intermittant DC power

[The Driver]

Greetings,
I’m new to these forums but apparently have been a “lurker” for some time. I now have an issue that could benefit from the collective knowledge contained here.
While dry camping at the Albuquerque Balloon Fiesta (Thanks Ken!!!) earlier this month, the Direct Current (DC) power on our 2007 Safari SE FB quit working. Or more appropriately it worked intermittently. I bought a new Airstream under the assumption that I would have years of worry free travel, boy was I wrong, but that is another story.
Anyway, one morning we went down to the field to see the mass ascension, when we returned we discovered there was no power at all (no lights, no refrigerator, no water pump, not even the little light on the battery disconnect switch). We connected the A/S to the generator and had power. However, when we turned on additional items, (another light, the water pump to flush the toilet, etc) I noticed that the other lights would dim, like you were using the batteries and placing additional load on them. In the past I never noticed lights dimming when we were hooked to shore or generator power.
Since we were at an Airstream rally, there were plenty of helpful folks around that immediately came over with volt meters, fuses, and even extra batteries. We (they) tested connections and fuses, and determined that I was not getting power to the Convertor from the batteries. A suggestion was made that the batteries may be dead (bad cell?), so we planned go to the local Costco for new batteries. However, as mentioned earlier, when running the generator we had power. We ran the generator until we had to leave to run the errands, but a funny thing happened when we turned off the generator, we had battery power. This lasted for a few minutes, until my wife flushed the toilet, then boom, no power.
After returning from Costco we switched the batteries out, to no avail. At this time I noticed that the trailer’s tongue lift jack also didn’t work. It is connected via a single wire to one of the Batteries’ positive post. It’s not connected to anything else in the trailer and I assumed (and still do assume) that it should work as long as the battery it was connected to was good, which it was.
I consulted some more people, and a suggestion was made that my battery disconnect may be going bad and therefore allowing intermittent power. So we overrode the disconnect, basically hardwiring the batteries to the Convertor. After doing this we had power again from the batteries. I did not test the tongue lift jack at that time. The power from the batteries stayed on for about an hour then, boom, just like turning off a light switch, the power stopped (we were not doing anything, just sitting). After a visit to the dark side, we woke the next morning watched the festivities and decided to go to an RV park with shore power (the batteries were still not providing power), as we knew we were functional with that option.
We went to a lovely RV park in Angel Fire, New Mexico (Hi Lynn and Maria!!). When we arrived we had no battery power, another volt meter was produced with the same results, no power at the convertor, power in the batteries, the tongue jack did not work and with shore power the lights would dim with additional load being put to the system.
The next morning we packed up and headed back to Denver. I did not check to see if we had battery power, I just kept the A/S plugged into shore power so we could lift the trailer. When we arrived home, lo and behold, everything worked on battery power, the lights, the tongue jack, water pump, refirgerator etc. Additionally, when we hooked to shore power there was (is) no dimming with additional load (my lovely wife ran a vacuum cleaner with lights ablaze using one of the outlets).
There were a couple suggestions regarding the cause of this problem and I thought I would see what you all think. The first is that my convertor is going bad, the second is that I have a short in the ground somewhere (as someone stated this would be the only reason the Tongue jack wouldn’t work). I am not saying these are the causes.
I have no clue, so I am placing myself in Airforums capable hands.
Please and thank you,
Patrick Phalen

[Jammer]

Patrick,

It is always with due humility that I give out electrical advice on the forums, because there is no substitute for being there in person and noticing small things that may seem unimportant or contradictory to most people.

However, I expect that you will find that you have an intermittent failure in one of the connections between the - post of the batteries and the trailer frame.

Most likely it is either one or more loose connections to the - DC bus or a loose connection or flaky crimp terminal on the wire between the - DC bus and the trailer frame.

I found several loose connections on the - DC bus in my trailer.

Be sure to exercise caution in working around the batteries and buses. The most important thing is to tape any metallic tools you're using so that if you slip or drop one you won't make a short.

[The Driver]

I believe we found the problem, and Jammer you were correct. the negative battery cable was not tightened to the "Ground" bus in the trailer. We believe this is the issue because when we were testing connections the cable literally fell out of the bus when my friend was testing it with a voltmeter (gotta get me one of those). we spent the next 20 minutes tightening all the cnnections on all the busses we could see and everything has worked since then. Thanks.

[Phoenix]

Same thing happened with our Airstream when it was new. I think whoever is supposed to check that the connections are tight on the bus bars was on break when ours came down the line.