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Old 05-17-2017, 09:15 AM   #1
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Can't reach the magic 12v

So I have 3 batteries, 2 of them are in parallel with one negative and one positive for the bus. For whatever reason, it reads 12.4 at the battery, but in the bus it only goes up to around 11v or so. Is this normal?
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Old 05-17-2017, 09:31 AM   #2
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I don't think so, I think I would go to A Batteries Plus or auto parts store and have each battery check individually disconnected from each other to see if there isn't a dead cell in one or more of the batteries that's keeping you away from the 12 you should be 13 or better

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Old 05-17-2017, 09:36 AM   #3
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well we took a voltage meter to each battery once we disconnected it from parallel and both of the batteries showed 12.4. For whatever reason once the engine is on it just reads 11v
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Old 05-17-2017, 09:41 AM   #4
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I'm not an electrical engineer or anything but I know when I took my batteries to the AutoZone they checked it with a battery tester which puts a load onto the battery and revealed a dead cell so I don't know if just checking it with voltmeter would reveal a dead cell or not maybe somebody else with better credentials in the electrical field ..... that was a joke, could help you out better than I

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Old 05-17-2017, 09:44 AM   #5
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If I'm reading this right you have 2 12v starting batteries cabled in parallel and a 12v house battery by itself.

If you see 12.4 at the battery and 11 inside the bus I'd be looking for bad battery cables and bad ground connections. It's not uncommon to have what appears to be a good battery cable that is all eaten up inside the insulation.
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Old 05-17-2017, 09:48 AM   #6
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Quote:
Originally Posted by Iheartbus View Post
For whatever reason once the engine is on it just reads 11v
Sounds like you may have a dead alternator. With the engine running test voltage at the alternator. You should be seeing ~14.5v.
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Old 05-17-2017, 09:52 AM   #7
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I concur with checking the alternator some of these buses came with under-producing alternators and need to be upgraded.

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Old 05-17-2017, 10:07 AM   #8
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If you have a diesel with glow plugs your battery voltage will stay low for a minute or so after the engine starts. After the glow plug relay shuts off the voltage should pop back up into the normal range.

We need more details about your engine and how you're testing.
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Old 05-17-2017, 10:30 AM   #9
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On my bus the batteries are brand new, and until the alternator kicks in my gauge reads a bit low (11 or 11.5 v), I've checked all cables with a multimeter and ammeter to see if I'm leaking current anywhere and it doesn't seem that way, my gauge just doesn't read that accurately, you may have the same problem. Once the alternator is running it pops up to around 14v.
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Old 05-17-2017, 10:31 AM   #10
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Yes my bus alternator has an Exciter which doesn't start producing anything until a certain RPM and then she kicks in.

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