Evaluating Gas Engine Drives for Generator Power

Evaluating Gas Engine Drives for Generator Power

Print Article
What do these items have in common: drills, circular saws, band saws, grinders, flood lights, small microwaves and compact refrigerators? These are common items and tools that small contractors and work crews use out in the field. Secondly, they all require a source of electrical power. To supply that electricity, you'll need a portable power source—ideally a small gas engine driven generator (sometimes called a gen-set). The following article discusses the most important factors you'll want to consider before investing in a portable power unit.
Published: December 1, 2007
Updated: September 26, 2015
You have the choice of hundreds of different generators. However not all generators are created equal. Like work trucks, certain generators are designed for specific types of applications, and they are available in a range of motor and generator sizes that produce different electrical outputs. Some gen-set models are less durable and reliable than others, and some are more conducive to being mounted on the back of a work truck. The following article discusses the most important factors you’ll want to consider before investing in a portable power unit.

A Great Value for Everybody

It may sound strange to talk about welding in a generator article, but even if you’re a landscaping contractor who never plans on welding, consider this key fact: a welding generator offers a better value than a stand-alone generator. There are three main reasons: cost, reliability and durability (actually four, if you count the fact that welding is fun, cool, easy-to-learn and comes in handy for a lot of repairs). Another great thing about welding generators is that they include the same high quality motors (e.g. Kohler, Robin and Honda) that are used in stand alone-units.

Buy One, Get One Free!

No, we’re not trying to sell you an extra Magic Bullet® blender that’s advertised on TV. However, when you buy a gasoline engine-driven welding generator that has 4,500 to 11,000 watts of generator power, you’re essentially getting the welder for free. In fact, you may even save $600 to nearly $1,000 compared to buying a stand-alone generator.

To help understand what to look for in welding generator, we recently spoke with John Leisner. John is a product manager with Miller Electric Mfg. Co., the world’s leading manufacturer of gas engine welding generators.

For work truck applications, “Contractors should really be using a welding generator with a 22 or 23 HP motor. A motor of this size can produce up to 11,000 watts of generator power and 225 to 325 amps of welding power, depending on the model,” says Leisner. “Welding generators produce sufficient power to run multiple tools, even while a second person is welding.”

The chart in Fig. 1 references the simultaneous welding and generator capabilities of Miller’s Bobcat® 250, the most popular welding generator sold. Note that 125 amps of welding power is about what it takes to run a 1/8-in. diameter Stick rod (the most common size) and that a microwave and fridge have combined requirements of about 3,000 starting watts and 1,325 running watts. Just imagine the ability to use a welding generator to run a microwave and fridge. You can have a hot lunch with a cold drink while you watch your buddy work his tail off!

Fig. 1 - For example, if you’re welding at 125 amps you also have 5200 watts available for powering lights or tools (either 43 amps from the 120 volt full kVA receptacle or 21 amps from the 240 volt full kVA receptacle).

*50 A, 120/240 VAC receptacle. See Owner’s Manual for additional information.

The primary drawback to powerful gas engine drives is that they weigh 500 to 600 lbs. However, if you have a hoist or a skid loader, there’s no problem moving them in and out of a truck bed (unless the unit stays permanently mounted). For more portability, add running gear to a welding generator.

Build to Last

Although you have the option of purchasing smaller, less powerful and inexpensive units, such generators units are typically not designed to take the punishment and constant performance of a welding generator. Welding contractors are not known for being gentle with equipment, and they work long days in extremely hot or cold conditions. Further, their livelihood basically depends on whether or not their equipment works. A welding generator that’s down can mean a lost day’s pay.

Fig. 2-These are some common tools used in the field along with their respective running and starting watts. Make sure the welding generator you select is speced to handle these loads.

Manufacturers of welding generators understand these demands and build products accordingly. Welding generators weigh more because they use a lot more copper and iron in the rotor and stator, which adds durability and increases their heat dissipation capabilities. For example, Miller makes sure all its engine drives can deliver nameplate capacity at 104 degrees F—conditions that significantly degrade the output of other units or even cause them to overheat and shut down.

Welding generators can also run for days on end (although you’ll need to add fuel. A Bobcat with its 12-gallon tank can run 14 to 20 hours under an average load). The days-on-end part really counts in an emergency.

“After a hurricane or ice storm, we always get thank you letters from customers telling us how their Miller generator provided power non-stop for a week,” says Leisner. “They also frequently tell us that generators from big box retailers burn out with hard use and high loads. That’s not going to happen to a professional quality welding generator.”

A True Test of Strength

When shopping for a car or truck, many people take a look at the vehicle’s estimated miles per gallon rating before they buy. However, most automakers conduct its MPG tests under the most ideal settings to ensure the best results. As a result, the rating provides a ballpark estimate.

Like automakers, welding generator manufacturers also subject their products to a variety of tests to evaluate its machines’ durability, reliability and electrical output. “Unlike most generator manufacturers, Miller tests for the worst case scenarios, which provides a more realistic snapshot of the machine’s true capability in the field,” adds Leisner. “To give people honesty and clarity when comparing generator power, Miller developed the Accu-Rated standard.”

The generator’s Accu-Rated peak power means that its stated peak capacity will deliver peak power for a minimum of 30 seconds. When encountering maximum generator loads, such as motor starting, plasma cutting or running a tool like a MIG welder, Accu-Rated peak power delivers all the power the machine promises.

To determine how much generator power you’ll need, find the running and starting watts of the tools that you want to run (see Fig. 2 and Fig. 3). Next, subtract each tool’s starting watts from its running watts to determine the additional starting watts. Finally, select the one individual tool with the highest number of additional staring watts, and take this number and add it to the total running watts. The sum of these two figures will equal the total watts needed. Or you can take the simple route and use the handy generator power worksheet and other tools available at www.millerwelds.com/products/generators/.

Worthy of a Mount

We’re not talking white-tailed deer or even jackalope. We’re talking about choosing a welding generator that’s specifically designed to be mounted and stored in the tight confines of a work truck bed without overheating.

There are two basic choices of welding generator case designs: open and fully enclosed units. Open units have partially exposed engines and cost less. The second option is a fully enclosed engine.

Fig. 3-This chart will help you determine the generator size you need.

Surprisingly, fully enclosed welding generator engine designs are efficient at keeping the motor cooler. The reason is that some these units have a specially built in air intake and exhaust ports that prevents hot air from re-circulating back into the machine. When it is mounted the air ports direct the hot air up and away from the unit instead of trapping the heat in a confined space like in the open design.

“Our fully-enclosed Bobcat 250 and Trailblazer® gas welding generators use a specially designed air flow path. This lets you mount the generator right behind the cab in order to maximize the bed space,” says Leisner. “This also happens to be the most popular mounting option for construction contractors because it also ensures that the unit will not be in the way when the crew is lifting large objects into the back of the truck and possibly damaging the unit (see Fig. 4).”

Fig. 4-The “behind the cab” mounting option (left and middle) conserves bed space and is by far the most common for construction contractor work trucks.

If you’re not convinced welding generators are your best value, visit a local welding supply distributor, ask their opinion, ask for a price quote and ask for a demonstration. To find the most reliable units, just ask one of the distributor’s service technicians. He’ll tell you which units last and which ones don’t.

The first time you need to weld, you’ll be glad you went the extra mile. But even if you never weld, remember that a welding generator costs less than a comparable stand-alone generator. You’ll also get a better value out of a welding generator because they are made to last (check out local resale values), and because a welding generator can take years of punishment and still run flawlessly.

For more information about welding generators and outfitting your truck with a welding generator, visit www.MillerWelds.com/products/generators and www.MillerWelds.com/truck. Also, contact your local welding supply distributor.