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Powering an AC with an inverter/PV array.


86rader

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Just bought an 87 Sunrader, 22 ft, rear dinette. I would really like to install a fairly robust PV system with the hopes that I might be able to have some ability to run an AC. This obviously wouldn't work powering one all day in the florida sun, but, I think it could work running the AC for short periods to cool a limited space. Here is what I would like to do....

The roof AC is a typical RV unit and it is mounted directly over the dinette. Not sure of its capacity but I suspect it is 13.5k btu. Really wish it was smaller, but it is what it is. I would like to hang an insulated curtain, or possibly even folding polystyrene panels at the forward edge of the dinette. This would turn this area into a fairly small insulated box which wouldn't take a hell of a lot to cool. Obviously the ideal solution would be a marine DC unit, but those things are priced like they are made out of gold. They use roughly 500 watts. A cheapo 5k window home unit uses a similar amount of power, so I don't see all that much of an advantage with the DC unit. I suspect I could cobble together some sort of adapter that would allow me to mount the 5K unit in one of the side windows. Or maybe I could just use the existing roof unit, but it would require a substantially larger inverter.

My question is, how much battery would it take to get, say 3 hours of run time with the 5K unit?  High capacity golf cart batteries put out 250ah. If my math is right, that is 3K watt hrs for a pair of them. This would be 6 hours of run time at 500watts. Obviously, there are all sorts of losses involved here, but assuming they total no more than 50%, I think 3 hours of run time is doable. And I would think that 3 hrs of run time would keep such a small area cooled enough to get through a decent cat nap during a long distance road trip. I remember our first attempt at a nights sleep in our first trip out west in Sunrader #1. It was in a truck rest stop. It wasn't stifling hot, but it was warm, too warm to close the windows, so we were serenaded by nearby large diesel engines. Would have been nice to not have to listen to that.

I would like to do a roof top PV array. Not sure if I have the acreage up there for 400 watts worth of panels, but it would be nice. 

Any thoughts, recommendations, ridiculing would be appreciated.

 

 

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I have one 100 watt solar panel that I use to keep my house battery topped off while camping over long weekends.  You should have no problem putting 4 or 5 panels on the roof.

 

Someone will correct this I am sure-- I checked and found that the average 5000 btu unit uses about 5 amps (120 volts.)   My conversion skills are really rusty so I checked BatteryStuff.com and their power calculator says that it will require 600 watts to run the unit.  That does not take into account converter loss.  

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11 hours ago, Bob C said:

I have one 100 watt solar panel that I use to keep my house battery topped off while camping over long weekends.  You should have no problem putting 4 or 5 panels on the roof.

 

Someone will correct this I am sure-- I checked and found that the average 5000 btu unit uses about 5 amps (120 volts.)   My conversion skills are really rusty so I checked BatteryStuff.com and their power calculator says that it will require 600 watts to run the unit.  That does not take into account converter loss.  

600 watts @ 120 volts so about a factor of 10 means 6000 watts @ 12 volts plus any loss in the conversion from 12 to 120. So you can see where this is going. 40"X27" is about the average size of a 100 watt panel it going to take a lot of roof. Toy home roof maybe 71/2 by 18' Tightly packed 10 panels maybe? 1000 watts. This was tried a few years ago on big motor homes and they gave it  up.

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18 hours ago, Bob C said:

I have one 100 watt solar panel that I use to keep my house battery topped off while camping over long weekends.  You should have no problem putting 4 or 5 panels on the roof.

 

Someone will correct this I am sure-- I checked and found that the average 5000 btu unit uses about 5 amps (120 volts.)   My conversion skills are really rusty so I checked BatteryStuff.com and their power calculator says that it will require 600 watts to run the unit.  That does not take into account converter loss.  

Solar panels on the roof won't do you any good if you park in the shade. You will be wanting to park in the shade to keep your unit cool so you don't need as much power to cool it using the AC. Catch 22!

 

 

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7 hours ago, linda s said:

A cheapo home unit, around 8000 BTU's, will run fine with a Honda 2000. A used Honda will probably cost far less than all that solar stuff

Linda S

Yes and a great deal more practical. Solar has it place but it's not powering microwaves for a three course meal and AC units.

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 Geeze, you people with all your practicality and facts raining all over my pipe dreams!!!!!

I suspect I will end up doing something that actually works like maybe getting a cheapo gennie. Kinda wishing I had bought the travelmaster with serious roof rot issues I saw a few weeks ago. Could have gotten it for a grand. Could have pulled the onan microlite off of it, had some sawzall fun then sold a low miles (42K) extended flatbed one ton toy pickup to some landscaper. I suspect such a rig would bring 3 grand in the spring.

I have decided that I would like to do a solar setup. Probably the single 100 watt panel. I have also been throwing around the idea of going to a pair of golf cart batteries. Just need to see how much trouble it will be to find a home for the extra battery.

I do have a small lightweight utility trailer that I would like to drag a light motorcycle on. I was thinking of trying to build a gennie doghouse on it that would do a good job of knocking the sound down to a reasonable level. The trick is to get sound deadening without losing airflow for cooling. I suppose some sort of baffle system coupled with a car radiator fan might work. I don't suppose there are any liquid cooled gennies out there for anything approaching a reasonable price. That might be a good solution

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In my latest HF flyer the HF 2000w generator is $439.00. It is a inverter type

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There is a romantic ideal of producing immense power with solar panels in the case of a motor home there really is not enough room to do much. The first trick is to reduce usage by doing so your chances of going solar go up, it is easy to use a 100 watt panel to meet your needs if you leave the big stuff home. When you camp you really only "need" lights and a water pump the rest you can power with propane there is a huge store of power in a 20# propane tank much more than you can carry in any other form so skip the microwave and cook a nice meal! A 12 volt cord will charge your cell phone needs and wants are far apart. I have a 100 watt panel that is on a home made aluminum frame it can be rotated and I can change the angle to match max sun exposure I can go out for a week no problem I do run a Fantastic fan on low when it's really hot and watch the news on a small TV for maybe 15-20 minutes a day with two group 24 batteries, every light is LED and I have an accumulator on the water system to reduce run time so it can be done if you expectations are low. Other wise buy a generator if you can stand the noise.

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Just some thoughts about matching batteries and solar panels.

A 100w panel will generate about 40AH per day and using the 50% discharge rule for the battery. It would take 6 days to recharge 2 T-105 batteries.

A 100w panel would be a match for a 100 AH battery.

I can't think of a scenario where a small panel and a big battery would be advantageous. 

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21 hours ago, WME said:

In my latest HF flyer the HF 2000w generator is $439.00. It is a inverter type

Is 1600 watts enough to power rooftop a/c?

Edited by redskinman
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I understand there simply isn't enough roof space to generate enough power to run even the smallest AC out there. My hope was to just be able to run a small one at night while parked somewhere like a truck stop to get a few hours of sleep in comfort. I don't have any illusions of boondocking in florida and having a nice cool camper all day from my solar powered AC.

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5 hours ago, WME said:

Just some thoughts about matching batteries and solar panels.

A 100w panel will generate about 40AH per day and using the 50% discharge rule for the battery. It would take 6 days to recharge 2 T-105 batteries.

A 100w panel would be a match for a 100 AH battery.

I can't think of a scenario where a small panel and a big battery would be advantageous. 

What comes outa must go back inta to stay ahead of the game.

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1 minute ago, 86rader said:

I understand there simply isn't enough roof space to generate enough power to run even the smallest AC out there. My hope was to just be able to run a small one at night while parked somewhere like a truck stop to get a few hours of sleep in comfort. I don't have any illusions of boondocking in florida and having a nice cool camper all day from my solar powered AC.

Got to be honest with ya I don't think it's going to happen. Ever notice that the big trucks at the truck stop run all night? Yeah they are nice and cool with a 600HP engine running their AC.

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A 1600 generator wont run a 13.5 K btu roof AC. But it will run a 5-6000 btu window AC. There several owners who have installed this size unit and report good results in cooling, but are reporting AC longer run times.

To run a 13.5 K unit you will need a GOOD 2.8 kw or larger generator

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I am running an 8000 btu window AC with a Honda 2000.  I am in Florida and the 8K is adequate in direct sun on those 98° degree days with 92% humidity. It is more than enough once the sun goes down.  

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I run my 11.5k btu roof ac with my Honda 2000 so it all depends.

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21 hours ago, WME said:

A 1600 generator wont run a 13.5 K btu roof AC. But it will run a 5-6000 btu window AC. There several owners who have installed this size unit and report good results in cooling, but are reporting AC longer run times.

To run a 13.5 K unit you will need a GOOD 2.8 kw or larger generator

I have seen a lot of new camper trailers with window units as their AC units.

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FYI the same HF flyer that had the 2000w generator $439 has the 4000w generator for $339. This generator is "sorta" quiet for a constant rpm generator. AND it WILL run a 13.5K RV  air conditioner.

SO if you serious about a trailer and dog house check it out. This would be about the cheapest way to go other than a used something.

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Don't listen to the naysayers... 4 golf cart batteries 5 panels and a wind turbine that mounts on a fold down pole could in theory run a high efficient roof unit, with a decent inverter and two pairs of welding cable at no more than 3 feet from inverter to array.

but man what a chunk of weight to haul...and you would need a decent breeze.

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