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How To Choose the Best Generator Size for the Job

April 14th, 2017


If you’re looking to rent a generator, it’s important to get the right size for the job. It will get you off on the right foot, so you can be successful and avoid wasted time, wasted funds, and headaches. Follow this guide to figure out the best generator rental for your next job.

Undersized Generators

One thing to remember is that the size of the power supply stays the same whether you’ll be using the generator all the time or if you’ll only use it as a backup to another system. If and when you turn the generator on, it needs to have the right capacity to run everything it’s supposed to.

Getting an undersized generator can lead to major issues. It can overtax the generator and cause damage to any equipment that it’s connected to, reducing the generator’s reliability and longevity. This can lead to a slowdown in production if you need to halt a job while you find a new generator.

Oversized Generators

If having an undersized generator can lead to so many problems, it may seem like the best solution is to have a generator that is large enough for the job, even if it’s larger than necessary. Although you should avoid getting an undersized generator, it’s equally important that you don’t get an oversized generator. The optimal energy pull is 70 to 90 percent of the generator’s capacity. This is the most efficient range while still providing some leeway if you need more energy from time to time.

If you have an oversized generator that leads to an energy pull below 50 percent of capacity, the unit won’t run efficiently. One example of this situation is wet stacking in a diesel generator. This happens when you have unburned fuel or carbon in the exhaust system, which usually happens when the energy pull isn’t high enough. This inefficiency prevents the generator from producing the proper amount of horsepower, which leads to a poor supply of power. If this happens, you may need to replace the generator.

Available Generator Sizes

The key to finding the best generator size is understanding what size of generator you need to rent. Clearly, it’s important to choose a unit that isn’t undersized or oversized, so it’s essential that you calculate what size you’ll need for the job. The range of power supply capacities is wide.

For personal and home use, you’ll find generators from 5 kW to 50 kW. However, if you’re looking for a commercial generator, these can range from 50 kW to more than 3 megawatts. It all depends on why you’re renting a generator and what the generator will be running.

Choosing the Right Generator

There are specific calculations that you’ll need to make to ensure that the generator is the right size:

  • What devices will the generator power? Make a list of everything that you’ll be hooking up to it.
  • As you make your list, note what the starting and running wattages are for each item.
  • Calculate the power requirements of all equipment combined.

To find the starting and running wattage, look for an identification plate or check the equipment’s owner’s manual. If it lists the power in kilo-volt-amperes, convert that number to kilowatts. You can do this by using the following equations.

For resistive loads:

amperes x volts = watts

For reactive loads:

(amperes x volts) x load factor = watts

You can also find calculators online that will help you convert the numbers.

Once you’ve figured out how much energy you’ll need, look for a generator that can provide that energy and still have 10 to 30 percent to spare. It’s important to estimate what will be running at any given time fairly accurately so that you rent the right size of a generator for your job.

Benefits of Choosing the Best Generator Size for the Job

By taking the time to choose the right generator size, you’ll enjoy the following benefits:

  • No loss of energy due to a generator blackout
  • Less maintenance, which saves you money in the long run
  • The generator lasts longer
  • Less chance of damaging equipment and property
  • No unexpected system downtime, which can lead to loss of productivity and endanger scheduled milestones for a given project

Now that you know what size of a generator will work best for the job, all you have to do is find one to rent. For more information on generator rental, give us a call. Our friendly staff will be happy to help you.

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