Alternator discharging!

[Canadian_Rainbi]

2002 Itasca Horizon DP 5.9 Cummins.
420 Watts Solar
Magnum 2 KW pure sinewave inverter/charger
SC 230 30 A Solar controller
Trimetric TM 2030 Monitor
500A shunt
4 GC House Batteries
2 Group 31 "Marine Deep Cycle" Chassis batteries
Xantrex Echo Charger (Charges Chassis batteries from house batteries)

All DC in and out through the shunt.

Suddenly, after being in storage for the winter, the house batteries died after not being checked: the shore power plug had been disconnected probably by passing deer. The solar was not working as I had disconnected it because the battery voltage hit 15VDC every sunny morning.

Now batteries charge fine from solar and/or shore power but DISCHARGE when engine is running according to the battery monitor. First noted when driving the rig with dead house batteries to the shop for new house batteries. Noted that the chassis batteries had discharged during the 30 kilometer trip to the shop.

Batteries were replaced, alternator checked OK.

Need to run generator to keep the batteries from discharging (15-20 Amps according to the monitor) Three hour highway trip to a rally and the same back, same problem. No observable over heating, no smoke, no fire. I would suspect that such a current draw would result in something noticable if it was due to a short. My mechanic and RV tech is away at the moment on holidays.

Anyone have any ideas? We need this rig in three weeks.

[MrWizard]

Sounds like the BCC /BIRD has a malfunction
Aka battery control center
Box with relays and control board
Or possibly a bad starter solenoid with pitted/stuck contact
This will eventually damage the starter motor by over heating

[enblethen]

I would find another place to have alternator checked out.
Sounds like the rig is running off battery

[Canadian_Rainbi]

Bikeboy57 wrote:
If you are running the generator and charging the house batteries and IF the house batteries and the engine batteries are electrically tied then the ammeter will show up h engine batteries to appear to be discharging. This happens because the alternator regulator is set around 13.7 volts and most battery chargers run around 14 v in the bulk mode.

I don't see how that can be all of a sudden. We have had this rig since 1008 and the Trimetric monitor for the last three and have not seen this until this spring.

As I mentioned in my first post I have a Xantrex Echo Charger. It charges the chassis batteries from the house batteries if needed AND the chassis batteries are at 13.V or higher.

AND it's mot just meter reading. When I first noticed this I left the house with the chassis batteries reading 12.2V, half way to the shop the battery warning light came on and I arrived at the shop with 11.8 volts at the chassis battery. The tech said the alternator chechked out. He has been away on holidays, just waiting to get back in.

[Bikeboy57]

If you are running the generator and charging the house batteries and IF the house batteries and the engine batteries are electrically tied then the ammeter will show up h engine batteries to appear to be discharging. This happens because the alternator regulator is set around 13.7 volts and most battery chargers run around 14 v in the bulk mode.

[Canadian_Rainbi]

Thanks all, been away, so has my tech. Will respond to individual comments later, Will let you know what the tech finds.

[MrWizard]

Where did you disconnect the solar?
Have you verified no battery drain when the engine is off
Do the chassis batteries charge with engine running and house batteries disconnected
Do house batteries discharge with solar connected and engine off
10 to 20 amps is c consistent with chassis running power needs
Could be house batteries are supplying the chassis needs and you have a back feed from house to chassis
and a fuse blown in the main engine run key on wiring

[YC_1]

SidecarFlip wrote:
Sounds to me like the bridge rectifier internal to the alternator is shorted.

Ditto: Not a common failure and a strange one when it happens but it does.

Disconnect batteries and then take the large charge line off the alternator. Put a test light between the wire and the alternator. Do not start the engine. Reconnect the batteries. IF the test light comes on there is current draw. Not a lot of meters will test up to 20 amps so even an old headlight will work.

[pianotuna]

Am curious about why the charge controller was doing 15 volts.

[enblethen]

Sounds like bad diode(s) in alternator. Grounded diode(s) can cause battery discharge.

[time2roll]

Canadian Rainbirds wrote:
Batteries were replaced, alternator checked OK.

Alternator is producing close to 14 volts and the voltage gets to the chassis battery?

Also the house battery should have an isolator so that no power goes to the chassis unless charging voltages (13.5+) are present.

So if the alternator works the chassis battery is close to 14 volts.... the house battery is fully charged at 12.7 volts... power should be coming toward the house battery only.

Got to revisit that alternator test.

[ScottG]

Classic symptom of diode failure in alt.
There are some great upgrades out there for not a lot of money over a rebuilt stock alt.

[wa8yxm]

If the engine is RUNNING and the alternator is not alting (Joke, Not charging) then the alternator is bad. Remove and take to a rebuilder.

IF the alternator draws power when the engine is OFF (Yes it can do that and not be bad) I had that happen on one car. Turns out the alternator case was not properly grounded to the engine block. NOW I know this is .... Rare... I mean the thing is tightly bolted to the engine block, but that was the problem.

I put a "Star" type lock washer on the bolt and all good.

[SidecarFlip]

Sounds to me like the bridge rectifier internal to the alternator is shorted.

[rgatijnet1]

Pull out fuses one at a time until the 20 amp draw stops. Vehicles in storage are subject to all kinds of critters chewing on the wiring and this can cause an electrical short which may be draining your batteries. You may have to crawl underneath the rig to find out if this is caused by critter damage.