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How many volts should a fully charged battery read?

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Old 08-22-2001, 05:17 AM   #1
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Default How many volts should a fully charged battery read?

Is 12.14 low?
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Old 08-22-2001, 05:18 AM   #2
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Default no, car batteries are 12v, they usually run 14v when the car is moving

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Old 08-22-2001, 05:28 AM   #3
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Default Mine reads 12.6 with the engine and all accessories off.

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Old 08-22-2001, 05:35 AM   #4
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Default To answer your question, no. Your alternator should put out between 13 and 14 volts

and your battery should be right around 12 volts fully charged.

Why do you ask are you having a problem?
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Old 08-22-2001, 05:41 AM   #5
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Default Alternators put out 14.4 Volts AC. The voltage regulator converts that to 12 volts DC. The ...

chopped off portion of the wave is the noise that shows up in cheap stereo amp installs.
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Old 08-22-2001, 06:01 AM   #6
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Default what voltage regulator? Battery charges to 12V, Alternator generates 14.4V...

If you test the voltage in the car when the car is running (ie when alternator is generating power), you will test ~14.4V. There is no voltage regulator that brings this down to 12V at a high level. (<- Hmm, that may be inaccurate) Perhaps individual devices bring it down, but they probably bring it down to 5V. Amps tend to use the full voltage (while adding capacitance to stabilize the voltage), as you'll see most are spec'd out at creating more power at 14.4V than at 12V. If they had a voltage regulator to bring it down to 12V everytime, this 14.4V power increase wouldn't be possible. So, at the battery, there is 14.4V when the alternator is supplying power.
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Old 08-22-2001, 06:01 AM   #7
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Default That's fine, a little above 12 is good with the engine off...

A little below (11.2 or so) is bad.
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Old 08-22-2001, 06:13 AM   #8
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Default cars do have a voltage regulator, but I'm not sure how they work :)

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Old 08-22-2001, 06:16 AM   #9
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Default Re: 2.2 Volt per cell ... 2.2 x 6 = 14.2 Volt

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Old 08-22-2001, 06:25 AM   #10
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Default Re: Wrong! Sorry. The correct answer is 13.2 V

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Old 08-22-2001, 06:36 AM   #11
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Default I was a little abbreviated in my response...

It's been a while since I researched this I thought the chain of events was...

1. Alternator put out around 14 volts of AC
2. Diodes converted the AC sine wave into a DC pulse
3. The voltage regulator monitored voltage to the battery to maintain a charge, regulating the voltage from 14 something down to 12.

Amperage output of the alternator was important because accessories really run off the alternator when the car is running, supplimented by the battery. If there is not enough oomph (technical term) in the alternator the extra needed amperage was drawn from the battery, running it down. Since our alternator is not keeping up with the accessories, it certainitly won't keep up with charging the battery.

If I'm way out on this I'm sure the good folks here will let me know.
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Old 08-22-2001, 06:58 AM   #12
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Default I've never seen or heard of an alternator that did not use a voltage regulator.It may be sperate or

internal.

For those that want to know how automotive charging systems work ,see the link.
I'm not about to do that much typing.
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Old 08-22-2001, 06:59 AM   #13
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Default Some facts

The alternator has to put out more voltage than the battery. You can not have current flow if there is not a voltage differnece. That is why the voltage from the alternator is higher than the rated voltage on the battery.

The alternator is designed and sized to supply all the equipment on the car with current when the car is moving. The battery is there to make up for the difference in power required when the car is idleing or off - and to provide the power to start the engine.

The voltage regulator is used to control the voltage to the accessories. It will step down the volatge to provide a constant 12 volts to things like the lights, radio, window motors, etc. Inadditon, things like radios, phones, etc that need even more voltage regulation will have their own power regulators to control spikes and noise that are on the lines that come from the alternator, and electric motors when used.

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Old 08-22-2001, 07:07 AM   #14
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Default It's 2.1 per cell which would be 12.6 Actually it is a bit more than 2.1 per cell and a fully.......

...charged lead acid type 12v automotive battery can be 12.7 fully charged. Some automotive gell cell batteries can be has high as 12.9 fully charged.
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Old 08-22-2001, 07:19 AM   #15
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Default At 11.2 the battery would be discharged. After the 12.4 sulfation of the batteries plates starts....

...which will eventually render the battery inoperative.
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Old 08-22-2001, 07:20 AM   #16
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Default right, but it doesn't clamp the voltage down to 12V

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Old 08-22-2001, 07:23 AM   #17
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Default I knew that 11.2 number came from somewhere.

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Old 08-22-2001, 07:30 AM   #18
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Default agree with everything...

but 14.4V DC is supplied to the battery. It isn't clamped down to 12V.

When you said: "Since our alternator is not keeping up with the accessories, it certainitly won't keep up with charging the battery.", did you mean this as a general statement, or are you having problems? Do you mean with a stereo system installed? I had a pretty elaborate stereo system and had no problems that required me to change my alternator due to insufficient supply abilities.
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Old 08-22-2001, 07:49 AM   #19
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Default OK, I didn't say it did. What an alternator generates and when is somewhat variable.......

....depending on the car. 14.5 is usually the max. with the regulater working. It will produce more if the regulator is bypassed when doing a charging system check with a tester.
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Old 08-22-2001, 07:51 AM   #20
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Default Almost any DC regulator....

Output Voltage goes through a set of resistors that form a voltage divider. This divided voltage is then fed back (negative feedback) to the input of a differential comparitor. The comparitor compares a reference voltage at one input to the sum of the negative feedback and input voltage on the second input; the object of the differential amplifier is to adjust its gain so that the difference between the reference voltage and the input+feedback voltage remains at zero; therefore, the gain is adjusted to maintain a constant DC output voltage.
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Old 08-22-2001, 07:51 AM
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