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Old 05-13-2017, 06:31 PM   #1
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Electrical Gremlins

During our current moho trip, we have experienced some weird electrical issues, and I am wondering if anyone has had a similar experience and/or can provide some guidance.

One of the 12V circuits powers the shower light, two ceiling lights and the fantastic fan in the rear bedroom. The circuit works fine when the moho is cool, but when it heats up (i.e., during a sunny day or when shower/hairdrying occurs), the fuse blows. When the fuse blows, it does so immediately - I have a short somewhere. This continues until the moho cools (in the evening), at which point the fuse/circuit is fine.

I have taken down the lights and fan shrouds, but don't see any obvious evidence of a short. I am kind of at a loss as to where to look for an intermittent heat-related short - not even sure how the wires are routed. Any guidance will be appreciated before I start taking the ceiling down when I get home.

Thanks for your help.

Dave
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Old 05-13-2017, 06:37 PM   #2
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Some hair dryers draw a tremendous amount of juice. Hot days when people are running the AC, drying hair, making coffee in an electric pot, etc it can easily over load the system. Also double check that you are using the correct sized fuse. Do not use a fuse higher rated than what is specified.
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Old 05-13-2017, 06:39 PM   #3
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I don't think its related to the hairdryer - which is on a different circuit. Anyway, the problem (blowing fuse) happens for hours after the hairdryer is off.
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Old 05-13-2017, 07:11 PM   #4
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I would start by disconnecting the items you mentioned for the day. If the fuse doesn't blow during the day you've at least narrowed it down. Then reconnect 1 item and try again. Process of elimination. We found a short in our trailer by doing this, which ended up being an added non factory item.
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Old 05-14-2017, 07:57 AM   #5
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That's an odd one no doubt. I'm with cliffcharb on how to proceed. It sounds like it may be a device problem rather than a wiring problem.....i.e. light fixture, fan, switch, etc..

Sure would be a easier to track down and repair if that's the case. My money is on a device rather than internal wiring.

Wondering here, does your Fantastic Fan have a thermostat control built in? That could explain the ambient temp relationship.
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Old 05-14-2017, 08:57 AM   #6
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lets get a few term defined before we go much further.

There is no connection between a 120 volt ac hair dryer and the 12 volt dc system in your rig. I doubt you have any fuses in the system but rather circuit breakers. Are you physical or is replacing a fuse or is the circuit breaker resetting as it cools down? Is anything turned on in the circuit in question when this happens or do you just realize the circuit is dead when you attempt to turn something in that circuit on?

I had a similar problem in that one of the 12 volt circuits in my trailer would trip the breaker and reset itself so quickly that the lights would flash on and off every few seconds. While I have never found the short the problem stopped after I moved the 12 volt wiring passing by the air conditioner in the ceiling. i was looking for a nicked wire in that bundle of wires but never found anything.
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Old 05-14-2017, 08:59 AM   #7
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Yeah, its weird for sure. The fantastic fan does have a thermostat control, but the problems (fuse blowing) happen when the fan is off. Happens even when everything is off. Doesn't that point to an internal wiring problem?

Dave
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Old 05-14-2017, 09:21 AM   #8
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HowieE:

Thanks for your response.

With regard to fuses, yes, I actually have fuses. This is a classic motorhome, not a new trailer. There are two electrical systems; I have 12VDC fuses (actual, physical fuses that need to be replaced when they blow) and AC circuit breakers (that trip and can be reset when overloaded).

It doesn't seem to matter whether anything is on or not - had the fuse blow with everything off, and just now it blew when a couple lights were on (after they were on for about 2 hours).

Dave
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Old 05-14-2017, 09:41 AM   #9
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Quote:
Originally Posted by dspaw View Post
Yeah, its weird for sure. The fantastic fan does have a thermostat control, but the problems (fuse blowing) happen when the fan is off. Happens even when everything is off. Doesn't that point to an internal wiring problem?



Dave

Not necessarily. That's why it's best to disconnect the items from the circuit. Could also be an overload situation.
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Old 05-14-2017, 09:42 AM   #10
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HowieE:

Thanks for your response.

With regard to fuses, yes, I actually have fuses. This is a classic motorhome, not a new trailer. There are two electrical systems; I have 12VDC fuses (actual, physical fuses that need to be replaced when they blow) and AC circuit breakers (that trip and can be reset when overloaded).

It doesn't seem to matter whether anything is on or not - had the fuse blow with everything off, and just now it blew when a couple lights were on (after they were on for about 2 hours).

Dave
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Old 05-14-2017, 09:43 AM   #11
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Cliffcharb:

I am obviously no electrical expert, but can you have an overload situation (without a short) if everything is turned off on the circuit?

Dave
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Old 05-14-2017, 09:49 AM   #12
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Originally Posted by dspaw View Post
Yeah, its weird for sure. The fantastic fan does have a thermostat control, but the problems (fuse blowing) happen when the fan is off. Happens even when everything is off. Doesn't that point to an internal wiring problem?

Dave
Right, but if the fan is off and the thermostat calls for the fan to start, the problem may blow the fuse before the fan even starts. I'm trying to make the relationship between heat (ambient temp) and the fuse blowing. Obviously the hairdryer is on the AC circuit and not on the 12volt, BUT it's blowing HOT AIR. So that's my path of thinking. Does the hair dryer get used anywhere near your Fantastic Fan for instance? Which would raise the ambient temp at the Fan and possibly activate the thermostat control. It sounds like there is a relationship between ambient air temp and the problem.......just trying to think that through.
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Old 05-14-2017, 09:52 AM   #13
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Try turning your Fan thermostat off (all the way to one side) so you take the thermostat out of the equation, at least you would iliminate it from the possibilities.

I also have fuses in my 82 310TD, we get to replace rather than just switching a breaker on or off.
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Old 05-14-2017, 09:55 AM   #14
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Mayco:

Thanks for these comments. The hairdryer is not really close to the fantastic fan. I appreciate your thoughts on the thermostat control. I will investigate this possible relationship to the fuse blowing.

Dave
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Old 05-14-2017, 10:01 AM   #15
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Total guess on my part but before you start digging into the internal wiring its a lot easier to look at all the simple possibilities first. With the electrical systems on our old beasts, Ive learned the hard way to check the easiest things first before you dig deeper. Been there done that too many times. Good luck, you'll find it, hope it's easy!!!!!!
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Old 05-14-2017, 10:05 AM   #16
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OK fuses and appears to be a temperature sensitive problem. That would suggest a short resulting from something expanding to cause a change is physical relationship.

You might try forcing the issue by turning on the over and engine heater on a cooler day and seeing if that cause the failure. Neither the stove or engine heater would have anything electrical to do with the 12 volt circuits.

If that works you can stat removing items from the far end of the circuit on the fuse in question and repeat the test. If you have removed an item and can not repeat the test failure you will know the problem is beyond the point of last removal. A time consuming test but shorts are not easy.
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Old 05-14-2017, 12:06 PM   #17
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You already know what is on the fuse so the problem has to be the wiring or a device on that circuit.
Could be a short from a screw pinching a wire this could be related to heat also a pinched wire between say the frame of the fan and the skin or the RV.

I would approach it as a device problem first could be any of the lights or the Fantastic fan so you will have to disconnect the hot wire in each of them one at a time until you figure out what is causing the problem. If you are good with a digital meter you could test each device hot wire for resistance to ground should be 0 ohms. If you don't find a problem with a device then you have to troubleshoot the wiring.
Intermittent fuse blowing is a real PITB and takes a lot of patience.

Good luck and let us know what you find.
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Old 05-14-2017, 02:34 PM   #18
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You could measure the actual DC current with a clamp on meter like:
http://www.ebay.com/itm/182531057849
With that you can watch the current as you try turning things on and off.

Or install something like this:
http://www.ebay.com/itm/112350626061
This meter has to be installed in the wiring. If you do a permanent
installation it is useful to keeping an eye on your batteries and charging
systems. This is also much cheaper.

Pete.
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Old 05-15-2017, 03:55 AM   #19
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Pete: Those are some interesting meters - I will have to investigate them further (I didn't know you could get a DC clamp on meter).

I thank everyone for their help, and will report back when I discover the cause and solution of the problem.

Dave
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Old 05-15-2017, 05:50 AM   #20
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Pete: Those are some interesting meters - I will have to investigate them further (I didn't know you could get a DC clamp on meter).

I thank everyone for their help, and will report back when I discover the cause and solution of the problem.

Dave
Dave,

I have one of these DC Clamp on Meters. I haven't used it a lot but it seems to be fairly accurate considering the price and the reviews were favorable.

Brad
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