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?

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.

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.

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

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

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.

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

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

R
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
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.
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.
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.
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.
pnichols
Explorer II
Jun 26, 2014
tpi wrote:
Reason I ask is in alternator failure scenario I am hoping to run generator and back power the engine from the power converter.

With an alternator failure won't the chassis battery run all of the engine components?

If so, the Boost Switch would allow the coach batteries to keep the chassis battery charged up while driving. The built-in coach generator could then keep both sets of batteries charged up if you keep the generator running while driving. Of course you'd have to tape the Boost Switch to keep it turned ON, since it's a momentary switch that you normally have to hold ON by hand.
tpi
Explorer
Jun 26, 2014
Mine has no boost switch. My goal with this is to have capability to get home from trip with alternator failure-beyond the scope of chassis battery.

I may need to wire some kind of emergency jumper.