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12 Volt System On My RV Does Not Work When Not Plugged Into 120 Volts

by Tom
(Indian Harbour Beach, FL)

Everything on my motorhome electric system works well with a generator or hooked up to 120v power. Once disconnected the 12 volt systems do not work.

I found a post similar to mine where it was suggested to look around and will find the answer. I looked around and was not successful finding an answer. Help!

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ANSWER: Hi Tom,bBased on your description it sounds like your House Batteries are not providing power to your 12-volt system when you are unplugged from 120 Volt electric or not running your generator. When you are plugged in or running your generator your RV's Power Converter provides your RV with 12 Volt DC power.

Prior to checking the house batteries on your RV you need to check to see if there are any blown 12 volt fuses or tripped 120 volt circuit breakers in your RV. You also need to determine if your Motorhome is equipped with a Battery Cutoff Switch. If it is you need to check the switch to make sure that it is not activated and cutting off the power coming from your house batteries.

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ries. I cannot tell you the exact location of your RVs house batteries as the location differs by RV Manufacturer and Motorhome model
you have.

Once you locate the batteries the first thing you should check is to make sure that they are properly full of electrolytes, if they are low on electrolytes you need to top them off with distilled water (never use tap water).

If the electrolytes are full then you need to check that the batteries are properly connected. Check for any loose wiring dirty or damaged connections and repair and clean them as needed.

If after you have done all of the above and you still do not get power from the batteries to your RVs 12 Volt appliances then the problem could be either that the house batteries are bad or your RVs Power Converter is not providing a proper charge to your house batteries. In this case, I would strongly suggest that you take your Motorhome in and have a Certified RV Technician diagnose and repair the problem.


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If you are looking for more information on the house battery systems on your RV you should read the answer I gave to Why Are The 12 Volt Lights On My RV Going Dim?

Hope this helps.

Happy RVing

RVing Al

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Comments for 12 Volt System On My RV Does Not Work When Not Plugged Into 120 Volts

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Rating
starstarstarstarstar 		But I have 12V at the fuses!
by: Jimmac

This baffles me.
Plugged 120 -> 12V system works.
Unplugged 120 -> no 12V system.

But there IS 12V on both sides of the fuses. Looking at typical schematics, I don't understand how that can be possible. I can't find a battery breaker or switch, but if that were the problem, there'd be no 12V at the fuses. If it were a stuck relay in the controller, again there'd be no 12V at the fuses.

1982 Sunline 16.5
Converter Systems Inc CS-835, no docs.
Rating
starstarstar 		How should the cut-off switch be positioned?
by: Denny B

Your instructions about the battery cut-off switch is a bit confusing to me. Should the switch be on so power from the batteries flows to the converter panel? Or, should the switch be off so the batteries Do Not Flow to the converter?
Rating
starstarstarstarstar 		12 volt circuit breaker
by: Anonymous

After the battery there is a terminal block hub terminal all posts on a breaker block has small reset buttons located in a dry protection red area found mine in underneath storage area Whan you have DCpower when plugged in that means the converter and fuses are good. But it is the 12 volt hub breaker
Rating
starstarstarstarstar 		hidden reset relay
by: Anonymous

I had no 12volt without shore power... After watching a number of videos, and reading a ton of replays, I came to the conclusion the guys building these RVs put the 12v cut out switch in a different place on every RV...
After hours of looking I found mine under a drawer, under the sink (2014 Thor 22e)... Good luck...
Rating
starstarstarstarstar 		Dometic 2852 No Cold
by: Chuck

Dometic 2852 2 way. RV plugged into pedestal power. Surge protector shows everything good. Fridge stopped cooling. Will not switch to LP. Fuses check OK. No power at plug in for fridge. Attempted to plug in to outside extension cord, still no cooling. Could it be circuit board? Appreciate your time and input.
Rating
starstarstarstarstar 		Same issue no 12 volt when no shore power.
by: Steve

Not even sure where to begin. Are there reset in the 12v converter. ?
Rating
starstarstarstarstar 		Electrical Plug
by: Anonymous

Before checking all connections and fuses, go to the park pedestal to make sure the electrical cord is completely plugged in and/or not tripped. We found one time that our cord was just slightly not pushed in all the way and 1/2 of all our outlets would not work, lights were getting bright and then dim. It took a long time to figure out what was going on. We were in the process of researching new batteries when my husband decided to check the connection one more time. It happens even to us long time rv'ers.
Rating
starstarstarstarstar 		12volt not working on RV
by: Anonymous

Before you go through all the hassle described above, check the 12v line coming into the fuse box, in my RV it’s under the bed, there is a manual reset button in the 12v line just before it enters the fuse box. Mine has a little box with 2 posts for the lines to attach to. Reset button was on end where you couldn’t see it.
Rating
starstarstarstarstar 		3 way RV Refrigerator
by: Jeff

Hi, I have a 3 way refrigerator in my travel trailer. It works fine on AC shore power; it works fine on propane power; and it works fine on 12 volt when plugged into AC shore power.

The issue is when it is unplugged from shore power, it does not operate on 12 volt power. It is getting 12volt power because it alarms and flashes. Everything else in the trailer operates normally on 12 volt, so battery and circuits are OK.

Very frustrating! Please help if you have any experience with this!
Rating
starstarstarstarstar 		12 v
by: Anonymous

I have a 1996 newmar mountain aire 39ft gas rv..everything on it works when plugged up to the house but when its not the lights in the rv will not come on..when i start the motorhome there is a tapping kind of shorting out sound and the lights on the dash blink with the noise then go back to normal..any advice? Thanks..
Rating
starstarstarstarstar 		Fixed my problem
by: Stan Straub

Thank you Tom for your answer to your problem. I thought something was wrong with my coach and didn't know what was causing the problem. I went out and pushed the switch on the dash that connects the coach batteries to the starting batteries. Then, I unplugged shore power and much to my delight, the 12 volt coach batteries came on and it's working like it is supposed to. I had pushed the switch and didn't realize what it does. Now, thanks to Tom and this site, my problem is solved.
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starstarstarstarstar 		rv power with or with out
by: Anonymous

ok so if you dont have it pluged into a power cord and you dont have the genarator on,and you have a new battery (deep cycle) and the power plugs dont work inside the rv is that normall.i thought they should work.only the lights come on.

Note from RVing Al: Yes it is normal as the lights are 12 volt DC and work off of battery power. Unless you have installed a power inverter to run some 120 volt appliances in your RV; the only way you will get 120 Volt power to the plugs is by being plugged into shore power or running your generator.
Rating
starstarstarstarstar 		My 12v system does not work when not plugged in to 120v AC
by: Bruce

Check the battery polarity fuzes on the converter. Depending on the converter system they may be located on the 12v fuze panel or on the converter itself. Look for 25, 30 or 40 amp standard auto fuzes usually 2 or 3 located together but separate from the from those for the individual load circuits.
Rating
starstarstarstarstar 		Transformer versus Inverter.
by: Leo.

You probably have a transformer instead of a inverter.
I bought a 19" TV in KMart with dvd Hd. 150.00
I got a Inverter 499 recomended sronger better

Now I can plug in my TV either into the inverter or with an extencion to the campsites 110 supply.

I also bought a (75c75) hanger for the TV and just
lift it out when I leave the van parked somwhere.
This way they wont breack a window to steal the TV.
With an inverter you dont need anything 12 volt.
Rating
starstarstarstarstar 		Problem Found!
by: Tom

After much agony and searchng out the wiring without a wiring diagram, I found the dash switch which pairs the chassis battery with the coach battery to assist in starting was a two way switch. Pressed in one direction pairs the batteries. Pushed in the other direction connects the coach batteries to the motorhome 12v systems and everything works fine. Nothing like a degree from the School of Hard Knocks to find the solution!

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