BAC Forum
General Boards => Technical Support => Topic started by: Bill Lampkin on May 31, 2020, 05:03:51 PM
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On the road with new inverter and residential fridge. When driving with the inverter on (for the fridge), the chassis battery volts drops slowly to 12.3V. Fearing the worst, I ran the generator to charge both banks. Once at the campground for the night, I read the Beaver book. It said the BIRD will open at 12.0v to recharge the chassis batteries via the alternator. My build sheet says I have a 160a alternator. I expected that, when driving, the alternator would to 'cover' both the chassis load (engine running) and house (30a dc draw) while running the fridge. Am I expecting too much from the alternator? Tomorrow, when we head north, I will see if the chassis batt volts drops below 12.0v and then if BIRD opens, charging the chassis battery. Plan to stop by an alternator shop in Eugene to have them check its output.
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Bill
To put it simply, when engine is running the Chassis batteries have priority for charging and once they reach a specific voltage (approx. 13.3 volts) the BIRD closes the BigBoy so as to also charge the House batteries. When on shore power, its just the opposite, House batteries have priority then Chassis batteries. I had a similar problem, that it was my House batteries that were not charging while driving, indicating that the BIRD is not signaling the BigBoy to close. Found the Ground wire on the BIRD was the culprit due to a cold solder (cracked solder) on the back side of the circuit board. However, you said it was your Chassis batteries that were not charging while driving, so you might have a different problem. Hope this might be of some help.
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Bill
Your alternator should handle both banks (house and chassis) to Maintain voltage. However, if you have overnighted with only house batteries for power, you should use the generator to bring the batteries back up and not rely on an alternator to handle that much charging. Usually we run our gen. about 2 to 3 hours once we hit the road after overnighting on house batteries.
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Bill
I would think a 160 AMP alternator would be ample to cover the loads from both the chassis and the coach loads up to at least 3/4 of it's 160 Amp rating .
I would be checking your bird controls to see if the problem is there.
You may find that like the echo charger system that it is prioritized to take care of the chassis batteries first and only charge the house batteries when the chassis batteries reach full charge or at or about 13.5 volts.
If you have low chassis batteries from extended camping or you have a high demand on the the chassis side while driving you may not be reaching the threshold voltage.
The other problem may be a weak or defective alternator .
Start by having the alternator ( charging system checked )
Then check the threshold voltage for your bird cut in
And check to make sure the bird solenoid is still working ( it wouldn't be the first solenoid with bad internal connections.
Hope some of this helps
Eric
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Bill,
From what you describe, I suspect a faulty alternator or bad chassis batteries. When the engine is running the alternator is directly charging the chassis batteries through a 200A fuse and the chassis battery disconnect switch, regardless of whether the Big Boy solenoid is open or closed. If it is closed and you had a bad or very discharged house batteries that could cause your symptoms but since they charge OK with the generator, it sure sounds like the alternator or bad chassis battery(s) are the culprit.
Steve
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Bill,
Steve is correct. When you engine is running, the engine alternator output is tied directly to the chassis batteries and the BIRD system is involved in only charging .the house batteries from the engine alternator. It sounds like you have an alternator problem.
Gerald
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Replaced alternator today, shop in Eugene had a rebuilt unit in stock. Good lesson in how the BIRD system works, and what to watch out for,, thanks all! One other thing, I never got any dash light to say ALT or other indication, just low volts (12) on the dash gauge and Aladdin.
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Did have a similar problem on the road. Pulled off the highway and stopped on the on ramp. Called for road service and the tech said the alternator was bad. Did not fix it. then he said the battery was bad. It got me running but was not charging. Ran the rest of the way home with the generator on. After checking the wiring diagram I saw a fuse in the compartment above the batteries. Checked it and sure as heck it had blown and was less than the rating shown on the diagram. Turns out I bought chassis batteries and an alternator I didn't need, got a h---l of big lesson though.