PORTABLE GENERATORS GUIDE

 

Portable electric generators remain the most common type of emergency power sources for residential use. Besides private homes, they are widely used on job sites, camping trips and in recreation vehicles. There are two main reasons for their popularity: low cost and perceived ease of use. Many people tend to think that portable generators are “plug and play”. Well, this is only partially true. While portables are indeed the cheapest kind of backup power devices, their use as home generators is not as simple as one would think. In order to decide if a portable generator is right for you and to pick the best one for your home, you might want to have a basic understanding of its operation. So, before discussing the portable generator types and selection, let’s briefly review how it works and what’s involved in its use and maintenance.

HOW THEY WORK

The picture to the right shows a typical portable genset. It consists of two main components bolted on a common frame: an engine and an alternator. The engines drives an alternator which produces AC voltage. The control panel has outlets which you can use to plug in your appliances. There are two key things to remember about portable generators:

  • They can be run only outdoors (even though they are not weatherproof);
  • They can’t be connected directly to your building wiring without isolating them from the mains.

Before buying a portable generator you need to decide that you are comfortable operating it. So, let’s review the main steps you would need to do to operate a portable genset:

  • Take your genset out of storage and place it on a level surface. Note that such a device  can weight a few hundreds pounds depending on its wattage. Since most blackouts occur during winter, dragging it may be challenging especially if it is muddy or if there is snow outside;
  • Fill the tank with fuel or connect your device to an external fuel source. Before the first use you also need to add motor oil;
  • Under certain conditions, the frame must be connected to a grounding electrode such as a ground rod. Refer to Article 250 of the National Electrical Code (NEC), the Code of Federal Regulations 29 CFR 1926.404(f)(3) and your product manual;
  • Start the engine. In some models you need to pull the recoil rope. More expensive devices have an additional electric starter for which you will need an external battery;
  • Let engine stabilize and warm up for several minutes;
  • Plug in and turn on your electric loads one at a time by using heavy-duty outdoor rated extension cords with ground wire. The cords have to be run through open doors or windows.
  • Let the output stabilize for several minutes after connecting each new load.

Transfer switch connection diagram
Note that the extension cords can be used to connect only stand-alone appliances, such as refrigerators and window air conditioners. You may wonder what to do with a furnace, central a/c, lights and other hardwired electric loads? Many people mistakenly think they can connect a generator directly to a wall outlet. Unfortunately, this is not the case. The only safe method to energize your home wiring is to use a professionally installed transfer switch. It will isolate your house from downed lines and prevent so-called backfeeding. If you installed a transfer switch, you connect your genset to the pre-wired inlet by using a single high-current generator cord (see the connection diagram above).

Like all engine-driven machines, gensets require frequent maintenance. Portable generator maintenance includes periodic oil changes, adjusting spark gaps, and cleaning. If you don’t mind doing the above operations and maintenance routine, let’s talk about choosing the right model. Otherwise, you may want to consider an almost hands-free automatic permanently connected standby system.

HOW TO CHOOSE

There are three main purchasing considerations for portable generators: the cost, the reliability and fuel availability. Depending on the fuel used by their drive motor, portable generators are classified as propane, natural gas, diesel, and gasoline. Many diesel engines will run on biodiesel as well. However, I don’t know any model that would be designed specifically for biodiesel. The broadest selection of portables exists for gasoline models. Gas portables are the cheapest among all- their prices start at few hundred dollars. Unfortunately, gas generators are also the least reliable. Most of gas engines run at 3600 RPM and may last for a few hundred hours of work if you are lucky. They are suitable only for intermittent short-term use. There are also gasoline-powered welder generators. Some of them run at 1800 rpm and are more reliable. However their cost typically starts at several thousands dollars. Diesel devices are the most reliable, but they are also the most expensive. Propane models are in between gas and diesel. Natural gas portables cost about the same as propane and are suitable for prolonged use. Natural gas being run primarily underground is the most reliable type of fuel. However you would need a professional to bring the fuel line outside. In addition, the selection of natural gas portables is quite narrow. A key factor to consider for emergency preparedness is fuel availability. During wide-spread blackouts gas and diesel pumps may not work. Propane cylinders can be refilled without the use of electricity (of course, if the road conditions permit to drive and you pay by cash). That’s why in my view, among portables, propane models are the best type of emergency power .

LESSER-KNOWN DETAILS

Advertised features of portable generators may be confusing or even misleading to the consumers. Here are some important lesser-known things to know.

  • Nameplate wattage is usually surge (starting) watts. The continuous (running) watts can be 65-80% of the nameplate value;
  • Runtime is normally specified at half-load;
  • The stated warranty is for consumer use. The warranty for commercial applications (if any) may be much shorter. If you need a device for a job site, read fine print;
  • If your device has electric start, you will need to buy a starting battery and a charger. Most models do not include them;
  • If a genset has GFCI (GFI), it will not work with a regular double-pole transfer switch without a modification.