Generator versus idling small diesel?

[rob_gendreau]

Where do you camp? I'm sure gonna want to avoid a diesel engine pulling an all-nighter....

States may have rules governing whether you can idle. If you're out in the boonies, no problem. But campgrounds, rest stops, etc you may not be able to. I've thought it odd that RVs, however, seem to get away with running gennies at rest stops while semis can't idle their engines. Smaller pollution level I guess. But the point is that you need to consider where you could use that solution. Lots of places restrict the use of generators.

And, as noted, A/C is the bugaboo of small rigs, and one reason lots of my friends moved to bigger vehicles or trailers. Good luck.

[E350]

At the risk of revealing more of my ignorance,* I wasn't suggesting ice for air conditioning. In fact, the only thing I would like to see is a low amperage draw 12v fan blowing over a cold plate or through a cold grid over the bed area to be exhausted, actually, by my fantastic roof vent.**

I know how hot these van's can get in the interior, but it has been my experience that moving air and preferably cool air moving over a body will usually provide enough comfort to enable sleeping.

* In response to my question during a group exam, the instructor said "There are no stupid questions, only stupid people asking questions." Everybody laughed but me...

** In lieu of installing a 40" home ceiling fan 18" above our sleeping area.

[Chance]

Originally Posted by rob_gendreau

Where do you camp? I'm sure gonna want to avoid a diesel engine pulling an all-nighter....

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We almost always stay in campgrounds with full hookups. In those instances air conditioning and heat is never an issue. We either run the small AC in summer or use a small electric heater in winter.

However, when driving to a destination like when visiting family we often drive late (to avoid traffic and save time) and pull into an Interstate rest area to sleep for a few hours (usually 6 to 8 hours – sometimes less). It is for those stops that it would be nice to have AC in summer. Again, this doesn’t happen all that often and why I estimated that it may add up to 100 to 200 hours a year at most. And even that is probably high so why it’s so difficult to justify a generator on the basis of fuel savings.


In rest areas we usually park far away from others who tend to park closest to restrooms. This reduces noise and lets us rest better. And you’d be surprised how many people idle their cars and minivans to stay warm in winter. In any case, the amount of fuel burned by a small idling diesel is about the same as a generator, so pollution shouldn’t be any worse. If anything automobile engines should run cleaner due to exhaust treatment.


If batteries lasted long enough that may be the best answer of all. Then there would be no issue with either noise or smell no matter where we parked (whether rest area, or National Park campground without hookups).

[Chance]

Originally Posted by rob_gendreau

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And, as noted, A/C is the bugaboo of small rigs, and one reason lots of my friends moved to bigger vehicles or trailers. Good luck.

I honestly can't follow what this means. How does moving to a larger rig solve any A/C problems? Isn't it just a matter of them being bigger?

[rob_gendreau]

Originally Posted by Chance

I honestly can't follow what this means. How does moving to a larger rig solve any A/C problems? Isn't it just a matter of them being bigger?

Bigger rig means bigger generator means fewer of the compromises you're considering. And sometimes more solar and more batteries. No penthouse fabric, better insulation, just all around more comfortable in bad weather. Having stayed in say a class A Newmar 36' coach I can attest it's a better crib than a penthouse SMB in hot or cold environments. Of course, there are other compromises involved. That beast had a 8kw gennie; it could power both them AND my van. And with the size of the tanks they could stay out in summer heat for a few weeks. So yeah, a matter of scale.

[Viejo]

Running any vehicle at idle to run AC is a double-plus bad idea. You're running a massive engine to extract a little bit of power for compressor and fan. Meanwhile all that waste heat from the engine is going out the exhaust, and the heat is radiating up into the van. The AC will be treading water, just trying to compete with the heat generated by running itself. And when you finally shut it down, you really bake from the heat in the block and exhaust system. AC works in a moving vehicle because you leave the heat behind you as you move. Not so in a parked vehicle. Not just theory, been there - done that.

[Chance]

Supporting data on fuel consumption and heat generation:

Regarding fuel consumption, and also total heat generation since modern internal combustion engines essentially burn the fuel completely for all practical purposes, I’d like to share some of the information I’ve researched. If not correct or applicable please don’t hesitate to correct me.

On this forum carringb reported his V10 Ford, with AC on, idles using 0.7 gallons per hour of gasoline (probably worst-case scenario due to engine size). That seems about right compared to 0.8 GPH for much larger diesel engines typically used on semis. It’s important to note that diesels are much more efficient at partial load. This difference is quite pronounced as they approach idle.

The European owner of an older Sprinter 2.7L 5-cylinder diesel reported fuel consumption idling at 1.08 liters per hour (.29 GPH) with AC on and .62 L/h (.16 GPH) with AC off. Compared to long-haul engines about 5 times larger that puts fuel consumption in the same order of magnitude. I expect similar fuel-consumption numbers should apply for the 3-liter Sprinter or upcoming ProMaster diesels, and somewhat lower GPH for the upcoming Sprinter 2.1-liter diesel.

For comparison the following are reported fuel consumption rates for various generators often used in RVs. Obviously the numbers are not exact due to rounding error:

Onan 2.8 KW gasoline:
0.2 GPH no load
0.4 GPH ½ load
0.5 GPH full load

Onan 3.2 KW diesel:
0.2 GPH no load
0.3 GPH ½ load
0.4 GPH full load

Honda 2000 (rated 1600 watt)
0.275 GPH at full load
0.115 GPH at ¼ load


I don’t see a huge amount of difference between generators and van engines when it comes to concerns about fuel consumption or heat buildup. I know it sounds counterintuitive but the numbers don’t support that larger van engines burn much more fuel than a small generator. In some cases they burn less. There are many reasons generators are great, but fuel consumption just doesn't seem like it should be one of them. At least if it's just going to be used to run the A/C.

Obviously a portable generator like a Honda when sitting away from the van (or bumper mounted) would not contribute heat under the van; but as previously stated any portable generator would not be my first choice for many reasons.

[chromisdesigns]

With regards to Sprinters, specifically the NCV3 models post 2007, long idling is a VERY bad idea. It leads to sooting up of the DPF and increased engine wear. Mercedes strongly recommends against it in their owners' manuals. If interested in the details, there is a lot of information available on this issue in the Sprinter Forums.

[E350]

This constitutes merely a gratuitous, off topic post, but I have heard that the 2.7 5-cyl inline Mercedes/Sprinter diesel was a great engine. So, my guess is that you are on the right track with the 3.2 5-cyl inline Ford Transit diesel.

What you posted is not counter-intuitive at all. Although I, do have friends who believe that a four cylinder engine will use less fuel than an 8 cylinder engine. But that is simply not true for the same weight. I.e., putting a camper of the same weight on an 8 cyl truck vs a 4 cyl truck. It takes a certain amount of fuel to move a given weight down or up the road regardless of the number of cylinders in the engine.

I think you are on the right track. Please keep posting your thoughts and explorations.

[86Scotty]

Originally Posted by Viejo

Running any vehicle at idle to run AC is a double-plus bad idea. You're running a massive engine to extract a little bit of power for compressor and fan. Meanwhile all that waste heat from the engine is going out the exhaust, and the heat is radiating up into the van. The AC will be treading water, just trying to compete with the heat generated by running itself. And when you finally shut it down, you really bake from the heat in the block and exhaust system. AC works in a moving vehicle because you leave the heat behind you as you move. Not so in a parked vehicle. Not just theory, been there - done that.

Well put Viejo, well put.