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Old 07-06-2013, 11:06 AM   #1
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Generator versus idling small diesel?

In researching options for a camper/travel van (including previous threads on this forum), I found two of the main advantages mentioned in favor of a generator are lower fuel consumption and reduced wear on van engine. Granted other important factors may also exist like safety and reduced noise, but fuel cost and engine wear/damage seem to come up most.

In our case we would only idle for extended periods to run the air conditioner at night maybe 100 to 200 hours a year at most. Using 200 hours a year as an upper limit, it seems fuel consumption alone becomes a non-issue. A small portable Honda-2000-type inverter generator may save a tiny bit of fuel over idling the engine (and even thatís questionable) but portables are impractical for us. And even if practical, fuel saving alone would never justify the cost of a generator based on 200 hours a year, not to mention having to haul it around or the space it takes up.

And on the issue of potential van engine wear/damage, I came across this from Ford which should apply to other diesels as well:
Quote:
Severe-service applications like courier and transport duty call for an engine to run many hours a day under constant idling and stop-and-go conditions. The answer: the available direct-injected 3.2L Power Strokeģ inline 5-cylinder turbo diesel.

http://www.ford.com/commercial-trucks/t ... =Feature10
Also related to the subject of possible engine wear, I found a government study estimating long-haul diesel trucks on average idle 1830 hours a year (seems high to me) to keep the cab warm or cool. The study also estimated these large diesel engines consume about .8 gallons per hour of fuel when idling so running a small generator (or AC off batteries) may make economic and environmental sense. However, idling a +/- 3-liter diesel consumes a lot less fuel than a 15-liter truck engine. And operating 200 instead of 1800 hours a year makes an even greater difference.

Obviously there must be other advantages to installing a small generator that Iím not seeing. What else should be considered?
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Old 07-06-2013, 11:23 AM   #2
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Re: Generator versus idling small diesel?

ford-trucks.com is my go to site for engines. For the 3.2L check out:

http://www.ford-trucks.com/forums/forum274/

I have a 7.3L so I frequent the 7.3L subforum.

I went with a Webasto diesel furnace tapped into the fuel tank because I didn't want to carry two fuels (either propane or gasoline).

And a 5KW Auragen generator running off the second alternator position for alternating current.

I have no air conditioning other than the van's, so I can't comment on that with any experience.

Before I had the furnace, believe it or not it took longer for the 7.3 to warm enough to blow warm interior air (say at 15F outside ambient) than it took for 1500 watt electric heaters plugged into an inverter or into the Auragen to warm the van interior. I bet the 3.2L warms up quicker.

The one thing that I will say for idling to warm up or cool your interior, park away from others, although the diesel really doesn't smell much when the engine is warm, at least the 7.3L is much louder than a comparable gasoline engine. But still much better than the constant whiney noise that a generator makes.
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Old 07-06-2013, 11:34 AM   #3
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Re: Generator versus idling small diesel?

I wouldn't personally worry about wear on a diesel engine, but that's only my opinion of course, and I take pretty good care of my engines. Can you tell us what type of air conditioner you're talking about? If you mean a roof air unit, your engine/alternator will not supply enough power to run it. Compressors kicking on use a tremendous amount of energy. If you mean running the van's air conditioner, that's not very reliable either. Some here may disagree but I have never had a vehicle's air conditioner to cool as well sitting still for extended periods. They are designed to have air flow over the condenser which is mounted up front on the radiator.
Since I live a very humid climate, roof air is a must for us. It's not the heat as much as the humidity. However a Honda 2000 (or similar) will not run a typical 13500 RV roof air unit either. I recently went with a smaller 9500 BTU low profile unit which my Honda generator runs perfectly. BUT, it is not without problems. It idles up considerably when the compressor kicks on and is not nearly as quiet as a diesel (or dedicated) RV generator. The Honda's are in a class by themselves for quiet operation, but it's still pretty noisy at full idle.
Camper vans are all about compromises, and this is a much discussed topic. Keep searching and you will find a lot of info about it online. The truck camper folks especially. The vast majority of SMB owners don't seem to need it since they live in less humid climates, but some of us do.

Check out this thread if you want to see how I set mine up. I am in the process of mounting the generator somewhere different, and of course you can always drag it several feet from your site and lock it to a tree. Then you won't hear it as much either.
http://sportsmobileforum.com/viewtop...103977#p103977

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Old 07-06-2013, 12:15 PM   #4
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Re: Generator versus idling small diesel?

Quote:
Originally Posted by 86Scotty
....cut......
Can you tell us what type of air conditioner you're talking about? If you mean a roof air unit, your engine/alternator will not supply enough power to run it. Compressors kicking on use a tremendous amount of energy. If you mean running the van's air conditioner, that's not very reliable either. Some here may disagree but I have never had a vehicle's air conditioner to cool as well sitting still for extended periods. They are designed to have air flow over the condenser which is mounted up front on the radiator.
Since I live a very humid climate, roof air is a must for us. It's not the heat as much as the humidity.
86Scotty,

Yes, I'm asking about idling a diesel van so the van's air conditioner will keep it cool; particularly at night for sleeping but would also like information for running during the day. I suppose it may need a fast idle option, but had not heard that factory van AC would not cool adequately. My Ford with rear AC has kept the unit very comfortable at night the few times I've tried it even though it's a window van with lots of uninsulated glass. During the day in bright sun it doesn't freeze us out but will keep it comfortable as well other than during hottest days. I have to admit I've never run the engine for AC for very long periods -- just an hour or two at most.

And for what it's worth, I also live in very hot and humid southeast Texas and drive along the coast to south Florida on a regular basis, so heat and humidity are not new to me.

And thanks for the picture of your Honda install. As mentioned above, a portable generator is not my preferred option because the few nights we don't have shore power is normally at rest areas, where I wouldn't want a generator running -- particularly setting away from van.
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Old 07-06-2013, 12:22 PM   #5
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Re: Generator versus idling small diesel?

Quote:
Originally Posted by E350
....cut.....

And a 5KW Auragen generator running off the second alternator position for alternating current.

....cut.....
E350,

Thanks for this information. I did not know such a system was available. It does not address my question here but does tie nicely to another question I've been thinking about for some time regarding air conditioners and other cooling options.

If you don't mind me asking, why a 5KW alternating current system if you don't even have an AC air conditioner? Do you use it for the van itself or to power other remote items? Seems like a nice unit for home use in case of power outage and to run power tools on job site.
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Old 07-06-2013, 01:04 PM   #6
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Re: Generator versus idling small diesel?

Before Webasto.

The Auragen was used primarily in the morning to wake up:
1. Heat
2. Coffee maker
3. Microwave
4. Charger for 250 Ahr House Battery
5. Occasionally power tools (like a remote concrete mixer)
6. Occasionally to power my house during a power outage

But when I used it to power the electric heaters, I was always afraid to fall back asleep even for a few minutes because I am afraid to sleep in a vehicle with the motor running. It probably is even worse in the snow because if you are not aware, the new fallen snow will build a dam around your vehicle capable of keeping the carbon monoxide under your vehicle -- which may find a way to sneak into the interior. So you scare me when you talk about running the engine while sleeping.

I like the idea of a remote generator better for your purpose. Some truck campers mount them on the front receiver hitch on their rigs. That seems safe.

I get the need for air conditioning. (It was 110F this last week in Sacramento. Although I use my van to leave Sacramento on the weekends!)

I am going to throw this out there for someone who moves faster than me to experiment with -- or to shoot apart without doing the experiment.

Engel makes a do it yourself 12v refrigerator kit:

https://www.engel-usa.com/products/frid ... ion-models

But there has got to be a cheaper way to do this.

I was thinking about removing one of the rear van windows and mounting a box in which is installed a 12v computer fan to blow over a cooler plate (like the ones pictured in the Engel link) and across the sleeping area and out the cracked open front door window. The box must be exterior mounted because (of what I believe) would otherwise constitute a condensation problem.

My guess that, unlike a real air conditioning unit, my idea will not remove humidity from the vehicle. So, YRMV.

Anybody have any thoughts on this idea?
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Old 07-06-2013, 02:19 PM   #7
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Re: Generator versus idling small diesel?

Quote:
Originally Posted by E350
....cut......

But when I used it to power the electric heaters, I was always afraid to fall back asleep even for a few minutes because I am afraid to sleep in a vehicle with the motor running. It probably is even worse in the snow because if you are not aware, the new fallen snow will build a dam around your vehicle capable of keeping the carbon monoxide under your vehicle -- which may find a way to sneak into the interior. So you scare me when you talk about running the engine while sleeping.
Thanks E350. I think safety is a very valid concern. I've never camped in snow, and obviously if it were that cold, I wouldn't be running the engine for air conditioning. And I doubt I'd ever run it for heat since it's easier to dress warmer, use a sleeping bag, or some other source of heater for sleeping. Basically I'd say snow wouldn't be an issue at all for me.

Regarding sleeping with engine running, I'm wondering why that would be different that running an underfloor generator? How will a 2.1 to 3.0 liter diesel running around 1200 RPM or so be any more dangerous than a small diesel generator engine at 3600 RPM? I'm not seeing a big difference as it relates to safety. To me engine exhaust seems just as dangerous from one as the other. In either case a good monitor is required.
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Old 07-06-2013, 02:37 PM   #8
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Re: Generator versus idling small diesel?

Quote:
Originally Posted by E350
....cut......


I am going to throw this out there for someone who moves faster than me to experiment with -- or to shoot apart without doing the experiment.

Engel makes a do it yourself 12v refrigerator kit:

https://www.engel-usa.com/products/frid ... ion-models

But there has got to be a cheaper way to do this.

I was thinking about removing one of the rear van windows and mounting a box in which is installed a 12v computer fan to blow over a cooler plate (like the ones pictured in the Engel link) and across the sleeping area and out the cracked open front door window. The box must be exterior mounted because (of what I believe) would otherwise constitute a condensation problem.

My guess that, unlike a real air conditioning unit, my idea will not remove humidity from the vehicle. So, YRMV.

Anybody have any thoughts on this idea?
If using ice for cooling, controlling humidity is not much of an issue if the design is done right. That is not the real issue.

The problem is the amount of ice required to do the job when a significant amount of air conditioning is required.

By definition a "ton" of AC, or 12,000 BTU/hr, is one ton of ice melting in a 24-hour period. So even if the equivalent of a very small 6,000 BTU/hr AC was used for design, we'd need 1,000 pounds of ice per day. And even for just 8 hours during the night to sleep we'd still need 333 pounds of ice.

These ideas can't work as a replacement for a real air conditioner of any significant size. There is no need to experiment because the numbers just don't support the idea at all.
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Old 07-06-2013, 03:33 PM   #9
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Re: Generator versus idling small diesel?

10-4. Thanks!
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Old 07-07-2013, 10:52 AM   #10
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Re: Generator versus idling small diesel?

Quote:
Originally Posted by E350
10-4. Thanks!
I appreciate all suggestions since brainstorming often leads to other viable options. While cooling with ice may not be practical for my needs, your suggestion made me take a second look at an old idea I put off for my existing van, but should reconsider for the next one.

My interest is primarily based on air conditioning at night when the amount of cooling isnít that great; particularly if my next van is much better insulated and has fewer windows. If so, I could probably run a small AC for up to 8 hours off a battery bank that while heavy, could be recharged during the day while driving. Or if I knew weíd be staying at a campground the next night I could wait and charge the batteries off the grid to keep my vanís alternator from working harder than necessary.

A very rough estimate based on my present air conditioner is that about 500 amp-hours of capacity at 12 volts should about do the trick for a small air conditioner like the one I have in my present van. Granted thatís a lot of weight using lead-acid batteries (in the order of maybe 300 to 350 additional pounds beyond one standard house battery), but itís not that much more than the 300 or so pounds for one house battery and a diesel generator. And at an incremental cost of about $1,000 or so the cost would be reasonable compared to a generator.

And if they werenít so expensive, the newest lithium RV batteries could reduce the weight to about 150 to 200 pounds total. Thatís much less than a generator plus one typical house battery. The cost for 6 kWh of energy would be in the $6,000 to $6,500 range which is really high but actually not as high as a diesel generator. Obviously a generator is more flexible in that it can almost run indefinitely but having that much battery capacity has some advantages of its own.

When I was recently visiting and camping in Yosemite they only allowed generators to be run a few hours during the day; roughly at meal times. With batteries the air conditioner could have been run at night if needed. And of course it would address some of the safety issues associated with engine exhaust.

By the way, Iím not entirely sold on a diesel van engine other than itís best if planning to idle for extended periods. If I knew ahead of time that I could run AC overnight off batteries it may sway me to stay with the standard gasoline engine and save the cost of the diesel option.


Not sure if this is the right forum section to ask this question, but Iíd love to hear from anyone who has tried to run a small air conditioner off batteries. Did it work? For how long? Any information is appreciated.
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