BAC Forum
General Boards => General Discussion => Topic started by: Jim Shunkwiler on August 19, 2013, 03:17:38 AM
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Looking for any thoughts as to why my low voltage fuse box would melt down and catch fire. We had just disconnected shore power and using generator power. I just finished hooking up the toad. I entered the coach and smoke detector was going off. I saw the smoke and found the source when I opened the bathroom door. The coach filled with smoke but I was able stop the burning by turning off low voltage in battery compartment and shutting down the generator. I have since taken the two power wires off the damaged fuse box and taped them together. I'm able to use generator so I have AC but no lights. It appears to be the wire harness labeled HOD Data that started the problem. I also need help finding a replacement board. I'm hoping the circuit board just failed and i don't have another problem. How do i know? Thanks for any feed back you can supply.
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Jim,
What year and model coach do you have?
Gerald
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2006 Beaver Monterey
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Jim,
I personally have very little experience with the multiplex wiring on your model coach, but normally a failure like the one you experienced is caused by a poor connection that causes high resistance when you are under a high amperage draw. You may contact Ken Carpenter at BCS (Beaver Coach Sales) for more insight into the problem.
As for the parts to make the repairs, BCS or Northwest RV Supply in Eugene Oregon will probably have the parts.
Gerald
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Jim,
Is this just a fuse board or are there electrical components on it also? Were electrical components on the board the source of any heat? Is it possible to take a photo or two and post them, at least one of them being a close up of where the burning started. Usually that is what appears to be the darkest spot. A close examination to see if something on the board moved, shorted, and caused the issue. Sometimes you can get sufficient heating with current flow when a connection point is loose. This seems like a more severe situation of over current than that. If components like resistors and ICs are on the board they can internally short out and become a heat source.
The other thing to look at is the HOD wire (I do not know its function), does it connect through a fuse on the board or is it a sense or supply wire with no fuse at its connection point. That wire could be shorted elsewhere and if there is no fusing at the board for this wire it could be the problem, pulling an overcurrent condition from the board. If it is fused, was the fuse the right size?
Assuming the problem is the HOD wire. If you get a new board and start on repairs, the function and normal current draw of the HOD wire needs to be understood. Maybe Monaco or BCS can help provide some info for this wire and if they have seen this problem before. If it is a design issue you are probably not the first.
In the repair I would add a fuse holder and appropriate fuse to that wire. If the new HOD fuse did not blow I would put a DC amp meter in series with it or a clamp on DC amp meter and get some measurements. If this wire was the source of the issue and not something on the board then tell whoever does the repair that you want this HOD line fused properly and the current measured as part of the repair.
As far as running on the genset that should not have had an influence given that supplies AC. It does power up the DC charging system but you had no indications that was an issue. As far as just hitching up the toad, that uses DC but source is usually comes out of the chassis side of the DC wiring and this seems like a house DC fuse box issue. Hope this helps in some way....
Later Ed
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As Ed mentions, a photo would be helpful, Jim. I have a 2006 Monterey too, and wiring diagrams, but I'm not sure which box you are referring to, since there is more than one 12 volt box in that cabinet. I also don't see anything labeled HOD, though it could stand for high output data, who knows, my deciphering skills are limited. For the benefit of Ed or others that may be able to help, see attached. Jim, I can email you better images if you'd like.
Nevertheless, just replacing it may be not enough; whatever created the short circuit needs to be sleuthed, as well as why the fuse system failed. Ed's suggestions have great merit. There are three 30 amp 10 gauge feeds into that cabinet, one each to the two multiplex dimmer modules and one to the 12 place fuse block, one 10 amp fuse of which I think feeds the multiplex control and its data flow between multiplex switch plates and the dimmer modules. There are so many fuses, and the 30 amp breakers, protecting this cabinet's components, it's hard to see why something didn't blow before fire threatened.
Joel
(click on the photos for larger versions)
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You guys are awesome. Thanks for the support. I have pictures but can't figure out how to get them on here. I have more problems then china has rice.
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Jim,
On Forum, click on General Discussion. 3rd "sticky" is instructions on resizing and posting pictures on forum.
Steve
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Thank you
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Worst case scenario, besides too much rice, I'll post a picture of my House breaker/fuse cabinet, and you just point out which box fried, Jim.
Joel
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The damaged fuse box is located in bottom left corner of the big fuse box in the bathroom. The upper left corner has two wires in the same wire harness. They are labeled MOD DATA or HOD DATA. The seem to be what got the hottest. The lower left corner of the circuit board burned the most. One wire is black stripped the other is yellow with brown strip. Hope this helps.
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I'll try to remember to check the cabinet tomorrow, as what you describe has me scratching my head - can't picture a "big fuse box". Perhaps I'm totally forgetting one. Aside from the obvious 10 amp fuses in the two multiplex modules, the only others are in the flush mounted little black one with a snap off cover. The other two boxes are the standard 50 amp Main and the 30 amp inverter breaker boxes.
MOD could refer to Multiplex Output Data, or be a tag for output module dimmer, but that's a wild guess. Obviously, determining what it is will help clue you to what circuit and devices are involved or at fault.
Joel
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Joel your description is correct. I'm talking about the House breaker/ fuse cabinet in the bathroom. The very bottom left corner. The two boxes at the bottom look the same.
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On the diagrams I attached previously, the second image, your culprit is the connection at J2 of Module A (10 CHANNEL OUTPUT MODULE DIMMER A), Jim. Intellitiec manufactures these Multiplex Output Data (MOD) modules, and it sounds like you'll need a new one. J2 on both modules A and B have only a white-striped brown and a red-striped yellow wire, tagged "MOD Data"; they are + and - data wires from the multiplex control, regardless, which splice to each multiplex switch throughout the coach.
As I understand Multiplex, and that's not very clearly, lighting is digitally managed - data sent to the controller on the above mentioned wires changes depending on how long a switch button is held, etc., and the two modules adjust dimming power to their respective lamps accordingly. The odd men out here are the two ceiling fans and the water pump, but they are on Module B. I would think the data circuit itself would use minimal amps, as opposed to the 10 amp lighting circuits they control, so it befuddles me (easily done) why your J2 connection would overheat. The multiplex controller itself I think is the "IPX CONTROL" in the diagram, and you can see it has its own red 10 amp fuse, which may be the one in position 9 on the inset 12v. house fuse block. Ed or Steve may understand this circuitry better, and can infer more from the diagrams and what you and I have written.
Before installing a new module A, I'd sure find out what caused the meltdown and why that controller fuse didn't blow to protect the data circuit. Did any of the switches get wet somehow? I know if I was anywhere near Bend I'd get in to have things analyzed by knowledgeable techs.
-Joel
click on the photo to enlarge it.
J2 is the white connector, nearest the fire extinguisher, on the circuitboard of Module A; they splice to the control, Com + and -, with the red wire supplying backlight power to the switches
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Thanks so much for the help. Another interesting result after the incident is all the light switches are lit up and stay on.I wish I was near Bend but I'm in Houston and will be taking coach to local shop Monday. Do you think water in the the battery compartment could've caused this problem.
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Joel do you think water in the battery compartment could've caused my problem?
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I wouldn't think water in your battery compartment to have caused this specific issue. Is the green lamp still on at the bottom left of the Multiplex Control Master? Or is it red for "Fault".
I'm no electrician but I'd consider pinching the sides of the 2 white connectors on the Multiplex Control Master and removing them. I would expect this to turn off your switch backlights that are stuck on, and may protect anything in the Multiplex system yet in jeopardy. Taking the cover off the black inset House Fuse Box and pulling the fuse to the Multiplex Control Master is also an option; I think that is fuse number 9, Multiplex CPU.
Of course if you haven't already lost some or all of your 12 volt lighting from either or both A and B dimmer modules, this will disable them. The fans may still be operative via their on-board switches, I'm not sure, but unfortunately the water pump likely won't come on if Module B is out of commission.
As Ed suggested, a call to BCS in Bend may glean experienced input regarding Multiplex and maybe insight into the overheated J2 connector with no blown fuses.
Be sure to print copies of the diagrams for your service tech. When the cause is determined next week, please advise us.
Joel
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My multiplex control is completely burned and melted. I could email you pictures but I've been unable to post them from my iPad. So the fact that my backlights are on and there is no control unit hooked up tell you anything.
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I thought the damage was just to the connector and board at module A. The CPU master control (IPX on the diagram) is fried too?
The schematic and CPU box markings indicate the red/white stripe wire from the 3-wire white connector supplies power to the switch backlights. Disconnecting it and/or yanking the CPU fuse should shut down the backlights.
Joel
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The upper left corner of the controller module A with a 2 wire connector was burned the most. It appears those two wires caused module A to melt then burn. It's just module A that's toast.
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Jim,
That multiplex controller contains a lot of electrical components and by design it should have probably had better protection for some circuitry breakdown that has occurred. Evidently it was not adequately engineered to be fuse protected for the internal short that was created. Water in the battery compartment (we are not talking under water here) should be of no issue. You have not had a low voltage situation that has affected multiple electronics in the coach and no alarms for your charging system I assume from what you have said.
I would try and read who the manufacturer is from the good board. If they are in business I would call them and tell them you have had a board burn up that luckily did not result in a fire. I would ask if they have seen the problem, and if there is a redesign? Say that you would like to find a source for a new unit and do they have a recommended source with the redesigned parts. If there is no redesign then ask if they would like your board for failure analysis given it could have burned down your coach. Monaco or BCS may have parts but you may learn more if the manufacturer is available and willing to work with you. It is not unheard of for a concerned manufacturer to provide you with a new one to get yours back if a possible fire was involved.
I did not see how badly this unit burned and if you feel there was a real danger of fire, it sounds like maybe it was. One option to consider is getting an aluminum box bent up that would contain these Multiplex units with some kind of open metal grill cover for heat dissipation and a cut out for the wire plug entries. From what I can tell in Joel's photos that would be an option to provide better protection from fire. That is sometimes done with electrical components that handle power and produce heat like these units. This does not have to be done as part of this repair and getting the lighting back on line, just something to consider a bit later for piece of mind.
I would also ask if anyone else on the forum has had a multiplex unit "smoke" to please let us know. If this is a completely isolated incident then you may feel better about it, if this has happened before then I would be wary, even once is too much when it comes to a possible fire.
Later Ed
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Jim,
I just read your latest post and it may have been a loose plug in connector creating the heat. Again only you can see the burn origin and result. If it was a connector then I would replace that along with the board.
Later Ed
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Ok thank you sir for your help.
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I just tried posting a photo here off my iPad and it worked fine, Jim. In fact it was easier than using my PC. The only problem is images taken with the iPad itself, especially from poorly lit subjects, are not very highly resolved.
The reason you may not successfully post here is that it won't work if there isn't already some text in the message field. Many people don't realize that. Plus, you must use the "More Post Options" in Quick Reply, or you can't add pix. Otherwise just use the field associated with the "newreply" button.
Add text in the message field, then click Choose File, then either "Choose Existing" or "Take Photo or Video".
From "Choose Existing" click the album and then the photo you want to post, then click "Attach (and add more)".
Or from "Take Photo or Video" take an iPad photo and hit "use" at the bottom; then click "Attach (and add more)".
The iPad-taken photos probably have low enough resolution as to not exceed the 1MB size limit for posting here. Other camera produced images need to be resized smaller as per Steve's post here, or the system won't accept them. The simplest way I use regularly, on a PC anyway, is to open a photo in the Paint program. Choose the "Image" menu tab and then "Stretch/Skew", change both size parameters from 100 down to about 25-30 percent, then save the result. That image should be sized well within the website's guidelines.
Joel
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My choose file Doesn't allow me to select it even with txt in Message area. I'll have to figure something else out. Must be my iPad 1.
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Thanks so much for the help. Another interesting result after the incident is all the light switches are lit up and stay on.I wish I was near Bend but I'm in Houston and will be taking coach to local shop Monday. Do you think water in the the battery compartment could've caused this problem.
Hopefully no to the RV Shack in Livingston! If so, be careful, very careful ... see my cooling unit posting of earlier today for details ... as these folks IMHO are competant to work on travel trailers (maybe) but NOT high end coaches.