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Post by wisconsinjoe on Sept 8, 2013 5:28:22 GMT -8
Warning, don't make my mistake. I have been converting my camper to an all 12 volt system by using the existing 120 volt wiring connected to a deep cycle marine battery (with a converter/charger for times when plugged into shore power). There are just a few connections: new wires to a new Fantastic Fan, and the existing two wire system to an overhead dinette light, a kitchen light, and two reading lights over the rear bed. I wired in the two new 12 volt fixtures in the back and ran new wires from the two twisted wire connections that had previously been connected to the fuse from the shore power. Those new wires were to be connected to the fan wires and then to my battery. I clamped on 1/4 inch washer connectors for the battery terminals, hooked up the positive, and dropped on the negative. IMMEDIATELY, smoke started and fearing getting burned I used a nearby hammer to yank off one of the battery wires. It took about 10 seconds for the damage to occur. The two new wires running back to the original wire cluster had melted 70% of the insulation in that time. Freaked out, I cut out those wires, drove home, and told my wife that I had fried all the wiring in our trailer, potentially erasing the 6 weeks of restoration we had done (new roof, J-rail, etc).
After calming down and thinking about it for an hour, I drove back to the place we have it stored to do further investigating. Turns out that the wires running to the fan were un-harmed. I made a continuity tester to see if I could locate any crossed wires in the wall, which would indicate burning there. I started with one of the two light wires in the rear and found continuity in BOTH the clustered wires at the original fuse point. NOT GOOD. Then I tore into the wall under the dinette seat to get a little more room to separate the three pairs of crudely twisted wires and found that a white and black wire had been reversed. In an A/C system, this would still work. However, in my new DC system those crossed wires essentially turned my new wires into an un-resisted filament.
The happy ending is that it was ONLY that new exposed wire that fried. I straightened out the crossed wires, ran new wires to the battery, this time with a fuse block and 15 amp fuses to the original and new fan wires. Hooked it up and everything works. LESSON: assume nothing with these trailers. Continuity test every wire first and install fuses.
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Post by universalexports on Sept 8, 2013 5:34:06 GMT -8
wow, you got lucky. thats one of the reasons I ran every wire new, after 50 years you have no idea who has done what in these things. if you cant see it to verify it, dont trust it.
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Post by bigbill on Sept 8, 2013 9:11:40 GMT -8
Most importantly never ever hook up a system to power without a fuse or a circuit breaker. a 12volt battery can melt a lot of wire insulation in a heart beat and those wires can be hotter than a branding iron. The trailer or life you save could be your own.
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mobiltec
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Post by mobiltec on Sept 8, 2013 9:13:59 GMT -8
wow, you got lucky. thats one of the reasons I ran every wire new, after 50 years you have no idea who has done what in these things. if you cant see it to verify it, dont trust it. Or at least test it before you trust it and this is one of the reasons I don't like to teach electrical. There are just too many things that can go wrong and every trailer will have different potential problems. I never hook up a system to any sort of power without fusing of some sort in the line first. An electrical fire start's very quickly with these old dried out materials and a trailer fire can get out of control very quickly... Another lesson. Always keep a fire extinguisher nearby inside and outside the trailer when working on it. I have about 5 of the lying around.
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Post by wisconsinjoe on Sept 8, 2013 13:09:00 GMT -8
Most importantly never ever hook up a system to power without a fuse or a circuit breaker. a 12volt battery can melt a lot of wire insulation in a heart beat and those wires can be hotter than a branding iron. The trailer or life you save could be your own. I really don't know how I could have been so careless, easily the most stupid thing I have done in many years. I've wired my house and workshop and know my way around A/C systems. But to forget the fuse?! Some guardian angel must have been on my shoulder. Hope others read this and take warning.
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Post by bigbill on Sept 8, 2013 19:11:45 GMT -8
Yes A/C will shock you and will even start fires but a 12volt DC battery unfused has enough Amps to melt the insulation off of a wire instantly. I have seen them go off like a flash bulb, leaving the bare wire glowing like a cig. lighter. While we are talking about DC electric some of the new electric cars and Hybrids have from 36 to 90 volts and that can be fatal, emergency personal are being given special training to deal with those systems. When you get into a/c it will tend to blow you loose, High voltage DC will hold on to you. So if you own one of these vehicles and wish to work on it yourself be careful. Also if you are working around your trailer battery take off all your rings.I have seen people lose a finger due to having a tool in there hand and bump a ground with a ring while working on a 12 volt system causing the gold or silver ring to become so hot that they lost a finger, and it only takes less than a second.
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mobiltec
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Post by mobiltec on Sept 8, 2013 19:22:17 GMT -8
And the battery can explode. Not pretty. Not fun. Can injure people very seriously.
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Post by bigbill on Sept 9, 2013 13:48:41 GMT -8
Larry I have seen two batteries explode in my life, next of kin to a hand grenade. One was in a 1/4 inch steel vented compartment and it blew it apart. My ears rang for a week.
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Post by mobiltec on Sept 9, 2013 14:43:33 GMT -8
Larry I have seen two batteries explode in my life, next of kin to a hand grenade. One was in a 1/4 inch steel vented compartment and it blew it apart. My ears rang for a week. I've only seen it once and it wasn't pretty. The hood was blocking my vew of the explosion thank God but I saw the aftermath. Every hose, belt and wire under there had to be replaced and the battery welded itself to the hood.
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Post by wisconsinjoe on Sept 9, 2013 19:38:27 GMT -8
Larry and BigBill, what were the conditions for those battery explosions? I heard that it is dangerous if the battery is frozen and you try to jump it. What else can cause it? I'm wondering if I should have some sort of battery kill switch installed in my system. Or can I merely remove the negative terminal wires when I'm not using it? I don't seem to get any sparking if all my lights and fan are turned off when I fiddle with the wires.
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Post by bigbill on Sept 10, 2013 4:44:13 GMT -8
Usually when a battery is charging and giving off gas and something causes ignition. One blew in cold weather the other blew in hot weather. In my case neither was being jumped. Although I have heard of them exploding while using jumpers. A master disconnect switch is optional if you have no battery current drain.
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Post by mobiltec on Sept 10, 2013 6:47:38 GMT -8
With mine the problem was that the battery was not tied down securely and it jumped up when I hit a bump and both terminals made direct contact with the hood which caused an instant major short which welded the battery terminals to the hood and it blew up. Had to replace all my hoses and belts in the engine compartment.
Of course that will probably never happen in a trailer but it really shows what a battery can do when things get hot enough. All 12vdc lines should be fused and all 110vac lines should have a good new breaker. There should be a seperate 30 amp fuse right out of the positive termimal of the battery besides extra smaller fuses for each 12vdc line.
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Post by wisconsinjoe on Sept 11, 2013 12:40:38 GMT -8
There should be a seperate 30 amp fuse right out of the positive termimal of the battery besides extra smaller fuses for each 12vdc line. That is very good advice. Thanks.
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Post by bigbill on Sept 11, 2013 14:10:19 GMT -8
I like to use an auto reset breaker as my main safety right next to the battery. This limits the amps output in to the system but will reset if you plug to much in and you unplug or turn off part of the load and I usually size it very conservatively. Then I like as short a run as reasonable to my 12 volt fuse panel. Much nicer than trying to replace a fuse in the dark. Also use the proper size fuses in the fuse panel. I have seen people put 30 amp fuses in a circuit designed for a 2 amp draw, this defeats a lot of the protection that is possible. Also make sure your wire is sized properly for the circuit you are running. 12 volts DC can start a fire as quick or quicker than 110 A/C.
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Post by mobiltec on Oct 4, 2014 14:05:57 GMT -8
In the original post...
WRONG.... You must NOT reverse AC wires.. EVER.... I'm not going to try to explain why because very few here would understand without going to at least 9 months worth of schooling in electricity. But the basics of it are that you can end up with the metal base of your lamps being hot and when you go to turn a light on or off you will get shocked pretty dang good. It could even kill you.
This is why I say it is a good idea to leave some things like electrical to the pros. Trailer brakes is another. Welding your hitch is yet another. If you don't have the money then either save it up or take up bowling.
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