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Old 12-30-2020, 08:35 AM   #1
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Beware of loose connections

As part of my trip preparation I check the current in the DC-DC isolated power supply circuits to make sure the device is functioning properly. During our prep for our recent trip to the Delmarva area I discovered a toasted terminal from an obviously loose connection. It lasted over 30k miles before the smoke came out. I think I need to be a bit more diligent checking connections.
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Old 12-30-2020, 03:00 PM   #2
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Name: Steve
Trailer: 2018, 21ft escapeó 2019 Ram 1500 Laramie
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I’ve found loose electrical connections / splices on every FG trailer we’ve owned
( Used Scamp — New Casita — New Escape 21 )
IE; Escape - loose battery connections - loose receptacle connections - loose connections converter - bad splices range hood & lights - loose power inlet connections , etc , etc .
Every Spring I check battery connections , 120VAC connections, converter connections , clean 7 pin trailer cord cap .

Some connections may have worked their way loose due to road vibration .
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Old 12-30-2020, 03:23 PM   #3
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Quote:
Originally Posted by steve dunham View Post
Some connections may have worked their way loose due to road vibration .
I don't know if this will work, but when I flew glow-powered radio controlled airplanes vibration was an issue with the radio gear and the servos that moved the control surfaces. When installing servos a rubber grommet was used to isolate the servo from vibration. Couldn't you do something similar on components like the original poster's?
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Old 12-30-2020, 03:56 PM   #4
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I don't think it is a vibration issue. There are a lot of connections in the trailer. This particular connection carries the current from the TV to charge the battery while driving. The output is a constant current source which forces the input to the DC-DC converter to increase depending on the voltage drop at the input terminals. If you have a bad connection(s) in this circuit the current goes up. This connection could have been loose for a long time and if the connection at the 7 pin happened to be poor during one excursion it would cause more current to flow, which could have caused the overheating problem. 1. I need to buy another DC-DC converter. 2. I think I will switch to a dedicated connector at the back of the TV.
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Old 12-31-2020, 08:41 PM   #5
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RV electricity maven Mike Sokol strongly advises checking ALL electrical connections at least once a year. Mike also cautions about OVER TORQUING these connections; something that is VERY easy to do. Mike recommends using a PROPERLY set TORQUE wrench.
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Old 01-06-2021, 04:04 PM   #6
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I too had connection melt: with my new DC-DC charger, I believe it put extra stress on my wiring, and the ground wire connection on my umbilical cord overheated. Fortunately I was able to take the whole thing apart, cut damaged the wire back, clean up the connection and get back in business. In this case I had been drawing 30 amps on a circuit designed for 30 amps max, and it found a weak spot in what turned out to be a sloppy wiring connection.
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Old 01-06-2021, 04:38 PM   #7
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Russ,

It sounds like you found your connection in time. My converter terminal turned into a post toasty. I expect my replacement tomorrow. An interesting characteristic of current sources is that the higher the load resistance the more power they draw. Higher power draw caused more heat in the wires which in turn causes them to draw more power and eventually the smoke comes out. Oversize wiring is certainly in order with these devices!
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Old 01-06-2021, 04:43 PM   #8
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Yes, I was fortunate to see the lights flickering, so was able to stop, identify and isolate the problem before it made too much of a mess of things.
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Old 01-06-2021, 08:45 PM   #9
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Current CSA electrical code requires an Arc Fault Circuit Breaker in the bedrooms of new houses. This little piece of technology is looking for that flickering electrical noise that happens when a wire comes partially loose. In home applications, the bedroom requirement is for the electric heaters that many people use in a cold bedroom. Since heaters are high load appliances, an arcing connection could quite quickly start a fire. Several breakers, and AC outlets are available for this application:
https://www.homedepot.ca/product/lev...fci/1001051307
Though it appears that false trips, especally in the presence of a ham radio transmitter, are a problem.

In domestic solar aplications this was made a code requirement in 2005.Under NEC section 690.11. However, I can't seem to find any actual products for a DC application. Lots of information though:
https://www.sma-america.com/partners...terrupter.html
https://www.nrel.gov/docs/fy14osti/60660.pdf
https://patents.google.com/patent/US20040027749A1/en

It seems that the voltage has to be over 80VDC to require an AFCI. Though as the OP has discovered, it might come in handy at 12VDC as well. Radio noise would be a symptom of a loose wire. I wonder if an AM radio might help find the faults?
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Old 01-07-2021, 08:47 AM   #10
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Dave, Thanks for the post. The NREL document was very interesting. I would have had fun doing that design. It is interesting to note that nearly all faults, both AC and DC are arc faults, bolted faults are not common, so an arc fault detector can be very effective. I think it would be quite easy to detect a fault in a wire by looking at the parasitic losses in a system. In other words look at the power in one end of the wire and power out on the other end. Any difference above a threshold would indicate a loss, either high impedance of a connection or series or parallel arc or a bolted fault. Implementation would not be trivial for large dispersed systems but could be feasible for a small system, however it would be a custom installation. In my case a few temp sensors on the board could have detected the failure long before it became catastrophic, however, you would probably only see something like that on a high reliability military project.

In the long run, I think the best solution is periodic maintenance. I am installing dedicated wiring from the TV to the DC-DC converter to reduce losses and will up my maintenance. The first converter did last almost 2 years and 30k miles and worked as designed.
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