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Old 10-23-2012, 04:55 PM   #1
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Inverter question

I am having a 1,000 watt sine wave inverter installed today for the MH so we can run the satellite dish and TV's while driving down the road so I don't have to run the gen and load it up with hours and waste fuel.

They way I figure it is the 2 TV's in the main cabin and satellite will draw around a total of 285 watts. I'm assuming the alternator will keep the house batteries charged even while the inverter is drawing that while traveling? Am I assuming correctly?

Also, while tailgating I plan on running an outside TV and Satellite using a total of 300 watts. How long can I expect my house batteries to last before I might need to kick on the Gen to start charging them back up?

I have two 12V house batteries and assume they are like new condition.

Thanks
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Old 10-23-2012, 06:08 PM   #2
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Hopefully you're getting a true sine-wave inverter vs modified?? If not you will have a higher wattage consumption on any inductive load, i.e. transformers etc. So let's take your inverter and assume it's 80 efficient at converting 12.6 VDC into 120 VAC modified sine wave. Then I'll assume you have 200 amp hours between the two batts. At 300 watts consumed by the device's you should have about 2.5-3 hours of use before depleting your batteries to 50% of capacity. That's a lot of beer and taco's...
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Old 10-23-2012, 06:15 PM   #3
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This is real easy.

Watts is watts plus overhead

Find the spec sheet for inverter to confirm effecincy, say it is 90%

Multiply actual load by 1+ 100-rating, so 1 +(100-90) is 110, so 300 watts would need 330 input watts

Next search online and find the rating of your batteries, some are rated amp hours and others for ups are rated watt hours.

Carefull the rating is time based, higher loads area less output.

Now assume two 80 amp hour batteries using this for demonstration and easy math,parallel at 8 hour rate, total is 160 amp hour, divide by 8 for actual load of 20 amps.

A load 20 amps or less will run for 8 hours to full discharge.

Now, volts is resistance times current and watts is voltage times current

Current will rise as voltage drops, use 11 volts to calculate, gives closer estimate.

300 watts out needs 330 watts in

330 watts divided by 11 volts is 30 amps peak so you will not get 8 hours.

You look at the rating of the Battery for the 30 amp local and calculate from there.

See...easy...

Make sure the power wires are large enough, low voltage dc power is critical to voltage drop in the wire at high current keep wire short as possible and larger size if you can
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Old 10-23-2012, 06:21 PM   #4
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Also...do NOT use the Battery that starts the generator for the inverter unless you have a boost switch to use another Battery.

Need to be able to recover after forgetting to turn off...

We installed additional floating batteries dedicated to small inverter to power friends dvd player, swapped tv to native 12 volt led so can run long time and independent of rest of system
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Old 10-23-2012, 07:26 PM   #5
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Good info guys, thank you. Yes it is a true sine wave inverter. Mainly I want it for driving down the road. I hate running the gen for hours on end while driving just so we can watch tv. I have a Honda 2,000 gen I can use for tailgating as well since it doesn't sound like I will get a lot of hours tailgating with the house batteries and we tailgate a long time. Lots of beer and tacos as Wardy said lol
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Old 10-23-2012, 09:10 PM   #6
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There ain't no free lunch - you are using fuel whether you use the inverter or the generator. The alternator adds load to the engine to produce the power for the inverter, so the engine consumes more fuel.
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Old 10-25-2012, 09:14 AM   #7
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Didn't realize that I guess but not to worried about the fuel consumption as much as I am putting useless hours on the gen but good point.
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Old 10-25-2012, 11:31 AM   #8
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I don't think you have to worry about wearing the generator out. have 1886 hours on my Onan, mostly running air conditioner will traveling in hot weather. But we use the inverter too, for lesser loads.
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Old 10-26-2012, 12:13 PM   #9
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Lots of words and numbers but what the heck did TQ60 say? LOL

It is probably better on the generator to use it more rather than less. One of the Onan mechanics I talked to said he knows OTR truckers with refer units with 10,000 hours and more on the generators and the're still going strong.
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Old 10-26-2012, 08:37 PM   #10
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Well that's good to know. I guess you always hear people making a big deal out of low hours on a gen when buying a used MH but really, they are awesome to have so why not use the hell out of it. Inverter is a good addition to the MH but yeah I'm going to not worry about running the gen as much as I want.

Thanks again all
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Old 10-27-2012, 12:08 PM   #11
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N ot enough information.. Here is the partial answer

300 watts, when converted to 12 volts, is roughly 30 amps. (This takes into account a whole bunch of things other than straight conversion, like effiency of the inverter. though using 10 instead of 12.6 is a serious shortcut, turns out to be surprisingly close to the mark.)

Now, a group 24 battery about 75 amp hours at the 20 hour rate
A group 27 95, 29, 105, 31 125 8-D 230

See the the problem here, Without knowing the size of your batteries I can not do the math. Also those figures are at the 20 hour rate, so less you happen to come out with "20" when you do the division, the smaller the number the more you need to reduce it.

IE: at 10 amps, a 75 amp hour battery may be good for as little as 4 hours.

Finally, Divide your answer by 2, so a 75 amp hour battery is good for perhaps 2 hours.

That 8D however, Well 230/10 = 23 so it's good for all day and night.

NOTE: If you switch to a pair of GC-2 Golf car batteries in series.. That too is 230 amp hours. PLUS being deep cycle they do not mind 50 percent state of charge (or less) nearly as much as the more common 12 volt Marine/Deep cycle types do (Those are really starting batteries)

You can get 12 volt deep cycle (Look for Trolling batteries or Golf Car batteries) but they are more expensive and harder to find than Marine/Deep cycle. And I might add, worth the extra cost.

Six volt golf car are cheaper.
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