Carry-Out Power

Cummins Onan P4500i and P2500i
Alone or in parallel, you have the option of powering something small all the way up to running the air conditioner for potential fuel savings. Photos by Shawn Spence and Chris Dougherty

With a new pair of portable inverter generators, Cummins Onan enters the market in a big way

The year was 1961, and Onan produced the first built-in generator for recreational vehicles. That demand would grow exponentially, and by 1985 RV gensets comprised more than half of Onan’s global business. Built-in gensets were primarily used in motorhomes, as well as some truck campers, large fifth-wheels and toy haulers, but not in the majority of towable RVs. Foreign competitors had taken over the lion’s share of the portable-generator business, leaving Onan without a viable portable for RVs. Finally, that has changed, and the company whose name is synonymous with built-in RV-power generation now has a line of quiet, portable inverter generators.

Onan is now Cummins Onan, and the company’s absence from this segment has been puzzling, but with products from Honda, Yamaha, Energizer and Champion in the space, it needed a portable generator that would stand above the competition in both quality and features. Enter the P2500i and P4500i, two inverter generators that are quite different from standard generators in a number of important ways.What is an Inverter Generator

Conventional generators tend to be loud. The reason is, there is a one-to-one relationship between the engine RPM spinning the alternator and the frequency of the alternating current (AC) power output. Our electrical grid produces AC at a frequency of 60 hertz; deviation from that can damage electronics, among other things. Because of the high RPM required to maintain that, conventional generators tend to be very loud unless they are extremely well insulated. They also can produce a lot of “noise” in the form of total harmonic distortion (THD), also known as “dirty electricity,” which can be harmful to electronics.

An inverter generator is a different animal. The engine produces AC power, which is sent through a rectifier that converts it to direct current (DC), after which it is fed into an inverter, which then converts it back to pure-sine 60-hertz AC power. Because the onboard circuitry controls the process, the output is far cleaner than a regular generator. Also, the system controls the engine RPM based on demand instead of being on high-idle all the time. Cleaner output, variable RPM and better fuel economy are the benefits.


Sibling Rivalry

We had the opportunity to thoroughly test the Cummins Onan P2500i and P4500i. A big feature that RV owners will appreciate is that these inverter generators are parallel-capable, and we had the parallel kit (MSRP: $69.99/50-amp, 59.99/30-amp) to put them through their paces. We also wanted to see what kind of noise the gensets produced, and how they handled the loads put upon them. And we wanted to evaluate the build quality of the generators, compare features and see how easy they are to use.

Paralleling portable inverter generators isn’t new, but it does offer a lot of flexibility for RV users. Paralleling allows two smaller inverter generators to have their output combined to power an RV electrical system, and it’s the onboard computer that allows this to happen. Instead of plugging the RV into the inverter generator, a special paralleling cable is plugged into ports on the control panel, and the RV is plugged into that.

Cummins Onan P4500i front panel
The P4500i, which is electric start, has a TT-30-amp receptacle, 20-Amp receptacle, USB charge ports, fuel shut-off dial, and both have the LED data center computer.

For this test, we decided to mix and match inverter generator sizes for a couple of reasons. First, it gave us an opportunity to see how the different gensets work, and second, we think many RVers will opt for a mixed set. If electrical loads will be light, running the P2500i will be adequate, and the smaller model naturally uses less fuel and is a tad quieter. Need more power? Use the P4500i. Running bigger loads and air conditioners? Parallel the two together. Owning both also makes the P2500i ready to go in a relatively lightweight package for other outings, beyond RV camping, where power may be needed.

Of course, the technology and appearance of portable generators have also evolved, and these two are right at the cutting edge. Sleek gray and black cases with modern lines and graphics make them look sharp at the campground. Each has a detailed and rather sophisticated front panel that contributes to the control and flexibility of these generators.


Little Brother

The two models, while sharing a similar appearance and controls, are far from twins. The P2500i is easier to carry (48 pounds dry), rated at 2,200 running watts and 2,500 peak or surge watts, which is 18.3 amps AC and 20.8 amps AC, respectively. It is fitted with a 3.4-horsepower, 98cc overhead valve, four-stroke gasoline engine and 1-gallon fuel tank, and is rated to run at 50 percent load for eight hours. During our tests, the pull-start engine always started with one or two pulls after the fuel system was primed for the first time. The fuel/engine-shutoff valve dial on the side of the case also operates the manual choke.

Cummins Onan P2500i front
The control panels on the P2500i and P4500i are intuitive and detailed. The P2500i has a 20-amp receptacle, 12-volt plug and USB charging ports.

The control panel is a techie’s dream, with plenty of data and connections to make it at home on the Starship Enterprise. The P2500i has a standard 120-volt AC, 20-amp duplex receptacle with a rubber cover on the front, along with a 5-volt DC USB duplex receptacle and an 8-amp DC lighter- type receptacle. There are AC and DC push-to-reset circuit breakers on the front, along with the parallel ports and a grounding terminal.

What makes these generators stand out is the LED data center. This dashboard for the inverter generator gives the status of the genset at a glance. The LED center indicates low-oil, overload and output-ready lights, fuel level, power output (both LED bars on each side of the panel, respectively), remaining run time and output voltage. No more guessing how much longer the generator will run before refilling. Slick as beets, as they used to say.

Lastly, an eco-mode switch allows the computer to decide the proper engine speed. If you’re using lighter resistive loads, then this is fine to leave on, and there will be a fuel savings. However, if you’ll be using inductive loads like air conditioners, the eco-mode should be off to avoid stalling the engine when a start-surge event happens.


Big Brother

The P4500i is the bigger model in the line, and while similar and compatible, it has more than size to make it stand out from the P2500i.

The P4500i is rated at 37.5 amps peak and 30.8 amps running at 120 volts AC, which isn’t too shabby. The genset is fitted with a 7.3-horsepower Ducar 224cc OHV four-stroke gasoline engine, with electric and remote key-fob start. That’s right, folks; if you’re in bed and need power, it’s only a click away. If the key fob isn’t handy, there is, of course, a start-stop switch on the front panel, and if the battery is dead, the P4500i has regular recoil start.

P4500i pull handle
Just like luggage! The P4500i’s telescoping handle and wheels make it easy to roll around, but it takes two to safely lift it.

The control panel has similar characteristics to the P2500i but adds a TT-30 receptacle (30-amp RV plug), and the fuel-shutoff dial is here. Additionally, the generator comes with a small plug-in charger to keep the battery charged while the P4500i is in storage, and it plugs in at the top of the panel.

The LED data centers are similar; however, where the P2500i’s computer provides remaining run time, power output, fuel level and voltage in a rotating data display, the P4500i adds lifetime hours. While the larger generator has the USB ports, the 12-volt DC lighter-type port has been left off — seemingly, for lack of space.

At 98 pounds dry, this puppy is twice the weight of the P2500i. Add the 20 ounces of motor oil and 3.2 gallons of gasoline, and you’re lifting well over 100 pounds. To make handling easier, this generator has roller wheels and a neat locking telescoping handle that retracts into the case like luggage. Aluminum grab bars at the front and back allow Thor, or two mortals, to load the generator into the back of a truck or on a tray.


Family Ties

The parallel cable is a pretty basic affair, and as we evaluated one of the first ones, which had no documentation or labeling, we had some fun figuring it out. Once we got it right, everything worked as expected, and documentation will be included with the production version. The parallel cable has a TT-30 receptacle, and the kit includes an adapter for a 50-amp RV connection.

Cummins Onan P2500i and P4500i connected in parallel
Connecting the parallel cable is simple BUT the order is important. The wires are color coded, but the two sets are not on this prototype version. We ran into an issue with an unbalanced load causing an overload and the computer shut us down. It turns out that there’s an order to plugging in the two legs to different generators. The unit that has the left set of wires will be producing the power at first. The second unit does not add power until the power demand calls for it. At that point the second unit will start to handle the load.
Once connected correctly, everything worked perfectly.

From a noise standpoint, both models are well-insulated, and noise was at a minimum during our tests. We used an iPhone with a sound meter to check the sound level outside, but the numbers were not valid enough to report here. However, both models are rated by Cummins to be as low as 52 decibels, which, by our account, is about right.

Those who are familiar with Onan gensets know that the company works hard to provide detailed documentation for everything, our preproduction parallel cord notwithstanding. These portable inverter generators come with a small pile of paperwork including a quick-start guide, owner’s manual, and warranty and emissions guides, just like their built-in RV brethren.

With these two entrants to the portable-generator market, Cummins Onan now can have RVers taken care of for mobile electrical power, no matter the RV type. It’s about time.

Cummins Onan Inverter Generator Specifications


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