RE: ONAN / CUMMINS Generators LP / Diesel

Reading up on generators today...Found some interesting statistics that some may not have remembered....

Altitude and Temperatures affect the overall performance of RV Generators as seen by these chart for the ONAN 5500, 6500 and 8000 Diesel:

I think another way to look at this is the concept of Density Altitude. Not to be too scientific, but density altitude is air density given as a height above mean sea level as a measure or performance.

"Density altitude" can also be considered to be the pressure altitude adjusted for non-standard temperature. This will effect any engine be it a diesel generator or even a tow vehicle.

The higher the "Density Altitude" to lower the performance of a gas/diesel or propane powered engine, basically anything that combusts using oxygen in the atmosphere.

Here's a basic graph that shows the relationship between altitude, temperature and density altitude as it compare to "Standard" conditions, being barometric pressure of 29.92, at Mean Sea Level and 72F.

Hope this makes sense.

I think another way to look at this is the concept of Density Altitude. Not to be too scientific, but density altitude is air density given as a height above mean sea level as a measure or performance.

"Density altitude" can also be considered to be the pressure altitude adjusted for non-standard temperature. This will effect any engine be it a diesel generator or even a tow vehicle.

The higher the "Density Altitude" to lower the performance of a gas/diesel or propane powered engine, basically anything that combusts using oxygen in the atmosphere.

Here's a basic graph that shows the relationship between altitude, temperature and density altitude as it compare to "Standard" conditions, being barometric pressure of 29.92, at Mean Sea Level and 72F.

Hope this makes sense.

Part time pilot?? I recognize this chart...

Further refining of the Onan Generators...

I was curious to see what happens when applying 30A's and 50A's to the rated capacity of each generator and moving up in elevation. The goal was to find a generator that could meet the rated loads that we expect to come across while future full-timing.

It's just a guess at this point, but it makes reasonable sense that as one moves up in elevation, the load requirements will trend downward until a certain upper altitude is reached (i.e. - we need more heat. The colder temperatures will likely increase the need for additional resources such as the fireplace, heater blower, more hot water, etc). It would be wonderful to find that we could stay at one constant temperature all year long. But I don't think that is reasonable to expect when moving around the country.

With that in mind, it appears that the Onan 5500 W Propane model would be the minimum acceptable wattage. Only with this unit, one would be forced to watch amperage loads closely. A washer/dryer may not be run at the same time that the dishwasher, hair dryer are running. If 2 A/C units are going, one unit might have to be shed in order to run the microwave, etc.

The 6500 W seems to be a trade-off in that it covers almost all but the more extreme circumstances. There is considerably less "monitoring" although it will have to watched.

The 8000 W Diesel seems to cover all circumstances and runs the generator at 50% loads most of the time. The down side is that it costs more to operate (fuel, maintenance), it weighs considerably more (by 130 lbs or so), and it is considerably more expensive.

There is thought to installing this generator into the bed of the truck to limit weight on the RV. But of course, we would need a cord to reach the RV and we would have to connect controls to remote start. We do plan to install an auxiliary 100 gallon fuel tank and tool box combo on the truck. It is a long bed, but I'll need to measure to remaining area to ensure this is achievable.

I'm sure many of you may consider solar as an alternative. I've checked into that, but due to cost and the sun angle of incidence annually, this may not prove to be the absolute best alternative. Of course, if a second hand unit or new unit comes along at a reasonable price, it may make a good backup unit.

For full-timers out there, I'd like to hear about your experiences (good and bad) with your generator. It may sound like I have my mind made up, but, I can be easily persuaded based upon your experiences. There are many of you who are strictly for FHU operations. I get that. But that's how "GipCTravelers" came about. We want to experience everything we can. And that means that we will be off-grid many times.

Looking forward to your responses.

you might be overthinking it a tad - I park my 5500 LP at 10,500 on the Wolf Creek summit and have lunch all the time and never noticed any depreciation in power from the generator. There just aren't many places higher than that I can get the Redwood.

I had the Cummins 5500 on my Alfa Gold 5er for 14 years and would run it 12 hr. and only used 1-1/2 gallons of fuel. how does that compare to the LP generators. I am asking because my friend is looking to buy a Onan for his rig?

I had the Cummins 5500 on my Alfa Gold 5er for 14 years and would run it 12 hr. and only used 1-1/2 gallons of fuel. how does that compare to the LP generators. I am asking because my friend is looking to buy a Onan for his rig?

Here is the data sheet on the 5500 for your friend. The gas and LP consumption rates are on page 2 based on load.

On this 5500, there is a small difference in consumption. But you also have to figure the price and maintenance of each fuel type.

Propane has little maintenance required.

Gasoline can "lacquer" and needs fuel filters. You also have to run it more.

What about the price difference in fuel types? Sometimes gasoline is higher than Propane.

Personally, I don't like the risk of gasoline fumes.

Then, if you use propane, you have to lug those 40 lb tanks around everywhere and it takes away from your heating or cooking.

There are trade offs to everything.

Diesel has advantages previously mentioned in this post.