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Old 04-04-2010, 06:48 PM   #1
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Battery and inverter question

When my RV refrigerator quit working I replaced it with a 4.5 cu. ft. dorm size refrigerator from Walmart. It works well and serves our purpose because we plug it into shore power atleast 24 hours before leaving home then load our items into it and make our trip. Usually our longest trips are within 3 - 4 hrs. from home, then our generator is started or we are plugged into shore power.

What I would like to do is install a inverter and a battery to run the fridge on for maybe 8 - 9 hours at night while we have the generator turned off. I would also like to be able to power a 19" flat screen TV and satelite reciever at the same time.

Am I totally crazy and asking too much? If not I would like to know what size inverter and what type of battery supply could handle this? Would it be possible to run a small battery charger off of the inverter to rechage the battery supply at the same time?

I havent had any problem turning the power off to the fridge for 8 - 9 hours at night and then having the generator running during the day, but I would like to use the inverter set up if it is feasable.

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Old 04-04-2010, 08:21 PM   #2
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The inverter is not a problem. You would probably want about 450 amp/hr of battery capacity.

2003 Winnebago Adventurer 38G F53/ V10 505 watts of Solar
1999 Winnebago Brave 35C Handicap Equipped
1999 Jeep Cherokee & 1991 Jeep Wrangler Renegade
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Old 04-04-2010, 08:25 PM   #3
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we need more info to help you.
you can tell us what type of rv you have in your ''signature block''.
how many and what type of batteries do you have?
how many amps or watts does your wally world fridge consume? is it operated by a freon compressor or some other way? many motors (freon pump) will not run at full speed and will overheat if operated off of a modified sine wave inverter.
full sine wave inverters are expensive while modified sine wave inverters are cheap.
my 750w modified sine wave inverter operates my entertainment systems (2 crt tv's, vcr-dvd recorder, and 2 digital converter boxes) just fine for several hours. (300w/12v=25 amps, times 6 hours = 150 amp hours.) my previous 300w and 400w msw inverters were marginal.
my house battery bank consists of 2 300ah lifeline agm 6v batteries wired in series. you do not want to discharge deep cycle batteries more than 50% regularly if you want them to last. lifelines are expensive.
here are some resources for you to check:

Electrical Tutorial
The 12volt Side of Life (Part 1)
Amps and Wire Gauge - 12V Circuit
RV Tech Library - True Sine Wave versus Modified Sine Wave
Lifeline GPL-6CT Battery
01 WINNEBAGO 35U W20.8.1L SW Wa, Hi. Good Sam, SKP. AMSOIL fluids. BANKS ecm program. SCAN GAUGE II w/ Ally temp. 2 LIFELINE GPL-6CT AGM Batts on their sides. TST tptts. K&N panel air filter. AERO mufflers. TAYLOR plug wires. ULTRA POWER track bar. KONI fsd shocks, toad '14 smart car
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Old 04-05-2010, 04:31 AM   #4
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Small refrigerators take around 500-1000 watts to start (Don't even try it with an inverter smaller than 1000 watts) and 100 running

100 watts (once you adjust for conversion loss, wire losses and such) is about 10 amp hours per hour.. Figure a 50 percent run cycle if you are lucky, 75-100 percent if you are not

So 10 hours is 100 amp hours.. that's a pair of GC-2 golf car batteries in series

JUST to run the Fridge

Norcold sells (Among other companies) a somewhat expensive chest type "cooler" (mine is an Engel,, Same product though) and Both Norcold and Dometic sell some rather expensive "RV Frige" type refrigerators that are true compressor units.. But unlike that small office/dorm job you have.. They draw a great whomping 30-40 watts running, and less than 100 starting.

That' s right, about 1/3 the power of your small unit. Or less

They are expensive though.. But worth it
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Old 04-06-2010, 05:43 PM   #5
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Thank you for the replies everyone. I guess my next question would be how do i determine how many watts total would I be using to power these items?

What I had in mind to do is have a dedicated battery or pair of batteries to run this system. One possibility would be to run only the fridge while traveling since it has no problem keeping the contents cold during the night without power, and just run the TV and satelite reciever on this system at night.

Thanks again for the responses, and please keep the ideas coming.
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Old 04-07-2010, 09:42 AM   #6
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That one is fairly easy.. Go to Harbor Freight and pick up a Kill-A-Watt meter

Plug it in to a wall socket or extension cord

Plug the fridge into it

Come back tomorrow and press the KWH button on the right.

Divide by 10 and that's how many amp hours you would have sucked off a 12 volt battery in 24 hours had you been running on battery.

You can also read the label on the fridge.. It will show the running watts (not starting) Starting can be as much as 5-10 times running watts. (That is how you figure the inverter size)
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Old 04-09-2010, 12:02 AM   #7
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I use a small generator, 1000 watt yamaha inverter type. Runs all night on less than a gallon of gas, and no one even hears it running, even me.

P.S. don't forget to put a cable lock to your wheel or frame, or you just might wake up to the sound of silence.

Damn, I'm Good!
"I've got dozzens of friends, and the fun never ends, that is, as long as I'm buying."
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