Generator Selection Guide...
Once you've decided to purchase a generator set, there are several considerations you must keep in mind when choosing which set to buy, where to install it and how to install it.
This guide will help you make informed decisions during the selection process. Choosing the right machine is not difficult if you take the time to analyze your requirements carefully. Electric Generator Mart sales engineering staff is available to help you with all steps of the generator selection and sizing process.
You will also need to know a few terms and have a basic understanding of the different types of generator sets and their operating principles.
Installation requires expert assistance and a strict adherence to local codes and regulations. We recommend that you have a contractor do your installation.
Stand-By or Prime?
The first determination you will need to make is whether you will require stand-by or prime power. Simply stated, prime power is required when you have no other source of power. A stand-by set is a backup to normal utility power.
Generator Types & Features
Generator sets produce either single or three phase power. Choose a single phase set if you do not have any motors above five horsepower. Three-phase power is better for motor starting and running. Most homeowners will require single phase whereas industrial or commercial applications usually require three phase power. 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.
Gas or Diesel?
We recommend diesels (see Why Choose Diesel) due to their longevity and lower operating costs. Today’s modern diesels are quiet and normally require much less maintenance than comparably sized gas (natural gas or propane) units. Fuel costs per kW produced with diesels is normally thirty to fifty percent less than gas units.
1800 rpm water cooled diesel units operate on average 12-30,000 hours before major maintenance is required. 1800 rpm water cooled gas units normally operate 6-10,000 hours because they are built on a lighter duty gasoline engine block.
3600 rpm air-cooled gas units are normally replaced – not overhauled at 500 to 1500 hours.
Because the gas units burn hotter (higher btu of the fuel) you will see significantly shorter lives than the diesel units.
Operating Speed
Electric equipment is designed to use power with a fixed frequency: 60 Hertz (Hz) in the United States and Canada, 50 Hertz in Europe and Australia. The frequency output of a generator depends on a fixed engine speed. To produce 60 Hz electricity, most engines operate at 1800 or 3600 RPM. Each has its advantages and drawbacks. 1800 RPM, four pole sets are the most common and least expensive. They offer the best balance of noise, efficiency, cost and engine life. 3600 RPM, two pole sets are smaller and lightweight, best suited for portable, light-duty applications.
In simple terms, it's like operating your car at 90 mph, versus 45mph – at 45mph your car will last longer, is quieter, less maintenance and longer life. Most 3600 rpm units are twin cylinder air cooled lawn mower engines, while the water cooled 1800 rpm units are comparable to those found in forklift and tractor engines…the 1800 rpm water cooled units will last longer, offer less maintenance problems and be more fuel efficient.
Features & Benefits To Look For:
Engine block – For long life and quiet operation we recommend four cycle, liquid cooled, industrial duty diesel engines.
Air or liquid cooling – Air-cooled engines require a tremendous amount of air and may require ducting. They're noisy too. Liquid cooling offers quieter operation and more even temperature control.
Intake and exhaust – Time and money savers include a large, integral air cleaner with replaceable filter element and a residential muffler, which is built into the exhaust manifold. This saves the need for an additional muffler.
The lubrication system should have a full flow, spin-on oil filter with bypass.
Major brand of engine – We do not recommend you purchase a Chinese built unit or off brand engine, you will not be able to obtain the necessary follow-on parts and service support available with our machines!
DC electrical system. Standard 12 volt system should include:
Starter motor and battery charging alternator with a solid state voltage regulator.
Diesel units should come with a pre-heat switch and start/stop switch.
Safety shutdown system to protect the engine in case of oil pressure loss, generator overspeed or overcrank and high water temperature.
DC system circuit breaker.
Generator End
AC generator should have a 4-pole revolving field. An automatic voltage regulator will provide "clean" power. Normal utility power is +/- 5% voltage regulation; our 1800-rpm models are even better +/- 2%! All of our models offer AVR – Automatic Voltage Regulation.
Lifetime lubricated bearing – some less expensive units are not supplied with these bearings…they often require complete disassembly every two or three years for bearing replacement. All Power Generators units are provided with industrial quality lifetime lubricated bearings
Engine Accessories and Controls
Upon determining the generator size you will need, make a list of optional and installation equipment you require. For noise abatement, we recommend a residential (not industrial grade) muffler. A good primary fuel filter/water separator is a must to protect your engine's fuel system. Stand-by sets may require a block heater to keep the coolant/water mix at an adequate temperature for easier starting.
AC Switchgear and Controls
Switchgear can be as simple or complex as you want or can afford. Of course, as complexity increases, so does cost. Balance and a good electrical advisor are the keys here. The diagrams at right illustrate basic configurations for prime power and stand-by systems. All generator systems require a circuit breaker and a distribution panel. The circuit breaker protects the generator set from short circuit and unbalanced electrical loads. The distribution panel divides and routes the connected loads and includes circuit breakers to protect these loads. Stand-by systems also require a main circuit breaker between the utility source and the transfer panel. The transfer panel switches power from the utility to the gen-set and back so that both aren't on at the same time. Auto-start, auto-transfer systems are available but are costly. Your supplier or contractor can help you determine what you will need.