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Old 02-25-2021, 04:38 PM   #1
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I have a 2021 flagstaff 21ds with the 15000 btu ac can someone tell me what size generator I need to run the ac
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Old 02-26-2021, 08:01 AM   #2
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A 15k A/C is typically on a 20a breaker.
20 amps x 120 volts = 2400 watts

That's provided you have no other loads using electric besides the A/C.

Converters (the thing that keeps your battery charged) can draw amps keeping things like your control boards for the refrigerator and water heater going, not to mention the furnace. Some newer refrigerators have 12v compressors and can make the converter draw even more amps.

You are going to need to decide what YOU want to run (both AC and DC) in YOUR R/V and then decide how big a generator you need. Many folks use two smaller generators in parallel when loads require greater needs than what one generator outputs.
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Old 02-26-2021, 09:02 AM   #3
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Welcome to the forum its a great place to get your questions answered. 5picker gave good advice. On my rig I run two yamaha's in parallel (two are lighter then one) so about 4K watts and I can run everything. I use just one when charging batteries.
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Old 02-26-2021, 09:25 AM   #4
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I have a 2608BS with a 12,500 and a 15,000 AC. I run either one on my Predator 3500. Never tried to run both.
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Old 02-26-2021, 09:27 AM   #5
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I would recommend picking one closer to 30A.

30 amps x 120 volts = 3600 watts

The problem is as 5 picker points out you have other accessories that you need to run at the same time as this AC your trying to run.
one example is the internal battery charger. this could use 5a or more (some chargers even have a 20a cord on them). If your batteries are low you want to charge them while running the generator as well as the AC.

I would recommend a 3500 generator. its not going to carry 30A continuous but it will support one AC, and other accessories together.

I would also recommend a Inverter since they are so much quieter.

also you need to know that a 2200 generator is not FULL TIME 2200, they are only rated at 1800w continuous.

the thing everyone will be quick to point out here is a 3500w generator weights 100 lbs, and a 2000 weighs 50. If they are inverter generator you can hook 2 or more together and add up the wattage. If your camping and don't need your AC you can carry one 50lb generator. but 2 smaller ones cost more than 1 larger one.

Also some will point out that a smart start on the AC could allow you to run a 13K or 15K generator off a smaller generator (but they are also expensive)

My MH has a (loud) onan that I use going down the road, or stopping at rest areas for a couple hours. Because 14 gallon tank will not last all weekend I take the 3500 if I know I will need it (its easier to go buy gas in the toad than unhook the MH to find propane at 2X the cost).

I also have a Honda 2000 I used on my Pickup camper).
I tested both my Harbor freight 3500 and my honda 2000 on my pickup camper that had a Coleman 9K btu AC.

The 3500 was quieter than the 2000 because it did not need to run as hard to power the AC.
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Old 02-27-2021, 05:35 PM   #6
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We have the 15,000 btu Mach 8 on our 2021 Micro Lite 21DS. I installed a Micro-Air EasyStart Model 364 on the AC in about an hour. Super easy install

Purchased a Honda EU2200i and appropriate 30amp to 15/20amp adapter. On a 66 degree day at sea level it tested ok. Will be headed to South Texas in a few weeks for warmer weather for further shakedown. Primary concern is cooling trailer for those warm nights camping. Wifey is high maintenance. Here are my test results: First pic is AC startup running fan only. Second pic is AC up, running and making cool air. Third pic is with converter/batter charger (batteries were fully charged so this might not be full load).

Observations: I think running AC alone on this generator will be no problem. And possibly, also fridge or converter. This might not be necessary if you have charged batteries and propane to run your fridge. High altitudes and higher ambient temps need more study.
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