12v symptoms I don't understand

Good luck. You may have to pull the fridge. See if you can locate the manual for your particular unit. The wiring diagram will help. What make and model is it?

By the way, my fridge comes off the circuit labelled "Front Lights". Go figure.

I just got off the phone with Northwood Mfg. They make Nash trailers among other things. The person I spoke with (I'm bad with names and can't remember his...) was very helpful and took a lot of time with me. So, he says there could be a fuse labeled "refer" or that the wire could run thru the "vent fan" fuse. I don't see a refer fuse and the vent fans both work so I'm still a bit confused about that wire comes from...

There is no fuse indicating "fridge" on the 12v dist panel in our 7355 power centre either. However, the "source" must be there, because the fridge works with no battery off the converter, or with no converter, it works off the battery.

It was posted that the fridge has its on circuit board fuse, so maybe that is why it doesn't have one on the dist panel?

So unless there is a shared fuse, not marked "also fridge" the fridge 12v wire must begin near the main lugs where both converter and battery wires meet. check the back of the positive battery wire lug on the DC dist panel. ISTR ours has two set screw holes that maybe one of them has an extra wire in it? Just guessing-- I haven't tried to find my fridge wire yet! :(

Now, why didn't that image show? Here's the url: http://flic.kr/p/gcet4v

I'm making progress!
I load tested the battery and check for 12v on either side of the "short stop" and then pulled the fuse panel and confirmed 12v going in on the main, then 12v going out from each fuse terminal. I then moved to the thermostat and confirmed 12v going in. I move the thermostat to the "on" position and expected to see 12v going out but got nothing. An examination of the thin wires in the thermostat control revealed an open wire (see pic). So, as a test, I grabbed a spare piece of wire and bypassed the thermostat and the furnace came on. Cool
Now to the fridge: I go out to the access panel and see a box that looks like the control panel, it has wires to a 12v and grnd connection. I pull these, test and find no 12v. I test from positive to grnd wire and also from positive to frame, no 12v. I test continuity between grnd wire and frame and find continuity. So, I THINK this means the 12v has no power to it but the grnd is ok. My current challenge is to trace the 12v wire back to source and all I've been able to do so far is see that it goes behind fridge. I don't see it at the fuse panel. There are no fuses labeled "fridge" and I can't for the life of me figure out where that wire comes from. I'm beginning to think I'll need to pull the fridge to look behind it but that doesn't sound at all fun. Any hints? I'll buy a vowel!
Milt

Harvard wrote:
The very instant in time that the wrench touches the frame kicks off a series of high frequency events. These high frequency events pack a tremondous amount of energy. At high frequency, all conductors become inductors (high impedance) and all capacitance becomes conductors (low impedance). The wire conductor from CHASSIS to BATT MINUS becomes the most significant inductor and allows the BATTERY to spike up to thousands of volts taking the +12 VDC wiring along for the ride. What this all means is during the arcing process there are AC voltages generated at amplitudes thousands of times the applied 12V battery. This high frequency activity may be too short in duration to blow fuses but pack a high enough voltage to blow Field Effect Transistors (FETs and MOSFETs). JMO.

Yes, which is why I'd start at a non-working device and see if it's getting 12v power. If it is, and it doesn't work, the device is broken and the focus needs to be on the fixing the broken device. It could be anything from a fuse to an active component as described above. OTOH, if the non-working devices are not getting power, the problem is in the 12v system, not the device and it's likely to be a bad ground, a blown fuse, a burnt out wire, etc.

The very instant in time that the wrench touches the frame kicks off a series of high frequency events. These high frequency events pack a tremondous amount of energy. At high frequency, all conductors become inductors (high impedance) and all capacitance becomes conductors (low impedance). The wire conductor from CHASSIS to BATT MINUS becomes the most significant inductor and allows the BATTERY to spike up to thousands of volts taking the +12 VDC wiring along for the ride. What this all means is during the arcing process there are AC voltages generated at amplitudes thousands of times the applied 12V battery. This high frequency activity may be too short in duration to blow fuses but pack a high enough voltage to blow Field Effect Transistors (FETs and MOSFETs). JMO.

I'm pretty sure that shore power was not connected.
I'm out of town today but will start my methodical work tomorrow and I'll report my progress (or lack thereof) and results back to the community here.
My wife and I used the trailer as a part time residence during my last two years of work and it was on shore power that entire time. I'm getting it ready for an extended road trip and that, of course, is when I cause myself problems.

scroller95969 wrote:
Wouldn't anything that was grounded to the frame have been briefly charged through the ground when the wrench touched the body?

If the shore power wasn't connected, the power flowed in a very limited area. If the shore power had been connected, it too would have received a direct short and a larger area would be affected.

My gut says that if the shore power was not connected, the battery has a problem or there is a ground wire problem. But anything can happen, hence the methodical search.

scroller95969 wrote:
Wouldn't anything that was grounded to the frame have been briefly charged through the ground when the wrench touched the body?

No. The current would have flowed from the battery positive through the wrench to the frame and through the frame to the point where the battery negative/ground was connected to the frame, then through the battery negative/ground back to the battery. Devices connected to the battery positive and to the frame or battery ground would see a drastic lowering of voltage, followed by a rapid rise, but it wouldn't have differed much from what they see when turned on/off with a switch.

Due to the high current, points along the path of the current through the frame and the ground cable would have briefly had a raised potential (voltage), but not higher than the battery positive terminal voltage. It's possible that the very high current through the frame sought out an unusual path through one or more wires connected to the frame. Corroded connections could have exacerbated the likelihood of that and resulted in damaged wiring or other odd problems. Clearly something happened and troubleshooting should tell us what (we're all curious).

I'm embarrassed to say that I've accidentally shorted batteries to the frame (briefly) also, but I've never seen any damage from it - just sparks and a little weld mark on the wrench to remind me to be more careful.