Alternator not charging house batteries

[jcavasos]

Greetings from a new member. I hope I'm doing this right. I have a 2014 Thor Fourwinds F550. I noticed my generator was running after we had stopped for gas, this happened a couple of times. I contacted Thor tech support and was told either a bad BIRD or contactor. I started the engine and had my wife watch the digital display. It was charging to 14.2 V. So we got ready to pull out, I turned my head lights on, my wife told me the display dropped to 12.9 V and was dropping. Turned the headlights off and the display went back to 14.2 V. I noticed the fog light switch was on with the head lights, so when I turned the fog lights off, my wife heard the contactor click and the display showed charging. Turned the fog lights on, contactor clicks and display shows discharging. The Emergency start switch works perfectly. Any suggestions?

[Oneilkeys]

I'm a little confused on what "digital display" you are referring to? If you are looking at a digital display for your house batteries and the house batteries charge when you start the engine then the BIRD and Trombetta are working correctly. If the digital display shows the house batteries discharging when you turn your lights or fog lights on, I would guess that you have a short somewhere in your system. The BIRD is designed to separate the coach and house batteries if the coach battery is discharging when the alternator is running. That is so that if you have a short in the house batteries they will not discharge your coach batteries.

[EA37TS]

Not positive but I imagine it is the digital display for the inverter. With an F550 he is running a Super C which should have the Xantrex Pro 1800 Inverter.

[Oneilkeys]

I guessed that from a previous Class C that I had. If he notices the generator running, I assume that he also has an autostart system on his generator. If the BIRD opens the Trombetta disconnecting the two battery banks because a short in the lights is discharging the chassis battery even with the alternator running, you would expect the coach batteries would slowly discharge. He needs to put a volt meter on the chassis battery and see if it is really discharging with the engine and alternator running and the lights on - confirming some kind of short. I do not understand why the generator runs unless the coach batteries were already down and he was running electrical systems off the coach batteries. With the Trombetta open, the coach batteries should be isolated from the chassis battery and any short in the lights.

[Oneilkeys]

I don't know enough about 12v systems to understand how the charging systems work when both the generator and engine alternator are running at the same time. The BIRD should keep the Trombetta open which would mean that both battery banks are being charged by both the generator and alternator at the same time. Since a lot of people run the generator and engine simultaneously, it must be OK to charge the batteries from two sources at the same time. However, if there is a short in either the coach or chassis battery electrical systems that is discharging one of the systems, it seems to me, that running both the generator and engine will keep the Trombetta open as long as one of the two systems is above 12.7v.

[jcavasos]

Thank you very much for the quick reply. I'm so sorry I didn't give enough detail. Yes, the digital display is from my inverter and I do have the auto gen start. The BIRD and Trombetta are working fine. What I found, is when I turn my fog lights on, it disinguages the Trombetta which makes it so the house batteries are not being charged by the alternator. This is a classic case of the fog light switch being miswired. The Emergency start switch works fine. It sounds like no one has heard of this problem. Everything works perfectly as long as I don't use my fog lights (driving lights).

[Oneilkeys]

I would look at the voltage on your chassis battery after you turn on your fog lights. It sounds to me that a short in your fog lights is draining your chassis battery. Once the chassis battery falls below 12.8v the BIRD opens the Trombetta separating the two battery systems so both do not drain down and leave you with no battery power. Sounds like the BIRD is doing what it is supposed to do and protecting you from shorts.