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A poorly running generator
can ruin your tools and in due time destroy the generator. In some
jurisdictions, you could end up losing a job because of excessive
emissions or too much noise coming from the gen set.
Whether you rent or buy,
providing a generator for the job site entails a lot more than running
down to Wal-Mart or picking out the cheapest unit from United Rentals.
A wise contractor puts a lot of thought into the process of acquiring
a generator - or at least he seeks sage advice from the experts.
"Generators are one of
the hardest things for people to select," observes Tom Pernice,
generator marketing and planning manager for American Honda Motor
Co. "You can't just get the cheapest, because you have to understand
what you're going to run, and [you have to] look for the right features
that are going to make it last on the applications you are using
it for. It's very involved. It's not as simple as buying a lawnmower
or a car where you kind of know what you want and what you need.
When it comes to a generator, unless you've been using them for
a long while, it is very involved and there are a lot of things
to consider."
"One of the common mistakes
that contractors make is buying a unit that is too small, then trying
to hook a high-current tool, like a chop saw, to it," notes Roger
Rieckers, general manager of Dynamic Power Source in New Albany,
IN, a company that produces a generator that includes a compressor
and a welding unit. "Then they can't figure out why their chop saw
burned up so quickly."
When it comes to choosing
a generator, the operator needs to assess what his needs are. To
estimate your electrical load, total the wattage of all the equipment
you'll operate at one time. Appliance wattage is usually listed
on the manufacturer's label. If only amperage is listed, the formula
to determine watts is: amps times volts equal watts. Many manufacturers
have information on their Web site that gives guidelines for the
running and starting requirements for various tools.
If you anticipate running
a skill saw (let's say at 1,800 W), a task light (2,000 W), and
a laptop computer (180 W) simultaneously, the total is 3,980 W.
To allow for the added demands of starting up an item while others
are already running, add another 20% into the equation (total is
4,776 W). According to Rieckers, the best policy is to obtain some
additional capacity. A contractor with these needs should be able
to get by with a generator with a 4,500-W capacity (assuming he
doesn't plan to start all three at the same time).
Selecting an undersized
generator might make it difficult to start motors. Starting load
causes voltage dips. For example, lights may dim when a large motor
is started. These voltage dips can be more than annoying - they can
ruin delicate electronic equipment such as laptop computers.
"Sizing is the most important
step," emphasizes Dan Hodge, president of Bowers Power Systems in
Kent, WA, a distributor that sells generators all over the world.
"Nothing is more critical in your choice of a generator. A set that
is too small won't last, will smoke, and can do damage to your electrical
equipment. If it is too large, the engine will carbon up, wet stack
[a buildup of carbon in the engine cylinders that causes overheating,
misfiring, and damage to the heads and pistons of the engine], or
'slobber' - excess fuel consumption and early failure. We recommend
that a generator set never run continuously with less than 40% load
- 50% to 75% is optimum."
In a perfect world, says
Jim Rose, product development manager for MQ Power in Carson, CA,
the optimum load for a machine is 80% of its capacity. "If the engine
is running at 100% all the time, you are going to tax that engine.
That would be like loading up your car and driving it up in the
mountains at a 6% grade all day every day. It's hard on the engine.
If you run it at 80% duty cycle, now you're optimizing your reliability
on that particular engine. But in the real world, sometimes contractors
are not afforded that luxury. They may have to put an engine in
there that is way oversized or is marginal. That's the challenge
that they have to work with."
Some contractors choose
to use a combination of generators of various sizes to help them
have the ability to put the load that is as close to optimum as
they can on each machine.
Another important factor
in sizing a generator can be whether you expect to use it at high
altitude or high air temperature. These conditions will lower generator
output. Consult your sales engineer for de-rating information. The
general rule is to allow for 3% loss in efficiency for each 1,000
ft. above sea level, according to Hodge. Basically, if you are going
to run it at 100ºF or 120ºF, output should be de-rated about 5%.
The most telling number
associated with a gen set is rated wattage, the wattage in which
the unit will run continuously. Many manufacturers list surge wattage
in their literature. Several professionals who were interviewed
for this article described surge wattage as bogus. "Just ignore
surge current or surge wattage because it's usually a number that's
two and a half times the rated [wattage] output of the machine.
Look at what the machine is rated for at a full output," advises
Rieckers. "For example, you may have a 2,000-watt generator that
may be rated for 6,500 watts of current of surge current and you
say, OOh, that's big enough.' But you put two drill motors on it
and one handheld grinder and you've burned it up the first day."
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"Surge basically
means for the first portion of a second [during start-up of an additional
tool], it can surge up to a certain output, but it immediately drops
back down," adds Pernice. "So just the surge number on the generator
is not a good thing to go by. You always want to look at rated wattage.
What does that generator produce consistently so your tool doesn't
run into an underpower or overpower condition. A maximum wattage
from our point of view is usually about 10% more. In other words,
if you have a 5,000-watt generator, you will see the rated wattage
at 4,500 watts. That's because in the first half hour of running
components, wires heat up. Heat causes resistance, and you have
a little less available power because of the resistance. As heat
builds up in wires and windings, it brings down the insulation of
the wire. It's kind of a slow-death situation; eventually that insulation
breaks down and you have a dead short in the windings and a very
expensive repair job. It doesn't happen immediately; it's a long
time process. That's what happens with your tools from the underpower/overpower
situation also."
Engine selection is another
important component. Buy a machine with a brand-name commercially
rated engine. "You could go to a big-box store and buy a generator
for $500," says Rieckers. "What you've got is a lawnmower engine
attached to a really inexpensive generator."
He recommends twin-cylinder
engines because they usually have a much longer life than the singles
do. "Japanese engines are good. From a longevity standpoint, stay
away from the Korean-built machines and the Chinese-built equipment.
It just isn't going to take the abuse."
According to Tom Hindman,
MQ Power operations manager, it is a must that contractors get a
unit that has an engine with the industrial-commercial designation.
"The big-box gen sets, which are intended for homeowners, have aluminum
block engines. An industrial-commercial model has a cast-iron cylinder
sleeve."
"The engine is a very
important component of the generator package," comments Tony Sabo
of United Rentals. "The most critical aspect to consider is what
customer service can be provided to you by the engine manufacturer
of choice."
According to Hodge, another
important thing to consider is if you are going to need both single-
and three-phase power. "If you are just going to run hand tools,
you are typically going to use single-phase 120/240. If you are
going to run dewatering pumps or trash pumps or any larger motors - typically
if the motors are over 5 horsepower - they are typically going to
be three-phase. If you have a combination of three-phase requirements
and single-phase, then that restricts the number of types of generators
that are available to you. There are only three or four manufacturers
who make a dual-voltage machine." Among the dual-voltage manufacturers
are Baldor, MQ, Atlas Copco, and Ingersoll-Rand.
"Three-phase power is
better for motor starting and running," continues Hodge. "Three-phase
generators are set up to produce 120/208 or 277/480 volts. Single-phase
sets are 120 or 120/240. Use the low voltage to run domestic appliances
and the high voltage for your motors, heaters, stoves, and dryers."
"The key to generators
is clean power," stresses Rieckers. "The main objective is to get
as close to utility-provided power as possible. Typically, brush-style
generators don't do a good job of that. Every time that brush hits
a notch in the commutator bar, you get a spike. So you get noise,
you get transients on your line. Those transients over the long
haul can actually break down the insulation in the tool and burn
it up rapidly. When voltage spikes very high, even if it's just
a millisecond, the current goes very high. You get heat buildup
and it just shortens the life of the tool. You need a brushless
alternator because in the grading and excavating environment, you've
got dirt or crushed stone, and when that gets between the rotor
and the brushes, you've got lapping compound and it's going to consume
the rotor and the brushes very quickly. Also, the brushes become
a maintenance issue, and if you don't maintain them properly - and
nobody does - they basically chew into the rotor and then you've basically
thrown out the whole unit.
"The other problem is
if you ever had a short, leg to leg or leg to ground, that alternator
turns into a giant heating element and it just burns itself up.
I've actually seen alternator cases that have melted because they
got so hot. We chose to go to an asynchronous brushless because
if you ever have a short, the field simply collapses and as soon
as you lift the short, the field comes back. So it's rather bulletproof.
If a guy drives a Cat over your cord, until that alternator burns
itself up, the chassis of that Cat becomes hot. It's live. It's
got a lot of electricity on it, and if you happen to make contact - well,
guess what? You're hot too, for a short length of time anyway. Whereas
with ours, if it shorts out, the field collapses and the whole thing
goes dead."
"Probably the most important
thing to consider in this day and age is environmental attainment,
with EPA being as stringent as it is," states Todd Howe, product
manager for generators for Atlas Copco. "Environmental friendliness
is one of the more important things. You want to make sure that
the machine has fluid containment. If any fluid were to spill, it
would be contained within the package. And also noise and air emissions
are important. In some jurisdictions, you can be shut down."
With regards to emissions,
data are typically published by the engine manufacturer, says Howe.
A good reading depends on the engine you are running. "Typically,
as far as the consumer is concerned, the biggest concern is that
the engine is certified for the area that it will be operating."
He suggests contractors contact the generator company to make sure
it will comply with local standards. Sometimes emissions information
is contained in the machine's specs.
How can you be sure to
get a quiet machine? "When you are looking around for a unit, you
want to make sure it has a good sound-attenuated enclosure on it,"
advises Howe. "All manufacturers are typically going to publish
their sound ratings measured at 23 feet around the unit. Typically,
machines today are in the 60s to low 70s. There are some nonsilent
generator sets out there that might just be in a weather enclosure
that are in the higher 70s to low 80s." Atlas Copco produces generators
that are in the mid-60s.
With regard to fuel efficiency,
manufacturers publish in their sales materials how long the machine
will run at 50% and 100% of full load.
Automatic throttle is
a feature that allows the generator to drop to idle when there is
no demand. "It saves fuel and also noise because the engine is only
idling," states Pernice. "When you get to the inverter technology
generators, then you have what's called Oeco throttle,' which is
a load-dependent operation where the generator will govern up and
down the load and only burn the fuel that's required to power the
tool that's being run. It makes them extremely fuel efficient, usually
20% to 40% more operating time on the same amount of fuel. Of course
that varies, depending on what your usage is."
According to Rieckers,
fuel tank size is one of the most overlooked features on a gen set.
"As a rule of thumb, the unit should carry enough fuel to run at
least eight hours at full load. This limits the need to carry extra
fuel in cans, which creates a safer work environment."
When it comes to the
decision of whether to buy or rent, Hodge says to compare the length
of time you will be using the gen set with the rental cost and the
purchase price of the generator. "Typically my experience is if
the generator is going to be on-site for more than 90 days, it would
be to their benefit to buy the generator."
"When you're renting,
you have to pay for the machine only during the time needed," states
Hindman. "It removes most of the maintenance responsibility. Also
it allows a customer to get the right-size generator for each job."
If you have a good rental
office standing behind the machine, renting can be the optimum choice,
notes Sabo, because if the generator suddenly dies, someone will
bring out a new one pronto. The rental businesses know that any
downtime for their customers is a black mark on their reputation.
The rental house also will be sure the machine is maintained so
that it doesn't break down in the field.
"For a portable out in
the field to run a couple of tools off of, he [the contractor] doesn't
need the bells and whistles," explains Sabo. "The end user just
needs to make sure the machine powers up his few hand tools. He
doesn't need to watch the engine temperature or the hour meters
or the things you'd like to watch if you bought it yourself. I think
the most important thing to him is OCan it run my eight-hour day
without me worrying about having onsite fuel?' With a long-term
rental, you manage it by having an onsite maintenance program where
you're [the rental company] out changing filters and watching the
hours of the machines running on a bigger machine. There are applications
where there's somebody from the rental house on-site 24 hours or
at least reachable for 24 hours. There are some large towable machines
that run 24/7, so he constantly needs to be monitoring when the
machine is going to need a filter change or any other kind of preventive
maintenance that occurs."
Another benefit to renting
is you can try out a machine before buying it, making sure it performs
the way you want before committing the cash toward a purchase, points
out Rieckers. "Also, if you have a temporary increase in business,
you can provide a temporary solution instead of committing the capital
toward a purchase."
According to Rose, another
component of a good generator is a low temperature-rise rating.
The more copper and iron in the alternator, the less heat is generated,
and more kilovolt amperes are capable of being produced. "There
is a NEMA [National Electrical Manufacturers Association] standard
to gauge alternator temperature rise, which is based on a basic
40º Celsius ambient operating condition. A typical rating is 150C
or 125C. If you subject the alternator to full-load operation at
rated current and rated voltage at ambient temperature, the temperature
of the alternator windings will not exceed 125C. The lower the number,
the better the alternator, basically meaning there's more copper
and iron in it, which means it is a better motor-starting alternator."
Rose reports that MQ
Power's machines have an 85C rating. "A lot of people think a 150C
alternator is better. The reality is that most people don't understand
it. It's terribly important. I don't think it gets the attention
it deserves."
There are a variety of
pros and cons regarding whether to use diesel or gasoline. If you're
not running large equipment off of your generator, Pernice recommends
gasoline powered.
"If you are running large
equipment and you need large-capacity output, a diesel would probably
be the right choice," he advises. "Generally applications on the
job are smaller capacity and gasoline gives you a much lighter unit,
much easier portability, and quieter, more fuel-efficient operation.
If you have a small diesel generator, it's very heavy, harder to
start in certain conditions like when it's cold. Usually your diesel
generators are going to be 12,000 to 15,000 kilowatts and up. You'll
see very few smaller than that. Even though they are available,
you'll find most of the demand for portable generators is going
to be for gasoline-powered. They are very fuel efficient, more compact,
and very lightweight and easy starting."
While diesels
are harder to transport, people traditionally buy diesel
units when they want a machine to last longer or for the simplicity
of having a common fuel, observes Rieckers.
"Typically the diesel
machine will cost 30% to 40% more than the gas. Diesel engines will
generally last in excess of 10,000 hours, while gas engines will
last between 2,000 and 7,500 hours, depending upon the application."
Diesel machines are usually
more economical to operate because they consume less fuel for the
same amount of work, he continues. In addition, the diesel unit
usually has better torque since there is more mass and the torque
curve is flatter. "This means it will operate at maximum load with
less voltage loss. The diesel engine is better at handling high-torque
loads."
There are a multitude
of features offered on generators, including:
- automatic shutoff
for when the engine and the generator are overheated. "You're
less likely to do long-term damage if you are in an underpowered
situation," notes Rieckers. "That's probably a feature that some
folks don't include on their generators."
- low oil cutoff. If
the operator allows it to run out of oil, instead of seizing the
engine, it shuts down automatically.
- switchable voltage,
which allows for high voltage settings for 80V or lower voltage
for 240V. You can get anywhere from household voltage at 120V
all the way up to 480V.
- external fuel connections
that allow the unit to be hooked up to the fuel source on a vehicle.
- protected outputs,
individual circuit protection for all the outlets. Outlets are
built so you can't plug the wrong tool into the wrong plug.
- automatic voltage
regulator, a component that senses the output and holds it within
10% so you have no more than 10% fluctuation.
- convenient voltage
selector switches, where the operator can switch the general output
voltage without having to disconnect and reconnect cables. A manual
reconnect requires an electrician or a contractor with a lot of
experience to reconfigure or rewire for different voltage output.
Writer Jack Beardwood
has more than 20 years of professional experience working with newspapers
and magazines.
GEC
- September/October 2003
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