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Old 09-25-2013, 07:07 PM   #1
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12v problem I don't understand

Today while switching out 12v batteries my wrench momentarily shorted positive to trailer body (it sparked a little), I already had negative connected. Since then it appears that I only have 12v power to some of the fuses in the panel. For example the vent fan works but the fridge and furnace do not. Additionally, the fridge does not show any sign of life for either AC or gas operation. Did my temporary short circuit do something? I checked the two 30 amp fuses in my power converter and they are ok. If I'd blown the "short stop" breaker near the from on the trailer wouldn't I have NO power to anything? Any help appreciated.
Oh, it's a '07 Nash 22H

Thanks! Milt
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Old 09-25-2013, 07:35 PM   #2
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OH boy, first always hook up the negative terminal last, that way the only thing you can touch that will give you an arc, is the positive terminal.
There should be low amp fuses , in the printed circuit board board on the back of the fridge , you will need a voltmeter to test them. My fridge has 2 , a 3 & 5 amp. Some where there will be a low amp fuse 5 or 10 amp for the thermostat that has to be checked. If all the fuses check out , try disconnecting the battery, then after 5 mins and making sure all interior circuits are shut off, re-connect the battery. Hopefully things will go back to normal operation.
Worst case , the circuit boards in the thermostat, furnace, fridge and even the roof A/C may have been burnt out by the short.
EDIT: There may be a manual reset 12v circuit breaker somewhere in your wiring, going to have to check everywhere.
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Old 09-25-2013, 07:54 PM   #3
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OK; sorry didn't get back in time to re-edit my original post.
2 things came to mind.
1 The last time I heard of this big an issue the battery polarity was reversed. Any chance that happened ?
2 Also you said 12v batteries ( plural ). Any chance they are hooked up incorrectly and giving you 24volts through the RV? The bathroom fan would tolerate this and maybe some bulbs , but none of the electronics will.
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Old 09-25-2013, 08:54 PM   #4
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sad part is on most Rv red and black are not + and -
you all ways have to make sure black is not + and wight -

it well get most ppl every time
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Old 09-25-2013, 08:57 PM   #5
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There are circuit breakers on the tongue usually. Get a test light, see what does and doesn't have power.
Then check fuses with your test light also.

Check with no shore power, just battery power.

To clarify, if you have red and black, red is +, black is -.
If you have white and another color, white is -, other color is +. Blue is also positive, if red and black are used.
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Old 09-25-2013, 09:10 PM   #6
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I agree with Skip426, check for correct wiring of your batteries and for any CB or fuses. Use a test light or multimeter to check for power from batteries on to and past fuse panel. Normally a short as you describe it shouldn't do damage to circuits down the wire. By it's very name, you 'short' the voltage flow from (+) terminal to ground, it shouldn't cause any current surge to damage or blow fuses, unless your 'short' created both batteries to connect in series and make 24 v.
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Old 09-25-2013, 09:41 PM   #7
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First, my thanks to all of you for your responses and help. I really appreciate it.
Only one 12v battery. I was swapping one for another and only one was hooked up at any one time. I carefully checked polarity and then rechecked after reading a few posts. My primary wires are red and white. That's red+ and white-. I traced them until I saw white attached to frame and red go thru a "short stop" fuses/breaker and then disappear into body.
It looks like I'll be having fun with my test light...
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Old 09-26-2013, 12:03 AM   #8
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hillm, sorry I panicked with the 24v thing, but when I re-read and saw batteries. I jumped to conclusions . Looks like you've done , due diligence with the wiring, and hopefully this just tracks down to a bad fuse or circuit breaker somewhere.
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Old 09-26-2013, 04:09 PM   #9
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I'm pretty sure that shore power was not connected.
I'm out of town today but will start my methodical work tomorrow and I'll report my progress (or lack thereof) and results back to the community here.
My wife and I used the trailer as a part time residence during my last two years of work and it was on shore power that entire time. I'm getting it ready for an extended road trip and that, of course, is when I cause myself problems.
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Old 09-26-2013, 04:26 PM   #10
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Over the years Ive worked on all kinds of trailers and 5ers. When it comes to 12 volts and troubleshooting a VOM is your best friend. Check firstly that the battery is connected correctly. If yes pull your vom and start checking where you have +12 volts. In all cases there is either an in line fuse or circuit breaker between the battery and the 12 volt DC fuse panel. Check your fuse panel and see if +12 is at your fuse buss. If not, the in line fuse or breaker is tripped. Some breakers are supposed to reset once the load is off but if too much current passes through them, they can burn and not reset. My old Jayco had an in line fuse hidden at the battery. My other trailers all had resettable breakers. Check at every point you can find between the battery and your fuse panel. If all is OK the go to your circuit boards on the individual appliences. Most all appliances in a trailer use 12 volts dc as a reference and will not function even on AC if +12 volts is not present. Tell us what you find and good luck.
-Paul R. Haller-
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Old 09-26-2013, 09:25 PM   #11
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Quote:
Originally Posted by terry735001 View Post
sad part is on most Rv red and black are not + and -
you all ways have to make sure black is not + and wight -

it well get most ppl every time
The convention:

Red + (hot)
black - (ground)

Is standard electronics. The convention:

Black +
White -

Comes from household wiring, and started with Edison. It meant black = death, white = good.

To make matters worse, red is often used in house wiring as the "alternate" use wire, used for anything from the 2nd phase of a 240 pair to the line that connects to hall lights.

I have noticed that my RV uses house wiring conventions. Cars and trucks, appear to use the electronics convention.

The moral of the story is NEVER TRUST THE COLOR ONLY. Besides the above conflict, someone could just have run out of a certain wire color and used the "wrong" color. Get a meter and use it ALWAYS.
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Old 09-26-2013, 09:32 PM   #12
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Quote:
Originally Posted by hillm View Post
Today while switching out 12v batteries my wrench momentarily shorted positive to trailer body (it sparked a little), I already had negative connected. Since then it appears that I only have 12v power to some of the fuses in the panel. For example the vent fan works but the fridge and furnace do not. Additionally, the fridge does not show any sign of life for either AC or gas operation. Did my temporary short circuit do something? I checked the two 30 amp fuses in my power converter and they are ok. If I'd blown the "short stop" breaker near the from on the trailer wouldn't I have NO power to anything? Any help appreciated.
Oh, it's a '07 Nash 22H

Thanks! Milt
If you had the negative hooked up, then it depends on where that 12v line went. If it sourced back to the battery, it could have melted that wire without doing any damage to connected appliances. If you had a 12v load wire, then that would have been downstream from the fuse, and you blew it. That would take out the loads on that line until you reset the breaker.

I had one deal once with a TV an idiot had poured beer on, and blown the breaker. Reseting the breaker didn't do anything, but replacing the breaker brought the (now dry) TV back to life. I think they managed to internally arc the breaker.

Go back to the line you sparked, test for 12v with a meter, then trace back to the panel.
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Old 09-26-2013, 09:39 PM   #13
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Quote:
Originally Posted by hillm View Post
First, my thanks to all of you for your responses and help. I really appreciate it.
Only one 12v battery. I was swapping one for another and only one was hooked up at any one time. I carefully checked polarity and then rechecked after reading a few posts. My primary wires are red and white. That's red+ and white-. I traced them until I saw white attached to frame and red go thru a "short stop" fuses/breaker and then disappear into body.
It looks like I'll be having fun with my test light...
I never use a "test light". They are for people who shop at radio shack. they tell you nothing about voltage, and I don't think they even tell you about polarity. Meters can be had for $10, and tell you fascinating things like exact battery voltage, from which you can divine things like battery charge.

Meters usually also have an ohm setting that can be used to trace wiring (do not use on live circuit).
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Old 09-26-2013, 09:48 PM   #14
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If you know how to use a test light right, you can find out polarity and let you quickly know where you do and don't have 12V.
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