On quality generators, voltage output is controlled through an electronic regulator. "The electronic voltage regulator monitors the voltage output to loads, much like a thermostat monitors the temperature in your house," says [Rick Bernier]. "The difference is the voltage regulator is lightning fast and responds to load changes in 1/100ths of a second. The faster the generator responds to load changes, the more stable, clean and equipment friendly the sinusoidal voltage output."

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      Generate Clean Jobsite

Not all generator sets are created equal.
                                                                     By Curt Bennink

A      ll generators look relatively the same, but
       don’t assume this makes them interchange-
able. Carefully examine the ratings and compare
                                                        the generator can produce for short periods of
                                                        time without overheating or causing damage. It is
                                                        important to note that extended use at the standby
                                                                                                                 you would have a reduced lifespan.”
                                                                                                                    Units used in emergency applications are typi-
                                                                                                                 cally sized according to the standby rating, because
the voltage regulation and frequency tolerances.        rating output can cause damage and reduce the            they are not going to run very much and therefore
    Start by choosing the most appropriate size.        useful life of the generator.”                           will have a useful service life. “A mobile application
“When determining adequate power for a task, it            Generator rating terminology differs between          for rental and construction, keeping it at the prime
is important to know how many pieces of equip-          small portable models and towable units.                 power rating, will ensure the unit will live to maybe
ment you are trying to power, how many amps are         “Typically, in smaller generator models (less than       a 10,000-hour lifespan,” says Howe.
required and what voltage is required,” says David      10,000 watts), the model number reflects a maxi-
Spears, product manager, power products, Terex.         mum power rating,” says Rick Bernier, national           Do the math
    Consider how you plan to use the generator on                                                                   The math to determine the required size for a
the jobsite. “Just get an understanding of what you                                                              single-phase generator is rather straightforward.
are going to be hooking up to it and do a rough                                                                     As an example, Bernier cites a generator that
calculation of how many amps each of those items                                                                 must supply combined 120- and 240-volt loads.
draws, either by looking at the data plate on the                                                                Assume that three 120-volt loads have amp draws
item or looking in the manual that came with it,”                                                                of 2, 3 and 5 amps, or a total of 10 amps. Multiply
suggests Todd Howe, generator product marketing                                                                  the voltage times the total amps to determine the
manager, Doosan Infracore Portable Power. “Then                                                                  wattage. In this case, it would be 120 volts x 10
make sure the total number of amps for everything                                                                amps = 1,200 watts. Let’s assume there is also one
you are connecting to the machine doesn’t exceed                                                                 240-volt load that draws 10 amps, or 240 volts x
the continuous rating.”                                                                                          10 amps = 2,400 watts. Combined, the total power
    It’s important to understand several key param-                                                              demand on the generator is 3,600 watts (1,200 +
eters. “Using generators to supply loads requires                                                                2,400). Consequently, you would need a generator
knowledge of what the continuous non-motor                                                                       that can supply both 120/240 volts and has a con-
load is and the horsepower (and resulting starting                                                               tinuous rating of 3,600 watts or greater.
kVA) of all the motor loads,” says Dave Dahlstrom,                                                                  Now let’s look at the surge rating. “The surge
marketing and business development, Shindaiwa           To choose the right size generator you need to           rating refers to the instantaneous amperage draw
Construction Products.                                  calculate the total wattage demand, then calculate       of a motor on first starting,” says Spears.
    Determine how the motors will be started and        the surge rating based on the motor loads.                  “This is the amount of power a generator can
the maximum voltage drop allowed during motor                                                                    supply for about two seconds to start motors,”
starting. “Will they be started across the line, with   product specialist, sales application engineering,       Bernier adds. “If all motors will start at the same
a variable-speed controller, or reduced voltage?”       Wacker Neuson. “This is the temporary amount of          time, add starting amps together and multiply by
Dahlstrom asks. “You also need to know what             power a generator can deliver for about 30 minutes       voltage to get total motor starting (surge) power.
sequence the motors will be started in, and whether     in a six-hour period.”                                   When in doubt about the sequence of motor start-
or not more than one motor will be started at    
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