Alternator not charging the House after battery upgrade HELP

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 :?

20 Replies

enblethen
Nomad
Nov 15, 2021
Before installing new fuse check polarity of the two battery systems.
Glad you found problem, but why did it blow!
IAMICHABOD
Explorer II
Nov 14, 2021
outstanding good to hear!!1

Now if you get your charging to house batteries back that solves that problem.
GrouchyOldMan
Explorer II
Nov 14, 2021
I just removed the fuse and it's Bussmann AMG 250 Amp, 32 volts. Already ordered one and a spare.

I guess it blew when I first connected the new batteries.

You guys RAWK, thanks so much for nudging me along with this puzzler!

Lesson Learned: Follow Da Voltage!!!

Edit: of course the knuckleHeads who installed that fuse originally put it in backwards so the clearly printed name & specs were hidden from sight! *sighs*
enblethen
Nomad
Nov 14, 2021
There is different lines of fuses that fit the holder. Will need numbers off old fuse. Needs to be a 32 volt type.
IAMICHABOD
Explorer II
Nov 14, 2021
It appears to be a Fuse holder just take it apart and replace the fuse in it they are listed in this link,the numbers should be on the fuse.
enblethen
Nomad
Nov 14, 2021
photo 2
Photo 1
Fuses Buss ANN fuses
You will need to look closely at the fuse to get correct amperage.
GrouchyOldMan
Explorer II
Nov 14, 2021
I think I found the problem, but it was nowhere near where I thought!

I fired up the chevy 4500 engine to produce 14.4 VDC from the alternator and started tracing that voltage back towards the RV house. The very first component downstream of the chassis battery is the item pictured below (the rubber cover says "Bussman").

With the engine started, on the left hand terminal, direct from the battery I read 14.4 VDC from the alternator. On the other side 12.63, the voltage on the house battery bank.

When I shut the engine off and test continuity between the two terminals it is an open circuit. Like a blown fuse. There are no part numbers on the Bussman device so how do I go about identifying and replacing it?

(Dang it, doesn't look like the pictures are displaying... try these links)

http://www.themeyergroup.org/bussman1.jpg
http://www.themeyergroup.org/bussman2.jpg
GrouchyOldMan
Explorer II
Nov 13, 2021
I ran tests today on your suggestions:

I used a volt meter at the solenoid in the RV battery control center. zero voltage with ignition key off, then I started the engine and....no joy.

The solenoid in the RV battery control center clicked when I turned the key indicating that the circuit was closed and alternator current should be available, but the voltage to the house batteries stayed the same and the Victron still showed a net loss of amperage as before I started the engine.

So I started looking upstream in the Chevy 4500. Clearly the alternator is working because 14.4 volts were going to the chassis battery.

The chevy 4500 fuse diagrams mention two "Auxiliary'' circuits, each with its own fuse and a relay. I only had time to check one of them, a 50A fuse & relay. That relay clicked when I turned on the key and the fuse was good. No problem there, no Eureka moment either.

That leaves me with only one candidate, the other Aux circuit in the Chevy fusebox. I'll check that in the morning but if that isn't it I'm not sure where to look next.

I also tested the theory that the alternator wouldn't charge the house until the chassis battery was fully charged,

- I charged the chassis battery up to full power using a charger.
- I pulled the new house battery bank down to 12.4 VDC using the inverter to power a household 120v fan for a few hours.

Thanks everyone for your ideas on this.

-Grouchy
IAMICHABOD
Explorer II
Nov 13, 2021
GrouchyOldMan
On my RV I bought the one linked on Amazon,it was a direct replacement for the one I had. Yours may be different.

I checked all the major parts houses around me and found that all were more expensive and some places they had to order it.

Being a Prime Member I got it the next day,it also helps that one of their largest warehouses is less than an hour away.

As for when I start the RV when plugged in my Solenoid kicks in and charges my coach batteries at 14.7,same as when I am driving.

One hint, you may try thumping it lightly,the points may be stuck.This was suggested by my long time mechanic.

Good luck and let us know how it all works out.
enblethen
Nomad
Nov 13, 2021
Battery control center differ between makes and models somewhat. Can you find a make and model for your rig? It should be on it somewhere. Maybe printed on circuit board. Could be on protective cover.
When you start the rig while connected to shore power, both systems will be trying to charge battery if it is like on my rig.
Continuous duty relays may differ from one posted. Some look like a Ford starter relay.