5-Model Genset Bench Test

If you want central air conditioning, you need a genset. In the popular 8 kW size, our test of five models found one-Northern Lights-that didnt perform up to its rating, and two-Fischer Panda and Kilo-Pak-that could handle overloads.


An article in the June, 1997 issue about small gensets struck a chord with readers. The report was of the type we call a Market Scan, in which, to make recommendations for a given type of equipment, we laboriously assemble, review and examine features, specifications and prices.

The intent is to determine which brands and models offer the best value. For the gensets, it was purchase price dollars per kilowatt. Because this is heavy equipment and weight aboard is always a factor, pounds per kilowatt also was calculated. Either way, the results varied and positions changed depending on the size (output) of the 32 gensets.

Readers wrote that theyd like to see actual tests. The original Market Scan included six gasoline-powered and 26 diesel-powered gensets. To test that many would be a monumental undertaking involving about $275,000 worth of gensets.

Obviously, some pruning was necessary…if the test results were to be published before the Millennium excitement starts. So the list was pared first to diesel-powered sets, then to those in the 8 kW range (the size most commonly installed on 40-50′ sailboats), then to seven manufacturers.

Included in our bench tests were Fischer Panda, Kilo-Pak, Kohler, Mase and Northern Lights. After initially declining to participate, Westerbeke offered a session at their own test facility in Massachusetts, with the testing set up to specifications like those used in the Practical Sailor bench test. Another big manufacturer, Onan, also declined. Instead, they offered to supply us with their own test data, but despite several reminders, it was never received.

Because both Westerbeke and Onan are prominent in the diesel genset business, basic data about their 8 kW units are included in the chart on page 14 and a short report on the testing we observed at Westerbekes plant in Avon, Massachusetts is on page 17. In the case of Westerbeke, the figures produced by the tests run by Westerbeke personnel can be compared with those we obtained in our testing of other makes.

The Test Set-Up
Our own test site was the workshop of Dan Kerrs Kiwi Marine Services in the Ted Hood Marine Center in Portsmouth, Rhode Island. It happens to be directly under our second-floor office. The workshop provided very advantageous conditions for gensets: Ambient air temperature of 56 and cooling water at a constant 42. If either temperature were higher (such as 95 ambient in an engine compartment and 78 water in the tropics), the performance would deteriorate. Thats why the genset repair business is very good in the Caribbean and other tropical areas.

The 1,800 rpm gensets-Kohler, Northern Lights and Kilo-Pak-have standard sea water-cooled heat exchangers for the diesels and air-cooled generators.

The 3,600 rpm units are different. The Mase has the usual heat exchanger on the diesel and uses raw water to cool a small radiator over which is drawn internal, recirculating air to cool the generator. The Fischer Panda circulates raw water (there is a freshwater option) through a housing that cools the generator. The water then goes through a heat exchanger for the engine.

Taking them one at a time, the gensets were unpacked and mounted in the same position on a rubber mat. Fuel and cooling water lines were attached. The exhaust was piped outdoors and through a muffler. Electrical cables and controls were led to a plywood panel. There were matched sets of everything. Instructions were meticulously followed.

Particular attention was centered on each gensets sound shield. The noise made by a genset may be of moderate concern when underway, especially if the main engine is being used. However, when the boat is moored a gensets noise level is very noticeable and often objectionable, not only to the owner but particularly to those nearby. The 1,800 rpm sets are inherently quieter than the 3,600 rpm sets, or to put it another way, the 3,600 rpm sets require much more intensive sound suppression.

Each genset was started and run for 30 minutes, during which all connections were checked. The test instruments showed clearly when the warm-up was complete.

Then came the actual testing.

What Was Measured
The output of each genset was measured in several steps.

Firstly, resistive loads (the kind produced by most electrical appliances) were applied with a SIMPLX Swift-e load bank that displays volts, amps and hertz. Loads can be applied in 500W multiples up to 10 kW.

Secondly, an inductive load (the kind associated with an electric motor) was applied with a shop air compressor with an electric motor that, with 60 psi, was measured to draw 49 amps at start-up and 20 amps to run. This could simulate the sort of load an air conditioner would place on a genset.

With this variety of loads, each genset could be burdened in steps up to its maximum rated capability. It could be hit with a sudden full load. Resistive and inductive loads could be mixed. Ultimately, it could be determined if the sets produced at the level claimed by the manufacturer. In addition, it was easy to check how much of an overload each genset could tolerate before the volts dropped, the cycles (frequency) deteriorated and the diesel engine labored or the circuit breakers tripped. Overloading any machinery is neither fair in a test nor recommended in actual usage. However, aboard a boat, it is bound to be a likely occurrence.

Repeatedly, throughout the testing, a Textronix TDS 210 oscilloscope and Hewlett-Packard printer produced images of the sine wave and digital read-outs. Besides a frozen image of the sine wave, the print-out recorded both the peaks of positive and negative voltages, the RMS voltage and the Hertz.

The peaks in the sine wave cycle provide power for a battery charger and good high peaks with rounded tops mean a generous supply of current.

Root mean square, one of those difficult electrical terms, is sort of an evened-out average. Electrically powered equipment likes it to be between 110V and 120V and steady. The RMS shall be referred to in this report simply as volts (V).

Also printed out precisely was the Hertz, or cycles, which should be at or near 60…especially if you have sophisticated electronic equipment.

Amperage readings on various cables (and checks on voltage and frequency) were made continuously with Fluke and ExTech multimeters.

The sound made by each genset (running under no-load and with sound shield installed) was measured carefully at distances of 4′ and 16′ with a Quest sound level meter that was checked for accuracy against a Radio Shack model. Although in the original thinking, a noise level check of the sound produced outdoors, downstream from whatever muffler and piping was specified, was not made because the exhaust system used in our tests was rudimentary. It also should be noted that because the gensets were not mounted in an enclosure (as they would be in a boat’s engine compartment), the noise levels recorded must be considered purely comparative.

The Results
On the chart on page 14 are the specifications and features of the models tested. For a quick check, the right end of the chart displays evaluative information and some data from the testing.

The June 1997 article included a worksheet on how to size a genset to your needs. It also included a discussion of the pros and cons of the 3,600 rpm vs. 1,800 rpm gensets, as well as comments about conventional vs. asynchronous alternators. Also explained was the sensitivity of any genset to ambient temperature.

Such information will not be repeated here. Instead, here are some observations along with a straight-forward account of what happened when each genset was subjected to a series of loads. Each was started, warmed up, had its noise level measured and then run at increasing loads while print-outs of its performance were made. Because the diesel engines and electrical apparatus spin at constant speeds, the decibels with no load seemed little different from those with heavy loads.

The series culminated with deliberate overloads, up to whatever the set could handle. Although the overloading might be considered unreasonable, it was done because of our belief that any genset sooner or later is hit with an overload-perhaps when the batteries are getting their morning charge, your refrigerator and ice maker kick on, both of your daughters are using hair blowers, you decide to warm up your coffee in the microwave and your wife, after saying, Its getting hot this morning, snaps on the air conditioner.

A big unit made by an old-line company widely known for robust equipment, the 8 kW Kohler is powered by a big 3-cylinder Yanmar engine (note its displacement compared with the others). The powder-coated aluminum sound shield is exceptionally well made with a number of access panels to service the engine. The shield even has a port into which a fire extinguisher nozzle can be inserted.

Mounted on an assembly that has an integral base, drip pan and frame, with the engine and generator isolated by rubber feet, the Kohler is a big, heavy unit that makes a little too much noise.

Running with no load, the Kohler made a sine wave with 368V peaks that are slightly sharp. (Its okay, but not outstanding to have a sine wave with anything but nice smooth curves.) The Kohler put out 122 V at almost 65 cycles, probably factory set so that when loaded the cycles go no lower than 60.

Running at half of its rated 8 kW, the sine wave settled into a nice curve and the output, at 63 cycles, was 121 V, with good peaks of 354 V.

At full load, the peaks dropped off (to 350 V) and the output remained good at 62 cycles, 119 V and 70 husky amps.

While loaded to 75% of its capacity and the compressor was turned on, the 50-amp starting load staggered the Kohler for less than a second or two, after which it picked up the rpm quickly and easily. The amps were an admirable 71.

The failure point came when the compressor was turned on while the Kohler already was loaded to its rated maximum (8 kW). The diesel engine slowed down immediately; the print-out showed a drop to 49 cycles, 98.8 V and peaks of only 286 V. When it became apparent, in less than five seconds, that the Kohler would not carry the added burden, the load was quickly reduced, at which time engine rpm and electrical output returned to normal.

Conclusion: Although a bit noisy, the Kohler is a tough workhorse bred by a company that likes to keep it simple, reliable and easy to service.

Northern Lights
Carrying an enviable reputation, the Northern Lights genset, powered by a 3-cylinder Lugger (Kubota) diesel, is a conservatively engineered and well-made unit. Because the company was re-designing its 8 kW unit, they sent us a 6 kW set instead.

For sound control, Northern Lights gensets come with rubber isolation mounts that the company says should be used with the thickest possible plywood…for stiffness and to minimize the noise made by a vibrating drip pan. The sound shield is a fair arrangement of foam-faced aluminum panels mounted in cast aluminum corners holding an extruded aluminum frame. The panels are attached with good knurled knobs that require only finger pressure. The full panel approach to a sound shield permits access to any side of the set. Its tempting to say that compared with the sound shields of the Fischer, Kohler and Kilo-Pak, Northern Lights effort seems rudimentary…except that it was the second quietest set!

Running with no load, the Northern Lights sine wave displayed a few (though not harmful) spikes, probably caused by voltage regulator switching. The output included good peaks (366 V), a steady 121 V and the customary high cycles (64) typically seen in 1,800 rpm gensets.

Running with a half-load (3 kW), the sine waves spikes disappeared, to be replaced with a slightly irregularly shaped wave that is not harmful. At half-load, the cycles dropped to 63 and the voltage was a good solid l19.

The Northern Lights ran happily at 75% of its rating (62 cycles and 117 V with excellent 382 V peaks).

However, when running at that 75%, the Northern Lights would not pick up the compressor load.

When the load was cut back to 50% (3 kW), the set withstood the added load of the compressor, but struggled mightily for four seconds before recovering from a severe voltage and frequency drop. The engine labored badly, however, and was relieved after several minutes.

Finally, starting over with a gradually increasing resistive load only, the Northern Lights handled only 5.5 kW. At 6 kW, the voltage and cycles dropped off badly, it was producing only 42.8 amps (its rated for 60 amps) and the load had to be removed.

Conclusion: Proudly dressed in gloss white paint, the Northern Lights genset is a quality piece of Plain Jane equipment, soundly engineered and made of good materials. The testing indicated that it should be rated at 5.5 kW. It would be interesting to check out this respected companys new 8 kW model.

The last of the 1,800 rpm models in our test, the 8 kW Kilo-Pak, is done up in gleaming white Awlgrip. Despite its modest price, it appears to be a quality piece of engineering in which great care has been taken to isolate the mix of carefully selected metals.

The Kilo-Pak has a lot of stainless steel parts, such as fuel lines, pan, exhaust elbows, valves and fluids manifold, some cupronickel parts in proper places…and a cast aluminum heat exchanger. However, the different metals are isolated so well that no zincs are needed.

A further example of quality, the Kilo-Pak also has a voltage regulator on soft rubber mounts whose components are solidly potted in epoxy. It is a thing of beauty.

The Kilo-Pak also is obviously designed with a view toward easy service. The air filter (which also serves as a silencer) is in a canister with a snap-off lid and can be changed or inspected in two seconds.

Somewhat unique is Kilo-Paks cover. It is a solid, hard case that uses a honeycomb sound barrier. Its not, perhaps, the best sound deadener but its easy to clean, easy to handle cover, and unlike those that utilize foam, should last forever.

After warming up, the Kilo-Pak, first of all, produced very even numbers. The 120 V output remained amazingly stable and the sine wave wavered little, even in the overload testing.

Running with no load and with 25%, 50% 75% and 100% resistive loads, the Kilo-Pak put out a steady 120 V, with good peaks, at from 62 to an 60 cycles. The cycles dropped .5 with each added step.

With inductive loads from the compressor, the Kilo-Pak was even more impressive.

Carrying no resistive load or one of 25%, 50% and 75% of the sets rating, the Kilo-Pak, when hit with the inductive load, produced a flat 120 V and the cycles ranged from 60.7 to an even 60.

With a full 8 kW resistive load when hit with the inductive load, the set produced 115 V at 59 cycles and ran very happily.

Pushing the Kilo-Pak even further, we tried a 10 kW resistive load, which it carried easily. However, the compressors inductive load finally produced the failure point. The voltage dropped, the cycles deteriorated and the sine wave went berserk. It was an extraordinary overload, not likely to be encountered in normal use.

Conclusion: We were very impressed with the Kilo Paks performance. Its big and heavy, but the price is right.

The 3,600 rpm gensets come from Europe. Because Europe uses 50-cycle electrical power, the engines used there are set to run at 3,000 rpm, a fairly comfortable and efficient speed for a diesel. For the 60-cycle US market, to produce the mathematical multiple required when the diesel is directly coupled to the generator, the engines must be stepped up to 3,600 rpm. Thats pushing the diesels a bit hard; overheating is a threat and cooling becomes more important.

Our first 3,600 rpm genset is the 8 kW Mase, which is produced in Italy.

Based on a Japanese diesel and a British generator, the Mase has a unique cooling system. Intake water is piped into a radiator over which air, drawn by a fan, is cooled to serve the generator. The same water cools the diesel. With all the marbles riding on the cooling water, a top-notch sea water strainer would be a must.

The engineering on the Mase suffers by comparison with the others. Examples are hoses poorly led around tight corners, the oil dipstick hangs up on nearby parts, the oil removal pump cannot be fully operated and most sub assemblies (like electrical boxes) seem jammed into tight places. These may be considered minor and annoying.

However, a major objection: The Mase was, by far, the noisiest of all.

Further, no matter what the load, the Mase does not make a very pretty sine wave. The small areas inside the peaks could cause problems with multi-step battery chargers.

The Mase ran reasonably with no load, a quarter load, half a load, a 75% load and a full 8 kW resistive load. It worked through the low-heavy cycle, losing 2 volts and 2 Hz on its way to a maximum rated load. The read-outs clearly indicate that the Mase has an effective voltage regulator.

Adding the inductive load of the compressor was a different story. The Mase handled the inductive load only up to a 50% resistive load. At a 75% (6 kW) resistive load, the Mases output fell within three or four seconds to an unacceptable 103 V and 56 cycles. The load was quickly removed.

At full load-8 kW imposed by the resistive load bank-the Mases sign wave and other vital signs went immediately to pot when the compressor was switched on.

Backtracking to ascertain the failure point, the Mase was permitted with no load to pick up and run the compressor. Then a 6 kW resistive load was added. It handled the load, but obviously was working too hard.

The Mase could handle the 20-amp running load of the compressor along with a 6 kW resistive load, but with that same resistive load could not cope with the 50-amp starting load of the compressor.

Conclusion: Only a fair producer, the Mases general quality of workmanship could be better and, although the price is low, the noise level is very objectionable.

Fischer Panda
The other 3,600 rpm genset in our test was the 8 kW Fischer Panda from Germany. Its the one with the water-cooled asynchronous alternator, a one-piece generator rotor that avoids the heat build-up of a wire-wound rotor but requires capacitors (devices that store electrical energy needed for heavy start-up loads). On the plus side, the expensive capacitors permit efficient customization to handle heavy loads. (See Mailport in the September 1997 issue for more on this subject.)

Very compact, the Fischer appears to be of extraordinary quality-with high-grade aluminum parts; metal braid-sheathed fuel lines; double-pole grounding to completely isolate the genset; a good oil change hose and fitting; a first-rate but complicated voltage control system, and a sound shield cover that works very well. The cover obviously has been the subject of thoughtful engineering. (Theres even an optional version that is reputed to be even quieter.)

Most surprising, the Fischer, despite everything turning at 3,600 rpm, was by a considerable margin the quietest of the gensets.

Some of its quietness may be because it is entirely water-cooled, the only genset so equipped. The generator end, said to be maintenance free, has only one bearing, which means little friction. little heat, little noise.

Throughout the testing, the Fischer produced excellent sine waves, no matter what the load.

Running with no-load, it produced 123 volts at 58 cycles, with a peak voltage of 368.

With a half-load (4 kW resistive) and a full load (8 kW resistive), it produced, respectively, 122 V, 61 cycles with 362 V peaks and 120 V, 61 cycles with 354 V peaks.

When the Fischer was overloaded-75% of resistive plus the compressor-it did not even flinch, but ran continuously, producing 122 V, 62.9 cycles with 362 V peaks. Its capacitors seem to do the job.

When the compressor was kicked on while the Fischer was carrying a 100% (8 kW resistive) load, the RMS voltage dropped to 111 V, the cycles to 60.5 and the peaks tailed off to 328V. The sine wave got only slightly ragged at the peaks.

Conclusion: The Fischers performance was impressive. Compact, tight and light, it ran quietly and smoothly. It is an expensive high-tech lightweight that can outlift all but one of the heavyweights.

The Bottom Line
Gensets are sufficiently complicated to warrant installation by a professional. With all of them, several levels of optional remote control panels are available with extra gauges. The better control panels seem worth it. Although the gensets have automatic shut-offs in case of oil or coolant problems, wed prefer to have the gauges somewhere where they can be at least loosely monitored.

Further, because these machines work hard, often in sweatshop conditions, routine maintenance schedules (primarily attention to the diesels lubrication and cooling systems) must not be treated casually.

A choice between the under-revved 1,800 rpm and high speed 3,600 rpm models? The 3,600 (2-pole) advocates say that at 1,800 rpm, a diesel is not running as efficiently as it might. The 1,800 rpm (4-pole) manufacturers say that a diesel running at 3,600 rpm may require service sooner or, to put it more bluntly, will wear out sooner.

One producer-Next Generation Power, 1732 St. Johns Bluff, Jacksonville, FL 32246, 888/463-9879)-has just announced a compact 2,800 rpm genset, with a reinforced helical timing belt drive (the belt was developed recently by Goodyear), that puts out 3.5 kW at the required 60 cycles. Another company-SMG Technologies, 6940 Wildglen, Dallas, TX 75230, 214/696-0501-is offering an 8 kW genset based on Kubota and Onan parts with variable (1,600 rpm to 3,200 rpm) speed controls.

Our testing of constant speed models indicated that based on their manufacturers ratings, the Kohler, Kilo-Pak and the Fischer are nicely under-rated, which means that theyll step up and do more work than might be expected. However, the Mases rating means what it says and the Northern Lights is slightly over-rated.

Using our test data as the criteria, which of those we tested would we prefer?

If headed around the world with not many stops, Northern Lights might be our choice, especially if electrical demands were not too heavy or sophisticated. Its price is second to the lowest.

If space was tight, weight was critical and we were willing to pay a premium for high-tech, the quiet, hard-working Fischer Panda would be nice to have.

But for something with lots of muscle at a very reasonable initial price, the well-made Kilo-Pak stood out. Of the 1,800 rpm models, it was the only one that, with a full resistive load, picked up and walked away with the added inductive load. A bit noisy, but its a workhorse.

Contacts- Fischer Panda, 413 S.W. 3rd Ave., Ft. Lauderdale, FL 33315; 800/508-6494. Kilo-Pak, Reagan Equipment, 190 S. Bryan, Dania, FL 33004; 800/824-8256. Kohler, 444 Highland Dr., Kohler, WI 53044; 929/457-4441. Mase, 74257 Hwy. 25, Covington, LA 70435; 888/606-6273. Northern Lights, Alaska Diesel Electric, 4420 14th N.W., Seattle, WA 98107; 206/789-3880. Onan, 1400 73rd Ave. NE, Minneapolis, MN 55432; 800/888-6626. Westerbeke, Avon Industrial Park, Box 181, Avon, MA 02322; 508/588-7700.

Practical Sailor has been independently testing and reporting on sailboats and sailing gear for more than 45 years. Supported entirely by subscribers, Practical Sailor accepts no advertising. Its independent tests are carried out by experienced sailors and marine industry professionals dedicated to providing objective evaluation and reporting about boats, gear, and the skills required to cross oceans. Practical Sailor is edited by Darrell Nicholson, a long-time liveaboard sailor and trans-Pacific cruiser who has been director of Belvoir Media Group's marine division since 2005. He holds a U.S. Coast Guard 100-ton Master license, has logged tens of thousands of miles in three oceans, and has skippered everything from pilot boats to day charter cats. His weekly blog Inside Practical Sailor offers an inside look at current research and gear tests at Practical Sailor, while his award-winning column,"Rhumb Lines," tracks boating trends and reflects upon the sailing life. He sails a Sparkman & Stephens-designed Yankee 30 out of St. Petersburg, Florida.


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