Technical A/C wiring question - Fiberglass RV


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Old 09-25-2012, 06:14 PM   #1
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Name: Dennis
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Technical A/C wiring question

I need some advice from an electrician and/or one of you wiring gurus out there. I have a 2011 Casita with the larger and more power-hungry rooftop A/C unit. Apparently, the pre-2010 Casita's would run the A/C with a 2000 watt generator just fine (well, at least if you didn't have anything else turned on). Since my A/C pulls about 200 watts more, I am concerned that I have even less margin and a cheaper 2000 watt generator might not be enough. But my budget is going to be wiped out just trying to afford a 2000 watt unit, I really don't have the money to have to buy anything bigger. So I've been trying to figure out how to get by with a smaller generator.


Plan A


Find an accessible spot in the power line leading to the A/C, cut the line and install a regular 20 amp male household plug on the side leading to the A/C, and a matching female plug on the end leading to the Casita’s 120 volt power. If you put a matching set of 20 amp plugs say, on the roof, you could temporarily unplug the A/C from the Casita's built-in power completely. If you then ran an extension cord up to the roof and plugged a generator straight in, the generator would be powering just the A/C. The generator wouldn't even "know" the rest of the trailer existed. So it wouldn't be trying to recharge the battery or power anything else. Meanwhile, you could also run as many lights, fans and whatever as you had battery power for. Note: this assumes you also have a solar panel to keep the battery charged.


Plan B


Install a manual switch that would temporarily disconnect the built-in battery charger(?). The objective would be the same as Plan A. Plug the generator into the regular shore power connection, make sure nothing else is plugged into a 120 volt socket, and use the generator to power just the A/C. I would not want the generator to recharge the battery or supply power to any 12 volt systems until the charging system is turned back on (again, this assumes that I have solar power to recharge the battery).


Question


Now, I am not an electrician. Even so, I'm about 99% certain that Plan A should work. Plan B I'm not so sure about. Do I need a need a disconnect switch on the battery charger? Do I need a switch on the (120 to 12 volt) converter? Again, the objective would be to temporarily isolate the Air Conditioner (and/or 120 volt system) from the 12 volt battery so that I could use a smaller generator to power just the A/C without the generator being overloaded by trying to power anything else. Conceptually, Plan A is simpler and more foolproof. Plan B might be easier mechanically, if the wiring is easier to reach. Is one method better than the other? For that matter, is my basic idea sound? It certainly seems like isolating the A/C would help me to successfully use a smaller generator, but I'm new to all this.


btw – Still trying to save up for solar panels next year. A generator is on my list. But I'm getting some electrical work done next month, so now would be the time to get some of the wiring redone.
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Old 09-25-2012, 06:35 PM   #2
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If your AC requires 2.2k watts and your generator only has 2k then once you're running, your generator is working very hard and your AC is under powered. You could be shortening the life of both. No savings there. Sorry, not what you wanted to hear. Raz
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Old 09-25-2012, 07:09 PM   #3
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Originally Posted by P. Raz View Post
If your AC requires 2.2k watts and your generator only has 2k then once you're running, your generator is working very hard and your AC is under powered. You could be shortening the life of both. No savings there. Sorry, not what you wanted to hear. Raz
Thanks for the honesty, but I worded my question in a clumsy fashion.

I have a 2011 17SD that has the newer 1450 watt (11.5 amp) rooftop Air Conditioner unit. Apparently the older units only drew 1260 watts (8.9 amps). In theory, the higher capacity A/C is still well within the limit of, for example, a Honda EU2000. However, I'm not sure if that's enough to run the A/C and the battery charger and any 12 volt items that might be needed (the newer fridges require some power even when running on LP).

Hence, if I could use use the generator to power just the A/C, I should be OK. But it's still 200 watts more than the older A/C's, and that doesn't leave as much margin if I tried to power the rest of the trailer as well. I might get by with it under ideal conditions, but conditions are often not ideal. I would rather have plenty of power for the A/C (and not work the generator to death), then push everything to the limit and keep blowing fuses.
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Old 09-25-2012, 07:12 PM   #4
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Quote:
Originally Posted by P. Raz View Post
If your AC requires 2.2k watts and your generator only has 2k then once you're running, your generator is working very hard and your AC is under powered. You could be shortening the life of both. No savings there. Sorry, not what you wanted to hear. Raz
I think that it is worse than that. If the running power is 2200 watts, the required starting (surge) power is going to be even more - like maybe a third or so more.

PS
The other power consumers like the converter are so small in comparison to the AC it is hardly worth isolating them.
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Old 09-25-2012, 07:33 PM   #5
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I think that it is worse than that. If the running power is 2200 watts, the required starting (surge) power is going to be even more - like maybe a third or so more.

PS
The other power consumers like the converter are so small in comparison to the AC it is hardly worth isolating them.
People have been running the 2009 and earlier Casita's on 2000 watt generators for years, successfully powering the A/C (if not much else at the same time). My 2011 takes an extra 200 watts for the A/C. If I could save 200 watts by not powering anything else in the trailer, then I should be back to where I would have been with the smaller A/C.
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Old 09-25-2012, 07:46 PM   #6
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Originally Posted by colliewagon View Post
People have been running the 2009 and earlier Casita's on 2000 watt generators for years, successfully powering the A/C (if not much else at the same time). My 2011 takes an extra 200 watts for the A/C. If I could save 200 watts by not powering anything else in the trailer, then I should be back to where I would have been with the smaller A/C.
Sorry, I posted this before you clarified the actual amperage. I'd try shutting off (manually) the other 110 volt devices and see if the generator will start the AC unit. If it does, you can modify the trailer wiring to shut the other stuff off with a switch of some kind. You'd be living on the edge, power wise, though. The converter shouldn't be drawing that much power. A 110 volt refrigerator would be significant.
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Old 09-25-2012, 09:12 PM   #7
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My 2000 will not power my air, but a 3000 will with out any trouble
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Old 09-26-2012, 04:28 AM   #8
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While the numbers seem to say yes (1450w from a 2kw source), I'm always skeptical of manufacturers claims. Similar to horsepower ratings on power equipment. My suggestion is to post your question on the Casita forum and see if someone is using the generator you have in mind with a similar model Casita. First hand experience is a better bet than my best guess. Good luck, Raz
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Old 09-26-2012, 06:23 AM   #9
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And depending on brand of generator, that 2000 watts may be its surge rating. The continuos rating could be only 1700 or 1800 watts. I found this out with a cheap Harbor Freight model.

Jason
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Old 09-26-2012, 07:52 AM   #10
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On a related but different note,If the Air Conditioner power line runs to the converter box/Breaker Panel which it must then it is right next to the shore power inlet already.
So disconnecting the Air Conditioner power at the breaker and wiring an adapter to plug in to the genset would be a lot simpler and shorter for any dangling wires right there.
Make Sense?
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Old 09-26-2012, 08:19 AM   #11
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..........Make Sense?

Yes, that's how I'd do it.
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Old 09-26-2012, 09:42 AM   #12
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Originally Posted by P. Raz View Post
While the numbers seem to say yes (1450w from a 2kw source), I'm always skeptical of manufacturers claims. Similar to horsepower ratings on power equipment. My suggestion is to post your question on the Casita forum and see if someone is using the generator you have in mind with a similar model Casita. First hand experience is a better bet than my best guess. Good luck, Raz
I checked with the Casita Club first. Lots of reports of people running the smaller A/C's on 2000 watts. There is one report of someone running a 2012 model with a 2000 watt generator. But like you, I'm a little skeptical. I'd rather have a healthy margin of error than push it to the limit.
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Old 09-26-2012, 09:44 AM   #13
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Originally Posted by Ed Harris View Post
On a related but different note,If the Air Conditioner power line runs to the converter box/Breaker Panel which it must then it is right next to the shore power inlet already.
So disconnecting the Air Conditioner power at the breaker and wiring an adapter to plug in to the genset would be a lot simpler and shorter for any dangling wires right there.
Make Sense?
Yes, that's a great idea! Much better than my idea of climbing up on the roof
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Old 09-26-2012, 09:54 AM   #14
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You might find this of interest re a hard start capacitor add on:

RV Air Conditioner Hard Start Capacitor | ModMyRV

Powering A/C with a Honda EU2000i
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