Lost all inside 12 volt power - help

[Dan Child]

Hello,

First I should introduce us. We are Dan and Lisa Child, currently working and spending most of our time in the San Francisco Bay Area of CA, though we call Helper, UT home.  We recently purchased a 2009 Marquis. It is the Moonstone floor plan with  Cummins ISX-15 for power.  

We have made a couple of prior trips with it and no problems until tonight.  We are on the first night of a five day dry camping trip.  We stopped for the night and all was well, then I reached over to turn on a light. When I pushed the multiplex button, the entire interior lost power, I mean nothing on the 12 volt side.

I am fairly capable of minor troubleshooting,  but I am lost on this and hoping someone can point me in the right direction. There is no power getting to the multiplex panel in the rear closet.  I have checked both the compartment outside in front of the driver's side wheel and the compartment in the engine bay - they both have power and seem normal, though I did find all but one of the thermal relays tripped in the engine bay compartment. I reset them and they look to be working properly.

I cannot locate a main fuse or breaker for the panel in the closet. Does one exist or is there a source of power that I need to go to?  I am in the middle of the Southern California desert with slides extended and no power.  I cannot drive it to a repair shop and I'm going to have to figure this out and fix it myself.

Thank you in advance and we look forward to meeting many of you soon.

Dan

[Joel Ashley]

Hey Dan-

There are others more versed in this than me, but they're probably asleep at this time of day, like I should be.  The one thing you might check is the Multiplex CPU fuse.

My house electric panels are virtually all in the bathroom cabinet over the toilet, but mine is a Monterey.  I'd look in the same location as the 50 amp Main and the 30 amp Inverter AC boxes, where there should be two black multiplex modules, A and B, 10 channels each, recognizeable by ten 10 amp blue spade fuses each.  Somewhere nearby should be a black box inset into the wall, maybe 4" X 6".  Gently pry the black cover off that box from the bottom.  Inside should be 12 more fuses, and in position #9 on mine is the 10amp Multiplex CPU fuse.  There may be spare blue fuses lurking there or at the bottom of the modules along with yellow fuse pullers.

Now if that black fuse box is what you meant by the multiplex panel that's not getting power, according to my diagram it's power appears to come from one of several 30 amp connections on a bus of what I assume are circuit breakers.  My diagram doesn't specify where that bus is unfortunately, but the other end of that connection goes to a Ford type solenoid, and I'm guessing it is the one on the wall of my engine electrical bay, inside the cabinet over the batteries that has the Big Boy and the BIRD inside;  that solenoid connects to one of the large heavy fuses in there, 125 amps, on the main 12v house fuse block.

I have no idea if this will resolve your issue, or if your Marquis has a house electric panel locale and configuration like my Monty, but it may be worth a shot.  Even if it is a blown CPU fuse, the question remains what triggered the overload.

The bay up front under the driver is essentially all chassis-related 12 v. stuff, and probably not involved here.

Crossing my late night fingers for ya
-Joel

[Keith Moffett Co-Admin]

Hi Dan
Welcome to the club and the forum.  We are still adjusting to our Marquis and it is seven years older than yours.  That said, sounds like a problem we had with our old coach and it was the inverter.  
In the passanger side bay just forward of the rear tire is the tank covers.  One bay further forward is open and e inverter is all the way to the back on the left bulkhead.  Make sure the brakers are not tripped.  Just reset them like a normal household braker.  This regulates the 110 demand from battery power.
Now there is also straight 12V power for ceiling lights and under cabinet etc. which I seem to recall on a breaker in the big master closet.
If these dont solve the problem, there will be better answeres on this forum soon so dont fret too much.  Absent all else, call Beaver Coach Sales in Bend Or. (1-800-382-2597) and I'm sure they will point you in the right direction.
Being a new coach owner, everything can seem overwhelming but it is rarely as bad as it seems.  Just try to not stress too much since you have five days and it is likely an easy fix.  Meantime do small things like a volt test on the batteries (house and chassis) and try running the genset to see if it makes a difference.

Have faith
Keith

[Edward Buker]

Dan,

Because all of this happened with the multiplex push of a button one would have to assume that system is at fault. I do not have a multiplex system but in general if you have a meter measure at the largest wire coming into the multiplex system for voltage. You said you did that and there was none. That was in the rear of the coach so from there the wire should either go to a DC main breaker panel in the rear of the coach or head toward the battery compartment. If it is labeled somehow you may be able to identify where it is tied in.

Turn off each rear DC breaker and then turn them back on, sometimes they can trip and not appear to be tripped. If you remove the cover to that panel see if the large 12 V feed has power in the main DC breaker panel. If items in the coach turn on and off with those breakers then you do not need to measure fro the 12v feed. The house batteries have a fuse and some electronic disconnect, solenoid/Big Boy etc. You need to follow the 12V path point to point from the battery terminal until it reaches the multiplex unit. Somewhere in that path there is an open, probably a fuse. If a single multiplex circuit feed fuse has blown in addition to the main wiring reason you do not have power I would not replace the circuit feed fuse until I returned given that a short in that circuit may have caused this whole issue. You would want to leave that circuit isolated.

When you said you had a thermal breaker in the rear that required resetting, did you measure after the reset that you had voltage coming out or did it trip again. One would think that breaker is involved also and may be defective. This is especially true if all the fuses in the multiplex unit are good. You can verify with an ohm meter or visually.

If you were to try things in the coach and see what worked and what is not, like the slides, it may help isolate the possibilities. BCS in Bend is likely to have the best information on where to start the hunt for the problem.

Later Ed

[Dan Child]

Guys,

Thank you for the advice.  I had done everything you mentioned with the exception of the inverter breakers/fuses.  I checked for them and could find none, however, my auto generator start panel is right next to it, so I pushed the test button and the generator ran for about two minutes and shut off.  I went back in to tell Lisa we were going to have to call someone and "Wa - La" everything  was working again. I have no idea why, but it must have been tied to the generator auto start. I had run the generator last night with no success.

Thank you for jumping to my rescue. I have been a motor home owner for over 15 years, but this one had me really scratching my head at 2 in the morning!

Thank you again,

Dan

[Edward Buker]

Dan,
These RVs can be a puzzle..... Now the questions, did the shaking of the generator vibrate a contact or wire connection that reseated itself, possible. Did the voltage get low enough where a solenoid like the big boy was not connect or latched and when you ran the genset for two minutes it was enough to get you back online. You may want to check your voltages at the batteries and whatever solenoid system you have in the battery compartment to see that the voltages are as they should be. I would say 12.4 to 12.6V if the charge is reasonable. If you were depleting the batteries and the voltage to the multiplexor was low, when you added a load like the lights it may have dropped the voltage low enough to disable the multiplexor circuit from working, this is a more probable scenario. The gen auto start would provide the ability to come online based on voltage levels but I do not believe that it has the ability to disconnect 12V going to the rest of the coach. Knowing the "why" behind all this will have you sleeping better at night. The fact that you were boondocking leads me to believe that low voltage is involved especially if no thrown breakers or blown fuses are found leading to the multiplexor boards. If your house batteries have never been changed they could be 6 years old and maybe not giving you the expected capacity. Hope this helps.

Later Ed

[Joel Ashley]

Dan, this will likely not be the last time this happens.  I'd have it checked into before too long;  the guys at BCS are well versed in this stuff.  

Ed, in studying my wiring diagram, the one commonality between the genset and the house DC panel is the Big Boy.  And I know the coach power solenoid, between the big House Fuse block in the Big Boy cabinet and the house DC panel, could be a player also.  I am no expert beyond that suspicion, and my diagram for some reason doesn't have the BIRD shown on it;  though I'd not think it involved, what do you think?  I do like your low battery voltage theory as a plausible culprit.

Joel

[Edward Buker]

Joel,

I was passing along some guesses as to what might have explained some of this 12V behavior. Until it happens again and it really gets traced we will just be speculating. If Dan gets lucky it will never happen again, and I bet he would drink to that outcome....
Later Ed

[Dan Child]

Well guys, after four days of searching and dealing with power on and then nothing, I finally found the culprit.  All of my batteries are brand new and the voltage at the batteries tested at 13+ volts, so that was not the problem.  When everything was working, I decided to check the voltage at the batteries - 13.4 - and then checked it at the input to the multiplex system - 11.2 volts!!!  Where was my voltage going and yes, the multiplex system was shutting down due to low voltage anytime I had more than a light or two on.  Running the water pump would kill it almost instantly and I was more than ready for a shower.   So, when I had power, I went back to the cabinet in the engine compartment that houses the Big Boy and tested it - full voltage on all cases.  I then tested the solenoid next to it - the one (it turns out) that operates the inside house disconnect for the batteries.  Power in 13.4 volts, power out 11.2 volts.  The solenoid was not making proper contact and the voltage was dropping drastically as it went through it.  I bypassed this solenoid by taking the "out" cable off and putting it on the stud together with the "in" power cable.  It was fixed - I had power for the rest of the trip with no problems.  I cannot shut off the power from inside, but I have a disconnect switch at the batteries that I use.  

Thank you for all of your help.  It took a little time, but the problem was found and we had a GREAT trip!  I hope to see you on the road!

[Edward Buker]

Dan,

Good job on that one. Having this problem/fix in the BAC archives should be helpful, given it will probably happen to someone else along the way.

Later Ed

[Joel Ashley]

For once I was on a right track  ??) ?   That latching solenoid (coach power solenoid) has been known to be a problem, and was for us once.  Probably another good reason not to ever switch that entryway "salesman's switch" off.  Ken at BCS will hunt you down if you even touch it, so that's a second reason   .

Joel