12v house battery not powering lights

Hi, everyone. I have a problem that's got me absolutely stumped, and I'm hoping that the community here can help me track down the culprit. After recently picking up a used travel trailer I'm having no luck powering any of the internal 12v systems from battery power; things work great when connected to 110 shore power (fridge, AC, lights, etc), but as soon as I switch to battery only I have no power anywhere, 0v when I check the battery cables coming into the converter from outside. I'm fairly handy with cars and feel comfortable chasing down the issue, but I'm not well versed in RV electrical setups so troubleshooting anything like this is brand new to me.

A few details for background:
1998 Rockwood 2108 (purchased used)
30 Amp electrical
Battery is brand new and tests fine (~12.7v)
Replaced the 12v30A circuit breaker on the tongue

Outside:
I get 12.7V on the "BAT' post of the circuit breaker, but only around 0.9V at the 'AUX' post.
All the wiring looks to be in good shape from the battery box back to the converter, junction box under the frame is a nest of wire caps however
SIDE NOTE: original 7-way pigtail cable was damaged (pulled off accidentally) by the previous owner and was replaced at a local shop several years ago

Inside:
Lights and all other electric devices function normally when connected to 110
All breakers and fuses in the converter confirmed working (tested with multimeter while on shore power)
No GFCI outlets tripped inside


I found some great advice in this older thread, http://www.rvforum.net/SMF_forum/index.php?topic=45973.0, which led me to try a few things already like replacing the circuit breaker, but I haven't yet tried rewiring the ground. First thought is that it's an open circuit somewhere, but does it stand to reason that the issue is before the wiring goes into the trailer, or could it be at the converter itself? I also suspect that the repaired 7-way might have something to do with the issue, or that the age of the wiring might be at fault, but I'm not sure where to start.

I'd be happy to post pictures if that could help with diagnosis. All advice is very much appreciated!

Hi and Welcome!!!

You mentioned that " Outside: I get 12.7V on the "BAT' post of the circuit breaker, but only around 0.9V at the 'AUX' post." (I assume that the battery is installed on the A frame (tongue) of the trailer.) I find it very suspicious that you don't see any voltage on the output of that breaker and would be very tempted to just bypass it (very!!) temporarily to see the results. First though, you might try putting the battery next to the converter connection and jumper it to the converter input as well, noting the result, and eliminate a wiring/mis-wire/breaker problem....

CAREFUL, the reason may be that the breaker has popped due to a wiring problem and is not resetting if it is an auto reset type breaker. Disconnecting the other wire should allow it to reset or you can disconnect both sides and check the breaker for continuity using a ohmmeter. If this proves to be the case, replace the breaker, then you will have to trace physically (where possible) that wire and find a break or mis-wiring somewhere.  (I would not longer trust that breaker in any case!!)

Alfa38User said:

Hi and Welcome!!!

You mentioned that " Outside: I get 12.7V on the "BAT' post of the circuit breaker, but only around 0.9V at the 'AUX' post." (I assume that the battery is installed on the A frame (tongue) of the trailer.) I find it very suspicious that you don't see any voltage on the output of that breaker and would be very tempted to just bypass it (very!!) temporarily to see the results. If nothing changes, you will have to trace physically (where possible) that wire and find a break or mis-wiring somewhere. If things then work, replace the breaker (again?). You might try putting the battery next to the converter connection and jumper it to the converter input as well, noting the result,  to eliminate a wiring/mis-wire problem....

Click to expand...

That's correct - battery and breaker are on the A-frame.

I'll try putting a jumper from the battery directly to the converter, I hadn't thought of that one!

Some background: Your converter/charger produces 12v from shore power and, in most RVs made in the last 15 or so years, the battery is in parallel with the converter so either can supply the +12 to the interior systems. Both have a chassis ground on the negative terminal.  In older designs the charger had a separate pair of wires to the battery, but in a 2008 I would expect that the same large pair of wires carry charging current from the converter to the batteries, and battery current back when charging is shut down.  That means you have a fault of some kind between the battery and the converter (which in turn connects to the 12v load center (fuse box).

I suspect the charger is also unable to charge the batteries for the same reason - no electrical path. When plugged to shore power, you should be seeing 13+ volts (usually 13.6) at the battery terminals, coming from the converter/charger. If its only 12.7, they aren't getting a charge from trailer charging system (but may still get one from the tow vehicle).

It is fairly common for there to be a battery disconnect switch between the converter/charger and the battery - have you looked for one?  Could be a manual switch or a relay activated by a small button/switch somewhere else in the RV.

Outside:
I get 12.7V on the "BAT' post of the circuit breaker, but only around 0.9V at the 'AUX' post.
All the wiring looks to be in good shape from the battery box back to the converter, junction box under the frame is a nest of wire caps however
SIDE NOTE: original 7-way pigtail cable was damaged (pulled off accidentally) by the previous owner and was replaced at a local shop several years ago

Click to expand...

The AUX post?  That does not sound like a circuit breaker,, how many terminals on this device?

Circuit breakrs have two posts,, Only two.. And you shoudl see the same voltage on both posts if not the breaker is either Tripped (manual reset) or Faulty.

However if it has FOUR wires.... Then it is the disconnect device and it is turned OFF. (or faulty)

Gary RV Roamer said:

Some background: Your converter/charger produces 12v from shore power and, in most RVs made in the last 15 or so years, the battery is in parallel with the converter so either can supply the +12 to the interior systems. Both have a chassis ground on the negative terminal.  In older designs the charger had a separate pair of wires to the battery, but in a 2008 I would expect that the same large pair of wires carry charging current from the converter to the batteries, and battery current back when charging is shut down.  That means you have a fault of some kind between the battery and the converter (which in turn connects to the 12v load center (fuse box).

I suspect the charger is also unable to charge the batteries for the same reason - no electrical path. When plugged to shore power, you should be seeing 13+ volts (usually 13.6) at the battery terminals, coming from the converter/charger. If its only 12.7, they aren't getting a charge from trailer charging system (but may still get one from the tow vehicle).

It is fairly common for there to be a battery disconnect switch between the converter/charger and the battery - have you looked for one?  Could be a manual switch or a relay activated by a small button/switch somewhere else in the RV.

Click to expand...

Thanks for the great replies!

The camper is a 1998 model, so I suspect it has the older setup you mentioned. There is a second black wire attached to the red positive battery cable, perhaps that's the charger connection?

I haven't been able to locate a disconnect switch anywhere so far, and unfortunately the previous owner didn't know of one either. The owner's manual is fairly generic and lists general information that applies to several models, but I'll take a closer look under the trailer and inside the cabinets.

The ground wire also connects to the breakaway switch on the A-Frame, if the switch was bad could it cause an issue like this ? I haven't tested it, (but probably should since it's 17 years old).

John From Detroit said:

The AUX post?  That does not sound like a circuit breaker,, how many terminals on this device?

Circuit breakrs have two posts,, Only two.. And you shoudl see the same voltage on both posts if not the breaker is either Tripped (manual reset) or Faulty.

However if it has FOUR wires.... Then it is the disconnect device and it is turned OFF. (or faulty)

Click to expand...

Only two posts, although I may be mistaken on the labeling of the second post. It's a short stop 12V30A, like this one: http://ecx.images-amazon.com/images/I/21Br%2B8qXwWL.jpg

The camper is a 1998 model, so I suspect it has the older setup you mentioned. There is a second black wire attached to the red positive battery cable, perhaps that's the charger connection?

Click to expand...

Could be. Is the converter/charger a Magnetec 63xx model, by any chance? That model has an internal relay that switches battery power on/off, so the battery is physically disconnected when shore power in present and the converter is working.

voodoozen said:

The ground wire also connects to the breakaway switch on the A-Frame, if the switch was bad could it cause an issue like this ?

Click to expand...

All the breakaway switch does is that when the trailer breaks away from the tow vehicle, the pin gets pulled out of the switch and the circuit is completed which sends 12 volt power to the trailer brakes stopping the trailer. The way to test it is to pull the pin and try pulling the trailer. The brakes should lock up. That switch will have nothing to do with your issue.

Well that Short Stop is a circuit breaker

If the battery side is 12 and hte other side is down around 1.. It's open. The circuit is broken,, Step one is to disconnect it for five minutes then re-connect it and see what happens.

Step 2, if same results,  Replace

NOTE: when you re-connect

First hook up battery wire, Measure voltages both side (Should be same) then hook up load side, again measure voltage  In fact take voltage measurement for a full minute from the instant you touch the wire to the post,,, THEN put the nut on.. IF it drops... You have a short.

THe 2nd wire is usually the emergency brake, and if the break-away switch is shorted, it can take the breaker out.. Or not.. Depnding on the breaker.

Gary RV Roamer said:

Could be. Is the converter/charger a Magnetec 63xx model, by any chance? That model has an internal relay that switches battery power on/off, so the battery is physically disconnected when shore power in present and the converter is working.

Click to expand...

It is, 6332! Looks like there's a single black relay on the right side, is that something easy to test and/or replace? I know next to nothing about relays, but I'm happy to learn.

Rene T said:

All the breakaway switch does is that when the trailer breaks away from the tow vehicle, the pin gets pulled out of the switch and the circuit is completed which sends 12 volt power to the trailer brakes stopping the trailer. The way to test it is to pull the pin and try pulling the trailer. The brakes should lock up. That switch will have nothing to do with your issue.

Click to expand...

Excellent news! One less thing to worry about this time.

John From Detroit said:

Well that Short Stop is a circuit breaker

If the battery side is 12 and hte other side is down around 1.. It's open. The circuit is broken,, Step one is to disconnect it for five minutes then re-connect it and see what happens.

Step 2, if same results,  Replace

NOTE: when you re-connect

First hook up battery wire, Measure voltages both side (Should be same) then hook up load side, again measure voltage  In fact take voltage measurement for a full minute from the instant you touch the wire to the post,,, THEN put the nut on.. IF it drops... You have a short.

THe 2nd wire is usually the emergency brake, and if the break-away switch is shorted, it can take the breaker out.. Or not.. Depnding on the breaker.

Click to expand...

Success! I need to be more patient with auto resetting c/b's. No drop in voltage after reattaching the wiring, I think we're on to something here.

Still 0V at the converter, but I do have power all the way back to the junction box at least.

The best thing you could do with a 6332 is replace it. It's a crappy charger, tough on batteries yet not especially fast or efficient. This site has some suggestions and info on Magneteks:
http://www.bestconverter.com/MagnetekParallax-63007300-Upgrade-Kit_c_64.html