Forum Discussion

coolmom42's avatar
coolmom42
Explorer II
Jun 26, 2014

Charging house battery from alternator---disconnect switch??

I saw a post (either here or in the Class B section) about exactly how to wire a house battery to charge off the alternator. The description included directions on how to wire a switch to disconnect the house battery from the chassis battery, so as not to run down the chassis battery. But then the switch can be turned to charge the house battery from the alternator while driving.

But now I can't find the thread. Can't turn up anything on a search.

Can anyone help me find this thread, or at least one with similar info?
Class C
  • tpi's avatar
    tpi
    Explorer
    Jun 26, 2014
    wwest wrote:
    My class C has a relay that couples the engine charging system to the house battery ONLY when the alternator is powering the rotor winding internally.


    In other words it requires alternator output to connect the two systems? Is this a typical wiring scheme, rather than ignition on to connect the batteries?

    Reason I ask is in alternator failure scenario I am hoping to run generator and back power the engine from the power converter.
  • JaxDad's avatar
    JaxDad
    Explorer III
    Jun 26, 2014
    The simple solution is to use a constant-duty rated solenoid. Run a fused wire from the alternator to the solenoid and then on to the house battery. Use a 12 volt source from the ignition, there's usually a spare or two beyond the one for the radio, etc., to put power to the trigger terminal of the relay.
  • coolmom42's avatar
    coolmom42
    Explorer II
    Jun 26, 2014
    rich85704 wrote:
    Wait -- doesn't the house battery *usually* charge off the alternator when driving? I'm confused.

    R


    Yes.

    But in a retro-fitted camper van--which I am thinking about doing--there needs to be a switch to isolate the house battery during use so as not to drain the chassis battery accidentally.
  • wwest's avatar
    wwest
    Explorer
    Jun 26, 2014
    My class C has a relay that couples the engine charging system to the house battery ONLY when the alternator is powering the rotor winding internally.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Jun 26, 2014
    Hi,

    Yes, in a class C. But the OP is not in one.


    rich85704 wrote:
    Wait -- doesn't the house battery *usually* charge off the alternator when driving? I'm confused.

    R
  • rich85704's avatar
    rich85704
    Explorer
    Jun 26, 2014
    Wait -- doesn't the house battery *usually* charge off the alternator when driving? I'm confused.

    R
  • pianotuna's avatar
    pianotuna
    Nomad III
    Jun 26, 2014
    Hi,

    You can add manual control to the relay as well. Any continuous duty solenoid can be used--mine are rated at 100 amps each but circuit breakered at 50 amps. I don't wish to have burned contacts in the relays.
  • Golden_HVAC's avatar
    Golden_HVAC
    Explorer
    Jun 26, 2014
    Hi,

    It is really easy to install what you want. Take a #8 wire and connect to your alternator, then to a 30 amp capacity fog light relay, then to a 40 amp automatic reset circuit breaker. Then to your second battery.

    That will do it.

    Fred.

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