Cummins Onan introduces its all-encompassing, fully automatic electrical power unit for diesel motorhomes.
By Jim Brightly, F358406, Technical Editor
Get ready to start using a new term “” “power unit” “” instead of generator or gen set when talking about a motorhome’s onboard energy provider. With the roll-out of the Hybrid Quiet Diesel (HQD), a fully automatic, two-button electrical system, Cummins Onan introduces the term. Why? Because the device that supplies a coach’s onboard power for the HQD system is not, strictly speaking, a generator. The engine/alternator assembly is called a power unit because its variable-speed operation means it is not putting out 120-volt-AC power. The power being generated first goes through a separate inverter where it’s converted to 120-volt-AC.
Unlike current generators that pretty much maintain one rpm level until more electrical power is needed, and then increase rpm to the next level, the HQD’s variable speed self-adjusts to whatever rpm is needed to supply the required power output. But I’m getting ahead of myself; let’s back up a bit.
The term “hybrid” used in the name is similar to what we’re accustomed to seeing in hybrid automobiles, but instead of using gas and batteries, the HQD uses a Quiet Diesel power unit and the coach batteries for an improved RV experience. HQD manages power from the power unit, batteries, and shore power and distributes the necessary energy for whatever appliances the RVer is using. When shore power is unavailable or of poor quality, the HQD system will supply the coach’s total electrical needs from the batteries and the power unit.
The HQD system includes an automatic transfer switch, inverter, and power unit, all controlled through a single display panel located inside the motorhome (although multiple display panels are available optionally). As mentioned earlier, the HQD is engineered to ascertain the amount of power needed (for example, up to four rooftop air-conditioning units, plus microwave oven, refrigerator, lights, TV, etc.) and supply that power demand through shore power if connected, or through combining the output of the power unit with energy from the coach batteries, and then routing it through one or two large Cummins Onan-designed inverter(s) to produce up to 18 kilowatts of power.
Three HQD models will be available: 8/10, 12/15, and 12/18. The numbers indicate the units’ output. For example, the 8/10 model designates an 8-kilowatt power unit with a peak output of 10 kilowatts using the 3-kilowatt inverter (the system is limited to a peak output of 10 kilowatts for technical reasons). Moving up the line, the 12/15 model has a 12-kilowatt power unit plus the inverter, while the 12/18 model has a 12-kilowatt power unit and two 3-kilowatt inverters. This latter setup is capable of powering up to four rooftop air conditioners or their equivalent in basement air-conditioning units. When dry camping “” not connected to shore power “” an 8/10, using both the house batteries and the power unit, can supply all the power needed for up to three rooftop air conditioners and other onboard electrical appliances.
By combining these previously separate components into one integrated system, the power unit can be sized for steady operation, rather than needing to supply peak power demand. This means a typical RV with three roof air conditioners only needs an 8-kilowatt power unit rather than a conventional 10-kilowatt generator. By using a smaller power unit, fuel economy is improved by almost 20 percent, noise is cut in half, weight is reduced by 300 pounds, and battery management is improved. Thus, an HQD is lighter, quieter, more fuel-efficient, and easier to operate than regular generators.
When the power unit isn’t needed, the inverter can supply up to 3 kilowatts from the batteries or charge them at a full 140 amps when shore power is present. An interesting feature of the new system is the separate liquid cooling system for the inverter, housed within the power unit, which helps reduce the inverter size (on average, about half the size of an equivalent non-fluid-cooled inverter) and improves its performance. This separate cooling loop includes a radiator, fan, and pump and operates independently from the power unit’s cooling system to keep the inverter cool “” even though the inverter’s cooling components are located inside the power unit’s case.
For motorhome owners, perhaps the biggest advantage is the large green “Auto” button on the control panel display. By selecting the “Auto” button and then pushing “OK,” the owner puts the HQD system in auto mode and lets it decide when to turn on the power unit, the timing of which is based on power demand, the time of day, and the status of the batteries. Its default “quiet time” is 10:00 p.m. to 7:00 a.m., the traditional quiet time at campgrounds. However, the system’s clock must be adjusted if you change time zones. In addition, although the HQD can be used while on the road, similar to your car’s cruise control, it must be reset by pushing the “Auto” and “OK” buttons each time the ignition key is turned on or off. Other than these two caveats, the HQD allows motorhome owners who don’t want to be electrical engineers to enjoy their time on the road instead of reading equipment manuals.
“HQD is one of those rare, truly revolutionary products that change the nature of how RVs are made,” said Ed Pickens, Cummins Onan RV motorized marketing manager. “Much like the original Quiet Diesel, we expect the HQD to sweep the market.”
According to Mr. Pickens, the HQD 8/10 likely will be the most popular model, meeting the power needs of most diesel-powered motorhomes, while the HQD 12/15 and the HQD 12/18 will have the capacity to provide additional power for the largest coaches.
The Cummins Onan HQD power system also seems to be a good value. For example, the HQD 8/10 system should cost about the same in a new 2008 motorhome as a current conventional 10-kilowatt generator system, while providing significantly better performance, improved fuel economy, and a greater array of features.
Finally, a key benefit that owners will appreciate is that one-stop service for the coach’s electrical system can be obtained at authorized Cummins Onan service providers. The entire system can be diagnosed in one stop, eliminating the need to visit different service locations if a problem is encountered. This also means just one stop in the responsibility sector should something untoward occur during the warranty period. The Hybrid Quiet Diesel is covered by the standard Cummins Onan three-year limited warranty, with service available at more than 1,000 locations in the United States and Canada.
The diesel engines in the HQD “” as well as the other Cummins Onan diesel RV gen sets “” are Kubotas and are fully compatible and compliant with the ultra-low-sulfur diesel fuel requirements of 2007. This brings to mind that the HQD is not available for gas-powered coaches, and will not be in the foreseeable future. And, unless you really, really love your current diesel coach and absolutely can’t leave home without it, retrofitting the HQD system on an existing motorhome would be far too expensive. Depending upon what has to be changed out in an existing coach, the conversion cost could well approach $20,000.
HQD will be featured on 2008-model motorhomes from a number of RV manufacturers this summer, however; so if you’re in the market for a new coach, you may want to see which ones are offered with the HQD.
For more information about the new Hybrid Quiet Diesel, see www.cumminsonan.com/hqd, or visit the Cummins Onan booth at FMCA’s 78th International Convention, August 13 through 16, 2007, in Redmond, Oregon, and watch the informational video.