Wire to nowhere

[Rick Daniels]

Starting to restore the slide out battery tray and replace the house batteries and I came across a wire that goes to nowhere.  It was tied off in the battery bay. I tried to trace it back to its source but lost it in the many hard to get at places.  Does anyone know what this type of a wire might be for? As you can see in the picture it looks like more of a communications wire than a power wire.  I have not fully utilized all the systems in my coach but as yet have not found anything that does not work to the extent that I even know how to operate it.  There are other wires connecting to nothing in the battery bay but have yet to try to trace them to their origin.  It is almost like something might be missing that would normally be in the battery bay.

[Russ Mann]

It looks like a Thermocouple Wire that would go to a sensor to display battery temperature.

[Rick Daniels]

Thanks for the reply. That just might explain why my old house batteries appear to have been overheated and gone undetected.  That leads me to a follow-up question.  What would the sensor look like, where would it be and where would the sensor send the signal? To the Xantrex which does have an over-temp indicator?  Clearly I am ignorant when it comes to the AC/DC systems.  Guess I better figure out what might have caused the undetected over-temp before I hook up the new batteries.

[Edward Buker]

The most likely cause of overheating is a shorted battery cell. The charger tries to get to a charged state voltage level by providing current. The current is being consumed in the form of heat by the short and the full charge voltage level can never be sustained by the bank with a shorted cell.

The charger could also be at fault but your new batteries should tell you that. There should be no heat after they have reached full charge and the current level on the readout should fall to near zero amps and the voltage around 13.8v when the coach is not using current for lights etc.

The main wires from the charger to the battery posts (large red and black) sense the voltage for the Xantrex. The temperature sensor is an optional item and is used to regulate the charge rate when the battery that it is on gets warm. It is used to modify the charge current lowering that rate somewhat but will not work to sense a shorted cell unless it happens to be on the post of the bad battery which by chance is not very good.

The sensor in mine is a yellow plastic maybe 2 inch by one inch item that bolts to the post. They have used others depending on the model.

https://images.search.yahoo.com/yhs/search;_ylt=AwrBFUL9LCFXf2sBXAAnnIlQ;_ylu=X3oDMTBsY2xzZWFmBGNvbG8DYmYxBHBvcwMxBHNlYwNzYw--?p=Xantrex%20Battery%20Temperature%20Sensor&hspart=mozilla&hsimp=yhs-003&title=%3Cb%3EXantrex%3C/b%3E%20%3Cb%3EBattery%3C/b%3E%20%3Cb%3ETemperature%3C/b%3E%20%3Cb%3ESensor%3C/b%3E%20-%20Image%20Results

You do not really need that sensor you just need to understand the voltage and current that is normal for charging and be watchful for a cell that uses more water, gets warm, and outgasses more then normal. If after a reasonable period of charging the current does not drop to near zero amps then it warrants attention. Hope this helps.

later Ed

[David T. Richelderfer]

When our original Xantrex inverter went bad this past winter we had to have it replaced.  With the new inverter comes a new battery temperature sensor and its new wire leading from the sensor to the inverter.  I noticed soon after the guys left after installing the new inverter and new temperature sensor that they had not removed the old sensor and its wire.  They had simply attached it in a bundle tied it off to the back of the battery tray with a nylon tie.  If your coach has had its original inverter replaced, then perhaps whoever replaced it also simply tied off your coach's temperature sensor wire instead of removing it.  Just a thought...

[Jerry Emert]

My coach had a xantrex when I bought it.  The sensor was a small piece of plastic stuck with double sided tape to one of the batteries.  The Magnum came with a small plastic sensor that bolts on to one of the battery terminals.

[Jim Edwards]

Hi if you have solar panels there may be a second temp sensor in the Battery bay as well. I didn't run across the Solar Panel charger temp. sensor  hanging from a wire bundle for about 2 years or so when other work was needed to be done. I will venture to say this is not the last unknown wire to oblivion you will find!  I think I am up to 7 or 8. I get the impression that the wiring harnesses were constructed for options that may or may not have been installed on any given coach.

Just a thought. The wire in the photo seems to be somewhat unique. You might want to check input wires to the inverter or near it to look for wire of the same type. Might find the other end.

[Rick Daniels]

Thanks to all for the comments.  It does appear that over the years, several things have either been disconnected or replaced and the old wires were just left in place.  There is no battery temp sensor at the end of the wire in the photo but there was at one time.  Why it got cut off from the end of the wire, who knows.  The previous owner(s) even replaced the diesel fuel lines to the hurricane and the onan genset and left the old ones in the coach.  We'll call them "fuel lines to nowhere".  Once again, thanks to all for your help