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Old 08-31-2011, 11:30 AM   #1
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12v to 120v converter to run fridge

I tried searching the forums but all i found was people that have the fridge in the bus and no mention of how its hooked up.


now i have a small apartment fridge that is not being used so it gets to go in the bus now, can i get a good sized 12v to 120v converter and power it that way? thinking for the road trips and such. I would have it on a power bar etc so i could manually turn it on and off before turning on and off the inverter/converter. will this work? that is my question.
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Old 08-31-2011, 01:10 PM   #2
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Re: 12v to 120v converter to run fridge

First you'll need to find out how much power the refrigerator draws, then get an inverter that will handle that load. On newer refrigerators there is usually a sticker in the inside of the fridge listing the amp draw. The fridges I checked just now range from a small dorm room fridge that draws 1.3 amps to a full sized fridge that draws 11 amps.

Take the amps and multiply by volts (120v) to get watts. In the case of my dorm room reefer, 1.3 (amps) X 120 (volts) = 156 (watts). Now you know what size inverter to buy. You'll probably want a larger inverter to power other 120v stuff like hair dryers and computers.

The size of your alternator will limit the size of your inverter. A 100 amp alternator will put out 1200 watts (100amps x 12v=1200 watts) and the inverter loses about 15% of that power in the conversion process so the 1200 watts input from the alternator now becomes 1020 watts output from the inverter. I'm not sure I'd want to load my alternator 100% all the time so, if 'twas me, I'd want to have a peak load well below that.

Some appliance labels show running amps as well as full load amps (FLA). The refrigerator compressor has a motor in it that draws lots of juice when it starts up then draws much less juice in run mode. So our 1.3 amp refrigerator will draw the full 1.3 amps for a second or two as it starts up then will draw probably half or a third of that in run mode.

Confused yet? When I first got into RV electrical I sure was.
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Old 08-31-2011, 01:56 PM   #3
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Re: 12v to 120v converter to run fridge

You need to at least double the running amps to allow for the surge the compressor needs every time it starts up. the motors that power compressors in refrigerators, freezers and air conditioners always take double or more surge amps. And you need the batteries to handle the power. But do you really NEED the inverter?

I have a 3 cf dorm fridge AND a 4 cf under counter freezer in our Class C. We have been fulltiming with this set up since Fall 2006. We have bounced these particular units from SW NC to S Ga, to N FL back to S GA, to SE TN, back to S GA, to N FL, back to S GA, to SW NC, to NE TN, back to SW NC, to Central NM, to S TX, back to Central NM. I think I missed a trip in there some place... When we came out west (the SW NC to Central NM trip) I ran the generator because we had worked an event a few days prior to leaving and we had a freezer full of hot dogs, sausages, etc. OTHER THAN THAT, we leave out with a fully chilled refrigerator and freezer unit. We do not open the door. We can travel up to 8 hours without the temps dropping. We pull in and either plug into a power pole at a campground OR run the generator for a few hours in the evening (watch a movie when wallydocking). Most refrigerators (even dorm type) can hold temps for up to 8 hours if you stay out of the units. My 2.5KW POS Onan has a hard time handling the surge with the compressors from the A/C unit, the refrigerator AND the freezer all kick on at at the same time. Which they cycle thru roughly every 1.5 to 2 hours or so. Run the generator for two or three hours and the units compressor will cool them back down. I do not make my units any colder than normal before traveling. We normally travel in one day trips but out west everything is farther away. So out here we make multi day trips. And we stay in parking lots at least one night, sometimes two.
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Old 08-31-2011, 07:17 PM   #4
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Re: 12v to 120v converter to run fridge

well this is what i have.



so 115v, 1.3 Amp, and 90 watt.

115*1.3=149.5 watts?? that doesnt seem like very much to me. might power a TV or light with it to. not quite sure yet but the fridge for sure!
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Old 08-31-2011, 11:26 PM   #5
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Re: 12v to 120v converter to run fridge

That's exactly the same reefer I have in one of our offices.

I like to design in enough capacity so I'm not maxing out my systems right away. As one of my teachers said, "Make your best estimate then double it."

Looks like you could set up your fridge fairly cheaply. From the label it looks like your unit draws 156w to start up and 90w running. Of course, the fridge doesn't run all the time and as Lorna said they stay cold pretty well as long as the door stays shut. If you want to add a tv, find the amp rating and add it to the full load amps of the reefer then buy an inverter that will handle both.

As far as lights go, I'd go with 12v lights powered by your "house" batteries. Much more efficient. Any time you're converting AC to DC or inverting DC to AC there's about a 15-20% power loss.
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Old 09-01-2011, 11:04 AM   #6
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Re: 12v to 120v converter to run fridge

ya im thinking that 12v lights are better. i have 2 strips down the side of the double positioning bulbs and 2 12v florescent lights. I can tell the strip lights are not wired right.. too many on = they start to dim... turn more on they dim even more.. i know that shouldn't be but that is how its wired... thinking LED bulbs but there must be 40 bulbs or more!
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Old 02-24-2012, 11:17 AM   #7
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Re: 12v to 120v converter to run fridge

You should be running a sediment filter at the least on all your incoming water. I pay less for a whole house filter than you do a refrigerator filter. My Whirlpool DB2 style costs $26.97 at Lowes. The housing the filter fits in is only $22. This way ALL my water is filtered. If you are only concerned about removing taste and sediment, then you can get by with a cheaper filter than I use. I change my filter every 6 months.

Before you buy a filter system, you need to factor in what the filter replacements cost plus the availability. My housing will use several different brands. I can use "good" to "best" filters.



Whirlpool Drop In Replacement Filter Item #: 149005 Model #: WHKF-DB2
Whirlpool Opaque Whole-House Pre-Filtration Housing Item #: 89374 Model #: WHKF-DWH (I believe this comes with a cheap filter)

On edit: No you cannot "clean" a filter. The only filters you can clean are the permanent screen filters used to filter debris like I use on our filter setup. They are often used on well pumps to filter out sand and debris to foot may pick up.

You might get better prices here... watch out for shipping $$
http://www.waterfiltersfast.com/
http://www.waterfiltersonline.com/
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Old 02-24-2012, 11:22 AM   #8
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Re: 12v to 120v converter to run fridge

When you say it will be plugged into a power bar, are you referring to a surge protector, like everyone uses to plug in electronics and multiple items?
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Old 02-28-2012, 01:48 PM   #9
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Re: 12v to 120v converter to run fridge

Hello? This thing on?

No response, but I'm going to pass on some info anyway. If people are using the powerstrips with a surge protector, DO NOT use what you think is a power switch to turn appliances on and off. It is a breaker that is not meant to be used as a switch. It can wear out, short, and cause a fire. I know people get away with it but a State Fire Marshal told me this is a common cause of house fires.

Anyway, in your first post it sounded like that was what you planned on doing so I wanted to pass that on.
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Old 02-29-2012, 07:12 PM   #10
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Re: 12v to 120v converter to run fridge

yes a power bar and no, it will not be a power switch. just plugging that in and stereo and some lights etc. nothing major. i will either work in a regular switch or get a converter with a switch.
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