unit is to be stored outdoors all year round - IP65 withstands rain and dust, while IP54 is intended for lighter outdoor use.

Application and safety

Working temperature: most units may be used from approx. 0 °C up to 40-45 °C. In winter weather, the battery must be stored and charged frost-free, and low temperatures reduce performance - plan consumption accordingly.

Enclosure and protection: look for at least IP54 class so that rain and dirt do not damage the unit in the trench. Do not place the unit in the trench - keep it on dry ground above the trenches.

Electrical safety: always use residual current device (RCD) protected distribution boards and watch out for damaged cables, just like with any other power supply. The power unit does not replace electrical safety regulations on site, it simply replaces the generator.

In brief

A mobile power unit provides the welding team with grid-quality power without generator noise, fuel or maintenance. For electrofusion welding it is ideal, and for butt welding smaller pipes it can replace the generator entirely. Choose based on continuous power, peak power, kWh and charging time, and remember that the unit must be suitable for the climate in which you work.