12 Volt Electrical Problem

[Mel n Melody Finnell]

We have a 2008 Beaver Patriot Thunder, plugged into 50 Amp shore power.  Last week the 12V house lights and multiplex switches stopped working.  (This includes lights, Aqua hot, toilet, slides, leveling system, thermostat, ...; everything from the 12 V power supply.)  We pulled out the house batteries and tested them, checked all the fuses in the bedroom closet and engine compartment, and checked the inverter.  We replaced the battery cut-off switch by the front steps.  We traced power to the fuse box in the engine compartment containing the solenoids.  We found the copper bar from the batteries to the Big Boy Solenoid was melted in two, not allowing current to pass to the solenoids and beyond.  We tried to bypass this break until we could determine what caused the short and have the copper bar repaired.  After turning off both master battery switches in the battery compartment, we hooked up jumper cables from the house battery in-line to the large posts on the right side of the Big Boy solenoid.  Then turned the master battery switches back on.  That put power to the other two solenoids and everything came back on for about a minute.  (Lights, compressor, etc.)  Unfortunately, when we started testing  things with the volt meter it stopped working again.  We immediately disconnected the jumper cables and turned off the batteries.  We rechecked fuses and did not find any blown fuses in either compartment.  We tried the jumper cables again and nothing comes on.  Using the volt meter we traced  power to the other two solenoids.  We are concerned about reinstalling the copper plate until we know where the short or bad ground is.  We are in an area that does not have any qualified technicians.  We cannot start the coach, level the coach or pull in the slides to try to take it someplace for repairs.  Navistar technical support is unable to assist us over the phone because we are not qualified technicians.  We would appreciate any assistance or comments regarding further testing. We are expecting snow and colder weather and could really use the Aqua Hot right now.

[Edward Buker]

This is a way to get temporary heat if you must and some space heaters will not be sufficient. It would seem that the most critical issue is to get some heat on in the coach.

If you go to the Aqua Hot there should be a main fuse and I suspect a large red wire that is the main power feed at a screw type terminal block. I think it had a 20 amp fuse at the block. You could buy some 10 guage wire and run a temporary plus lead from the battery bank to that termnal block input and screw it in place. Pull the normal coach feed wire (I think red wire feed) and tape it off. The 12V feed will be the largest gauge 12V wire with the largest spade fuse of the set. You need to have a fuse as part of that temporay wire circuit at the battery end. Automotive supply places will have a small rubber enclosed spade type inline fuseholder with a pigtail that you can use crimp connectors on as well as a source for the wire.

There is a terminal strip that the thermostats tie into. Each zone has a terminal and if you ground the terminal to common ground (coach frame, aquahot metal) that leads to the thermostat manually the zone should be enabled. You could manually do this with a switch and several wires run into the coach through a window or the door. Not elegant but you will not freeze. This may be outside of your comfort zone wiring wise but it is possible if this becones an emergency.

My coach does not have a big boy system so I am not going to involve that in this discussion. When you talk about the copper bar I cannot picture it and perhaps a photograph is in order of what burned up. Usually there is a metal strip fuse that is a failsafe for high current so you do not burn up the wiring and that may be what you are refering to. I will assume that is what is now open and you have no power to the coach side of that fuse. If you are familiar with an ohmeter you can place one lead on the coach side of the fuse or the open copper buss and ground and see what the value is. Pull all the fuses and turn off all the house breakers for 12V dc. You are looking for near zero ohms and a short to ground causing this problem. What you need to do is trace the large wires from that fuse/buss through the main switch and beyond. If a solenoid is in series with the coach you are now testing up to the solenoid and if that is fine then you will move to the output side of the solenoid and test to ground. You can test each leg of a single circuit by turning on one breaker or putting in one fuse at a time and see what the ohmmeter indicates while tied to the common feed 12V wiring harness. It is unlikely that any single small circuit is causing this problem. It is likely that one of the large feed wires is shorting somewhere to ground. Look for some arc marks or melted covering along the large wires. I think the chassis side of things and starting the coach should be working seperately from the house side of things. Usually the house and chassis battery sources are fused seperately with large metal strip fuses. I am a little puzzled that everthing is dead. There is some chance that this could be caused by a loose connection or crimp in the large wiring so wiggle and pull a little on those bigger lugs as you go along checking things. Sorry this is not so easy and I hope that some of this helps you. If you cannot make any headway then maybe a long drive to get someone who can help is in order.

Later Ed

[Edward Buker]

I was just cruising the web and came across a post of a Dynasty with a Big Boy that showed the copper buss bar wiring. What I noted was that the panel behind the buss looked like metal and I confirmed what looked like a ground lug screwed into that panel in another one of the photos. I was wondering if there was any chance that the copper buss might have touched the metal panel behind it due to being bent or a little out of place. The tolerances look close and it does look like grounded metal behind it in the photo. Is that true? It would take a lot of current to melt that buss from a remote short someplace else. A few photos of the melted  buss and what is around it on that panel would help.

http://forums.motorhomemagazine.com/Index.cfm/fuseaction/thread/tid/25490317/srt/pd/pging/1.cfm

Later Ed  

[Mel n Melody Finnell]

I attached photo's of the melted copper fuse.  Your comments are appreciated.

[Edward Buker]

Mel,

I magified your photo and saw that the buss to the right might be touching. If that was so, under some conditions, that could create an excessive load. I do not think that is your problem but it could contribute to heating of this buss and changing its characteristics over time, setting up a weak point for a fail. When you get a new one, install it assuring these do not touch. It would seem that Navistar should be more help here. Will they furnish a schematic of the main wiring from the battery compartment through to the DC fuse and breaker panels? If anyone has one can they post it please.

 Are these busses there for wiring convenience or are they meant to be fuses? Does your manual give you any insight. I am posting what is a traditional high current fuse and would ask if you would look and see if you have several of these in the wiring path coming from the battery banks, typically one for each bank. What is important about that, is if you are protected from damaging your wiring. If you find them check and see if they are good with an ohmeter as long as 12V has been turned off. The fuse is usually beyond the main power switches. What may have happened with your problem is that the buss failed first under the high current demand and when you used the jumper then the fuse failed next. If so you need to order several fuses and the buss to be sure and have what you need to get back online. If the buss is a fuse then you need one from Navistar and if not then a lugged wire of the gauge that comes out of the Big Boy could be fashioned to temporarily replace the buss to get power back online assuming the short can be found.

Mel, you need to let me know if any of this is within your comfort level. If you can get the parts to get back online, obtain a schematic so that you (if you have enough understanding to do this kind of work) or a good technician, have what they need to find the shorting problem and get you back online. This may be expecting too much without getting the coach to a shop. You need to decide what will work best for you.

Later Ed  

[Keith Oliver]

Mel:

When you check for a failed ANL 250 amp fuse (as in Ed's picture) be aware that they can fail and still pass some current.  I had a failed fuse of that size in my DC system that was difficult to identify due to passing enough current that the DC voltage I got after the fuse was over 5v.  Not enough for stuff to work, but enough to confuse the diagnostics.  Once the ANL fuse was replaced, all was well.  God luck with your diagnostics.

[Mel n Melody Finnell]

The schematic, High current, Low voltage.

[Mel n Melody Finnell]

Schematic for battery cut off switches

[Edward Buker]

Mel,

The schematic is not clear enough to sort out what is written in the smaller print but from what I can gather there are no fuses before the copper buss so that failed as the weakest link. The four square items in the middle of the black rectangle that also contains the solenoids, are those fuses? Maybe I could see more with a photo of that section of the panel. If those are fuses and all current output from the buss that failed is fused through one or more of those fuses then the next question is are they still good? If for instance they are fuses and that buss feeds all four of these and one is now open that is the leg that has the problem. If for instance all the fuses are good then that would mean that the buss failed before the fuse and that means something also. Not sure what you would like to do next and if this forum thing is a help or a hinderence. If you have those schematics in bigger files and you downsized them for the forum you can direct mail them to ednjillb@hotmail.com.

later Ed  

[Mel n Melody Finnell]

Larger image of schematic, High current, Low voltage.  Multiple sets of eyes and thoughts are always good.  I will also take a picture.  In the meantime I will continue testing.

[Edward Buker]

Mel,

One thought is that the Big Boy could have shorted to ground internally given it has a metal casing tied to ground. It is a mechanical device with movement and wear. You could test that with an ohm meter and the large wires tied to the buss disconnected.

Ed

[Edward Buker]

Mel,

If I read this right and it is still unclear I think the buss feeds the big boy and then is connected to what looks like two fuses. Those fuses feed two solenoids. One solenoid feeds the rear bedroom breaker panel and the other feeds the charger converter. I would isolate each component by pulling the wire off the terminal and test the big boy terminal to ground. Then I would isolate by lifting the wires and test each of the other solenoid inputs and outputs to ground. With all the breakers off in the bedroom panel you should have that wire isolated when you pull it from the solenoid and test that wire to ground. The other wire, while you have it lifted from the solenoid, the other end can be pulled at the charger inverter and that tested to ground. If all that is good you should be able to leave the charger inverter wire disconnected with tape on that end.  Make a wire jumper to bypass the buss open, might try 10 gauge wire temporarily, and then power up what you have measured and isolated. Next power each bedroom breaker on and off one at a time while you measure the voltage at the temporary jumper to ground and see if the voltage drop is normal like several tenths of a volt or so. The 10 gauge wire should not be getting hot but has limits which is why we are going one circuit at a time. The fact that all of this circuitry has its own breakers and they did not trip would mean that likely the problem is elsewhere but with this test you would verify that. The next question is the inverter charger. You could use a heavy wire to jump the buss break by installing a lug on one end and the other and connecting the coach back up. If everything can be powered up in the coach this would lead one to believe that the inverter charger is the culprit. I would consider leaving that disconnected and use a temporary portable charger until you can get to civilization. Hope this helps.

Later Ed

[Edward Buker]

Mel,

One more thing. If those are fuses represented by the squares on your diagram and they measure good with an ohm meter then that would indicate that those legs have not seen a major current fault and it is likely that the high current went elsewhere. The buss that burned up I do not think was meant to be a fuse. If it was it would have been necked down on a region and typically would have been protected in some way by mica or glass or ceramic to not send hot metal helter skelter. So if the fuses are good and if you measure and the big boy itself is not shorted then test and see if the big boy is stuck connected on. If so it looks to me like the other main wire goes through a fuse and then out to the starter. If the fuse on that leg is good, then all the high current paths have not seen excessive current load through the fuses (that is good) but the buss has fused itself. It could be that with the big boy on, the starter was tied into this circuit that the buss was burned up on, and under these conditions the very high current load could have caused the fail. If the big boy tied the banks together and the starting batteries are down in charge, while the house side is up in charge, then the current load this buss would have to handle would be both the inrush of current to the starter as well as an inrush through to the starting battery bank all at the same time, along with the house load and inverter charger load. I do not think it was built for that.

The net of this is if all the fuses are O.K. and the Big Boy and the other solenoids are not internally shorted then all the proper curent paths beyond the buss that failed appear to be fused.(best I can tell from the diagram) It seems possible that the sum of all the available current paths could cause this buss to fail under the right conditions, especially if the starter was involved with the Big Boy contactor closed. If you do not find a short and you are left scratching your head, consider this possibility.

Later Ed

[Edward Buker]

Mel,

How are you making out?

Later Ed

[Joel Ashley]

I've been watching and waiting on this one too, Ed.  You are more of an electrician than me, for sure, and I'm not sure those particular schematics helped my analysis much as I can't quite make out all the devices and small lettering.   So I didn't put in my 2 cents until now.  My money at first glance was on an internally shorted Big Boy;  that's a low ohm high current direct to ground meltdown if there ever was one.  After the fix, Mel might want to check his battery posts.  Current high enough to fry through that copper link can make a puddle out of lead posts too... been there, done that about 22 years back.

The strange thing is the melted buss link appears, from the schematic, to connect to a 4/0 wire clamp that runs to the house battery switch and then to the second wire clamp from the bottom, marked Domestic Batt Hot.  That second clamp appears to go through a big fuse, which should have blown before the copper buss melted.

Joel