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Old 07-01-2019, 08:02 PM   #1
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Alternator Issue?

So I have 2-27DC batteries for starting. When I fire it up, the gauge shows 16v. the batteries are only showing 12.37 and 12.43. Surely if the alternator were putting out 16v, I would see that at the batteries.
My weak battery did end up taking a charge to 12.74.

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Old 07-01-2019, 08:36 PM   #2
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It's the old volts v.s. amps thing. Without trying to 'splane it, during charging when the batteries are low their volts will show low regardless of alt out put, but the amps will show high. As the battery charges up the amps will drop and the voltage reading will go up. It's all about Ohm's law. V=IR. Confusing as hell-- until it isn't.
Jack
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Old 07-01-2019, 08:45 PM   #3
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Cranking can be well over 400A as a transient.

Lead batteries' voltage will dip even when Full and healthy.

The degree to which the batteries are near Full 100% SoC, their Ah capacity and SoH%, the CAR of their chemistry, the actual Amps put out by the alt. All these factors combine to produce a "compromise" voltage on the charge circuit

A poor connection will cause just as much a problem as a bad battery.

Where is "the gauge" connected?

What are you using to measure at the battery terminals?

What is the highest voltage you see at the alt output after the batteries are Full, without other loads running?

Where did you get 16V?
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Old 07-01-2019, 08:55 PM   #4
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Quote:
Originally Posted by john61ct View Post
Cranking can be well over 400A as a transient.

Lead batteries' voltage will dip even when Full and healthy.

The degree to which the batteries are near Full 100% SoC, their Ah capacity and SoH%, the CAR of their chemistry, the actual Amps put out by the alt. All these factors combine to produce a "compromise" voltage on the charge circuit

A poor connection will cause just as much a problem as a bad battery.

Where is "the gauge" connected? Don't know, haven't pulled the dash

What are you using to measure at the battery terminals?

What is the highest voltage you see at the alt output after the batteries are Full, without other loads running?

Where did you get 16V?
Don'kt know where gauge is hooked until I pull the engine cover.
Haven't accessed the atl. till I pull the cover.
16v showing on the gauge.

I can check the alternator tomorrow.
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Old 07-01-2019, 11:40 PM   #5
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With a run-of-the-mill single 12V battery system, 16V would be a sign of overcharging. But with 2 higher-voltage batteries, it's possible the system is designed to put out 16V after a start, split (as it were) between the batteries. Think of it as a a trickle-charge for EACH battery -- i.e., they're sharing the charge voltage as well as the starting load.
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Old 07-02-2019, 12:49 AM   #6
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No, either the gauge or the alt VR is broken.
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