How do I determine what size Generator I 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 difficult. 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 understanding of some of the key things that are involved.
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:
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.
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
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.
For resistive load: Watts = amperes x volts
For reactive load: Watts = (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. 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.
What is the difference between standby, continuous, and prime power ratings?
Standby power generators are most often used in emergency situations, such as during a power outage. It is ideal for applications that have another reliable continuous power source like utility power. It’s recommended usage is most often only for the duration of a power outage and regular testing and maintenance.
Prime power ratings
This can be defined as having an “unlimited run time”, or essentially a generator that will be used as a primary power source and not just for standby or backup power.
A prime power rated generator can supply power in a situation where there is no utility source, as is often the case in industrial applications like mining or oil & gas operations located in remote areas where the grid is not accessible.
Continuous power
This is similar to prime power but has a base load rating. It can supply power continuously to a constant load, but does not have the ability to handle overload conditions or work as well with variable loads.
The main difference between a prime and continuous rating is that prime power genset are set to have maximum power available at a variable load for an unlimited number of hours, and they generally include a 10% or so overload capability for short durations.