Driving with the generator on

[sato4000]

Just curious if anyone knows the difference in MPG when riding with and without the generator on. Has anyone done any measurements on the gas mileage they get?

Thanks

[JaxDad]

I don't know about the insurance part of it, but in several Canadian Provinces it's illegal to go down the road with open propane cylinders unless it is the fuel source for the vehicles engine.

I suspect if it's illegal then the insurance company would deny coverage purely on that basis even if you're not from there.

[Dakzuki]

Fastpaddler wrote:
I dont know about the US or even specific Canadian provinces but my understanding is that if you have the propane turned on in your rv while driving on the road(presumably it is being used for fridge or aircon), you may invalidate your INSURANCE if you have an accident. I used to keep my propane on for the fridge but now I use the house battery while on the road. Just saying...

AL

Can you provide any documentary support for your assertion? A significant portion of RVs only have AC/LP fridges. The are designed to operate on LP while being driven.

[Mich_F]

maillemaker wrote:


I think a big part of our problem is even with the cab vent/air shut off outside air still comes in from somewhere down by your feet.

Steve

We haven't noticed any outside air coming in on either side of our's.

[maillemaker]

Our Itasca is fine up front with the roof air running. Our Coachmen was fine when it had a 13,500 Btu Dometic followed by a 13,500 Btu Carrier, but it's not fine with its' current 15,000 Btu Advent AC. It must be due to the positioning of the forward vent on the Advent. The Itasca has ducted AC, while the Coachmen doesn't. My previous Class C was also fine with its' nonducted roof AC.

I think a big part of our problem is even with the cab vent/air shut off outside air still comes in from somewhere down by your feet.

One year we went to Disney and our heater core blew as we pulled in. The mobile tech ran a bypass so we could get home, but we had no cab heat. It was unbearably cold in the cab as there was a freezing flow of air on your legs. We tried putting a blanket on our legs but eventually we stopped and bought a little space heater to put by our legs and ran it off the generator.

Steve

[JaxDad]

darsben wrote:

JaxDad wrote:

darsben wrote:
All in all I feel the economic part is close to a wash but the convenience and comfort level is much greater.

A typical dash air system takes maybe (on average overall) 2hp, on an engine making 200hp, that is a 1% increase in load, therefore an increase in fuel consumption of 1%.

At 8.5mpg and 55mph that equates to 6.47 gal. / hour. A generator burning 0.5 gal. / hour would then be an increase of 7.7% in fuel consumption.

That's the equivalent of your mileage dropping from 8.5mpg to 7.9mpg.

I'd hardly call that "a wash".

Now factor in the savings from not using propane to cool fridge and it makes it CLOSE to a wash

Just how big is your fridge???????

Again, rather than 'gut feelings' lets actually look the FACTS.

There's roughly 91,500 btu's in a gallon of propane. Today that costs about $3.00 / gallon.

A typical 12 cubic foot Norcold RV fridge burns 2,400 BTU / hour.

So one gallon of propane will last about 38 hours of actively cooling time.

If you completely discount ANY rest time (not actively cooling) and not the 1/3rds running, 2/3rds resting time average that means the fridge would cost $3.00 divided by 38 hours or roughly 7.89 cents per hour.

A generator burning 0.5 gallons of $4.00 an hour gasoline would cost $2.00 / hour.

You really think $2.00 versus $0.0789 per hour is "CLOSE to a wash"?

That's more than 25 times the cost per hour. Hardly what I'd call "a wash".

[pnichols]

4K-Ranch wrote:
Might run both.

We have only had to do that once - never while going down the road - while parked with the V10 idling and the Onan running during August when it was hotter than blazes in the Texas panhandle. The DW turned all red when boondock rockhunting in the middle of the day -> got her back into our motorhome and fired up both the dash and roof air conditioning systems to cool the whole rig down in a hurry.

The later model Ford dash air con systems in their V10 chassis are superb. Ours cools the entire coach area (only a 24 foot Class C) in fine order, but our worst situation has only been while driving in the low-humidity 90's in Death Valley in March and around a high humidity 100 in the Deep South during August. With both A/C systems running we could probably handle any hot temps in North America, if not the Earth, in our relatively small interior volume rig.

FWIW, we have run both the propane furnace and roof air at the same time once or twice in very rare situations in the Deep South in August: Extreme humidity during only moderate (low 80's) warm temperatures. We needed the roof air full blast to remove humidity and the furnace full blast to keep from freezing. We wound up with 70 degree dry air in the interior -> kindof an emergency situation dehumidifier. You gotta love these modern self contained RVs that can handle a large variety of expected and unexpected fun situations!

[4K-Ranch]

OK, sounds like I'm glad I have mine in the shop getting dash AC fixed, gets pretty warm in AZ. Might run both.

[4K-Ranch]

Mich F wrote:

maillemaker wrote:

I'm from Florida, and most trips, most of the year involve using the air conditioner. I was told way back in 1995, when I bought my first Class C that it was more economical to use the generator to run the roof AC than it was to run the dash AC. I was told that a generator will use around .7 gal per hour. I almost always use the generator for air and not the dash air.

I don't know about your RV, but for ours, running the roof AC will not do jack for people riding in the cab. I know because when we bought our RV the cab AC was broken. We tried just using the roof AC (with generator) but I still sweated my butt off up front. We even bought a little fan to try and blow house air at the driver but it was still miserable up front.

Steve

Our Itasca is fine up front with the roof air running. Our Coachmen was fine when it had a 13,500 Btu Dometic followed by a 13,500 Btu Carrier, but it's not fine with its' current 15,000 Btu Advent AC. It must be due to the positioning of the forward vent on the Advent. The Itasca has ducted AC, while the Coachmen doesn't. My previous Class C was also fine with its' nonducted roof AC.

[4x4van]

My older class C has a wide open layout, so the dash air was ONLY good for the cab; did nothing for the huge living space. The roof air, however, is positioned such that I can direct some of the airflow down into that cab, keeping it reasonable while at the same time keeping the living area cool. This while traveling in 115-120 degree heat across the CA/AZ desert.

Now that dash air gave up the ghost some years back, and rather than spend $700+ to fix it, I just continue to run the generator and roof air when needed. Honestly, I've never "noticed" a difference in MPG.

But let's do the math; I average about 6.5 mpg towing the PWC trailer round trip to the river. Traveling at 65mph that means 10 gallons per hour during the trip. Now I use the gen/ac on the way home, but not on the way down, so assuming the generator adds .5 gal/hr (?), that means 9.75 gallons per hour on the way down (6.67 mpg) and 10.25 gallons per hour on the return trip (6.34 mpg). That's a 5% hit to my mileage.

For my river trip (180 miles one way), that means that I burn an additional 1.4 gallons coming home. Well worth having the entire coach interior cool and comfortable. And realistically, one good grade or a heavy headwind can eat up more than that, and so can just running a bit faster. So I drive at a speed that I'm comfortable driving, run the roof air when needed, and gas up when empty. After all, if I'm going to stress over an additional 0.33 mpg, I have no business driving a MH in the first place. 🙂

[darsben]

JaxDad wrote:

darsben wrote:
All in all I feel the economic part is close to a wash but the convenience and comfort level is much greater.

A typical dash air system takes maybe (on average overall) 2hp, on an engine making 200hp, that is a 1% increase in load, therefore an increase in fuel consumption of 1%.

At 8.5mpg and 55mph that equates to 6.47 gal. / hour. A generator burning 0.5 gal. / hour would then be an increase of 7.7% in fuel consumption.

That's the equivalent of your mileage dropping from 8.5mpg to 7.9mpg.

I'd hardly call that "a wash".

Now factor in the savings from not using propane to cool fridge and it makes it CLOSE to a wash

[Fastpaddler]

I dont know about the US or even specific Canadian provinces but my understanding is that if you have the propane turned on in your rv while driving on the road(presumably it is being used for fridge or aircon), you may invalidate your INSURANCE if you have an accident. I used to keep my propane on for the fridge but now I use the house battery while on the road. Just saying...

AL

[DaCrema]

What are you going to use the generator for? If your going to pop some corn or make lunch it will not be on long enough to make a real dent in MPGs. I think stopping to get out and buy some thing then get back up to speed - combine the cost of gas and food and the value for time. If it is just a few minutes for a lunch or dinner in the micro wave, I think in the long run your better off using the generator. If you want to run it for more than 5-10 minutes to watch tv and run the computer and all the other do dads the equation starts getting more difficult and it is a question of how much those things bring peace of mind to the driver.

On my RV, a 2007 Lazy Daze Mid Bath built on a e450, the dash AC cools the rig just fine on the road here in the Mid Atlantic when the temps are in the mid 90s and humidity is in the 90% range. I added this statement because different rigs may cool at different rates.
John

[Mich_F]

maillemaker wrote:

I'm from Florida, and most trips, most of the year involve using the air conditioner. I was told way back in 1995, when I bought my first Class C that it was more economical to use the generator to run the roof AC than it was to run the dash AC. I was told that a generator will use around .7 gal per hour. I almost always use the generator for air and not the dash air.

I don't know about your RV, but for ours, running the roof AC will not do jack for people riding in the cab. I know because when we bought our RV the cab AC was broken. We tried just using the roof AC (with generator) but I still sweated my butt off up front. We even bought a little fan to try and blow house air at the driver but it was still miserable up front.

Steve

Our Itasca is fine up front with the roof air running. Our Coachmen was fine when it had a 13,500 Btu Dometic followed by a 13,500 Btu Carrier, but it's not fine with its' current 15,000 Btu Advent AC. It must be due to the positioning of the forward vent on the Advent. The Itasca has ducted AC, while the Coachmen doesn't. My previous Class C was also fine with its' nonducted roof AC.

[maillemaker]

I'm from Florida, and most trips, most of the year involve using the air conditioner. I was told way back in 1995, when I bought my first Class C that it was more economical to use the generator to run the roof AC than it was to run the dash AC. I was told that a generator will use around .7 gal per hour. I almost always use the generator for air and not the dash air.

I don't know about your RV, but for ours, running the roof AC will not do jack for people riding in the cab. I know because when we bought our RV the cab AC was broken. We tried just using the roof AC (with generator) but I still sweated my butt off up front. We even bought a little fan to try and blow house air at the driver but it was still miserable up front.

Same thing for heat. Our heater core blew one year just as we pulled into Disney. Mobile tech ran a bypass so we had no cab heat on the way home. Ended up buying an electric space heater to heat the driver's legs on the way home as freezing cold air was coming in at the driver's feet from somewhere.

I can also tell you that if you have passengers in the house the cab air will not be sufficient to keep the house cool.

So - if you're in the South in the summer and you have passengers in the cab and in the house, you will probably be running the generator as you go down the road so that you have AC in the rear.

If you do that you may as well run your fridge on AC, too. No pilot light to burn propane or worry about at gas stations.

Steve

[pnichols]

wwest wrote:
Non-inverter gensets MUST run at full RPM constantly.

Yes ... they must run at full RPM constantly ... but they do not necessarily run at full load constantly.

A non-inverter generator uses less or more fuel depending upon the load on it's crankshaft. For a given load range, the fuel usage advantage that an inverter generator brings to the ball game is reduced friction and reduced wasted-heat inefficiencies ... due to spinning less fast with small loads.

Also, FWIW, I have a small non-inverter Honda generator that is only 1 dB louder at idle than an inverter Honda generator is at idle. However, my small generator under full load is way below the noise level of an inverter Honda when it's under full load. My RV's non-inverter built-in Onan generator acts the same way - about the same low noise level all the time and with fuel consumption that goes up and down with heavy and light loads.