oakback
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Post by oakback on Feb 7, 2019 8:40:48 GMT -8
I'm building my camper, so there was no previous fan, everything is new. So the wiring hasn't been tested in any way, until we installed our new fan. We haven't camped in it yet (build still in progress), but the fan is installed permanently. We tested it a few times, and it worked (4 speed settings, on/off function), then discovered the fuse was blown the 2nd time we tried to turn it on. I wasn't sure what caused it, put a new fuse in, and it worked fine. Next time we tried to use it, the fuse was blown.
Before I start ripping wires out of walls, what usually causes this? I need some direction to start diagnosing.
The wiring for the fan is on its own circuit from the converter. 12v power from the converter, and a ground from the fan to a bus bar (shared with all other 12v circuits, and the converter), which is grounded to the frame. The fuse is 20A. The wire is 12AWG stranded. The shore power is a regular outlet on our house, we don't use anything in the camper except lighting while working on it. The house outlet breaker has not been thrown. There is no battery in the system.
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kudzu
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Post by kudzu on Feb 7, 2019 10:51:59 GMT -8
If you are saying it blows the fuse when it is turned off, you just about have to have a short to ground somewhere. Something is putting to big a load on the fuse.
If it is breaker instead of a fuse, it could be that it needs replacing. I have seen those fail.
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oakback
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Post by oakback on Feb 7, 2019 11:19:33 GMT -8
I'm not sure if the fuse is actually blowing while it's turned off. I understand it better now, so I'll start by checking continuity with either side of the fuse...receptacle? Whatever it's called, where the fuse plugs in. If main power is on, and fan is off, I should see no continuity. If I see continuity, then there's a short. Do I have that right?
If no continuity (no short), then there's something wrong with the fan itself.
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kudzu
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Post by kudzu on Feb 7, 2019 16:43:03 GMT -8
Well it there was a permanent short, it would blow the fuse as soon as you put it in. I suggest you approach it one step at a time.
Disconnect the fan and leave it and see what happens. if it blows, you know there is a problem in the wiring.
If not then connect the fan, leave it off and see if blows a fuse.
If nothing try leaving the fan running and see if that cause it to blow.
You need to know what is causing it and since you can't inspect the wiring easily this is how I would go about it.
Just approach it logically, do one step at a time. Eliminate one and then move to another. If you do two things at once you never know which one was the problem.
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Post by vikx on Feb 7, 2019 22:11:44 GMT -8
I've never installed a MaxxFan, but Fantastic Fans have a built in fuse, about 5 amps? I run my fan on a 10 amp circuit with a few lights on the same circuit. If your circuit is 20 amps, did the Maxxfan call for that high of amperage? Does it have it's own fuse?
If the fuse is blowing, you've got a short. As said above, try the fan both on and off. I know that a wayward screw can easily cause this (yup my bad), even a tiny copper "hair" of misplaced wire.
I suspect the above rather than the fan, but it's possible. Take your time.
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oakback
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Post by oakback on Feb 11, 2019 17:21:35 GMT -8
It blew with power on, and fan unplugged. Ugh, not looking forward to this next part.
There's no way for me to inspect 90% of the wiring to the fan. I may just run new wiring, pulling it through with the parts I have access to. I dunno, we'll see what I can do.
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aslmx
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Post by aslmx on Feb 11, 2019 18:49:42 GMT -8
It blew with power on, and fan unplugged. Ugh, not looking forward to this next part. There's no way for me to inspect 90% of the wiring to the fan. I may just run new wiring, pulling it through with the parts I have access to. I dunno, we'll see what I can do. Are you reading a short between hot and ground? If not, I’d check the hot to the actual metal in the trailer. If the hot is shorted to the metal and the ground is not then I would swap the wires and use the around for the hot and the hot for the ground.
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oakback
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Post by oakback on Feb 12, 2019 11:15:42 GMT -8
It's possible hot and ground are shorted together with a staple. I had to staple the wires to the walls. I was very careful, but it's possible.
It's also possible a screw from the vent fan mounting flange hit a wire and ground to the skin. The skin is not intentionally grounded to the frame, but I believe it contacts the frame somewhere. Not sure if that matters for this.
Aside from the fan mounting flange, I can't recall any metal anywhere near the wires. I'll take a closer look at our cabinet installation and compare to reference pics of the build to see if there are any candidates for grounding with those screws.
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nccamper
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1962 Forester- 1956 Shasta
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Post by nccamper on Feb 12, 2019 12:21:25 GMT -8
It's possible hot and ground are shorted together with a staple. I had to staple the wires to the walls. The previous owner of the Shasta I'm working on couldn't figure out why the lights kept tripping the breaker so he threw away the lights and cut all the lines off at the walls. He then bought ridiculously small AAA battery lights. This is what I found when the skin came off:
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oakback
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Post by oakback on Feb 13, 2019 7:18:20 GMT -8
Disconnect the fan and leave it and see what happens. if it blows, you know there is a problem in the wiring. It blew on this step. I still have an unfinished opening in the wall right by where the wires pass. It's an opening for a slide-out window unit a/c. I identified which wires were for the fan (there are several in one run) by using my DMM probes and stabbing the wires while the lights were on (the other wires there). Positive voltage for the lights, zero for the fan. I cut the fan wires, then tested for continuity between pos and neg on the top half, which runs up to the ceiling and over to the fan (which was disconnected). No continuity. Connect the pos and neg wires at the fan, and there was continuity, so I knew I was at least testing it right. I tested continuity between pos and neg for the lower portion of the wires (that run from the a/c cutout to the converter) with the fuse removed, and there was continuity. I interpreted this as a short between pos and neg wires, somewhere between the a/c cutout to the converter, inside the wall where I have no access. So my current plan is to run a fishtape down to the converter location, attach a new pair of wires, and pull them through the wall to the a/c cutout, then reattach to the preexisting fan wires that run up and over. There are no horizontal supports blocking this path. I shoved the fishtape down there last night, but didn't have time to do the rest. This evening I'll have results.
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oakback
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Post by oakback on Feb 13, 2019 15:45:10 GMT -8
That went well, works great so far. Cycled everything on and off, all speeds, etc., no problems. Thanks for all the help!
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