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Old 07-28-2015, 09:40 AM   #1
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Generator Sizing?

My '04, 28' Classic, bought used 2 years ago, came with the built-in connection for a generator, but no generator. The AS Owners manual says something like "a minimum 5.5 KW generator with a 30 amp breaker is needed for 30 amp service."

But none of the generators I've read about others using that big. So I'm thinking that what the manual means is that if you want to run enough stuff to fully utilize the 30 amp service, you need a 5.5 KW generator. Is this correct?

I'm in Texas and definitely want to run my 13.500 Btu/Hr AC unit and some lights off the generator, but have no need to be able to power everything.

So what size generator is really needed to do what I want to do? I've read enough on the Forum to know that Honda and Yamaha seem to be the preferred brands and I'm not trying to reignite that debate. Just looking for some guidance from those of you with real world experience with generators.

Thanks in advance
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Old 07-28-2015, 09:52 AM   #2
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5500 watts @ 120 volts = 45.8 amps. That is peak loading but even if you reduce it 10% that is well above 30 amps. Most folks seem to use 3000-4000 watts to run most everything in a 30 amp trailer.
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Old 07-28-2015, 09:55 AM   #3
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I have the 3kw Yamaha. It's heavy, but it's quiet and reliable and has no problem running the AC and converter-charger on my Argosy. If I had a more modern trailer I'd probably force the fridge to stay on propane while running the AC off the generator, and I'd definitely use LP for heating water. Other than that I'd have no worries about relying on one of the top-tier 3kw units.

If you want easy portability and the option to just use one in the winter months, a pair of 2kw units in parallel works for most everyone. It's not a quiet as one of the single 3kw inverter generators, but easier to load/unload and you can just take one when air conditioning won't be needed.
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Old 07-28-2015, 10:15 AM   #4
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Many folks have two 2,000 watt generators that can be paired together for 4,000 watts which is ample for RV air conditioners up to 15,000 BTU in size. The issue with air conditioners is not so much the running current but the huge inrush of power to start them up.

A 3kw unit may work for the 13.5K BTU air conditioner, but cycling on and off could preclude the fridge or water heater from being on at the same time. The LED lights or television are not big loads today.

The advantage to two smaller units is that just one could run a microwave or recharge the batteries so is more sized to the job at hand.
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Old 07-28-2015, 11:18 AM   #5
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A lot of people successfully run a 13.5k btu AC with a 2400 watt generator but you have to be careful about other loads (fridge, HW heater, microwave, halogen lights, etc..) If you have LED lights inside and run the fridge and HW heater on propane and don't use the microwave, you should be OK with the 2400. This is not going to give you 30 amps obviously, but enough to run the AC.

However, if you can handle the weight and slightly higher cost, a 3000 watt generator will give you a little bit more cushion for the AC (still need to run the other stuff on propane and LED lights are still highly recommended since they generate less heat than the halogen ones.)

Some people pair two 2000 watt generators to lower the weight factor since each 2000 weight a lot less than a 2400 or 3000 unit. You also get the flexibility of running only one generator if all you want to do is charge your batteries or watch TV.

With a 5500 watt generator you could probably run the fridge and HW heater and AC if you wanted to.
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Old 07-29-2015, 08:37 AM   #6
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The Honda 7000 watt unit would allow operation of everything in the trailer as it has a 30 amp 240 volt power outlet. Each air conditioner would be on it's own leg. Then a microwave would be on the smaller air conditioner leg. The water heater and fridge could be on the other leg.

The only issue is the need for a crane to lift the unit into the truck....
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Old 07-29-2015, 09:04 AM   #7
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Because of the shape of the power and torque curves for most internal-combustion engines used to power a generator, the generator will operate most efficiently— that is, most electricity produced for the amount of fuel consumed— when the generator is loaded between 50% and 75% of the rated load. So if you add up all of the users of electricity that are likely to be running at the same time, consider that to be 75% of the rated load that you need.

At the same time, getting too much generator is a waste, so consider the full 30 amps (or 50 amps if that's what your RV is wired for) to be 100% capacity. That means for a 30-amp unit, you want 3.6kW of generator. For a 50-amp unit, you need 6kW. Or as close to those numbers as you can get.

But if you have a 30-amp RV, you can get by with 20-amp service on a generator— Airstream Interstates are set up that way. They have a 2.5kW generator to provide 20 amps of 120vAC power. You can't run as many things at once, but the sizing is actually pretty good. The air conditioner draws about 15 amps and so the A/C by itself loads the generator to 75% of rated capacity, the sweet spot in the power and torque curves.

This is where the dual Honda 2kW generators really shine. Run one generator to provide 1kW to 1.5kW (50% to 75% or the rated 2kW) when you aren't using a lot of power. Add in the second one to provide over 2kW to about 3kW (50% to 75% of the combined 4kW) when you need more power. And even when you're running everything at once in the trailer that you can, 4kW is only slightly above the 3.6kW you need to provide the full 30 amps of 120vAC power. You haven't quite maxed out the generators; you still have 10% reserve capacity, but you haven't bought too much generator.
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Old 07-29-2015, 03:40 PM   #8
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I have a Honda 3000 EU and use it to run the A/C in the Texas summer whenever not plugged into shorepower. When the A/C unit cycles, occasionally the power in the camper will flicker briefly (clock on the microwave always resets to 0:00). From the thread it appears I need to switch all other appliances to propane to give the A/C all the power.
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Old 07-29-2015, 04:06 PM   #9
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Generator Sizing?

I have an onan Emerald III. When loaded down twin 13k btu AC, 400 watt fridge element, 900 watt converter and 1000 watt water heater, I use a half gallon of gasoline per hour. It's a real genset, not inverter type. If needed I can weld as well, in the long run much cheaper, but I need a small forklift to move it!
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Old 07-29-2015, 04:16 PM   #10
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Quote:
Originally Posted by Chilicook View Post
I have a Honda 3000 EU and use it to run the A/C in the Texas summer whenever not plugged into shorepower. When the A/C unit cycles, occasionally the power in the camper will flicker briefly (clock on the microwave always resets to 0:00). From the thread it appears I need to switch all other appliances to propane to give the A/C all the power.
Does it do that with the eco switch off?
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Old 07-30-2015, 02:18 PM   #11
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Thanks everyone for all the info. This has been helpful.
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Old 07-30-2015, 02:25 PM   #12
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Yes this occurs even with the Eco switched off. The brief power flicker happens when the AC unit compressor cycles on.
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Old 07-31-2015, 09:41 AM   #13
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That may create issues down the road for the air conditioner. The flickering lights could imply that the surge of power associated with starting the compressor is dropping the voltage below the level the lights need to operate or causing the battery charger an issue.
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Old 08-25-2015, 07:40 PM   #14
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OK, read all the replies as looking for similiar information as you had requested. We just bought a new 2015 InterNATIONAL 27'. we just did our first trip and took it ON A LONG TWO WEEK LONG TRIP. we were plugged in for about a week in the middle but the rest of the time we basically boon docked in BC proivincial campgrounds which have no services. We ran off battery power and propane and all was great except no hair dryer for the wife or microwave or toaster etc. I have not purchased a generator yet but I think I can get by with one honda 2000 and just manage the power use. let me know if I am wrong but I think if we need to run AC we can as long as nothing else is on and same goes for other things like toaster or hair dryer or microwave. I want to hear from anyone who has been doing this as i dont want to use electric for things that can use propane anyway and I am hoping to keep it to one 2000 watt unit vs coupling a pair. Being in Canada more apt to need heat that AC anyway and would run heater on propane plus fan. anyway anyone out there using just a single unit and "managing" their power use with success or not let me know.
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