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Old 02-07-2009, 09:47 PM   #1
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Inverter Questions

I have a few questions about wiring up an inverter. can you have it so that the inverter can power all of your 120v plugs in the trailer, or are you only able to have a certain amount of plugs wired up. For my trailer(Roo 233) I would like to be able to power the microwave, 2-3 mattress heaters and maybe a small tv.. not all at the same time though. Is this attainable? Does anyone have a schematic as to how to wire up an inverter or know of a good website that shows this. If an inverter is wired up, do you have to worry about hooking up shore power? Any help would greatly be appreciated..


thank you
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Old 02-07-2009, 10:43 PM   #2
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Having just done this I will first tell you that your expectations are unrealistic. The size of the battery bank you would need to do all of this even separately would be bigger than I think you want to install. Remember that you can only draw X-amount of amp hours from a battery. As far as I know most trailers only have 1 battery at most 2. More than likely they are 12volt batteries which have much less amp hours than 6volt batteries do. A single 12 volt battery of the type most RVs come with runs about 105 amp hours. If you have two then you would have 210 amp hours total. By comparison, 2 6volt batteries of the type I use has about 240 amp hours. I have 6 of them so my rig has about 720 amp hours.

So to give you an example of what I am talking about, I have an 1800 watt inverter (a little overkill) and plan to run our satellite receiver, 32" LCD TV and or perhaps the DVD player or our Nintendo Wii. Not all at the same time mind you but at an average of 2-3 hours of use a day. I expect the batteries to only last about 2-3 days at the most without having to recharge. You have to realize that you also will be using juice for the lights, water pump, appliances, furnace etc. Furnaces being the biggest drain.

Since the most expensive inverters on the market are only about 88% efficient at changing DC to AC and because things like a microwave, heated blankets, hair dryers are all high amperage items you can expect that even using things sparingly you will do your battery in very quickly. I don't even expect a single battery to last 1 night with temps in the 40s and the furnace running to stay warm. I will start the generator if I have to run the microwave.

As to your questions, yes the inverter can be hardwired in (as I have done) to power your outlets and your microwave, etc. You may have to add a separate power center if you want to power more than one circuit (breaker). What you want to find is an inverter with the ability to be hard wired and has a transfer switch. The transfer switch will not allow the shore power when connected to get crossed up with the inverter power. The inverter will automatically switch the circuit to shore power if it is available. If shore power is disconnected or fails and the inverter is turned on it will automatically supply power (from the batteries) to the circuits that are connected to it.

I have the Xantrex XM Pro 1800 which is billed as being specifically designed for RVs and Boats. However I am not happy with it as it produces interference on the LCD TVs due to the modified sine wave output. I am going to sell it and get a true sine wave inverter instead but the price is almost 3 times that of a modified sine wave inverter. For anything but some of the pickiest (read cheap) electronics MSW inverters work great and are a real bargain. However my TVs in the motorhome just don't like them so its a TSW inverter for me on the horizon.....(sigh)

My advice is to buy a small inverter to run your TV (you will have to unplug the TV and plug it into the inverter if you don't have shore power) and stock up on some good warm down blankets for the bed (they don't use any power).

Clear as mud right?
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Old 02-08-2009, 10:07 AM   #3
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Excellent write-up NWJeeper! Good point about the Modified vs True sine wave issue. I've seen several people have problems with the MSW inverters.

Stealth3ltt ~ You should take the advice offered. You won't get better advice anywhere.

I'd suggest looking into a nice Honda or Yamaha generator and a small TSW inverter as NWJeeper suggested.
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Old 02-08-2009, 11:18 AM   #4
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Quote:
Originally Posted by Bama Rambler View Post
Excellent write-up NWJeeper! Good point about the Modified vs True sine wave issue. I've seen several people have problems with the MSW inverters.

Stealth3ltt ~ You should take the advice offered. You won't get better advice anywhere.

I'd suggest looking into a nice Honda or Yamaha generator and a small TSW inverter as NWJeeper suggested.
Thanks Bama, I have been down the road before and it truly can be very confusing. Your suggestion of a small (1kw-2kw) portable Honda or Yamaha is good advice. With our old motorhome I had a 1kw Yamaha that I would carry for running the TV, Satellite and charging while dry camping. They are incredibly quiet and fuel efficient and would be my first purchase if I owned a trailer. I don't carry the Yamaha anymore as the 5.5kw Onan on our Georgetown is installed inside a sound enclosure and inside a compartment so it is as quiet to my neighbors (If I have any) as the Yamaha was setting outside the rig. Even with 6 batteries, 2 solar panels with 260watts of charge capacity on the Georgetown we still use the down comforters and turn the heat down at night when dry camping.
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Old 02-08-2009, 07:41 PM   #5
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Right now I only have 1 battery, a deep cycle group 24. I am thinking about going to 2 6v (golf cart) batteries this summer. I also have a decent no name generator 900watts continuous. I just got a 30 watt solar panel for christmas that i am excited about trying out. I know that i am running too small for the solar panel, but they are soo expensive. I cant find the 130 watt panel that most of the bigger rv's have for a decent price. I would really like to get some LED lights also to lower the drain on the battery. The main reason for the inverter is that I see most people say that the furnance takes the most power, i just thought that if i can lower the furnance to about 60 degress and then have the heated mattress' going it might save more power than having the furnance jacked up to 72. ( why heat the whole trailer when you could have the bed heaters on)
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Old 02-08-2009, 09:04 PM   #6
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A single group 24 battery is at best 80amp hours. Using an inverter to power your 2 mattress pads and you would use the formula:

ACwatts/12voltsx1.11=DC amps The 1.11 is to compensate for a 90% efficiency of the inverter which is being conservative.

2 heated mattress Pads, 180watts each (which is a number I found for some popular pads on the net) you get 360 watts per hour. Multiply that by 5 hours (an assumption that it will run for at least 5 hours in an 8 hour period) and you get a total 1530 watt hours. Divide 1530 by 12 (12volts) and you get 127.5 times 1.11 and you get 140.25 which is the amount of amps you will need to draw from your batteries. You can see that your 1 group 24 battery having at most 80 amps will be dead before morning, like I said you will be using lights, the furnace (even sparingly), water pump, lights, etc. It will not work on 1 battery

Now with 2 6volt batteries you will do a little better with around 220 amp hours but that means you will last about half way through your 2nd night out without recharging.

If you plan to run generator during the day to recharge the batteries then you can do it but you will be running the generator EVERY day. This gets old very quickly when your aim is to be out and enjoy some peace and quiet in the great outdoors camping. Not to mention if you have neighbors they won't like you much at the end of the first day.

Lots of great information about 12 volt systems and the formulas I have used here area available at:

http://www.ccis.com/home/mnemeth/12volt/12volt.htm

With our old motorhome we ran 4 6volt batteries. I installed a digital programmable thermostat which ran on A-cells available from Home Depot with which I could program the furnace to automatically drop temperature at night and come on just before the morning. The furnace would typically run once during the night maybe twice depending on outside temps and the inside temp would be around 55, then we loaded up the bed with lots of blankets and a down comforter to stay warm. We were usually good for about 3 to 4 nights out this way and would occasionally have to run the generator to put a bit of charge into the batteries. Keep in mind I wasn't using an inverter to power anything at that point. Just a light here and there, water pump and the furnace.
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