What are the benefits to having a power inverter?

[alot2nv]

I just bought a 2007 WW fb2200. It came with 2 6v deep cycle batteries. It has a 5.5kw generator. Many camp grounds have quite hours so my question is how long will I be able to watch a 19inch (old style tube TV/dvd combo) on my batteries. Can I make a pot of coffee in the am w/o running the gen? Are there hidden cost of other things I am going to need. I found a 3000w power inverter installed for $700. Thanks for the help. As you can prob tell I am very new to this trailer camping thing.

[RickO]

Welcome to the forum! We don't do much (any) dry camping so I'm afraid I can't help with your questions but you've come to the right place. I'm sure some of our experts will chime in soon.

Rick

[wa8yxm]

How long watch TV? Several hours at least.

Coffee in the AM.. Well, depends on how many hours TV.

With a 3KW inverter I would consider adding another pair of batteries... Or two pair.

[travelhawk]

The answer is simple in concept but can get complex in details. The inverter takes 12 volts DC IN and "inverts" it to 120 volts AC OUT.

The key formula is simple: Watts = Volts X Amps

Therefore, Volts = Watts / Amps, and Amps = Watts / Volts

Ignoring a bit of inefficiency (lost watts) in the inverter, and rounding the probably 117VAC to 120VAC and the probably 13VDC to 12VDC to make it simple, if you need to run a 600 watt coffee maker...

On 120VAC, 600 watts / 120 volts = 5 amps

On 12VDC, 600 watts / 12 volts = 50 amps

In round numbers the AMPS of current draw on the 12VDC battery is about 10 times the AMPS of current draw on the 120VAC power.

What makes the question complex is deciding how much current the battery can handle before it poops out.

Batteries are commonly rated in ampere-hours. If a battery is rated 250 ampere-hours and it is providing 50 amps, it can do so for 5 hours -- IN THEORY.

I'm using a coffee pot as a simple example, and 600 watts for simple math, but real coffee makers might draw more or less (mine draws about 350 watts because it doesn't have a warmer, it has a thermos carafe. This saves power making the coffee, and uses no power to keep it warm after it is made.

TV power varies depending on type, but might be 100 watts.

Coach batteries vary in power too, so my numbers are just for example.

And of course everything else that is sucking from the battery counts too, such as lights and an external TV amplifier or DVD or VCR or satellite, etc.

The devil is always in the details.

Final note: If an inverter is mounted in the coach, wired into the AC system, it might not run ALL the AC devices -- coach makers do odd things in this area, such as assuming you want to watch TV but not make coffee, or vice versa. Some people use external inverters at each device, matched to what the device needs.

[alot2nv]

Thanks for the great advice. Clearly I have some studying to do. It's good to know that there people out there with much more experience to help us newbies out. Hopefully some day I will be able to help someone with their trailer questions. Sam

[PugPug]

You obviously know your stuff. My 5er has a built in invertor/charger that I can run a few appliances. I installed an invertor in my sailboat to run a small microwave, blender, toaster that has worked well but yes it does suck the old batteries down.

[Shadowcatche]

There are a number of on line calculators that will help with figuring out what you need and the basis is the care and feeding of DeepCycle batteries, and one of the better sources is Handy Bob (who posts in the solar and boondocking areas on this forum) his blog The RV Battery Charging Puzzle « HandyBob's Blog
calculator abut half way down the page Inverter FAQ - DonRowe.com - Frequently Asked Questions about Power Inverters