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Old 10-01-2015, 12:16 AM   #1
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2 AC units on a 4000 watt gen.

I know I will draw out some skeptics on this but I have to see if anyone has tried something similar. I know the AC units draw the most at start up and then generally run below 2000 watts after. I have one 13,500 BTU unit now and I want to add a second 13,500. I have seen people start one unit with a 2000 watt generator by adding a larger capacitor to the AC. I am wondering if anyone has tried to add large farad capacitors on both AC's and ran them off a 4000 watt generator?

I plan on testing my current AC with a kilowatt tester then add a large capacitor and test again to see the difference in the peak draw at start up. If its less than 1700 I think I will try it with 2. I think I would set at least one AC to run continuous so they don't end up starting at the same time as they cycle.
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Old 10-01-2015, 12:36 PM   #2
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Since you are adding additional cooling capacity, perhaps a smaller and or more energy efficient air conditioner may also work for you; with added benefit that it would draw less power after startup as well.

I've researched air conditioner's start-up current for a different reason (to run off inverter), and think it "may" be possible to run two smaller 11,000 BTU/hr Power Savers off a 4 kW generator and or 30-Amp service (depending on other loads). These units are marketed as ideal for smaller generators (perhaps they are referring to the common Honda 2000???).

As an example, many Coleman 13,500 or 15,000 ACs momentarily draw 63 AMPs at startup (Lock Rotor Amps), but the 11,000 PS has an LRA rating of only 45.6. The difference is around 17 Amps, which "may" be enough for the 4 kW generator to keep powering a first unit already running while the second unit starts up. Unfortunately it's not quite as simple as adding the Amps, but I think it has a good chance of working.

Once running these smaller ACs are rated at 9.9 Amps under standard conditions (higher for dessert conditions), which should allow two units to run off 30-Amp service while providing 22,000 BTU/hr combined.

I don't know if Coleman ACs are any good so I'm not recommending this particular brand. I'm just suggesting that it may be worth looking at ACs that draw less current while providing your cooling needs.
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Old 10-01-2015, 12:49 PM   #3
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That is a good idea. I've heard there are high efficient units that draw less power. I haven't gotten far enough with my idea to do anything but order the kilowatt tester. Hopefully I will have something better figured out by spring. The ac that came on my unit is terrible.
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Old 10-01-2015, 02:23 PM   #4
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What brand and model AC do you have? Are you not satisfied with cooling, or is it about noise?

In case you don't already know, a current meter needs to be able to save the nearly-instantaneous start-up peak current because it likely happens so fast you won't be able to see it. My meter doesn't have that capability so it was useless for that. Fortunately the LRA is labeled on compressor.
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Old 10-01-2015, 03:12 PM   #5
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Dometec if I remember right. It doesn't put out enough air and it doesn't even come close to cooling the motor home down even on cooler days. If I close all but the bedroom vents it will cool that one room down but that's about it. My motorhome is brand new so it shouldn't be an age problem just a cheap factory unit.

I made sure the kilowatt meter I ordered had a high low recording ability.
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Old 10-01-2015, 03:40 PM   #6
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Quote:
Originally Posted by West View Post
Dometec if I remember right. It doesn't put out enough air and it doesn't even come close to cooling the motor home down even on cooler days. If I close all but the bedroom vents it will cool that one room down but that's about it. My motorhome is brand new so it shouldn't be an age problem just a cheap factory unit.

I made sure the kilowatt meter I ordered had a high low recording ability.
I don't know why but Dometic A/C's don't put out as much as Coleman units. I have a lot of friends that have replaced new Dometics for same sized Coleman's and swear they are much better. I have a Coleman 15K on a 32 1/2 foot motorhome and it does a good job of cooling
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Old 10-01-2015, 05:26 PM   #7
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That's good to know. Coleman Power Saver series have promising specs except for the height being listed at 13.8-inch high -- although only 26.1-inch wide. Because of narrow width it may not add much drag compared to some low-profile units (not that it makes that much difference), but it may add a few more inches to motorhome height depending on what else is on roof. Added room for larger coils apparently helps make these more efficient.
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Old 10-01-2015, 10:54 PM   #8
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That does look like very good option. It says it draws 10.2 AMP's. That's only about 1200 Watt's. I could't find the peak start up draw listed anywhere though. Two of those might be the key. I would imagine with large capacitors the start up wouldn't be to bad. Have any of you seen what they say the start up draw is?
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Old 10-01-2015, 11:10 PM   #9
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Here is data i mentioned above in photo form:
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Old 10-01-2015, 11:20 PM   #10
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Is the "locked rotor cooling amp's" the start up draw? I dont know what that one means but its a pretty high number
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Old 10-02-2015, 12:09 AM   #11
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Is the "locked rotor cooling amp's" the start up draw? I dont know what that one means but its a pretty high number
Yes, it's the amount of current the AC will pull for a very short time until the compressor starts to pick up speed -- we are talking about a fraction of second in most cases.

By comparison you can see the number for a 13,500 BTU/hr Power Saver. Notice running power isn't all that different, but LRA is quite a bit higher.
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Old 10-02-2015, 12:12 AM   #12
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And standard 13,500 BTU/hr (non Power Saver) use much more power.
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Old 10-02-2015, 01:50 AM   #13
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Thanks for the info. That helps a lot knowing what that means. So about 7245 Watts to start the bigger one 6716 for the smaller unit. Still a lot. I'm really curious to see what the meter reads. Specially after adding a larger capacitor. I'm loving the running amps on those two units.
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