Small Gasoline-Powered Generators

Advanced small-scale generators circumvent the need for constant motor speed by converting the generated AC to regulated DC, and then using a power inverter to generate AC from that DC. If the motor speed changes, the DC voltage stays the same because the regulator circuit holds it constant, so the output AC voltage stays constant too. In the best commercially manufactured generators, the inverter produces a near-perfect sine wave to ensure that the machine can properly operate sensitive electronic devices, such as computers, printers, scanners, modems, and routers. A “raw” generator will produce a facsimile of a sine wave, but not of the quality needed by microcomputer- and

microcontroller-based devices in common use today.

Figure 4-1 shows a popular portable gasoline generator with a power inverter that can provide up to 2 kW of clean sine-wave AC electricity when needed. This machine can run any of my computers, microcomputer-controlled furnace, and microcomputer-controlled amateur (“ham”) radio transceivers perfectly well. It has a tank that holds 1.1 gallons (4 liters) of high-octane gasoline. With a load of a few hundred watts, that amount of gasoline provides several hours of continuous, reliable AC

electricity. This generator has proven itself worthy as a backup power source in winter storms when utility failures would otherwise have meant no heat for my house, as the furnace electronics and fan require 117 V AC to function!

FIGURE 4-1 A portable gasoline-fueled generator, capable of providing up to 2 kW of clean sine-wave AC power at 117 V RMS.

The tied-up cord is the ground wire.

Did You Know?

Any backup generator, if poorly designed, can cause problems if you try to run sensitive electronic equipment from it. However, a well-engineered generator with a power

inverter, even the small gasoline-fueled type, will work fine with computers and other sophisticated systems as long as you keep it in proper working order. If you want your generator to be available when you need it, you must adhere to a maintenance schedule that involves cleaning, spark-plug replacement, and periodic testing.

Quick Question, Quick Answer

• How large can home-based and business-based generators get, from an availability standpoint?

• Medium-sized diesel-, propane-, and methane-fueled generators can supply several tens of kilowatts, and can power an entire home, business, or agency. Large

institutions typically have two or more generators. These machines, if properly operated and maintained, can operate all kinds of equipment, even sensitive and

complex medical devices.

My Arrangement

A Honda EU-2000i portable gasoline-fueled generator (Fig. 4-1) forms the heart of my emergency backup power ensemble. In addition to the generator, I use several extension cords and power strips to distribute electricity to the points where I need it the most during a utility outage. I always keep in mind the maximum power that the generator can provide; I never let it come close to “maxing out” at the full 2-kW limit. You can use this general configuration as a template for your own system, if you want to install one, tailoring the specifics to meet your needs.

Did You Know?

Honda, Yamaha, and other manufacturers offer several portable generator models, some of which are a little smaller than mine, and some of which are quite a lot bigger.

Whatever brand of generator you decide to buy, you should make certain that it produces a “clean” sine wave for sophisticated electrical and electronic devices. Always check not only with the generator dealer (who will tell you the truth in a perfect world, but in the real world, maybe not), but also with the manufacturer’s specification sheet. E-mail or telephone the manufacturer and ask for details about the model that interests you.

Remember that the best generators employ power inverters to produce clean, regulated, sine-wave AC. Don’t scrimp on this investment!

Figure 4-2 shows the two outlets of my generator. The cord on the left goes to the furnace fan and electronics. The cord on the right goes to my computer workstations, by way of a power strip in the garage. Figure 4-3 shows that power strip, which includes a light bulb that tells me when the generator is running, and also illuminates the garage at night. This power strip does not have a transient

suppressor (or “surge protector”) because the computer workstations both have uninterruptible power supplies (UPSs) with their own transient suppressors.

FIGURE 4-2 My portable generator has two AC outlets. The cord on the left goes to the furnace electronics and fan; the cord on the right goes to the computer workstations.

FIGURE 4-3 Power strip for the cords leading from the generator to the computer workstations. The cords lead to uninterruptible power supplies (UPSs).

You should never connect devices with transient suppressors in cascade (one after another) in the same circuit. For example, you shouldn’t use a UPS along with a power strip if both devices have

transient suppressors. You’ll need a power strip without a transient suppressor (they’re cheaper that way, anyhow). Transient suppressors in cascade will sometimes interfere with each other’s operation, a conflict that can produce bizarre malfunctions! I’ve seen a UPS “go crazy” with a transient

suppressor connected to one of its outputs.

For Nerds Only

Always try to balance the loads among multiple outlets in a generator that has more than one outlet. Ideally, each outlet should do roughly the same amount of work. This

precaution ensures that the generator will operate at maximum efficiency. In some generators, the outputs appear in different phases. If I were to connect the entire load to, say, the left-hand outlet in the situation of Fig. 4-2, it would be like seating all the

passengers on the left-hand side of an aircraft. The generator would work, but probably not at peak efficiency.

In the event of a utility power failure, I follow a rigorous procedure to disconnect the appliances I want to use from the utility lines before I activate the generator. For example, during a winter storm, the power went out, and I needed to keep the furnace running. I switched off the breaker that controls the furnace, and then followed a step-by-step procedure that I have provided here as Table 4-1. You should devise a similar procedure for your own home situation, with the help of an electrician, to ensure that you stay absolutely safe. Write the procedure down in detail, and tape a copy to your furnace. Then, when an outage actually occurs, follow those instructions to the letter.

TABLE 4-1 Procedure for Generator Use with My Furnace in Case of a Utility Failure

As a final precaution to keep the generator operating at peak efficiency and safety, you should connect the generator’s ground terminal to a known electrical ground, which you have tested for continuity with the main ground for your whole house. Figure 4-4 shows my arrangement, which comprises a single heavy length of wire and a clamp going to a cold water pipe. By performing the ground test described earlier in this book, I’ve satisfied myself that the cold water pipe connects directly to the main electrical ground for the house.

FIGURE 4-4 Ground clamp for the generator, in this case to a cold water pipe that has been tested to ensure continuity with the main electrical ground for the house.

Warning!

into the house, a situation that can arise with amazing ease, as I discovered when I ran my little Honda generator in the woodshed under my dining room. My CO detector sounded its alarm after only a few minutes of generator time!

Warning!

individual appliances into the generator through dedicated cords that have nothing whatsoever to do with your house wiring. If you don’t follow these rules strictly, backfeed can occur, in which electricity from the generator gets into the utility lines near the home or business where the generator operates. Backfeed can endanger utility workers and damage electrical system components.