What size generator?

[utee94]

I think it has been well documented that an inverter is not sufficient to run an RV A/C. Did you see someone suggest that it might work?

As far as numbers, I have read and posted all of them, for my A/C unit, and several different potential generators. Some are clearly insufficient, like the 1000. Some are marginally insufficient, like the 2000.

Some might work, according to the numbers, like the 2400 or 3000. And yet some people assert that a 4000 or 5000 is the only safe choice.

I appreciate your anecdotal evidence (which is precisely what I asked for), but I do not appreciate or understand your hostility. If that will be your approach, I'll take my questions elsewhere. Sorry to be such an offensive bother to you...

[olddog299]

Originally Posted by mustang

If you need only 500 or 1000 watts I reccomend an inverter. They are silent, Small, and can stay plugged in to ciggerette lighter. No oil to change or mix.

Mustang, I don't know about the wire size in your unit, but the 12 volt cigar socket in the rear bedroom of my unit is fed by a number 16 AWG wire.

NOT something I can feed a 1KW inverter with for any length of time, say overnight to drive my CPAP. Just a "for instance." Your mileage and the wire size may vary...

[RoadKingMoe]

There is a significant difference between low campground voltage and using a generator that's marginally adequate. What destroys air-conditioner compressor windings is current in excess of that which would be drawn at the rated running voltage, over time. When voltage is below the rated value, the motor draws higher current and higher current causes hotter windings. The hotter the windings and the longer they are hotter, the more the insulation on the windings breaks down.

Even during a normal voltage start, current temporarily goes higher than it would be at the rated running voltage until the motor reaches its rated speed. But that's for a very short time, a second or two. In a low campground voltage situation, it's for a very long time because the motor is continuously operating with excessive current.

When using a marginally adequate generator, the start time increases, but the excessive current from the marginally adequate generator is limited. As long as the generator can supply full voltage during the running period subsequent to the start, there shouldn't be excessive current during that time. That's vastly different than low campground voltage where excessive current is continuous.

Most of the air-conditioners on Airstreams, during steady running conditions, draw more than the 13.3A continuous rating of the Honda EU2000i. However, if the ambient temperature is low enough that the compressor is cycling, one could make the case that the Honda is rated for 16.7 amps for up to 30 minutes and the compressor draw falls within this since it cycles more often than this. However, the manual doesn't say how long the generator must be operated at the continuous rating or lower outside that maximum 30 minutes above it (i.e. the duty-cycle). At worst, running an air-conditioner with greater than a 13.3 amp draw on Honda EU2000i will probably just result in having to replace the air-conditioner and generator sooner than if the situation weren't as marginal. In my opinion, both cost too much to shorten their lives. YMMV

One Yamaha EF2400IS is adequate for most air-conditioned Airstreams while not running another power-hungry appliance. One Honda EU2000i is marginal, in my opinion. My biggest problem with the Yamaha is the 80 pound wet weight compared to about 53 pounds of the Honda. The Honda is about as much as I can lift onto the 4WD truck tailgate and about as much as Barb can even lift enough to move. To give them longer life, and to be able to operate the microwave with air-conditioning, we went with two EU2000s.

[malett]

Most of the AS are set up for 30 Amp 110 v service. This amp and voltage take into account the starting current for the AC or the microwave (the dag blasted forget every time switch in the cabinet), but not both at the same time. If you add an electric element to your hot water heater this has to be factored in also when choosing what to run with 30 amp service.
The wattage require to run your AS with 30 Amp service 30 Amp x 120 v. = 3600 watts or 3.6 kw. This calculation is fine for our needs, but I'm sure that someone will pipe up about PF etc. Who cares, where not running a 500 Mw power plant here.

If you don't want to run everything, just look at the breaker amperage supplying that item and multiple it by 110v. If you are headed into higher altitudes I would derate the generator capacity by 10%.

Last but not least your power cord has to be rated for the amperage you plan on using. I use the highest power rating in the my system to determine the size of the cable. No 12 wire minimum up to 20 Amp. 30 Amp = No.10. If the generator is rated for more than 30 Amp go to the next safer higher gauge wire.

Also you must rember that very rarely will you have a ground to earth when using a generator. The consequence of this can be very shocking.

Mark

[utee94]

Originally Posted by RoadKingMoe

There is a significant difference between low campground voltage and using a generator that's marginally adequate. What destroys air-conditioner compressor windings is current in excess of that which would be drawn at the rated running voltage, over time. When voltage is below the rated value, the motor draws higher current and higher current causes hotter windings. The hotter the windings and the longer they are hotter, the more the insulation on the windings breaks down.

Even during a normal voltage start, current temporarily goes higher than it would be at the rated running voltage until the motor reaches its rated speed. But that's for a very short time, a second or two. In a low campground voltage situation, it's for a very long time because the motor is continuously operating with excessive current.

When using a marginally adequate generator, the start time increases, but the excessive current from the marginally adequate generator is limited. As long as the generator can supply full voltage during the running period subsequent to the start, there shouldn't be excessive current during that time. That's vastly different than low campground voltage where excessive current is continuous.

Most of the air-conditioners on Airstreams, during steady running conditions, draw more than the 13.3A continuous rating of the Honda EU2000i. However, if the ambient temperature is low enough that the compressor is cycling, one could make the case that the Honda is rated for 16.7 amps for up to 30 minutes and the compressor draw falls within this since it cycles more often than this. However, the manual doesn't say how long the generator must be operated at the continuous rating or lower outside that maximum 30 minutes above it (i.e. the duty-cycle). At worst, running an air-conditioner with greater than a 13.3 amp draw on Honda EU2000i will probably just result in having to replace the air-conditioner and generator sooner than if the situation weren't as marginal. In my opinion, both cost too much to shorten their lives. YMMV

One Yamaha EF2400IS is adequate for most air-conditioned Airstreams while not running another power-hungry appliance. One Honda EU2000i is marginal, in my opinion. My biggest problem with the Yamaha is the 80 pound wet weight compared to about 53 pounds of the Honda. The Honda is about as much as I can lift onto the 4WD truck tailgate and about as much as Barb can even lift enough to move. To give them longer life, and to be able to operate the microwave with air-conditioning, we went with two EU2000s.

Absolutely what I have been driving at RKM, perfectly stated. Thanks for the input.

[mustang]

Well when the voltage drops on a generator, you enter into a realm of clean power. All the other issues become second. Clean power is the inability to maintain 60 cycles constantly.

So yes low voltage at a campground is different , meaning the cycles stay consistant. Low voltage on a gen set is alot worse.

4000 watts is the minnimum need for a 13500 unit to run properly along with small items.

I posted it earlier in the thread. Not a Genset bragging there unit up but the A/C company stateing requirements.

[RoadKingMoe]

Low voltage on a contractor generator is usually associated with low frequency because of the slower engine speed. On an inverter generator, frequency is independent of generator engine speed. So no, it's nowhere near as bad as low campground voltage.

The other problem with contractor generators we've seen in another recent thread is that while they are rated for twice the amperage at 120VAC as they are at 240VAC, that's divided over two circuits. The wattage available to power an Airstream is half their rating and the amperage no greater than that at 240VAC.

Clean power is characterized by stable voltage and frequency within the specified rating range, with a good sine waveform free of spikes, surges, and sags. Clean power is a good thing, not an inability to maintain frequency.

[mustang]

This is kind of fun, Of topic jiberish.

The question I answered and backed with real data was 31 ft airstream... 1200 watt genset kept tripping... what size?

Simply put 4000 watt.

[2airishuman]

Originally Posted by utee94

Absolutely what I have been driving at RKM, perfectly stated. Thanks for the input.

hey ya utee', good question and finally 'moe takes the time to post some good answers.

for members who don't wanna think through/understand the issues "just git a biggin' is a fine suggestion.

IF however ya wanna learn, i suggest popping back into many of his genset/solar posts, they are most useful.

i'm in agreement with the overall utility (beyond ohm's law) of 2x2000 vs a smaller 2400 or larger 3400...

1. so much easier to move around 2x2000s and service and store...
2. take or use only ONE during the non-ac seasons, which is the majority of my use
3. keeping one in the truck 24/7 and use it regularly even when NOT camping.
4. while the 2400 yam will handle many of the rv a/c units there are compromises...
5. like tweaking the settings for everything else during a/c use (fridge, water heater and so on) these are easy to forget.
6. how about altitude? the gensets loose capacity so a marginal start becomes LESS adequate...
7. noise level, 2x2000 will make less noise than 2400 at full throttle.
8. when it's really hot (70+nights/95+days) the a/c would run 10-14 hours/day

so if ya rarely plan to use the ac and mostly at sea level, and with EVERYTHING else powered another way...

the 2400 is worth a go, if ya can lift it. 2400 yams can be paralleled as well, so another can be added IF needed.

with a fixed mounting location and the desire for remote start and LOTS of a/c needs boon docking, a larger (34-4500w) might be a better choice.

there are some creative folks here, who've mounted 2x2000 on the tongue and 3k units and so on...

low campground voltage is a killer without clues UNLESS using a good gauge and inline protector...

usually an overloaded genset will provide some signals but the gauge is still useful...

at the salem international (100+ for several days) the big cummins gensets were overloaded with users.

voltage AND frequency dropped. NONE of the folks maintaining the gensets realized this.

by using my coach and meter as the canary,

they were able to kick up the cycles a bit during high use times and move folks OFF the genset grids as needed.

cheers
2air'

[DKDarrow]

Just a quick note on "real world input".
1989 Excella
15K Heat Pump
Honda 3000 (7 years old, maybe 3000 hours, runs continuous weeks at a time)

We have run this for many years, especially on video jobs. Often times, we are editing in the desert with 2 puter systems, tape decks, frig, dual monitors, tv monitors, and charging the batteries for the various video devices.
NEVER had a problem doing this. I run a voltmeter from time to time to just check and the voltage remains constant. ALWAYS........

This clean voltage business is not a problem with an inverter type genset. If one has a contractor type, 4K Generac, then yes one will get voltage variance.

Most often the generator stays in the TV inside the camper shell; but it has spent MANY weeks out chained up to the trailer exposed to irrigation sprinklers, rain, and snow.

Hope this is real life enough............Dennis

[Tom Bray]

Maybe I can add some clarity to all this (then again, maybe not)

Motors:

Motors work best when there is plenty of reserve current available so they can start quickly. They also run most efficiently, i.e. cooler, when the voltage and frequency are matched to the motor design.

The motor in an RV air conditioner is designed to run at 120V and 60Hz. If the voltage is low but the frequency is still 60Hz, the motor can't turn at the speed it is supposed to, so it draws more current to try and compensate. More current means that the motor runs hotter. Heat is what destroys motors. If a motor runs continuously too hot, it will fail much sooner than it would if it were running as it was designed. That is why low voltage at a campground causes your compressor to fail. Trying to cool your RV down to 68 degrees when the temperature outside is 115 has a similar effect, it will kill the motor.

At the instant the motor in the A/C is turned on, it can require up to 6 times the current it uses when running. As soon as the motor starts turning, it starts using less current. The current drops to the rated value as soon as the motor reaches full speed, usually in about 1 second.

If a motor doesn't have enough power to start turning, it continues to draw huge amounts of current. Depending on its design, it may burn up in a matter of few seconds.

There have been several questions brought up about why manufacturers don't tell you this stuff. The rating on an A/C unit, and any other appliance for that matter, is used to size the wiring and the circuit breaker or fuse. All this other information about requiring more current at start up has already been taken into account with normal household and RV wiring and the circuit breakers. For the most part this extra information isn't normally relevent and would only confuse us.

Even in a house, when the A/C compressor kicks in, the lights dim for an instant. This is the result of the high start up current to get the motor started. The lights immediately go back to normal a second or so later. If the computer you are using crashed during the A/C start up, that is a different issue, maybe you need to upgrade the wiring in your house if that happens, or buy a UPS.

Now to the Generator:

When using and sizing a generator it is often difficult to find good information. I have talked to electricians that don't have a clue about how to size them (very scary, especially when they have been hired to install a generator transfer switch for me). There actually is a lot of information available but it is often described in mathematical terms that are not particularly easy to understand. It also gets complicated very quickly and it doesn't always translate into easy to follow guidelines.

I am going to try an analogy, I don't know if it will work.

Think of a generator like a Microwave Oven and the power coming into your house like a regular oven. With the regular oven, it takes about an hour to cook a baked potato. It also takes an hour to cook 5 or even 10 baked potatoes. The oven cooks using a constant temperature. It will reach 400 degrees and hold it there whether there is 1 potato in it or 10. This is sort of like the power in your house, ask for it and its just there.

A microwave oven will bake a potato in something like 10 minutes. Add a second potato and it takes almost 20 minutes. The microwave oven has a constant amount of power available, if it has to heat up twice as much food it will take twice as long.

A generator has a limited amount of power, just like a microwave. If I need to cook 2 baked potatoes in 10 minutes I need a 2000W microwave instead of a 1000W model. If I need 4000 Watts, even for an short time, if the generator can only deliver 2000, I am going to have a problem.

One thing that generator has that the microwave doesn't have, which is common to all rotating machinery, is inertia. Within limits the generator won't change speed immediately (if it does something will probably break) so it will actually try and supply the requested current but not for very long. The generator speed will drop quickly and the governor attempt to compensate by more throttle, but hopefully the motor has already started to spin by then. I have never seen this rating on a generator other than the vague "peak power" which provides a clue to its capability but doesn't provide many details.

A larger generator not only supplies more power continuously but has the ability to provide even more instataneous power to start motors. Not only does the engine deliver more power, the rotating components weigh more. So, for a motor that needs 1500 Watts while running, it may require a 3000 or 4000 Watt generator to start it.

For the record, inverter generators can do the same thing as conventional generators but they use capacitors to store the extra energy needed to start motors and they can compensate for the falling speed of the engine electronically. They have other capabilities that make them really desirable, but that discussion is best saved for another post.

By the way, motors aren't the only electrical devices that demand lots of power at startup. Ordinary light bulbs do the same thing. They to are almost a dead short when power is first applied and quickly go to their rated current as they heat up.

Recommendations:

I haven't said a lot about what you should or shouldn't go out and buy.

I recommend you talk to your generator supplier, assuming it is a factory authorized dealer, they should be able to provide you with guidelines and recommendations to better select the generator for your application.

I also recommend you shop around and get other opinions.

I have seen good information in owners manuals and sales literature about sizing generators and what what types of loads they can handle. Ask to see the owners manual when at a dealer!

Unfortunately the sales people at the "Big Box Stores" and many low priced internet sites don't have a clue. The floor model may or may not have the manual with it.

Do I have a generator? Yes, it is a contractor grade unit that I bought when the lights went out a few years ago in Michigan. It powered our house in Southeast Michigan just fine but it was a bit noisey. It wouldn't run the pump at our house in Northwest Michigan so it sort of sat around. It will run our new house in Alabama, or the camper with its AC on.

I haven't decided on what I want for the Airstream and camping.

Tom Bray

[1963tradewin]

I think for the weight the hondas are the way to go. My question is will 2x2000is power my Airstream sufficiently? I have a 13500btu penguin I just bought new last year and don't want my compressor going out on me.

[Saddletramp]

Be sure to check on the specifications for whichever generator you are considering. Most generators are rated at the maximum KW they will generate at or near sea level. As you go up in altitude you will notice they are actually derated. A 2KW generator will not deliver that much power at 1500 ft. of elevation or above. Since I spend a lot of time above 5,000 feet, I bought 4KW. It handles my AC and microwave and battery charger all at the same time. I keep a digital voltmeter plugged in to my 120V circuit so I can monitor whether voltage should ever drop. If it did I would shed load to bring it back up to a safe level for the AC motors.

[1963tradewin]

I'm sitting at 1000 ft above sea level here in MN. So If i have 2 honda 2000's I should be fine even if Im above 5000 ft?