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Generator Fuel Consumption
Over the years I have tried to track generator fuel consumption for planning purposes. It is not an exact science because assumptions have to be made.
The most confidence in consumption was obtained when I was able to fill prior to an extended period of use, and refill immediately following its use at a truck stop less than 2 miles away. In that instance the generator ran 171 hours and consumed 71 gallons for about .415 GPH.
In other instances I had more driving between extended use of the generator so more precise estimates were not available but consumption was estimated to be no more than .5 GPH.
In the above two examples most of the power (and fuel consumed) was to keep batteries charged plus run a couple of A/Cs, the HW tank, and occasional use of the grill, range, TV, and lighting.
This past week I was able to put 66 hard hours on the generator. It was hot out with temps at 92 degrees, I ran 4 A/Cs all the time (they cycled obviously), and was an energy hog using lights. HW tank, grille, range, microwave, aux compressor, water pump, etc. I saw 40 plus amps per leg often so the generator had a good workout.
Unfortunately there was about 550 miles of driving involved so my guess as to how much fuel was burned by the generator was influenced by how many MPG I was getting while driving. I have a range I know represents the minimum MPG and the likely highest MPG so at best I can only come up with a range of consumption for the generator. For the 66 hour period the range with the generator loaded as heavily as I could make it appears to be somewhere between .6 and .7 GPH.
My 20 KW generator output never got above 50 amps per leg, stayed at 40 plus amps per leg a lot of the time and on occasion was as little as 20 amps per leg.
The reason this information is valuable to me is that when I have extended dry camping periods with a lot of generator use I can make some reasonable assumptions regarding fuel needs. I think this last week running the generator loaded as much as I could possible get it represents a worst case situation and only when dealing with a lot of high temps. The more reasonable estimate however is going to be in the range of .5 GPH.
The generator was run from around 6 AM to around 9 or 10 PM every day so it was not controlled by auto-start.
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21 Replies
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I ran mine 89 hours without a shutdown in August in Louisville,KY and I calculated .63 GPH so Jon and I are very close to the same range.
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Good information.
On another venue out in the ether there is a guy who proposes going sans generator in his coach and use the alternator on the DD to charge his house batteries.
Does anyone know what a DD burns at high idle with the DN50 pulling a medium to hard load?
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Would be interesting to find out how the guy is going to get 14.4 volts out of his alternator to adequately charge the house batteries.
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Isn’t that one of the things that the Vanner does?
I thought that the engine driven alternator would charge the engine and house batteries on a Liberty or Marathon conversion.
Is my thinking wrong?
More learning for me to do!
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The alternator regulator controls alternator output.
Depending on the type of regulator, fixed or adjustable, internal or external, there is some control over output, but the charge current for bulk and absorb on AGMs has to be higher than the typical 27.7 V setting Prevost calls for. I believe the setting is meant to be a safe one that will not “cook” a battery, especially one likely to be exposed to temperatures significantly greater than ambient.
Regarding the use of the generator let’s just say some people have different ideas and are willing to try things. I think it will ultimately prove inadequate and likely to bring about some battery life issues. What I want to know is why it is being considered.
The Vanner equalizer only maintains a relationship between the 24V value and the 12V value, and it maintains the 12V value at 1/2 of the 24V value within 1/2 volt. I can’t and won’t increase the 24V value.
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First Tom wrote: “Would be interesting to find out how the guy is going to get 14.4 volts out of his alternator to adequately charge the house batteries.”
He wasn’t aware of that until I enlightened him (using knowledge that I’ve learned on the PC Forum).
Then Jon wrote: “Regarding the use of the generator let’s just say some people have different ideas and are willing to try things. I think it will ultimately prove inadequate and likely to bring about some battery life issues. What I want to know is why it is being considered.”
He believes that he can save the weight and space of the generator by using (1) solar and (2) the DN50 on the DD to charge the house batteries. I wasn’t alone in suggesting this path might not be the best for him to start down. He provided me with a series of calculations (which I had difficulty comprehending) which resulted in him concluding it would take 0.29hrs to recharge the house batteries with the DN50 on the DD. I haven’t had the opportunity yet to tell him that I suspect that calculation is extremely optimistic. I think I also told him that his coach might be the only coach without a generator.
Then Tim T checked in: “I thought that the engine driven alternator would charge the engine and house batteries on a Liberty or Marathon conversion. Is my thinking wrong?”
I know it will on a Liberty … … OK, OK, OK … most other if not all Prevost conversions will or should charge the engine and house batteries with the engine driven alternator. Even Marathon’s probably have this functionality.
The issue is that the engine driven alternator puts out less volts than what a full charge on the house batteries represents (Tom please correct me if I’m not 100% accurate). So if you don’t have a generator and you’re dry camping (not hooked up to shore power) and you’re using the engine driven alternator on the DD to charge the chassis batteries, they will not reach a full charge which I have come to understand is NOT good for them.
I think your “thinking” is right, but make sure you fully understand in what context your thinking is being applied.
I think we’ve experienced thread creep, probably its largely my fault and somewhat expect to be held accountable.
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If he’s running wet cell batteries for the house, gasp, he’s probably OK with the alternator. What’s not known is how many batteries and what size. No point in trying to make sense of this, it doesn’t.
Of course our coaches maintain the house batteries while running, but they’re not being fully charged like the inverters do in Bulk and Absorption at 14.4 or 28.8.
If he’s running AGM’s and thinks he can bring them back to 100% charged with the alternator, make sure he has my information Dick for batteries.:)
This thread has creeped bad, it’s too much of a PIA to Move some of it to electrical.
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So far let’s leave this discussion as is because I strongly suspect the urge to get rid of the generator (because of its weight) is associated with fuel consumption.
But let’s expand this discussion because some facts should be a part of it.
Our banks of house batteries range in size of 3 8D batteries to as many as 8 4D batteries. That is a lot of battery power and it has to be replaced when depleted. Unless the entire roof is a solar panel and there is a lot of sun a coach without a generator is going to become an energy management challenge unless the user wants to live as though the bus is a tin tent.
During warm weather when dry camping my generator is running and depending on battery state of charge and outside temps I am pulling anywhere from 20 amps per leg up to 40 amps per leg. To enjoy our coaches we look for cool inside temps so we know we are running A/Cs, but we also are using lights, the refrigerator, maybe the microwave, coffee maker, and TVs. We heat water, maybe cook on the grill or range, and we might have other less steady but measurable loads like the water pump and aux compressor.
But we also have to replace power in depleted batteries. When we charge our AGM house batteries, even from a 50% discharge we are going to start out with the voltages Tom listed and until fully charged they are not going to go into float of about 26.6 or 13.3. Depending on how much power is generated by the sun or a running engine the charge current could be as low as 10 amps or 40 amps and the length of time to reach float corresponds to the amount of charging current. At 10 amps charging current I think almost an entire day will be required to get house batteries on some coaches to float, and maybe never depending on how deeply they have been depleted.
A 50DN has about 270 amps output at 27.7 volts. So to put that in perspective a single roof or Cruisair is going to draw about 65 of them. Remember as voltage goes up the amp draw goes down. Or if 2 A/Cs are drawing power 130 amps (at a nominal 24V) is being used. Of the 20 to 40 amps per leg at 120V that means the A/Cs are only drawing about 26 amps total or more than half of the lowest 120V amp draw and a very much smaller percentage of the larger 120V amp draw of 40 amps per leg. In other words it will quickly eat up the total output of an alternator if you want to stay comfortable and charge batteries. Forget about using power for much else.
A lot of solar panels would need to supplement the 50DN.
We spend a lot of money to own, drive and maintain our coaches. Most of us have them because of the luxury they provide. I won’t waste my time hooking up to less than 50 amp service, and if none is available I am going to run my generator and become an energy hog, enjoying more power output than I can consume. I cannot imagine why anyone would see a benefit to doing away with such a great means of having instant and abundant power so we can enjoy all the coach has to offer.
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I initially thought that if we drove the coach 8-10 hours after drawing the batteries down to 50-60 % state of charge, the house AGM batteries would be fully (100%) charged.
I seems as though the charge from the engine driven alternator may/will never charge the house AGM batteries to 100% state of charge.
Is this because the engine driven alternator doesn’t get to a high enough voltage for the batteries to reach absorption and or float charge levels?
Dang…the more I learn the more I really don’t know.
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Tim: That is the way I understand it. I kinda had that notion for a while, then the Pros from Dover enlighted me to the voltage coming out of the 50DN and I quickly connected all the dots.
We’d travel all day with the generator off, presuming the 50DN was doing its job and keeping the house batteries fully charged. Stop at say 9 or 10pm at a rest stop. Leave generator off, didn’t need A/C, and go to bed after about 10 minutes or so. Early in the morning (5 or 6 or 7) the generator would fire up just before we got up. Thought … hmmmm … batteries can’t carry us through the night.
Then we’d drive similar amount of time, stop for the night at a rest stop. Fire up the generator for one reason or another for maybe 30 minutes to an hour, turn it off. Then head for bed. Generator wouldn’t auto-start in the early morning. I thought, HUH. Tonight the batteries carried us through the night, I wonder why.
Once I saw Jon’s or Tom’s original post about max voltage on the 50DN, then suddenly I realized what was going on. Concluded best way to keep the generator from auto-starting early in the morning was to run it for a while before heading to bed.
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If you can go to bed on float, you’re good to go.
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We really don’t need a generator or more than one house battery if all we do is drive and then plug into shore power.
But the use of the coach is not like that.
As Dick points out we often are in the coach ovenight “dry camping” and for that we need fully charged house batteries, or we have to do without the ability to use house A/Cs, use a lot of lights watch TV, or any of the multitude of things we do that require power.
We also need to be cognizant of the fact that our inverters are the only way we currently have on board of assuring our batteries will be charged to “float”, even if the current setting is low such as 10 amps. When connected to shore power our inverters are working while we sleep so the batteries get charged overnight while there are little or no other loads. When dry camping however without a generator we would need a lot of solar panels to charge batteries that likely were being used during the day to run A/Cs or TVs or lights, etc and the problem is the sun doesn’t shine much at night except in Alaska.
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I have 5 Lifeline 8d AGMS. So thats bout 1200+ a/hr.
I find when dry camping after a total of 9hr charge in 2 sessions,
3hr in morning around 0600 if the auto start didnt already start, and
heat of day time for 6hr when we run A/C’s and shut down by 2000hr.I find that in the parks you have to adhere to quiet times, but I would expect to operate the basics in my basic Royale coach in the winter when the Aquahot runs on and off, atleast a 8-10 hr inverter run.
So I think that turning up the 270a/12v DN50 to a healthier voltage might help, why cant I get 130a to the house bank?
p.s. I seem to burn about 1+ g/hr under 3 a/c load and charger on.
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As coaches got more loads the batteries had greater demands.
When we are on shore power, no problems as long as we manage loads.
When we are dry camping if we shut off the generator we have multiple loads going on all the time. Phantom loads are always there ranging from TV memories, alsrm systems, refrigerators, etc. Most coaches are fine running all night long, but when you have to use the webasto or A/Cs all bests are off because both can draw a lot of current.
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Jon
Can you call me (think you have my cell number) I’d like to take you to lunch and pick your brain as I zero in on a new (to me) coach, since mine was lost to fire. Lot’s of questions???? thanks
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