Inverter Questions

I was considering installing an inverter in my 1995 Sea Breeze 5th Wheel.

I went to the article in Tech Tips about the installation and found the installation to be rather complicated.  Certainly not as simple as I was hoping.

I was hoping purchase one (other than a cigarette lighter model) that I could stick in there somewhere and be able to just watch TV. 

My rig has two batteries and my truck two, so I figured I could get three-four hours of TV watching without electricity or
recharging my batteries.

Am I all wet???

Thanks,

Jim

Jim,

Sorry if that article appears complicated. If you know what you're doing, the job is really straightforward.

If you really only want power to watch TV, the plug-in inverters work just fine and are a lot less work. Alternatively, find a TV that can be powered from either AC or DC and run it off the RV batteries. I suggest you don't use the truck battery(ies) for any of this, or you'll end up not being able to start it.

Tom said:

Sorry if that article appears complicated. If you know what you're doing, the job is really straightforward.
If you really only want power to watch TV, the plug-in inverters work just fine and are a lot less work.

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The article was nicely written, Tom.? It's just that it entails more work than I want to do (smile).

You mentioned the "plug-in inverters".? Are you referring to the cigarette lighter types?? Or is there another one that doesn't have to be wired in permanently?? I don't think I have a lighter plug in the RV.?

Thanks for your info, Tom.

Regards,

Jim

Hi Jim, yes I was talking about the cigarette lighter types. If you don't have a 12V receptacle in the RV, you can always cut the plug off the cord and hard wire it to the battery. Of course, you do need to keep the correct polarity and you might want to add a switch so you can turn the inverter off when not needed.

One caution when using the plug-in kind of inverter - keep the wires between the inverter and the battery short and use an AC extension cord if the inverter is too far from the TV. Don't use a 12V extension cord between the inverter and the battery because the voltage drop along the wire could result in the inverter not working. But, if you want to substitute larger diameter wires, it should work OK. It's just sometimes easier to use an AC extension cord between the inverter and the TV.

If you remove the plug, then you must put a fuse in line if you wire direct to the battery.  The fuse is usually in the plug.  Never wire anything direct to the battery without a fuse of the proper size.

Good catch Ned. Yes, a fuse is needed.

You could also bou one with Crocodile clips that just clip straight onto the Battery with an inline fuse normally alaready on the live cable. Make sure it is Positive to positive and Negative to negative.  ;D

with Crocodile clips that just clip straight onto the Battery with an inline fuse

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That would avoid the need for a switch, although I'm not a big fan of connecting stuff to the battery that way. Nothing "wrong" with it though, as long as the fuse is inline.

You can also buy an adapter that has a cigarette lighter (12V utility outlet)  plug on one end and a pair of alligator clips on the other to clip to the battery. Then plug a small inverter into that.  You can usually find them in an auto parts store, though sometimes the wire is a bit undersized for the job.

If you just want to watch tv or  maybe charge a cell phone battery, a small portable inverter will do fine.  No wiring experience needed.  I recommend something in the 400 watt range, though 300 watts might do for smaller tvs.  As Tom says, keep the wiring to the battery short and use a regular  home-type extension cord to reach whatever you need to power. I suggest a 16 (or larger) gauge extention cord and of the outdoor type if it has to run outside or underneath the RV to reach the inverter location.

An inverter can suck a LOT of power from the battery in a short time, though. Be especially careful if using the vehicle's starting battery or you may find yourself walking for help.

Thanks for all the tips, guys.

To bad nothing is as easy as it should be <smile>.?

Looks like I'm gonna have to wire it one way or another.? If so, I'll probably go with a larger unit.

HFT has a 700w Wagan on sale for $50.......or........I could just buy a new rig (smile).

Regards,

Jim

RV Roamer said:

An inverter can suck a LOT of power from the battery in a short time, though. Be especially careful if using the vehicle's starting battery or you may find yourself walking for help.

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Does the inverter itself drain the batteries?? Or just what is used "through" it?

Regards,

Jim

An inverter draws some power whenever it is turned on - the "Idle" amperage is typically 0.5A-1.0 amps but varies with size and brand. When something is actually being powered b the inverter, it is important to remember that it takes 10 times as many DC input amps as the output load requires.  A trivial 150-200 watt load, e.g. a tv, uses only about 1.5 AC amps but requires 15 DC amps from the batteries. A 1000 watt load (9 AC amps) such as a coffee pot or toaster sucks an incredible 90 DC amps from the batteries for as long as it is runing.

As RV Roamer said, think about other things you may wish to run off the inverter as well... Mine can run quite a lot.

400 to 500 watts should run a TV and Sat receiver, likely 300 will but check the labels on the devices and don't forget to double up for starting surge.

Do wire them up hard, not through the lighter.  Lighter plugs can't take a 400 watt load

Someone mentioned idle current,,, this is proportional to the size of the inverter.  A killowatt inverter will draw more when on standby than a 300 watt.  Also an inverter that is too large will often not work well with a small load

Finally there are two kinds of inverters, True Sine Wave and modified sine wave.. True sine is better, much better, however it is much more expensive and it will also draw more current when not working and also draw more current WHEN working

A good rule for current draw however still remains 10 amps per hundred watts of load  No where near accurate but by the time you do all the math, including the overhead and conversion efficency and such... Amazingly close

As Gary mentioned, there will always be some current draw by the inverter unless shut off completely. Modern inverters have circuitry that sense when a load is present, and switch from their quiescent state (perhaps as little as 50 or 100 milliamps. to an idle current of .5-1.0 amps or sometimes more, automatically. This is when the inverter is ready to supply whatever power is required by the load, and is independent of the type (modified sine or pure sine) of inverter. The power rating of the inverter or whether it's pure or modified sinewave has little to do with the idle current; it's more a matter of design. Some small inverters will draw the same idle current as a larger unit with no load attached at all - the cooling fan or other power cunsuming components run continuously regardless of need.

While it's true that some appliances work better on pure sinewave power (indeed some things like clocks, electric blankets, and other devices with electronic controls may not work at all), most will, and you have to decide for yourself if paying almost double for pure sinewave is cost justified for those few that don't. My microwave doesn't like a modified sinewave at all, but I can run my generator for many hours on what it would cost to upgrade to pure sinewave. Besides, running a 1500 watt micro on batteries would run them down in short order! 

One thing I noticed:? The inverter I'm considering purchasing (modified type) says for use with 12v systems only!

I was thinking that my RV has two 6v batteries, wired in-line, to create 12v.? Haven't checked the paperwork yet, but does this seem logical?? The batteries each have three cells.

I do know my "stuff" runs off 12v, so, then, couldn't the inverter be used?

Thanks,

Jim

Yes, your RV has a 12V electrical system.  You can use the inverter.

Ned said:

Yes, your RV has a 12V electrical system.? You can use the inverter.

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12v system, but what batteries, with three cells?? Forgot if it's 4x3 or 2x3.

Anyway, may I ask some advice.? Money doesn't grow on cacti down here in NM, so which concerter should I purchase?

I can get the 700/1800 model for $50 or a 200/4000 model for $140.

Remember, this will be used maybe once or twice on a vacation.? Our concerns are:? AC when necessary and an Electric Blanket when necessary, TV, and lights.? Maybe the micorwave, but we have a gas stove, so no big deal there.? I believe our one airconditioner is a 15000 BTU.? That's about it!

I appreciate your help.? It's great to share, isn't it? ?

Regards,?

Jim, down in the windy desert today!

6V gof cart style batteries have 3 cells and connecting two of those batteries in series gives you 12V. That will give you nominally 220 amp hours capacity. But, since you shouldn't discharge them much lower than 50%, you really have 110 amp hours capacity. If you were able to add another two of those batteries, it would double the capacity.

The inverter size should be chosen based on your expected maximum power draw at any time (i.e. the total power drawn by any appliances that are switched on at the same time). Check the labels on the appliances &/or the owners manuals for the correct values.

Next step is to calculate the amount of power that you'll be drawing from the inverter and for what duration of time. Then convert that to amp hours of capacity to see if two batteries is sufficient or if you need more batteries. The following is from the article in our library:

Calculate how many batteries you need.

Take your list of 120 volt appliances, power consumption in watts and estimate of operating hours and calculate the amp-hours of capacity drawn from the batteries in a 24 hour period from the formula:

Amp-hours = (watts x hours)/11 (allowing for efficiency).

The following example might help, but be sure to use the actual power consumption from the owners manuals of your own appliances and adjust for your own usage of each:

<pre><b>Appliance          Watts    Hours  Amp-hours</b>
Microwave oven    1500      0.5      69
Coffee pot        1200      0.5      55 
TV                  180      3        49
DVD                  55      2        10
Computer            100      2        18
Stereo              60      3        16

<b>Total                                217</b>

Number of pairs of batteries required = (total amp-hours)/110
                                      = 217/110
                                      = <b>2 pairs of 6 volt batteries</b> (or 4 12 volt batteries).</pre>

desertjim said:

12v system, but what batteries, with three cells?? Forgot if it's 4x3 or 2x3.

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Doesn't matter, it will be a 12V system.? As Tom states, 6V batteries have 3 cells, so 2 batteries will be 2 batteries x 3 cells.? Still 12V.

Anyway, may I ask some advice.? Money doesn't grow on cacti down here in NM, so which concerter should I purchase?

I can get the 700/1800 model for $50 or a 200/4000 model for $140.

Remember, this will be used maybe once or twice on a vacation.? Our concerns are:? AC when necessary and an Electric Blanket when necessary, TV, and lights.? Maybe the micorwave, but we have a gas stove, so no big deal there.? I believe our one airconditioner is a 15000 BTU.? That's about it!

Click to expand...

You don't say what brand of inverter (or is it a converter?).? Inverters/chargers for RV use such as you desire are typically rated at 2000W or more and cost upwards of $1000+.? You won't run an A/C on an inverter, and I wouldn't recommend running an electric blanket either.? You'll have dead batteries before morning.? Use Tom's table to estimate the actual power requirements and then decide on the number of batteries and size of inverter.

Ned said:

You don't say what brand of inverter (or is it a converter?).? Inverters/chargers for RV use such as you desire are typically rated at 2000W or more and cost upwards of $1000+.? You won't run an A/C on an inverter, and I wouldn't recommend running an electric blanket either.? You'll have dead batteries before morning.? Use Tom's table to estimate the actual power requirements and then decide on the number of batteries and size of inverter.

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Must be outta my head today!!  No, I don't want to run those power-hungry critters off an inverter!!  Basically the TV, and maybe my laptop.
I was confusing the issue with why I wanted a generator (smile).

The inverter is a Wagan.  Name doesn't mean anything to me.

What's the difference on what you run off them.......I mean you used the term "rv use" above.  What's the difference if the inverter is gonna run a TV in an RV or in a Tent.......or a Boat?

Thanks,

Jim