Sizing a Generator: How to Determe What Size Generator You Need
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Sizing a Generator - How to Determine What Size You Need

Getting a generator that can handle all your power generation needs is one of the most critical aspects of the purchasing decision.  Whether you are interested in prime or standby power, if your new generator can't meet your specific requirements then it simply won't be doing anyone any good because it can put undue stress on the unit and even damage some of the devices connected to it.  Unfortunately, determining exactly what size of generator to get is often very difficult and involves a number of factors and considerations. 

Making a choice amongst single phase, three phase, kW, KVA, welder, standby or motor starting generators can be mind-boggling. To prevent such confusion, this article was developed to help you get a better idea of how the sizing process works and some key things to keep in mind.  This is not a substitute for a certified electrician, which we always suggest talking to before buying, but it should provide you with enough information to get a solid understanding of some of the key things that are involved.

Generator Size Variations:  With the latest advancements in the field of electrical engineering, generators are now available in a wide range of sizes. Generators with power supply capacities of 5kW to 50kW are readily available in the personal and home use markets, while industrial generators are anywhere from 50kW to over 3 Megawatts.  Handy and portable gensets are available for homes, RV's and small offices, but larger businesses, data centers, buildings, plants, and industrial applications need to use the much larger sized industrial generators to meet their higher power requirements.

Generator Sizing - How Much Power?:  Many people believe smaller generators can be used for standby electric power because they are not running all the time. This is not only a myth but can actually be very detrimental. Unfortunately, generator under sizing is one of the most common mistakes committed by buyers.  Not only does it involve the risks of damaging your new asset (the generator), but it can also damage other assets connected to it, create hazardous situations, and even limit overall productivity of the unit and/or the business relying on it.  If nothing else, the key thing to remember here is that more is always better than less.  

How to Determine the Right Size Engine or Generator: While there is no substitute for having a certified electrician perform an inspection and calculate everything for you, the guidelines below do offer some great starting points and should at least get you started in the right direction:

Know Your Requirements:  Going to a dealer and buying the best or cheapest generator available without any other consideration is clearly not the best approach. It is always better to delve deep into your power generation requirements before making a choice. You can do this in the following ways:

- Make a list of the items that need to be powered by the generator
- Make a note of the starting and running wattage of the respective items
- Calculate the total power requirements in KVA or KW

How to Find the Starting and Running Wattage: Getting the right starting and running wattage of the devices you intend to power is crucial for calculating the accurate power requirements. Normally, you will find these in the identification plate or the owner's manual in the buyer's kit of each respective device, tool, appliance, or other electrical equipment.

Ampere - Watt Conversion:  You may often find power requirements of tools stated in amperes. In order to convert the power requirement of a tool from ampere to watts, follow these calculations, or you can also use our handy conversion tool on our power calculator web page.

For resistive load: Wattage = amperes x volts

For reactive load: Wattage = (amperes x volts) x load factor

Power Requirement Charting: It often happens that you lose the owner's manual or for some reason can't find the power requirement specification of the tools and/or other electrical devices you're running. Here is a sample power consumption chart that demonstrates some of the typical wattages used for common appliances and tools.  The chart is simply provided as an example to demonstrate how starting and running wattages differ, and how each device has specific consumption needs.  If you have questions over any particular items you can contact the manufacturer, consult an electrician, or contact us for a free consultation.

Different ways of Calculating:  Depending upon the type and number of devices, and the way the generator is scheduled to be used, there are a few different ways of calculating power requirements:

-  Single motor running 
-  Multiple motors running simultaneously
-  No electric motors.

Advantages of choosing the right size generator: Now that you have an idea on how to choose the appropriate size of generator to suit your needs, here's just a few of the benefits obtained by going through that process:

- No unexpected system failures
- No shutdowns due to capacity overload
- Increased longevity of the generator
- Guaranteed performance
- Smoother hassle-free maintenance
- Increased system life span
- Assured personal safety
- Much smaller chance of asset damage

Where to Buy & Role of Dealers and/or Service Providers:  Since you are not only purchasing a substantial company asset, but most likely an item you will need to rely on for prime or emergency electrical power at some point, probably in a crisis, deciding where to buy is also a key consideration not to be overlooked.  The seller's years of experience, whether they are a full service dealer or small commissioned broker, and so forth, all play a role. 

Having been in the business for over a quarter of a century, here's just a few of the reasons why you should always consider Diesel Service & Supply as your first stop for all your industrial power generation needs:

- 30+ years of industrial experience
- Full service multi-port garage
- Highly qualified mechanics and the industry's top diesel technicians
- High-end testing equipment and de-installation tools
- Helpful support desk and knowledgeable office staff
- We test all our products
- Always a competitive price!

As this article demonstrates, there are obviously numerous considerations to account for when selecting the appropriate generator for the job.  If you are having a difficult time with it or would like more specific suggestions and recommendations for your situation, contact us today and one of our knowledgeable sales and support staff will be more than happy to assist.

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