Alternator not charging the House after battery upgrade HELP

[GrouchyOldMan]

The 4-year old batteries in our 2016 Coachman Freelander 21QB motorhome were getting tired and I decided on a replacement before we begin our winter travels.

The old bank consisted of two 12 VDC 80 AH "deep cycle" AGM batteries wired in parallel with a Victron 712 battery monitor to keep an eye on them. They still worked ok but the usable output was headed down hill and we'd gotten almost five years out of them so... replacement time.

After research and some very helpful advice on this forum I decided to upgrade to two Trojan T-105 GC-2 golf cart batteries wired in series for a useful capacity of about 225 AH @ 12VDC. The install was tight due to their height nudging the insulation foam on the doorstep battery box. Otherwise all went well and after an initial charge using the WFCO charger on shore power I ran a draw down test and found everything spot on.

The problem is that after the upgrade I noticed something strange: when I unplugged from shore power and fired up the engine on our Chevy 4500 it didn't seem to provide charging power to the house batteries from the alternator. Didn't matter whether the battery disconnect switch was on or off.

I've racked my brain as to what's going on, and soon realized that I have no real idea of how my Battery Control Center does its job or how it might even detect the difference between two 12VDC batteries in parallel, or two 6VDC batteries in series? Or maybe something in the Battery Control unit needs to be reset? Or something with the WFCO WF-8900 converter/distribution center?

I have a little voltmeter plugged into the dashboard that shows the engine battery voltage and I can see it jump to 14+ volts when I start the engine, but there's no current flowing to charge the house batteries!

I've always counted on the house batteries charging while we are driving, so I think this is a new problem but I've never ran any tests, just took it for granted. The engine battery isn't fully charged at the moment (12.4 VDC) and the new house batteries are fully charged (13.6VDC). Is it possible that no alternator current flows to the house UNTIL the engine battery is topped off?

Can you experts enlighten me, or at least provide some hints on where I should look for an answer?

Thanks in advance,
-Grouchy :?

[IAMICHABOD]

When I had this happen to me on my Chevy Based Chassis RV,the alternator was not charging the house batteries,I found that the CONTINUOUS DUTY SOLENOID had failed.

When you start your RV the voltage should go up to 14.4 or so then within a few seconds the solenoid will click and you will get power to the house batteries.If you can find it it is easy to check with a simple volt meter.

Mine was in the battery box area. Check that out,you may not have put the wires back on that lead to it from the battery or it has failed.

[GrouchyOldMan]

Thx folks.

- enblethen: Good call, I will check fuses. I was careful hooking up, final negative terminal last...

- theoldwizard1: I'm hoping to avoid replacing the existing components, it was working great before.

-jdc1: no trailer, this is a class C RV.

-jkwilson: Exactly!!! So, what could have changed? I'm on the hunt for a "Missing Wire" but honestly the only extra wire in the replacement job was the Victron battery monitor wire from their shunt to the positive terminal.

Go figger folks, I'm baffled.

Is it possible that the alternator has circuitry that won't deliver current to the House battery bank until the engine Starter battery is fully charged? That's a condition that I might never have noticed, because why would ya? In the end, after making some mileage, you pull into camp with both batteries topped off.

[enblethen]

Battery control center should haven ignition and/or a charge relay to allow alternator to charge coach batteries. It should have a control fuse. Verify that all fuses are good.

[theoldwizard1]

Not exactly answering the question being asked, but installing a quality DC-DC battery charger is always good option for charging your house batteries while driving.

[jdc1]

Did you check the connection at the truck/trailer plug? Is there power there?

[jkwilson]

There is no difference between 2 6V batteries in series and a 12V battery other than the connection between the 3rd and 4th cell being external. Rule number one when a problem happens is to go look at the last thing you messed with. It’s easy for a wire to retract when disconnected and be missed upon reconnection. Also, any errors, even brief, during hookup could blow protection devices.