12v in TT won't work unless it is hooked into truck's 12v plug at hitch...

[magstar67]

I recently bought this trailer and hadn't needed to use the 12v system (interior lights, pump, etc.) until last weekend when we camped without a 110v hookup.  The trailer has no power through it's own battery, but everything will work when it is plugged into my truck.  I put a new battery in the trailer but still doesnt work without the truck.

Any suggestions? :

Thanks,
Jeff

 

[Carl L]

Step one:  Check out every fuse in your trailer.

 

[magstar67]

No fuses blown.  I checked all of them at the converter with an ohmmeter. 

 

[magstar67]

I did notice that the ground for the battery is a much smaller wire than that of the positive wire.  It appears to be grounded through the breakaway switch (my battery is hitch mounted), that is the only wire from the negative side of the battery.  There is a typical ground cable for the battery that has been taped up and unused in this same area.  I hooked it to the battery and still no power to the trailer.  Another note, I tested across the battery terminals (with the positive and negative wires still attatched to the battery) to check the voltage in the battery and got a big spark like it is a direct short when I test across the posts!  I didnt check it with the wires disconnected.

Any thoughts? :-\

 

[Frank B]

Magstar67:

Just a guess:  You don't tell us the age of the trailer, but my 25 year old first trailer developed a problem with the converter relay.  On 110v, it worked fine.  When the power was off, the relay was supposed to put the battery into the main circuit, but it didn't always do that.  The contacts were dirty on the relay, and the battery connection did not 'make', leaving the trailer in darkness.  Cleaning the contacts on the relay did the job.

Not sure if this is your issue, but it is an avenue to explore, depending on the age of your unit.

Frank.

 

[magstar67]

It is a 2001 Coleman Caravan. 

I am stumped by the fact that it works fine when hooked to my truck, but not when unhooked.

 

[Frank B]

I am definitely not an expert in this.  However, does your converter have a relay that cuts the battery out of the circuit when on 110v?  If so, have a look and see if that is working correctly.

I mention this because we had the same problem with our unit, and the relay in the converter was the culprit.

If it has no relay, then I am stumped as well.

Frank.

 

[rbell]

You shouldn't get a spark testing with a voltmeter. If you did you may have a corroded or loose terminal and pushing on it with the probe of the meter helped make the connection & the spark. I'd start by unhooking both terminals cleaning the posts & terminals with a small wire brush to get off all that grayish corrosion. That stuff is a pretty good insulator. Also check your battery while disconnected with a digital voltmeter. If it reads 11.9 vdc or below it's fully discharged. 12.6 - 12.7 vdc is fully charged.

The fact the negative cable was disconnected means something isn't right. I'd be cautious trying to use it hooked to your tow vehicle using only that plug and having the battery cable disconnected. It would be very easy to overload the smaller wires. Also make sure the cables are hooked to the proper terminals. Red to + & black to -. Most batteries have different size posts so they can't be hooked up wrong, BUT some don't.

While it's disconnected put your meter on the ohms scale and check the black cable to a good ground. You should get no more than .1 - .2 ohms with a good ground. If it's more follow the black cable to where it's grounded & remove and clean there also. Make sure it's a good shiny metal connection with no paint under it.

When you hook it back up hook the black wire last so you won't accidentally make a spark and scare yourself. With it hooked up put your meter on dc volts again and check from the black wire terminal at the battery to your good ground spot. There shouldn't be any voltage present. If there is look at your cable for a white powder like stuff coming out around the ends or swelled spots in the insulation. If you have either replace the cable.

You can also check your converter/charger by checking the battery voltage at the battery with the trailer not hooked to anything. That voltage should be 12.6 - 12.7 with a fully charged battery. Then plug the trailer into 100 vac and the voltage at the battery should go up to about 13.7 - 14 vdc while it's charging.

Let us know how you do and we can continue on.