Generator Fuel Consumption

[JIM KELLER]

We dry camped at our daughter's over the Christmas Holiday. Always wondered how much fuel the generator used. Nine days of dry camping with six to eight hour brakes daily and some wabasto assistance took 100 gals of fuel for nine days. The generator logged 165 hours with one oil change at the 100 hour mark. Obviously 100 gallons of fuel at todays diesel price exceeds the cost of campground fees.

[JIM CHALOUPKA]

Hi Jim, with that much usage it might be a good idea to pay for the daughters 50A RV service install, probably a lot cheaper in the long run.

JIM

[sawdust_128]

We were cold in Raleigh until right before Christmas. What was it like in Western NC?

[JIM KELLER]

Sawdust, Had some 17 degree nights. Lots of rain, fog, clouds, grey skies etc. I think we had two days of sun. We are glad to be headed South to our Florida home !

[mike kerley]

Jim, Remember, the larger the electrical load, the more fuel it burns, so you may burn much more next summer when the AC's are running hard.

We'll burn about .3 gal per hour just charging the batteries. Kick on the AC's and water heaters and we go to about .8 GPH. That's with a 17.5 Power Tech.

Yep, its still hot in Florida. 80 degrees yesterday.

Happy New Year!!!!

Mike K.

[Ray Davis]

Jim,

Just so I understand, when I first read your post, I read 9 days at 6-8 hours per day. But, that's nowhere near 165 hours. Then I re-read, and I think you indicate that you had 6-8 hours per day where you were not running your generator?

Dividing 165 by 9, I get 18.3 hours per day of generator use! Wow, that's a bit. All in all, about 0.6 gallons per hour? Not too bad.

Ray

[Yankee802]

Because we haven't drycamped yet, how long does it take to charge up the house batteries? Obviously it depends on the amount of charge/use, does anyone have some numbers?

Jim, why would you run your generator that much? Using your Wabasto for heat, you should be able to run off batteries and only have to run the generator to charge them, right?

Geoff

[Ray Davis]

I've found that my batteries charge in about 3-4 hours, but generally I have not severely depleted them during the preceding day/evening.

Depending upon your electrical use, batteries could wear down significantly faster, requiring additional charging? Things like TV's, video games, lights etc all add their draw to the batteries while dry camping.

Ray

[Petervs]

Geoff,

It depends on a bunch oif things:

How big is your house battery bank?
How old is your battery bank
How discharged is the battery bank?
How big is your generator?
How many other things are you running off the generator at the same time?

So, 2-4-6 hours is usually the right answer depending on how you answer the questions above.

[jack14r]

On real hot days I have burned as much as 15 gallons a day.

[Jon Wehrenberg]

Geoff,

I'll piggy back on what Peter said. The charge rate of your inverters or converters also contributes to determining how long it takes to charge your batteries.

But to address the question of why run the generator, I think it is a matter of preference. I do not rely on auto start. I prefer to maintain a higher charge in my batteries than the auto start is set for so I run the generator often for two reasons. The first is to keep the battery voltage level in excess of 12.3 or 12.4.

But primarily the reason is I want to use all the features of my coach. If I wanted to conserve I would buy a tent. I run my generator in a rest area if we are going to stop for a long lunch. I run my generator in a rest area if we stop for the night from the minute I shut down until I go to bed. I want to run my airs, or my heaters, or every appliance we have on board if I choose and I don't want to "manage energy". If I was spending a week at Quartzite (that ain't never going to happen) I would be conserving energy.

[Petervs]

Interesting post Jon.

We do the exact opposite it seems.

First off, I dislike hot places, so we rarely need the AC. The house bank is plenty adequate for everything we use in the bus for an afternoon or evening stop. We do need the generator for a little while if we happen to use the cooktop which only operates on 220 volts. If we run the generator for that for a half hour or so, that again tops up the batteries.

If it is cold out, we have the Webasto running, it keeps us very toasty and is way more efficient than running the generator and the heat pumps or the toe kick heaters.

We often have the windows open when we stop, generator noise would then be a negative.

The big alternator on the Detroit charges the batteries way faster than the generator. I see 90 amps going into the batteries from the generator, and 270 from the engine. I see no reason the batteries need to be fully charged if we are planning to drive anyway.

I often run the generator a while longer than we need it just to get it warmed up thoroughly not so much because we need the power.

Neither way is better, just depends on your style I suppose.

[Jon Wehrenberg]

Peter, this goes back to our original bus that had a manual selector switch instead of an automatic transfer switch. After 15 years of ownership Di still had a hard time remembering what position the black selector knob had to be in to make a cup of coffee or watch the TV.

So for simplicity sake I just cranked up the generator and the selector know was switched to "generator". That way Di did not have to think about anything and she could use all the outlets or do whatever she wanted. When we were plugged in she just had to switch the knob to "shore" power.

While this coach is virtually all automatic with the automatic transfer switch and auto-start there are still things that do not run through the inverter, so to avoid even the slightest inconvenience I just run the generator. After all it is a luxury coach right?

[bluevost]

when we boondock in Quartzite I run the generator about 4-5 hours a day. In the morning to warm the coach up and fix breakfast, and again in the evening to fix dinner and charge the batteries for the night. We are usually at the swap meet during the daytime. I never hear the pitch of my generator change, it runs at one constant speed no matter what is turned on. It is a power tech, 17.5 kw. I figure .8 gph and that's pretty close. So maybe 4 gal per day. If we have everyone inside watching football, I of course run it during that time, and the numbers change slightly.

Question to anyone -- Can you run the Wabasto off the inverters. I have 2 Heart 2500, and 8 4D batteries, that just turned 2 years old.

Jon -- Come to Q for 4 days instead of a week!! I hear there is a fresh water oyster farm on the Colorado River.

Happy New Year everyone,

Ken

[Petervs]

Ken, YES you can run the Webasto from the inverters, actually, the inverter is not even in use, it just runs on 12 volt battery power. That is the whole point of having the Webasto.

If the generator was running, you could use the heat pump AC/heat but that would use more fuel and make more noise for the same heat output.

Jon, I suppose you are still driving stick shift cars so you know what gear you are in? Come on now, you really can teach some old dogs new tricks, the only thing you need to do is forget some previously learned habits that are no longer necessary.

Try not running the generator when you stop one day, you will not die, no less comfort will be felt by those in your coach ( unless you need AC) and all of a sudden that warm glowing feeling will come over you because you have now saved some fossil fuel and are delaying the global warming process by a few minutes.

Try it, you'll like it!

[lewpopp]

Ken,

Are you sure you have 8- 4D batteries and not 6- 4D batteries?

[truk4u]

The worse thing you can do is to not run your gen long, hard and often. Powertec explained to me in detail, "you bus guys with the big gens don't use them, they're designed to run 20,000 plus hours before overhauls."

I dry camp often and if not real hot and don't need the air, I do the same as Ken, run in the morning and again in the evening and I always let the chargers get to float before shutting down. You can't top a battery bank unless you get to float!

Like Jon, I won't use the auto-start while dry camping unless it has the capability of starting at 12.2 volts.

This thread is going to get real interesting!;)

[rfoster]

I am convinced global warming is over, oil/gas prices are down, I am running the generator and when I grow up I want to be like Jim Keller.



Flying J-- Knoxville fuel $2.19.9 gal. Sunday night.

[Coloradobus]

We run our generator all the time, all the time when dry camping. In National Parks we run it the entire day before quiet time sets in.
At the flying J, we run it all night from the moment we stop for the day.
Kohler, like the Power Tech guys, and Marathon (Leon), have over and over lectured us to RUN the genset.
We Rarely use the Webasto, now. I wish we didn't have one. Superbus1 doesn't use a Webasto or like product, their coaches are completely electric.
After seviceing our Webasto recently (been 2 years of running only to assist for hotwater), (Jon pointed to our smoke in Spearfish), we needed a new burn tube and ofcourse a nozzle and filter.
Nozzle was $14.00, burn tube was several hundred dollars from the source,(we live 35 miles from Vehicle Systems/Aquahot.) For the money spent on Webasto parts, it wiould take a many hours of running the genset to burn that much diesel.
Our cruise airs, and definitely the Webasto, makes more noise than our genset. We were even accused of running our genset during quiet hours one chilly Yellowstone night by the campground host (nazi), We needed a civil assist from the Grant Village local Ranger to help prove the noise from our coach was from the Webasto, and not the genset. since that time, we don't use the whining Wesbasto.
We often ask ourselves why Marathon installs 3 different froms of heating in the coach, its more cost, more weight, and more maintenance.
As Jon said, if you don't use the genset and really make it work, it will carbon up and not run well.

[Jon Wehrenberg]

Peter,

I believe you are catching on. The two vehicles I drive almost exclusively are manual transmission, and if I had my way the bus would have one also.

Automatic stuff is for sissies.

[jelmore]

Flying J-- Knoxville fuel $2.19.9 gal. Sunday night.

Flying J in Ft. Pierce, all truck islands closed (no fuel?). Pilot was $2.51 or so. Monday.

[JIM KELLER]

Ray, You did the math right. After the first day I watched the Auto Start crank up the generator at 12.2 volts. I was surprised the voltage got that low after eight hours. I have 6-4D batteries and they are two years old. Some of the draw was from running the Wabasto I think unless it is supplied power from the engine batteries. I was unable to use A.C. heat pumps at 17 to 20 degrees. The Bus sat outside the entire time and perhaps the temps lowered the performance level of the battery bank.

Mike, Happy New Year to you and Karen. We are glad to be back in the Florida warmth. I like having to turn on all the AC 's to stay cool ! That is why I reduced the charge rate on my Inverter. It takes longer to charge the 4D's but I think it is better than hitting them hard each time I charge them. While traveling in the South I noticed Three AC 's, the oven, and misc other items plus the Inverters charging full rate was to much for some of the 50 amp outlets in some campgrounds.

And Jim C. You are correct. I told our daughter to hire a contractor and send me the bill !

[JIM KELLER]

Flying J in Ft. Pierce, all truck islands closed (no fuel?). Pilot was $2.51 or so. Monday.

Stopped at the Flying J at the Fla Ga line upon our return to Fla. Pulled into the RV pumps and found them to be real slow. Pumped about 3 gallons per minute. Obviously their filter needed replacing. Went inside to complain and told the cashier I was going to pull over to the truck lane. She said fine but wanted me to know it was 6 cents a gallon more on a credit card in the truck lane ! Wonder if this is a new strategy for their reorganization.

[JIM KELLER]

I am convinced global warming is over, oil/gas prices are down, I am running the generator and when I grow up I want to be like Jim Keller.



Flying J-- Knoxville fuel $2.19.9 gal. Sunday night.

Roger, When I grow up I want to be like YOU because " You just can't hide money! "

[bluevost]

Peter -- Thanks for the answer

Lew -- definitely 8 4-D's

Happy New Year everybody,

Ken

[Ray Davis]

That is why I reduced the charge rate on my Inverter. It takes longer to charge the 4D's but I think it is better than hitting them hard each time I charge them

What was your charging rate, and what did you reduce it to?

Ray

[JIM KELLER]

Ray, If I recall correctly there are three levels of charge rate for my Heart 2500 Inverters. I had Nick Hesler walk me through it and we picked the middle rate. I think I remember a 25 number.

I sure do miss ol Nick. He is a wealth of knowledge. I called him the other night when I had a question. Have you talked to him lately ?

[Ray Davis]

Jim,

No, I haven't spoken with him recently. I too miss him. Maybe I'll give him a call tonight, and wish Happy Holidays!


Ray

[truk4u]

Jim the Tool Man,

I fueled a day before you at Flying J, 201 marker and had no problem with the RV pump. At least 4 of the truck islands were closed and they had a back-up on the truck side. It's slower than the truck for sure, but at least my shoes weren't covered in diesel fuel after pumping 160 gallons. 2.20 a gallon, not bad!:rolleyes:

[Jeff Bayley]

I won't keep reposting the same thing about my aux. generator fixation but I use it and like it. The link below will suffice for those interested. To add a comment or two, most small inverter gens have a 12volt charger built in and you use cord with two alligator clips and the other end plugs into the gen. If I just want to keep my batteries topped off to keep up with the fridge, TV or using the Aqua Hot, I open the battery bay and connect that to the battery bank. Ultra quiet, uses less fuel but mostly give me peace of mind if I want to keep my batteries up all night, like if I'm using the Webasco. I'm had the turbo burn up on the gen one time about 10pm at night and ambled out of the coach and happen to see the smoke. Ever since then, I can't sleep well with the gen on and my batteries wont' make it through the night to keep above 12.2 for the Webasco or to keep the fridge going. Most would say that I'm not maintaining the batteries right and that may be the case. I bought new Interstate batteries, made sure not to abuse them.....kepping them above 12.2 and they still suck. Had them load tested recentley by independent (not Interstate) and they said they were ok. My battery issues getting off topic, but that's why I gave up on getting a good cycle out of them and toss the small aux gen on them when I want to keep them up. I can also plug it into the shore power cord, turn down the charge rate on the inverters/chargers and run one A/C all night long on 2 gallons of gas. The only drawback to all this is keeping a couple 5 gallon jugs of gas in the bay but so far no explosions. Still here.

More details below.

http://forum.prevostownersgroup.com/showthread.php?t=2367&highlight=generator&page=4

[Petervs]

Why all the worry about charging your house batteries back up when they hit 12.2 volts?

Lifeline says 10.5 volt is fully discharged.
From their site:

"As a battery chemically transforms from fully charged to discharged, it's voltage drops from 13.5 - 10.5 volts for a 12 volt battery. As the voltage drops this affects the amount of amps required to drive a load. (Watts law: amps x volts = watts)
13.5 volts x 10.00 amps = 135 watts
10.5 volts x 12.86 amps = 135 watts
As such, this calculator is for sizing purposes only. All systems should be thoroughly tested as they are installed to insure that the battery bank is appropriate for the load on site.

AGM Batteries are not harmed by high amperage charge and discharge so long as the input voltage is carefully regulated.
Charge 12 volt batteries at 13.2 - 14.4 volts


Ratings: Capacity ratings are after 15 cycles and are at 77°F (25°C) to 1.75 volts per cell.

What depth of discharge should be used when sizing a battery?
To get the best cycle life, the average depth of discharge should be as low as possible. Concorde
recommends the average depth of discharge be no greater than 50% of the battery’s 20 hour rating"

There are 6 cells in a 12 volt battery, so 6 times 1.75 is 10.5 volts. This is how they measure capacity. A fully charged battery is 12.6 volts. If you recharge at 12.2 you have used but 45% of the capacity you have paid for.

From the Lifeline site they want the AVERAGE discharge to be 50% which is 12.13 volts, there is no harm in occasionally going as low as 10.5. If we are dry camping I do not worry about it overnight, if it is low in the morning we fire up the generator for a while

I routinely let mine run down to 11 volts before starting the generator if we are dry camping. 12.2 volts is not some kind of drop dead number like that last 1.0 gallon of diesel in the tank.

[Jon Wehrenberg]

Peter,

That is the nice thing about our coaches. Each of us gets to use them as we choose.

This is strictly my opinion and thinking on the topic, but I fall into the "keep the batteries charged up" category. I think nothing of shutting of the generator at night and not turning it on in the morning if we are going to drive if the batteries are still 12.2 or above. We can make coffee, watch TV or do almost anything we need to do and we are still OK.

But from the battery charts that I have seen (and haven't been able to find quickly) once the batteries do get below my preferred charging point their power falls off quickly. So for me it is no big deal to start the generator.

Everything mechanical has limits, and as we use our stuff at the limits I suspect it adversely affects the product life, whether it is a battery voltage or an airplane engine CHT.

I think your analysis is absolutely correct and folks that are dry camping can get more time between charging cycles by following what you said. But a deep discharge has its price in the number of charge cycles. Someday I will try to figure out if batteries actually last longer by only allowing moderate discharges, compared to deep discharges. I believe that if the number of cycles of deep discharge is 1000, but the batteries get 5000 by never letting them go below 12.2 for example, you will need many more charge cycles, but do you need 5 times as many?

BTW, I like running my generator and loading it up. I spent a lot of money to get a coach that has one, I spend a lot of money to drag that dead weight along on trips, so my attitude is to run it until it wears out, which is not likely to happen any time soon.

[jack14r]

Jon,The Lifeline battery, MK battery, and the Deka battery web sites all have charts on percentage discharge that agree with what you are saying.MK and Deka charts agree that the Gel is better than the AGM for deep discharge use.A battery that is 75% discharged has a much shorter cycle life than a battery that is only 50% discharged.I rarely let my generator auto start,like you I like them topped off.

[Jeff Bayley]

I thought I had been informed from several sources including POG postings that letting the batteries fall below 12.2 was bad for them. I attributed that to my batteries giving bad peformance so the next time I changed them, I gave special attention to keeping them up. Still, I got cruddy performance. My batteries drop from 12.9 or 12.7 to 12.0 or so within a half hour to an hour. The drop from 12.0 to 11.0 takes a lot longer, actually giving "better" performance in a manner of speaking. But if I go to bed dry camping, it's a toss up if the fridge is still on the morning.

[gmcbuffalo]

Jeff
Have you compared the voltage reading on your meter with a voltometer attached to the battery bank. I have two voltage meters above the dash, one will read 11.9 while the other one reads 12.4. The 12.4 one reads the same as a direct reading off the battery bank with a voltometer.
GregM

[jelmore]

I'm just passing on what I've read. I don't know that I really understand it.

http://www.lifelinebatteries.com/manual.pdf is my reference.

Their literature says "For repetitive cycling, chargers should have a current limit of at least 0.2C (20 amps for a 100 Ah battery). If the charge current limit is less than this value, the cycle life is adversely affected."

These 8D batteries are rated at 255 amp hours. Does that mean the batteries should be bulk charged at 50 amps (2.55*20)? If so, would that indicate 2 chargers at 25 amps each? Makes me think my charger settings are set up wrong with 20 amps on one and 5 amps on the other and power sharing off. Then again, I don't really know how my chargers should be set up with regard to power sharing, dual ac inputs, etc. I do know that I seem to need all the amps I can get inside.

The last page in that pdf file shows that the number of cycles dramatically increases the less the battery is discharged between charging cycles. For example, 50% (12.13 volts) = 1000 cycles and 10% (12.65 volts) = 5000 cycles.

Liberty has their Watchdog set to start the generator at 11.5 volts which is about an 85% discharge which would be about 500 cycles.

If someone would care to, please correct anything that I've got wrong.

[Jon Wehrenberg]

I doubt if there is a universal answer. We all use our coaches in different ways, and even that changes from time to time depending on circumstances.

We previously dry camped when on the seminar or trade show tours in our first bus. We often found ouselves parked next to one of the regional sales offices / warehouse and I would do several days of sales calls and seminars with the sales agents. Weekends were ours so we would go to a campground, dump and fill and stay hooked up or be driving to the next city where I was scheduled to help the sales reps.

We ran the generator as needed. It was easier than screwing around with a coach that had manual switching and wasn't always user friendly.

Today the only time we run the generator is if we are on the road and stop in a rest area. The rest of the time we spend in campgrounds with an occasional rare spell of dry camping. So our charge rate is set at the minimum and it does not recharge the batteries, as much as it maintains the batteries.

By setting it at the minimum, we can be energy pigs on 50 amp shore power without worrying if the chargers in the inverters will kick on and pop the shore power breaker. We can run a couple of AC units per leg, plus the HW heater and make coffee or watch TV. If we dry camped often I would have the inverter charge rate set up to the max allowed.

In about 6 months my batteries hit the five year mark and thus far there is no indication they are ailing or in need of replacement. I am tempted to see how far they go before they do start acting up, although I know once one does start to fail it creates a lot if problems, especially likely on ours because of the programmable logic controllers that run so much of the coach.

[jelmore]

Starting to make some sense. We use our coach the same way as you Jon, though we're in it full time. So I guess the batteries are maintained in the float stage most of the time, when driving and when plugged in. The only time they drop down and they have to bulk charge (cycle?) is when dry camping.

[Yankee802]

Automatic stuff is for sissies.


After all it is a luxury coach right?

Seems kinda like an oxymoron. :)

(I couldn't resist)

[dmark1]

Ok a newbie question: No one ever explained this to me (threw me the keys) so....

When you stop at night (say at a rest stop) enroute do you run the generator at night when you have the air conditioners on or do you (assuming no shore power) just let the inverters run the whole thing until the generator kicks on (auto position) to charge them? If that is the case doesn't the constant discharging and recharging of the battery banks cause a shortening of life of the batteries? What do most of you do in this case?

Thanks again

Mark

[jack14r]

I have found that if I use the inverters at night and some during the day I will save about 5 gallons of diesel a day.I guess it's pay now or pay later.I also usually try to be a good neighbor and turn the generator off by 10 pm if anyone is camping nearby.

[Jon Wehrenberg]

Geoff, Nobody likes a smart ass.

Mark, Energy is energy is energy. What I mean is that if we ignore efficiency losses which I have no way of calculating, running an AC unit takes a certain amount of energy. If you run the AC from power created by the generator, or shore power, or from the battery through the inverter the energy is the same.

If we take shore power out of the equation, and look at just power generated on your money directly, you can be fairly confident if you run the AC from the generator, or from the batteries which them must be charged from the generator or the bus engine you will spend some dollars for fuel. Probably the same amount of dollars no matter how you accomplish it.

So to answer the question, running the generator continuously, or letting if be controlled by autostart is probably going to result in similar costs of energy. I don't have the ability to run my AC units from my inverter, so we just run the generator as long as we want AC.

[Joe Cannarozzi]

I think that when a converter sets an autostart below 12.2 they assume you are pulling amps out of them and that 12.2 magic number is a resting rate.

In other words say you have your fridge working off the inverters overnight yes it will have your batteries going down below 12.2 sometimes maybe towards morning but if you shut down all the loads you have on and allowed the batteries to rest some they actually would still be above 12.2.

If someone was using the autostart for storage to keep the batteries up and there was no draw on them then that sub 12.2 start mark would be bad.

[Yankee802]

Jon,

I didn't mean to offend you, so I appologize. It seemed there was a good amount of good natured ribbing going on here (POG), and it was my attempt at that. Again, sorry.

Geoff

[Jon Wehrenberg]

Geoff, If you think my remark about you being a smart ass meant I was offended nothing could be further from the truth. I was amused and thought I would give you a shot right back.

I get offended when Peter picks on the high quality paint job on my plane. I get offended when people like Brian make their engine look better than mine. I get offended when people make fun of my high speed runs at 62.5 MPH. I get offended when I get the Anal award. And let's not forget how Lew offends me for spelling errors, or when Dorinda picks on my because I don't have a fancy push button awning.

Now I'm all pissed off and it is your fault.

[Yankee802]

LOL, ok I wasn't sure, it's sometimes hard to tell tone online. :)

[Jon Wehrenberg]

Now you are catching on. Don't take anything said on this forum serious, and don't believe anything anyone tells you.

[Yankee802]

So if I hear you correct, I shouldn't listen to you, right? :)

[Jon Wehrenberg]

I believe you have finally found the truth amidst all the blather on this forum.:D