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willo's avatar
willo
Explorer
Jun 28, 2016

Sorting out 12v system on 85

My project RV is a 1985 Monitor class C. I'm working on the 12v coach system and hoping to get it sorted out. My coach battery drained dead multiple times over the winter, even when the RV was on shore power.

1) There is a battery isolator. I checked last night and found that on shore power, no charge is applied to the coach battery.

2) When running, the RV does charge the coach battery.

3) I am going to switch over to a pair of 6v golf cart batteries.

4) I am going to add a solar charging system as well.

5) I have no idea where the farkin 12v rectifier is. The main breaker panel is under the stove. Maybe it's hiding behind that.

6) The power steps only work when a battery is present and charged. Shore power doesn't supply that system. (Not a surprise, it extends when door is opened and retracts when ignition is on fired.)

Clearly, I need shore charging to actually work.
(I'll be much happier once I find the rectifier and get the specs off of it.)


Questions:
Any ideas where that rectifier lives? Under the stove maybe? The breaker panel is directly under the stove.

Should I consider a dedicated battery charger and leave the wiring as is?

If I find the rectifier and don't like the specs, perhaps I should update it and rewire the isolator so that it can charge.
Class C
  • willo's avatar
    willo
    Explorer
    Jul 09, 2016
    I thought I'd follow up with a bit of status.

    I poked around and found no 12v coming from the converter at the main 12v distribution panel by the battery. I disconnected the charge wire and hooked up my new battery pack. I found 12v on the charge side, so the issue appears to be the converter itself.

    Here's my plan:
    1) eliminate the isolator pack. I'm going to use a battery combiner to allow charging from either side.

    2) Replace the converter with a modern one. I want the hum to go away and since the battery charger portion is dead I have an excuse. (OK, I could repair the thing but I'm not going to.)

    3) Install a luna national dual battery monitor.

    4) Resize the battery compartment to hold a pair of golf cart batteries. It's too short right now. It'll be a fun welding project.


    Later projects:
    5) Install solar charging.

    6) sine inverter - On my to do list will be a power inverter for laptops, etc.
  • DrewE's avatar
    DrewE
    Explorer II
    Jun 29, 2016
    That looks about right for a block diagram. There are some (generally minor) differences in circuit topology that aren't too terribly important--for example, the connection on the engine side between the battery, alternator, and isolator can be rearranged in a few ways, any of which would work fine provided the wires are heavy enough.

    Sometimes the aux start solenoid and the isolator are the same gizmo with a somewhat more complicated control wire from the start switch. (Pressing it connects the solenoid control to a house +12V circuit; releasing it connects it to a switched circuit in the chassis, either switched with the ignition or something a little more complex to permit the chassis battery to get recharged before connecting the house battery.) Sometimes they are separate systems, as your diagram shows.
  • willo's avatar
    willo
    Explorer
    Jun 28, 2016
    Found it! it was hiding under the rear bed. 30 amp with battery charging. I' will probably upgrade that sometime soon.

    Here's what I think the wiring should be. Did I get it right?

  • jorn's avatar
    jorn
    Explorer
    Jun 28, 2016
    I whole-heartedly concur with the above, and add that if you listen carefully when it's plugged-in, you should be able to hear the hum of the converter. That might help you track it down.
  • tenbear's avatar
    tenbear
    Explorer
    Jun 28, 2016
    What DrewE said. Good advice.

    There may not be heavy wires from the battery to the converter since old single stage converters charge at a very slow rate. My 2010 MH used a #8 wire that was about 20' long. I changed my converter and changed the wire to a #4.
  • DrewE's avatar
    DrewE
    Explorer II
    Jun 28, 2016
    By "rectifier" I assume you mean "converter," the gizmo that takes 120V shore power and spits out 12V power to charge the house battery and power the house systems.

    Often the converter is mounted on the same chassis as the breaker panel and 12V fuse panel, usually in the lower portion of this chassis. Sometimes it's a separate deck-mount converter, in which case it could be pretty much anywhere. At the age of your RV, it's likely a simple linear (ferroresonant) converter, which means there's a good chance it hums in operation, and if you can hear that hum it might help guide you to where it is located. Of course, as it isn't working, there might be no hum.

    Failing that, you might be able to trace the heavy wires from the battery and/or 12V distribution panel to find where it is...or just start poking around behind and underneath any removable access panels you can find, and under all the drawers, and so forth.

    Given the age of the RV, if it's the original converter, you'd be well served to replace it with a modern multistage converter, such as a PD 92xx unit. It would be gentler on your batteries, charge them faster, and provide cleaner power to your 12V systems.

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