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Old 09-24-2021, 10:11 AM   #1
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Generator sizing for travels at altitude

A question for those who have camped at altitude - which, for the purposes of this discussion, is higher than mean sea level (MSL) and consistent with altitudes found out west - say in the Black Hills or proximate to the area around Mt. Rushmore for example.

We have (on order) a 2022 Classic 33FB with a delivery sometime in the early spring next year. Our goal is to travel and see some of the sights out west where we would expect to boondock at least some of the time. Our Classic 33 comes with the new Airstream solar package with a pair of Battle Born lithium batteries. The solar is advertised at 270 watts...we'll see how that holds up. So we have some juice natively available.

The question I have for the Airstream Brain Trust is the size of generator to get if I'd like to run one of the 15K BTU ACs. My plan is to add a soft start to both ACs. I also like the idea (at least weight-wise) of the smaller Honda EU2200 gensets as they are lightweight, reliable (generally), and have a successful history of starting/running a 15K BTU AC at sea level (or close to it).

Now, generators lose efficiency with altitude. This I know...Has anyone been successful using a single small genset (like the Honda) at altitude - say 5000' or so - and successfully started and run their AC? I really don't want to lug a heavy genset around if I don't need to. None of us are getting any younger...
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Old 09-24-2021, 10:56 AM   #2
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Hi

Folks also like to run generators on propane. That knocks down the output as well. On a typical trailer, the converter charger womps in when power is hooked up. It's 5 to 8A on top of the 13 to 19A the A/C *might* pull adds up to a lot of power.

Most find that running on gasoline, the 2200 (in reality) puts out the same peak and average power levels at 5,000' as at sea level. If you can manage your loads properly, it should work.

Also understand that a lot of "two A/C" trailers have a 13,000 and a 15,000 BTU unit. The 13K will pull a slight bit less than the 15K. Fan settings do matter, fan on full blast is an amp or two more than fan on low. Humidity matters. Sea level on the Gulf coast with 95F and 112% RH is a struggle. Lots of variables even looking only at the A/C.

Fun !!!

Bob
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Old 09-24-2021, 11:53 AM   #3
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I went through this process last year, and I’ve only got a single AC unit. I often camp at 8,000 feet or more. For the reasons above, I decided to stick with gasoline and I bought a larger generator. I was originally considering the Champion 3450 with remote start. It weighs about 95 lbs. I then stumbled across their 4500 with remote start, which only weighs 6 lbs. more at 101 lbs. I’m very pleased with the 4500. It is a bit on the heavy side, but it has two large handles and my wife and I can easily lift it into the truck. It powers everything in the Airstream with ease. I don’t regret the decision at all. It’s a nice little unit and the remote start is a nice feature.

Good luck with your decision.
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Old 09-24-2021, 01:21 PM   #4
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Thumbs up

I hear you with regard to the propane options. I'm aware and have considered some of the dual-fuel generators or doing the gas-to-propane tri-fuel conversion myself using one of the commercially available options such as the Grenergy Tri Fuel Conversion Kit.

For my use case, I haven't convinced myself that I'd spend the premium for a conversion kit, plus having less total wattage available due to the lower total energy content in LPG vs. gasoline, so I've kind of resigned myself to using a gasoline powered unit one way or the other. LP is more expensive per gallon - at least where I shop. And gasoline seems to be more readily available...but, I now have to bring a gas container with me in the back of the truck. Not ideal, but it's a tradeoff.

I do acknowledge however, that the gas generators will have more issues with the carburetors owing to the ethanol in todays fuels. I've gone through several carbs on my house backup generator over the years even when using Stabil fuel stabilizer and turning off the fuel supply so as to empty the carb float bowl. Seems that whatever I do, the gas powered generators seem to go through carbs every few seasons. Kind of the price to pay I guess for a machine that is run only intermittently at best - and whose fuel supply could probably be better. I now keep a spare carb on hand just in case.

Sounds like I could squeak by with a single small genset - or pair it with a companion which would certainly work (at twice the cost). Or, get a slightly bigger...and heavier...genset.

Still haven't decided yet...Keep the comments coming.

Thanks!
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Old 09-24-2021, 04:14 PM   #5
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I completed a propane conversion on my new never before used Honda 2000 using the Hutch Mountain kit.

Our 2017 Serenity 25 has 500 watts of solar and we rarely have a need for AC or a generator.

However, we'll be dry camping at the Grand Canyon North Rim at 8300 feet during the last week of the season and later in October in Southern Utah dry camping at 6000 feet plus.

Hutch Mountain provides a special orifice for 5000 feet plus. They are located in Southern Utah and feel that their system performs well at high altitude. Since we plan on using the generator to maintain the batteries at a level safe for running the furnace and fans I don't anticipate a huge impact by a slightly reduced performance due to altitude.

I'll report back in a month.
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Old 09-24-2021, 06:18 PM   #6
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Quote:
Originally Posted by InvertdEagle View Post
I hear you with regard to the propane options. I'm aware and have considered some of the dual-fuel generators or doing the gas-to-propane tri-fuel conversion myself using one of the commercially available options such as the Grenergy Tri Fuel Conversion Kit.

For my use case, I haven't convinced myself that I'd spend the premium for a conversion kit, plus having less total wattage available due to the lower total energy content in LPG vs. gasoline, so I've kind of resigned myself to using a gasoline powered unit one way or the other. LP is more expensive per gallon - at least where I shop. And gasoline seems to be more readily available...but, I now have to bring a gas container with me in the back of the truck. Not ideal, but it's a tradeoff.

I do acknowledge however, that the gas generators will have more issues with the carburetors owing to the ethanol in todays fuels. I've gone through several carbs on my house backup generator over the years even when using Stabil fuel stabilizer and turning off the fuel supply so as to empty the carb float bowl. Seems that whatever I do, the gas powered generators seem to go through carbs every few seasons. Kind of the price to pay I guess for a machine that is run only intermittently at best - and whose fuel supply could probably be better. I now keep a spare carb on hand just in case.

Sounds like I could squeak by with a single small genset - or pair it with a companion which would certainly work (at twice the cost). Or, get a slightly bigger...and heavier...genset.

Still haven't decided yet...Keep the comments coming.

Thanks!
I use Trufuel in my generator. It’s expensive, but it doesn’t contain ethanol and it doesn’t gum up the carburetor.
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Old 09-24-2021, 07:37 PM   #7
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I use two Honda 2000i to run my charger (when the sun is not out) and occasionally the A/C at 7400 feet and above. I have re-jetted the generators for 9000 feet and have used them for five years this way. I run them in parallel. They work just fine and provide enough power. I run 87 octane fuel with Stabil added. No problems. At ~50 pounds, I can load them into my truck bed myself which my wife appreciates.
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Old 09-24-2021, 09:18 PM   #8
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Our H2200is works great here in the mountains of MT. We also carry a companion, but have yet to need it!
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Old 09-25-2021, 07:00 AM   #9
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Quote:
Originally Posted by uncle_bob View Post
Hi

Folks also like to run generators on propane. That knocks down the output as well.

Bob
I've not experienced that. Eco mode runs the same RPM on patrol as it is on LP.
I guess I'm just thinkink the old fart way.
Unless we are referring to the difference between the BTU efficiency of the two fuel's.
I can't see the alternator caring whether it's on either one as long as the revolutions are the same?

If I was to buy new it would be dual fuel Honda 2200i...👍 We use a 2000i D/F bought in 2005.

Bob
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Old 09-25-2021, 07:20 AM   #10
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Try the Honda. If not enough buy a larger gen or an additional 2200. I have not used the AC at those elevations when camping with no hookups. I did leave a forest service site without hookups in the TRNP to find a commercial site with hookups because we were hot and I decided I would rather move than run the gen all the tine.
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Old 09-25-2021, 07:30 AM   #11
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Cost is obviously a consideration in this decision. I love Honda products, but they’re expensive. My Champion 4500 was about 1/4 the price of two smaller Honda units. This may or may not matter to the OP, but it was important to me. Bang for the buck outweighed (pun intended) Honda quality for me.
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Old 09-25-2021, 07:56 AM   #12
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Originally Posted by ROBERT CROSS View Post
I've not experienced that. Eco mode runs the same RPM on patrol as it is on LP.
I guess I'm just thinkink the old fart way.
Unless we are referring to the difference between the BTU efficiency of the two fuel's.
I can't see the alternator caring whether it's on either one as long as the revolutions are the same?

If I was to buy new it would be dual fuel Honda 2200i...�� We use a 2000i D/F bought in 2005.

Bob
����
Hi

Here's the problem:

On a good generator, the engine is oversized relative to the electrical side of things. You have a 2,200 W electrical tied to a "2,800W" engine. The output power only starts to drop when the engine can't keep up with the electrical side.

They never are very clear about the engine ratings in any generator spec I've ever seen. You have to rummage around looking at the equivalent engine here and there and make some reasonable guesses.

If the engine is 20% over rated and you go from gas to propane .... no noticeable impact. The generator still puts out what it should. If it's 1.5X what it needs to be, go up to 5,000 feet and run on propane ... no noticeable impact.

The 2200 is rated for 2200W surge and 1800W "running" capacity. Which one worries you more? Which one does the engine run out of "watts" on first? One might guess that the 1800 side is easier on the engine, I'm not 100% sure that's true ....

Once you hit whatever the magic limit is, you will see power drop off as you go up in altitude. Temperature, humidity, fuel, and the carburetor all will get into it as well.

Folks rarely test generators into a calibrated load. They see if the A/C runs. There are a range of startup currents (even with a soft start) and running currents that an A/C will present to the generator. What it does today here, may not be what it does tomorrow somewhere else.

One of the reasons new generators come with an overrated engine is that the engine wears out over time. Its power output drops as this happens. A generator that is intended to run for years and years is going to come with more than a bit of margin when new.

So lots of zigs and zags.

Bob
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Old 09-25-2021, 08:20 AM   #13
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Generator choice is *almost* as controversial as tow vehicle choice. It doesn’t lead to the nastiness often seen in towing threads, but it’s definitely controversial.

The key is to pick the one that’s best for you. Consider your usual camping style and locations, average power consumption, alternate power sources like solar, portability and weight, cost, preferred fuel source, how you’ll transport it and the fuel it needs, etc.

There’s no single right generator for every person.
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Old 09-25-2021, 09:04 AM   #14
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Quote:
Originally Posted by uncle_bob View Post
Hi

Here's the problem:

On a good generator, the engine is oversized relative to the electrical side of things. You have a 2,200 W electrical tied to a "2,800W" engine. The output power only starts to drop when the engine can't keep up with the electrical side.

They never are very clear about the engine ratings in any generator spec I've ever seen. You have to rummage around looking at the equivalent engine here and there and make some reasonable guesses.

If the engine is 20% over rated and you go from gas to propane .... no noticeable impact. The generator still puts out what it should. If it's 1.5X what it needs to be, go up to 5,000 feet and run on propane ... no noticeable impact.

The 2200 is rated for 2200W surge and 1800W "running" capacity. Which one worries you more? Which one does the engine run out of "watts" on first? One might guess that the 1800 side is easier on the engine, I'm not 100% sure that's true ....

Once you hit whatever the magic limit is, you will see power drop off as you go up in altitude. Temperature, humidity, fuel, and the carburetor all will get into it as well.

Folks rarely test generators into a calibrated load. They see if the A/C runs. There are a range of startup currents (even with a soft start) and running currents that an A/C will present to the generator. What it does today here, may not be what it does tomorrow somewhere else.

One of the reasons new generators come with an overrated engine is that the engine wears out over time. Its power output drops as this happens. A generator that is intended to run for years and years is going to come with more than a bit of margin when new.

So lots of zigs and zags.

Bob
Well I guess we only zig... But to be honest we never overtaxed the 2000i.

So knowing the limits of whatever it is you're demanding oomph from is the key.

Point of fact, we've never tried to run the AC, microwave, turn all the lights on, watch television and blow hair at once.

So, that's the most likely the reason that the old Jenny just keeps put'n along without a hernia.

Bob
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Old 09-25-2021, 10:05 AM   #15
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I have been trying to gather good information on this question. I offer this as what I have learned so far and welcome any comment, positive or negative. With the A/C you will have start amperage and run amperage thresholds to meet. The soft start capacitor will reduce the start amperage demand. You will want your generator capacity to be greater than your total demand. Two ratings usually offered for the generator, surge and run. Size the generator so demand is at 80% of the run rating. Generator engine RPM varies with an inverter type generator but not with non inverter type. You want an inverter type with a THD <3%. In regard to altitude the standard derating formula states that for every 1000 ft above sea-level, a gasoline, diesel, or liquid propane generator usually should be derated by 2–3% of its standard output. In case of generators using natural gas, the derating factor is typically closer to 5%. A good rule of thumb for most gensets is that you will lose 10% of the rated output every time you gain 3,000' in altitude. This means that a 7,500 watt generator running at 9,000' of altitude will only be capable of producing a bit over 5,000 watts at that altitude.
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Old 09-25-2021, 10:16 AM   #16
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I have been trying to gather good information on this question. I offer this as what I have learned so far and welcome any comment, positive or negative. With the A/C you will have start amperage and run amperage thresholds to meet. The soft start capacitor will reduce the start amperage demand. You will want your generator capacity to be greater than your total demand. Two ratings usually offered for the generator, surge and run. Size the generator so demand is at 80% of the run rating. Generator engine RPM varies with an inverter type generator but not with non inverter type. You want an inverter type with a THD <3%. In regard to altitude the standard derating formula states that for every 1000 ft above sea-level, a gasoline, diesel, or liquid propane generator usually should be derated by 2–3% of its standard output. In case of generators using natural gas, the derating factor is typically closer to 5%. A good rule of thumb for most gensets is that you will lose 10% of the rated output every time you gain 3,000' in altitude. This means that a 7,500 watt generator running at 9,000' of altitude will only be capable of producing a bit over 5,000 watts at that altitude.
@9,000 ft elevation AC is rarely needed.
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Old 09-25-2021, 10:51 AM   #17
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@9,000 ft elevation AC is rarely needed.
That is true but what if you take your hammer drill camping with you to carve out a good spot?
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Old 09-26-2021, 12:08 AM   #18
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The only difference between gasoline, propane and natural gas performance on tri-fuel generators modified with US Carb's Snorkel conversion is the amount of gas by volume used. That is because gasoline, propane and natural gas each have lesser BTUs per unit of measure. It takes more natural gas, than propane and propane takes more gas than gasoline, but the output is the same. All generators have diminished output as operating temperatures and barometric pressure rises. This is called the Koch Effect. Volumetric inefficiencies occur as you go up in altitude and as the day gets warmer. Let's face it you aren't at sea level any longer. What these Genny's need is a turbo charger, but that costs more money.
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Old 09-26-2021, 07:26 AM   #19
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The only difference between gasoline, propane and natural gas performance on tri-fuel generators modified with US Carb's Snorkel conversion is the amount of gas by volume used. That is because gasoline, propane and natural gas each have lesser BTUs per unit of measure. It takes more natural gas, than propane and propane takes more gas than gasoline, but the output is the same. All generators have diminished output as operating temperatures and barometric pressure rises. This is called the Koch Effect. Volumetric inefficiencies occur as you go up in altitude and as the day gets warmer. Let's face it you aren't at sea level any longer. What these Genny's need is a turbo charger, but that costs more money.
guskmg
Hi

Peak output of the engine ( full throttle, trying to do everything it possibly can) *will* change as you go from one fuel to the other. There's only just so much you can cram in at max RPM's. You don't get to put 20% more in when running natural gas .... Since the engines start out overrated for the job, this may or may not actually affect output.

Bob
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Old 09-26-2021, 07:47 AM   #20
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Dual Honda's are a good solution especially if you do not like lugging around one of the heavier 100 lb plus generators, your choice to make. A bigger problem is keeping them fueled and the noise levels down especially if you are running them at night. Higher elevations out west and you may not need one except to keep batteries charged. In Texas trying to keep one or two generators running for AC at night is not a very easy solution. For summertime heat we look for a campsite with electrical hook up. Cooler months dry camping use a Honda or solar for battery recharge then rely on internal systems (furnace if needed) for staying warm. You will need to find the system that meets your needs.
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