DC power question

[mikegascon1]

Thanks Bill. That was my exact plan. I am more curious of why the Fuse is blowing.

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[rickst29]

But this should not be difficult, because the battery pack(s) have "+12v" connections to only 1, 2 or at most 3 endpoints:

1. The Power Converter's "DC Distribution Fuse Board".
2. (Maybe) the two Trailer Brakes, via one wire into the breakaway switch.
3. The electric tongue jack (only if you have one).

In my own TM, the breakaway switch is wired into the 12v circuit from the Tow Vehicle cable's "trailer battery charge wire", which actually connects to the TM DC Distribution Board as a "downstream" wire. So mine doesn't directly connect to the battery, it can only reach the batteries through the First Link (the batteries to the main 12v fuse board).

If you have an electric tongue jack, it is probably given a wire all by itself. Following your "battery fuse", is that wire split into two segments? If so, both are suspect. If not, 12v battery power is reaching ground improperly in only 3 possible ways:

#1: Your main 12v wire, between the battery fuse and the DC distribution fuse board, is damaged. It touches the frame or shell on its way to the load center. The wire should probably be replaced anyway, I recommend buying a new segment of stranded wire (color red, size 8-AWG). The red color helps you to distinguish it from other wires, the bigger size reduces resistance if the batteries are being charged or discharged with high current.

#2: There is something wrong at the DC Distribution Fuse Board. Maybe the other "main" wire, coming from the Power Converter Main Board assembly, has a ground fault (damaged wire, or failed Main Board Assembly "MBA"). Or, the entire fuse board is failed and grounded.

#3: Or maybe, although less likely, your short circuit is "downstream" from an otherwise good DC Distribution Board. This is less likely because the "downstream" fuses are smaller, and should blow individually before the battery connection does.
- - -

To isolate, turn EVERYTHING off, using an electric battery lantern inside the TM for light (Or your wife can hold a flashlight). Be sure that the TM 120v power plug is also disconnected.

You do not need to insert a new battery fuse. Switch the voltmeter to test for "resistance" rather than voltage. Turn it on and set one probe on the DC Circuit Board "battery in" wire connector. Set the other probe end on the 120-VAC bus of BARE wires (This safety-grounding bus is connected to the TM frame, via the 12v "white wire" bus connectors). Because you have a short circuit, you should see non-infinite resistance on the meter.

With non-infinite resistance confirmed, remove the "battery in" wire from its connector. Re-test between the now disconnected fuse board connector and the 120-VAC safety-grounding lug.

If resistance is now infinity, the problem was the wire, and it must be replaced. Attach a new and long enough wire to the bare end, go back to the battery compartment, and pull the disconnected old wire until the new end has reached into the compartment. Throw away the old wire, and connect the new wire into your battery-side protection fuse. Back at the DC Distribution fuse Board, connect the other wire end (new wire) back into its "battery in" connection port.

Re-confirm infinite resistance, then insert your battery fuse. It should function without further difficulties.

If "resistance remained non-infinite" between the fuse board lug and the 120-VAC grounding bus, after disconnecting the battery wire, then the problem remains present on the fuse board itself. First check the other "main" input power connector, from the Power Converter. If you pull this fuse or disconnect it's wire, does resistance go back to infinity? If yes, then either the Power Converter MBA is blown, or the wire from the MBA into that power port has been scratched and shorted out. (You probably need a new Converter assembly "main board".)

If resistance stayed low AFTER pulling the Power Converter MBA connection fuse, start pulling all of the other downstream fuses (one by one), keeping track of the size for each slot. With each removal, re-check resistance. If resistance recovers to infinity after a particular removal, then the "guilty circuit" is downstream - and an immediate question is, why didn't that fuse blow first? NONE of the downstream fuses should be larger than 20A. Verify that resistance remains infinity while all of the other downstream fuses are put back in, leaving only the "guilty" party without a fuse.
- - -
In the extremely unlike even that resistance remains non-infinity with ALL "downstream" fuses removed, and with the power converter fuse removed as well, stop and post back - you need at least a new fuse board, and might consider replacing the whole load center at once.
- - -
Short circuit in individual downstream circuits are well covered by other posts ("search" is your friend to find them). The most likely of these involve a failed connector behind the fridge, disabling overhead lights and possibly shorted out against the aluminum skin "floor". But, in order of likelihood, you are most likely to find (1) a bad battery wire to the fuse board; (2) a bad Converter; (3) a failed "downstream" 12v circuit; and then (4) a failed board.

[mikegascon1]

Thanks Rick. Very helpful. Do I need to remove the bathtub to get to the DC Distribution Fuse Board?

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[mikegascon1]

I found the distribution panel.
I connect my meter to neg and then I touch the POS wires and the resistance is zero, when I tough the POS, it jumps to approx 12 and then back to zero. I replicated this over and over. I just don't know why it jumps at first. This tells me u need to replace the wire running to the battery correct?

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[rickst29]

Zero voltage difference is a result of low resistance between the two test points. The "jumping" implies an intermittent short circuit along the wire.
You may have already figured this out, but those wires come into the WFCO panel from behind. You can remove the screws which mount the WFCO load center to the wall and pull it out a couple of inches, that gives you access to all the wires behind the WFCO.

I don't know the 3124 battery compartment in great detail, but might find that the old wire "shorted out" by being scratched against the sharp edges of a metal access hole. If so: Increase the size of that hole and fit a rubber grommet to prevent future scratching.
The WFCO DC Distribution Circuit Board terminals, IIRC, will not accept a wire size bigger than 8-AWG, and ATC fuses are generally not available in size greater than 40A (which matches 8-AWG). With Lead-Acid batteries, there is not a significant advantage in increasing the wire size above a single AWG-8 wire into one of the terminals, for two reasons:

#1: For Lead-Acid batteries located in the rear battery compartment, the distance is fairly short. The original WFCO charger doesn't create high current while charging lead-acid batteries, because the internal resistance of FLA/SLA/GEL/AGM batteries is fairly high.

#2: The WFCO charger is also inclined to use low levels of charging voltage, unless excess loads draw the overall voltage down pretty far. Even then, it will not maintain "boost" voltage for very long.

If you were to have LFP batteries and a better DC Charger "main board assembly" (as I do), then would want to use a pair of 3-way or 5-way DC power distribution blocks (one positive and one negative) behind the WFCO. Each would connect

1. the small wire (12-VDC or DC Ground output) from the DC Charger Board;
2. An 8-AWG wire for either a DC grounding Block or the +12V DC Distribution Board;
3. A fatter cable (AWG-6 or even larger) back to the batteries.

In my own case, I have AWG-6 going out to LFP batteries, and a 5-way "grounding block" interconnects both of the original TM bus bars. A 3-way looks like this: https://www.amazon.com/Distribution-...dp/B09MS6S3NR/

[Bill]

Just a couple totally random points.

Zero voltage difference is a result of low resistance between the two test points. The "jumping" implies an intermittent short circuit along the wire.

Sometimes true, but not always. When you put an ohmmeter on a test point, and it jumps up and then settles back, this can also mean that there is a big capacitor connected to that test point. An ohmmeter doesn't actually measure ohms directly. Instead, it works by putting a voltage across the probes, and measuring the current that flows when you connect the probes to something. Ohm's law says that Resistance = Voltage divided by Current (R=V/I), so the meter measures the current, and the scale is conveniently printed directly in ohms to save you the trouble of calculating. That's why the Ohms scale reads backward - more current means less resistance.

So why does the needle jump? When you put a voltage across a capacitor, the cap accepts current as it charges up. Once charged, the current stops. A small capacitor charges so fast that you don't even see the quick current flow. But a large capacitor charges relatively slowly, and the charge current lasts long enough for the meter to register it. And big electrolytic capacitors are exactly what the converter uses to smooth out the 12-volt DC power that it generates. Bottom line - if you put an ohmmeter on the output of a DC power supply, you would expect to see the needle jump up and settle back.

... (you) might find that the old wire "shorted out" by being scratched against the sharp edges of a metal access hole.

Does this TM have a replacement toilet? The wires from the battery are routed under the aluminum floor skin, directly in front of the toilet. If the toilet was replaced, it is at least possible that the skin in that area was cut, and the abrasion/short you describe was the result.

Bill

[Wavery]

Originally Posted by Bill

Does this TM have a replacement toilet? The wires from the battery are routed under the aluminum floor skin, directly in front of the toilet. If the toilet was replaced, it is at least possible that the skin in that area was cut, and the abrasion/short you describe was the result.

Bill

Thanks for posting this Bill........ I am currently developing a plan for building a custom black water tank and one of the alternatives that I am exploring involves cutting the upper layer of the floor (and removing the Styrofoam core) 20"x20" directly under the toilet.

Do you happen to know the distance from the outer wall that those wires are run?

[ShrimpBurrito]

I don't know this measurement off hand, but you can see the tunnel in the bottom left of the cabinet under the kitchen sink. You may have to unscrew a thin odd-shaped box-like cover the factory made to hide it.

You can see the other end of the tunnel if you simply slide out the converter.

Dave

[Wavery]

Originally Posted by ShrimpBurrito

I don't know this measurement off hand, but you can see the tunnel in the bottom left of the cabinet under the kitchen sink. You may have to unscrew a thin odd-shaped box-like cover the factory made to hide it.

You can see the other end of the tunnel if you simply slide out the converter.

Dave

Thanks Dave. I'll check that out before proceeding.

[mikegascon1]

The trailer in question has a stock toilet.
I am waiting for the weather to dry out before proceeding with my wire replacement. The battery is located at the front of the trailer. It sounds like 8 gauge wire is what I will replace it with.
Thanks again. I will post my findings, and hopefully my fix when I get back to it.

2007 3124
Vancouver, WA (close to Portland, OR)