Fridge on Power Inverter?

Refrigerator, stove, furnace, water pump, air conditioner, microwave, water heater, fans, lighting
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bobbyv
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Fridge on Power Inverter?

Post by bobbyv »

In reading a question from 'chasing rain' dated April 24, 2009, it brought up the dilemma I'm having right now.

When I'm traveling I usually run the fridge on 12v, which is not too bad if the weather is not too hot and it's not open and closed too much. In

12v it is pulling around 10 amps per hour which really taxes my one and only 125 amp battery.

I don't like to run it on gas because it's not as efficient as AC and I have to turn it off and back on again every time I fill up. It seems that even when dry camping it would be better in AC mode.

I was given a Black&Decker MAXXsst 750 watt power inverter Model VEC1047BD, built by Vector Mfg. awhile back but have never used it because it's kind of a hassle to hook it up with the alligator clips direct to the battery, and then run an extension cord to the inside. I was wondering if it could be mounted in the outside fridge compartment and permanently wired into the motorhome somehow. Then I could just plug the fridge into the converter right there in the fridge compartment.

I really don't want to run anything else off the inverter but the fridge. If anybody can shed some light on this I would greatly appreciate it.

Thanks for a wonderful forum - lovin' my B190.
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skater
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Post by skater »

First: In mine, the 12v mode is only active when the engine is running, because it'll kill the battery so much. I verified this with a multimeter. The 12v mode is really meant to maintain the fridge while you're on the road and not much else.

With the inverter running the fridge, you're still going to draw your battery power down pretty drastically. It doesn't matter what mode you use (12 v versus 120 v), it's going to kill the battery. 3 amps (what the fridge draws on 120 v) @ 120 volts is 360 watts, divide 360 watts by 12 volts and you get 30 amps - so that's even worse than the 12 volt mode... and that doesn't take into account losses from the inverter. Also, you have to check to see whether the inverter can deal with a resistive load - I'm not sure if they can.

This is why your fridge has a propane mode - it'll run for weeks or months on that mode, even with the relatively small tanks we have. You're right, it's not as efficient as the electric mode, but it should still work almost as well as it will on 120v electricity, and you won't be killing your battery in a matter of hours. And, yes, you have to shut it off now and then, but it'll stay cold for the time it takes to get the propane refilled.
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bobbyv
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Post by bobbyv »

Thanks alot skater, guess I'll just run it on propane when not hooked up to 120. When traveling it should be OK to run it on 12V since it will be charging from the alternator. Am also considering installing an 80 or 100 watt solar panel to help when dry camping. Do you think my present Magnetek converter will handle one of those, and where do the pre-wired red and white wires hook up to the converter? We are planning a trip to Yellowstone this spring and will probably be camping alot in National Parks without hookups. Will also run the Gen. when needeed and allowed. Really appreciate all your help.
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skater
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Post by skater »

Generally you should install a solar controller (the exact name is escaping me at the moment) so as to avoid overcharging the battery. With 80 or 100 watts, you might be able to get away without one, but any more than that you'd definitely want one.

The converter doesn't really care so much, just like it doesn't care when the alternator starts powering the camper's systems.

My guess for hooking it up: I would connect the red wire to where the battery connects (top right lug in the following picture), and the white wire to the lug with the white wires (kind of obscured in the picture):

Image

I would also install a fuse on the red wire just in case there isn't one. One of those inline automotive fuses would be fine - it's not carrying much current, and the main point of it is to avoid a fire if a wire somehow shorts out. It's a couple dollars but adds so much in protection.

Then on the cells, hook the red to positive and the white to negative, of course. (I have to say I've never noticed an extra white wire in my setup, unless it's the one that's already hooked to the negative lug in mine.)

With this setup, the solar cells will always be charging the battery and powering the 12 volt system (up to their limit of course).
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bobbyv
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Post by bobbyv »

Thanks for the quick response skater, in my search for solar panels most 80W and up come with a controller, which I agree is good insurance against overcharging. Since I have 4 extra terminals on my converter I guess I could hook my red wire to one of those and fuse it. Not sure yet as to what amp fuse to use. There is red and white wires with a wire nut on them in the bottom of my converter. I'm assuming these are for the solar panel? My next question is what size and lengh of bolts to use on the roof to attach the solar panel. Don't know whats directly underneath the fiberglass. And a good grade of caulking, preferably gray.
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Alaskan
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Post by Alaskan »

Adding to the house battery capacity would be another option.....

http://b190.com/modules.php?name=Forums ... opic&t=487

The fiberglass is fairly thick... I'd use large diameter stainless oval-head phillips screws for attaching solar panels and 3M 5200 sealer...no need to attempt to bolt all the way through the ceiling.....we have a thread on that here somewhere.
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Post by bobbyv »

Thanks Alaska, can always count on you and skater for great info. Would really like to add a second battery just like your article, if I can talk my wife out of the space, lol. Is your battery an AGM or a reg deep cycle, and is it vented? Present battery is Walmart group 27 deep cycle put in Sept. 2010. Really tight fit but so far so good. Thanks for the tip about the SS screws and 3M 5200 sealant. Got a marine place not far from me that has the sealant. I found a company on Amazon called HQRP 'high quality reasonable prices', that has an 85W solar panel kit with a 10amp controller for $299.91. Am still researching them. Will keep you posted.
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Post by Alaskan »

Sealed battery would be suggested for that application...

Correction, that would be pan-head phillips...

ImageImage
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