Before hiring a generator, it is important to understand how to choose the right generator for your construction site. Choosing too small a model with insufficient power output can result in time delays and worker downtime. If all relevant equipment cannot be powered at once, workers and equipment will be left standing idle. This will reduce worksite efficiency, wasting time and delaying completion of the work. Conversely, hiring too large a generator will be a costly mistake, wasting money that could be put to better use for other elements of the project or saved entirely. Luckily, assessing which generator is best suited to the job in hand is a relatively straightforward process. With a little planning and forethought, you can easily ensure you have the best model for your job before investing money in generator hire.
This is without doubt the most important element in work site generator selection and can seem daunting, but is actually quite simple. Make a list of tools and electric appliances needed for the job that will need to be powered by the generator. Obviously, tools with their own independent power sources won’t qualify, but will need to be charged periodically. Generator power output is measured in Kw, so the total wattage required will need to be calculated. Find the tag on each piece of equipment and make a note of the power in watts for each individual piece. For example if four power drills would be used, the wattage would need to be listed four times. The power may be listed on the tools in amps and volts or horsepower for motor driven equipment, but this is easily converted to watts. If amps and volts are listed, multiply them together to determine wattage: amps x volts = watts. To convert horsepower to watts, remember that 1 hp is equal to 746 watts, so ½ hp equals 373 watts, 1/3 hp equals 249 watt, ¼ hp equals 186 watts and so on. Once wattage is listed for all equipment, add these together to derive the total power required from the generator.
Starting power should also be taken into account, some motors can require up to four times as much power to start and this should be factored in. Similarly, some tools such as compressors or circular saws need more power to start than to run. If equipment has a higher starting wattage, this number should be used rather than running wattage to calculate the total power required. On some tools, the starting wattage may be referred to as ‘surge wattage’, describing the surge of power needed to start the equipment. Using this will avoid any accidental capacity overloads that could cause unexpected shutdowns or system failures. To compensate for future additional power needs or mistakes made in calculation, add 10 % to the total. Use this final figure to decide the power level of the generator you will hire. Obviously this figure represents the maximum power needed to operate all site equipment at once. If this will not usually be the case, consider hiring two smaller generators with a combined output equal to the maximum. Connecting these in parallel allows them to act as a single unit but when less power is needed, one generator can be shut down. If one generator breaks down, the second can still provide some power as the first is repaired, allowing some work to continue.
When referring to generators, the ‘cleanness’ of power refers to a consistent, stable power output with few fluctuations. This is expressed using sine wave charts, with the sine wave being one cycle of electric current (60 – hertz cycles per second). Sensitive electronic equipment such as laptops, PCs or tools with microprocessors can be damaged or forced to shutdown or reboot by a sine wave distortion of more than 10%. Conventional generators use an Automatic Voltage Regulator to minimise voltage fluctuations and avoid this. For extremely sensitive electronics, inverter generators run power through an inverter board for a sine wave distortion of less than 2.5%. For most construction sites, this will not be necessary and capacitor – style generators will suffice. Even though they can have sine wave distortion of up to 40%, this will not negatively affect power tools or air compressors. Due to their relative simplicity, they are also usually the most cost effective choice.
When working in severely noise – restricted or residential areas, the quieter the generator is, the better. Inverter generators are extremely quiet due to their lower level of noise producing resonance compared to standard generators. However, there are a number of components and design features conventional generators use to reduce the decibel level during operation. Large mufflers and air cleaners are designed to reduce or suppress volume while the generator is running. Automatic idle control reduces the number of engine rotations when the generator runs idle, reducing noise and saving on fuel consumption. Pairing a diesel generator with a hybrid generator can further reduce fuel use and power critical equipment silently outside of peak use.
Generators used on construction sites need to be sturdy, efficient and reliable to cope with a heavy workload and tough working conditions. Before hiring, there are a number of design features to consider.
For work in confined spaces or indoors, will the generator physically fit? Will it need to be moved around the site? Even large generators often now come with fitted wheel kits to for ease of movement, if not, look for a generator with a lifting hook or eyes. This will allow a crane or forklift to lift it into place.
Make sure smaller generators have a sturdy, solid wraparound frame, preferably steel with a large diameter. For large generators an enclosed steel canopy and weatherproof coating will protect them from the elements and impacts. A large metal fuel tank will reduce time between refilling and be less prone to puncturing than plastic.
Try to use generator brands with a good reputation for engine reliability and efficiency. Fuel efficient engines cost less to run and need less refuelling, reducing downtime. Check the maintenance, service history and warranty with your plant hire company. Clear, prominent hour meters and fuel gauges allow you to monitor running times between maintenance and fuel levels and consumption.
Diesel is by far the most common type of fuel used for construction generators, with low operating costs and long storage time. As most construction equipment runs on diesel, it is likely to be readily available on site already. Red diesel used for generators is still taxed at the lower rate, lowering overall fuel costs.
SERV Plant Hire are plant and machinery specialists offering a huge variety of construction equipment for hire to the North West of England. This includes a wide range of diesel and hybrid generators of many power ratings, portable generators and power accessories. Contact us to discuss your requirements, we will be happy to help and ensure you have the correct equipment for the job.