12 volt bus bar melting wire insulation

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batflaps

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The bus bar near the inverter on my RV apparently got really hot to the point it started melting the white wire insulation (shown in picture) and eventually caused connection issues on the DC negative side of things, making the DC rail drop down to around 4 volts.

I'm wondering what caused this? I borrowed this RV from a friend that had it sitting for years, and the battery was only holding about 1.2VDC charge (I found that out as a process of troubleshooting) so I swapped it for a better battery. Could that have been causing this, since the inverter would've been working so hard to charge a reeeally dead battery, or do I have other problems?

I'm looking to remove the rivets on the bus bar, put a new one in, then restrip or replace the wires with the burnt insulation, is this the right thing to do? After I removed some corrosion off one of the 12VDC negative 8 gauge wires and re-tightened it, my voltage came back up to 13.6 when plugged into the RV power service plugin where I'm staying. Sometimes the inverter cooling fan comes on though, so I wonder if there's too much of a load somewhere. I have a clamp ammeter, should I look at the current draw that way? What should it be?

 

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Probably was the loose terminals and corrosion which increased resistance causing the heat damage.
 
JFN said:
Probably was the loose terminals and corrosion which increased resistance causing the heat damage.
Click to expand...

I agree with JFN.. And have seen that with my own eyes.. NOTE: You said "Inverter" but that box looks more like a Converter (Inverter 12 volt wires are MUCH bigger).

Two problems RV's have. that most Sticks and Bricks do not have.

ONE: Traveling down the Washboard Highway at 60 MPH... Vibration, from the engine, drive train, road conditions, out of balance wheels and the like "Encourages" screws to work loose.

Heat/Cold range.. Most houses remain within a few degrees, year round, Summer they are Air Conditioned, even if not they stay under 100, Winter heater, 70 give or take a few. 

RV's on the other hand get down to serious low temps in the winter (I have seen -40 more than once) and well over 100 when not in use in the summer.

Due to differences in the metal of the bus bar/screw and the copper wire,, The wire flattens and .. Becomes loose.

The result is many RVers have a few screws loose (don't say it). and you need to

1: UNPLUG (you do not want to play with live 120 volt wires)
2:Tighten every screw, holding every wire, on every bus bar and every circuit breaker you can find.  This includes the power inlet if you have a detachable cord.,
 
You have to find out where that buss is getting the ground to the frame, and fix it. Just cutting the wires back won't fix the main problem, it'll do it again if you don't find and fix the buss ground first. Don't be tempted to ground the 12 volt side to the house side. I've never seen a clamp on amp meter for dc, do they even make them? My clamp on meters only do AC amps.
 
the dead battery may be causing it.

the converter may be over-heating trying to keep up with the 12 volt demand.  this can cause low low 12vt voltage and thus higher amperage at the bus bar.

 
The dead battery *might* have contributed, but I'd agree with the loose screws theory first. You probably don't need to remove the buss bar. Just clean it well. Remove all of the screws and clean everything well. Wires... If there is enough slack you should cut and strip behind where the damage is to expose clean conductor and insulator. If not, cleaning the wires and conductors well should work fine. You can get some heat shrink tube and slide a piece over the insulation to sort of add a layer of insulation to the damaged insulation.
Another sort of helpful item are crimp on ferrules. You crimp the ferrule to the end of the exposed conductor and that gives a nice surface for the buss bar's screw to compress against. Note that you might not be able to fit as many wires per hole in the buss bar, but it looks like there are plenty of spare holes.

Note that the cooling fan should cycle on and off pro-actively to keep temps inside relatively cool. If it won't turn off then there could be excess heating going on still.

Here's a neat video about ferrules. Note that you can get uninsulated ferrules, even though this video only shows insulated ones.
https://www.youtube.com/watch?v=os66cID30Ek
 
Most of the wiring in that picture appears to be 120vac stuff, and it's almost surely an integrated 120v load center and 12vdc converter/charger. Those white wires look like 120v neutrals to me. Maybe a loose or corroded 120v neutral connection for the 12v converter?
 
That's what I initially thought, that the white wires were just 120VAC neutral like on a house, but the bottom two wires are larger gauge and seem to go to the converter/inverter from this terminal block. I guess if they set the "ground plane" at a certain level then that could be used for both DC/AC? Usually the green wire is house ground, and white is neutral, am I missing something?

The problem is that I don't understand the intersection of house wiring and auto wiring here, like it wasn't obvious that the frame was (or wasn't) ground, or whether two wires were needed for every DC/AC connection.

If indeed the wires have loosened over time (plausible), I can certainly believe that created resistance which caused heat. I'm inclined to open up the unit farther (with line/battery power disconnected) and swap the wires that are melted as a first step. I guess at that point I need to determine if there is still a high static current draw somewhere, how would I determine what and average/max should be with things like the fridge and trailer lighting on, and also what the blower motor on the heater should draw? I know the a/c draws a heavy load, but I haven't been using that for awhile.

I don't know whether the clamp ammeter would work, but my inline ammeter only goes to 10A, and I'm fairly certain I might have a higher static current draw than that, which would blow up my meter.
 
92GA said:
You have to find out where that buss is getting the ground to the frame, and fix it. Just cutting the wires back won't fix the main problem, it'll do it again if you don't find and fix the buss ground first. Don't be tempted to ground the 12 volt side to the house side. I've never seen a clamp on amp meter for dc, do they even make them? My clamp on meters only do AC amps.
Click to expand...
Yes there are DC amp clamps.
http://en-us.fluke.com/products/clamp-meters/
 
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