Coach Batteries - Somethings not right

Discussion in 'General RVing' started by atamians, Oct 1, 2009.

  1. atamians

    atamians New Member

    Sorry for the longer post, but let me give you a little history. I have a 1986 Beaver Marquis DP. Four 12V batteries for the coach and one for the chassis. No idea how old the batteries were but everything worked fine for the first couple of years.

    Dry camping this year and I thought it would be nice to use the inverter to make coffee instead of the generator. No problem, 15 minutes pulling about 100 amps according the analog meters.

    Couple hours later I went to adjust the level and as soon as the pump came on, everything went dead. Battery meter showed 10 volts. OK, figured the batteries were old and I shouldn't try that again until I changed them out.

    I bought four new interstates, 110Ah, checked em, charged em, installed em.

    Next time out, when leveling, couldn't finish. Same problem. This time, once I quit using the levelers, the battery voltage came back up. I figured the initial charge was not good enough, we were connected to shore power so I just ran a battery charger for the weekend. 10A initially, then at 2A. The batteries show 13.5V.

    Getting ready to put the coach away for awhile and I thought, let me try those batteries. Same thing, lights go out, propane alarm goes off and monitor panel reads 7V.

    Now I begin to troubleshoot the issue.

    Coach batteries = 13.5 volts
    Chassis battery = 12.9 volts

    Wiring diagram shows coach batteries wired to Hot Block on frame. From there, one wire to Hydraulic pump and then chassis 12V hot bar (Radio and Vent Fan) another wire to Boost Start Solenoid then Isolator then 12V house Panel.

    With nothing on, Batteries measure 13.5 Volts, monitor panel indicates 18V. Voltage at Hot Block on frame measures 13.5V. Voltage after the isolator measures 18V

    With nothing on, !2V main CB off, batteries = 13.5 Monitor Panel = 0V Hot Block = 13.5, After Isolator = 13.5

    With the 12V panel back on, I turn on one light, batteries = 13.5, monitor panel = 5V, Hot Block = 13.5, After Isolator = 5V (Nothing works)

    Start the engine and things are similar, but the voltage only drops to 10V with anything turned on.

    I can't help think the initial drain started the issue. If the pump was bad, why is the battery voltage good and nothing works. If the isolator is bad, why don't I kill the chassis battery. If there is bad ground in the coach, why doesn't the pump work...

    Anyone have any thoughts???

    Sounds like a fun winter project.

  2. Triple E

    Triple E Senior Member

    Re: Coach Batteries - Somethings not right

    Are you only having this problem when you try to level the coach?
  3. atamians

    atamians New Member

    RE: Coach Batteries - Somethings not right

    The problem initially started while trying to level the coach. Once the batteries were charged, I didn't experience any trouble until the next time I tried the level the coach. It cleared up again while I charged the new batteries. This last time, I tried the levelers and the problem occurred again. The problem has not cleared up this time.

    Whichever piece was failing has probably completely failed.

    Gonna keep troubleshooting, just not sure which direction to go.

  4. Triple E

    Triple E Senior Member

    Re: Coach Batteries - Somethings not right

    JMO, but it sound like your pump cannot handle the load. Maybe a short in the motor, low on hyd. fluid, blockage in one of the hyd. hoses or the pump is going bad. For some reason the leveling system is drawing to much power and sucking up your voltage. Are you able to separate the motor from the pump. If you can isolate the motor from the pump, run the motor. If you do not lose any power than the trouble is in the hydraulic system. If you lose power while running just the motor, replace the motor. Good luck and keep us posted. Would like to know what you find.
  5. atamians

    atamians New Member

    RE: Coach Batteries - Somethings not right

    I think that may be where it started, but it doesn't explain the current condition. The battery voltages are fine and I have no power in the coach. The house monitor reads 18V until I turn something on. Once I try to turn on a light or something, the house monitor drops to 5V and still nothing works. A DVM on the batteries still shows 13.5V.
  6. Kirk

    Kirk Senior Member

    Re: Coach Batteries - Somethings not right

    The monitor reading is strange and makes me wonder if it is part of the problem. Where could it get 18V, if all of the other DC sources are reading as they should? As one who made a living trouble shooting electrical equipment for 40 years, that would be one question that I would address first. Find the location that it connects to and measure that with a reliable meter to see what that says.

    I would also lift the lead to the leveling system just to make very sure that it is not in any way having an impact upon what you read. Where is your battery isolator connected into the circuit? It should be immediately after the positive connection to the coach batteries and as such if open there should be nothing from the coach batteries, into the system. If you want to eliminate the coach batteries from the mix, just lift the negative cable where it connects to the ground side and that means it is out of the circuit. You could do that same thing for the chassis battery.

    Since you don't know what is good and what is bad, I would first eliminate all multiple sources for power, as we have to know what is there, before there is any way to know what should be there. Your battery isolator and the solenoid which allows charging of the coach batteries from the chassis alternator are both suspect, so I would also check both in the on and off conditions, with battery cable lifted. Use an ohm meter so that you know that you are only measuring those contacts and no parallel paths.

    Do you have a schematic of the electrical system? If so it should show how things are laid out, but with an RV that age, there is no way to be certain that everything is original. I would trace the main power cables, drawing myself a schematic as I did so, to know exactly what is there now. I would also lift the connection to anything that I didn't know where it goes. Then by reconnecting one at a time you can determine where each goes and you will narrow the possible problems.

    As it is now, you are looking at a total system and probably don't know exactly what it has in it. The fact that things did work for two years and that the problem showed up twice when you tried the leveling system would to me lead to a strong suspicion that it is the problem, or caused the problem. You need to have a point to start where something is a known fact. So far, all that I can see is that your batteries seem to be charged, but that don't mean that they are not damaged since they may not have any significant capacity now.

    Your battery voltage is exactly what a fully charge battery should read, so it probably has not been seriously harmed. I would not test the leveling system again until I knew what the problem is/was as do it enough and you may destroy them. You could also eliminate different loads which are possible problems by removing fuses from the fuse panel and put those back one at a time.

    Your long post is no problem as to know much and not just guess, we need all of the information possible. What I would do is to separate the electrical system into as small a sections as possible. Once you do that, make sure that your starting point is all normal. I would make that the coach batteries. You can then start by verify all readings and slowly begin to reconnect things. Never assume that any contact is good, but verify that it works by first checking with an ohm meter, then connect the power and close it to verify its operation with volt meter readings.

    To give you specific ideas about what your problem is would be no more than guessing. If you can find an electrician who has worked on the same RV as yours, you might get some better ideas, but barring that I strongly suggest a systematic approach. As you learn more, post it here and we will be happy to try to point you in directions or to advise as best we can.
  7. Triple E

    Triple E Senior Member

    RE: Coach Batteries - Somethings not right

  8. atamians

    atamians New Member

    RE: Coach Batteries - Somethings not right

    Thanks for the feedback, I too am not new to electrical troubleshooting and I tend to agree. The hydraulic pump most likely caused the failure, but why the 12V system is still not working has me puzzled. I have the wiring diagrams and the coach appears to retain the original layout.

    18 Volts is odd. The only thing I could think of was grounding. The measured voltage is only a difference of potential but I still can't come up with a way that I should come up with 18V.

    Tonight I'll pull the pump out of the system and isolate that component. Hopefully that will drive this in one direction or the other.

    The house batteries are mid-coach, the chassis battery is mounted in the engine compartment. The isolator and boost solenoid are on the firewall about a foot from the chassis battery.

    One thing I can not see well is the physical connection between the house batteries, the converter and the 12V panel. Does that wiring normally run together after the converter, or does the 12v supply run into the converter and then the converter output to the panel?

    Attached is a partial wiring diagram, one note, this is a Gillig chassis, so the leveler pump is connected to the coach battery.
  9. atamians

    atamians New Member

    RE: Coach Batteries - Somethings not right

    No wiring diagram. The attachment was too large. Didn't realize there is 100k limit. I'll post it tonight elsewhere if we still need it

  10. Triple E

    Triple E Senior Member

    RE: Coach Batteries - Somethings not right

    Chris, I would disconnect the wire from the pump motor, before pulling the motor, then test your 12vdc. That way if the problem no longer exist, you won't have to pull the motor. I am not sure how the wires are ran in these units. If I would have to guess I would say that the monitor is down stream from the convertor. I say this because when I hook up to 120vac that will provide 12vdc to my monitor and automatically energize my 12vdc equipment. Keep informed on what is happening.
  11. atamians

    atamians New Member

    RE: Coach Batteries - Somethings not right

    Got it. Sometimes a little patience and a couple of adult beverages and things make more sense - go after one issue at a time.

    The pump was not blowing the circuit breaker so I decided to troubleshoot the 12V system first. Just to make it fun, I checked the inverter and made a pot of coffee (110v Coffee Pot) using battery power, but could not turn a light.... hmmmm

    The trouble turned out to be two fold. A slightly loose ground from the house batteries to the frame and a slightly loose ground at the 12V distribution panel. (I'm not sure how much the panel ground was contributing because I found that first. It did make the interior 12V system better, but not the levelers)

    I did measure 18V on the 12V panel and 13.5 on the batteries, but I was measuring the batteries across the posts and the panel to chassis ground. Once I realized that, a quick check on the positive post to the frame showed the same 18V. --- Had to be a ground. Negative post to the frame showed 5V.

    The only thing common grounding to the entire house was the 12V panel ground. (there it was)

    I tried the levelers and the battery voltage went to "Zero", no pump.... This time, the 12V system came back up. Checked the negative post to frame and was still showing about 2.5V. Chased the main wire from the negative to a connection on the frame rail that was slightly loose. Couple of turns and I am back in business.

    Thanks for the help, I hope this helps someone in the future.


    1. On this coach, the 12V main from the batteries is connected to a terminal block at the converter. The output from the converter is also tied to that block and then to the 12V panel.

    2. The inverter uses a separate ground coming off the house batteries. (Hence the coffee in the dark)


  12. Kirk

    Kirk Senior Member

    Re: Coach Batteries - Somethings not right

    That still doesn't explain the 18V reading, but I have a thought that may. If you have pairs of 6V batteries for the coach and a 12V battery for the chassis, then it is possible that due to poor connections your monitor was seeing one 6V and the opposite side of the chassis battery.

    The lack of a return wire in 12V systems makes them cheap and easy to wire but it also causes some really strange problems when you loose one ground and an item feeds back through some other item to find a ground. Since you found more than one questionable ground, if this were my RV I would go through the entire 12V system checking all connections for sound/tight connections and I would remove, clean and reconnect every ground point and major power connection, using a dielectric grease on all of them, especially any that are exposed to weather under any condition.
  13. Triple E

    Triple E Senior Member

    Re: Coach Batteries - Somethings not right

    Alright Chris, Amazing what a couple of adult drinks can do. Next time you will have to add a good cigar in the mix. Thanks for keeping us up dated. -Steve :)

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