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Old 24th November 2019, 12:50   #1
pletevl
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Default Alternator output. Battery dying

Hi all.
I posted a few weeks ago about my battery going flat.
3 weeks ago I bought a brand new Bosch battery. It was giving out 12.7 volts when I unpacked it.
I haven't used the car for a week so decided to check it today. Its down to 11.7 volts.
My alternator is pushing out 14.6 volts.
I've checked the power consumption with the car all locked up and if I remember correctly it was drawing 18 miliamps.

Is my alternator killing my batteries? This is my 3rd one in as many years.

The last one before the Bosch was a Halfords one. It's charged up sat in my garage and is holding its charge.

Anyone know what's going on?

Can an alternator give 14.6 volts and not charge the battery????

Pete.
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Old 24th November 2019, 13:57   #2
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First of all Pete, which of your six cars are you talking about?

An alternator output of 14.6 volts is at the very top of the acceptable range. It might be "overcharging" your battery.

Simon
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Last edited by SD1too; 24th November 2019 at 14:04..
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Old 24th November 2019, 14:10   #3
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Old 24th November 2019, 14:23   #4
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Not your alternator with that voltage.

Did you charge your battery before use ?? It can make a difference.

The voltage you saw at the start was there simply because that's what happens when acid is poured onto dry plates as the battery comes off the production line. It was NOT charged !!!!!!!!

If you check the voltage at the battery terminals immediately after you start the engine you will see anything up to 15 volts. It slowly drops from this and won't harm your battery.
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Old 24th November 2019, 14:30   #5
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Hi, yes I charged the battery fully with my optimate.
When I start the car, the voltage goes up after a few seconds, up to 14.6 volts and fluctuates around 14.4 to 14.6. It never goes under 14.4. (I use a volt meter that I plug into the lighter socket)
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Old 24th November 2019, 14:30   #6
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Further to the above post.

Almost everybody who buys a new battery and finds it starts the car immediately assumes the battery is fully charged It's not so.

Lots of batteries get off to a poor start in life because of this.

It doesn't matter to the salesman because you will be back sooner rather than later to buy the next one. Good for the manufacturers as well.

The first charge is the most important one in the life of your battery so make sure it gets off to a good start by giving it one. ( If you catch my drift. Lol. )
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Old 24th November 2019, 20:02   #7
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12.7V is a more than adequate starting voltage, damage is likely to occur if it is regularly allowed to discharge to around 12.2V or less, and it is also likely to present starting problems at such a low voltage, and discharge the battery further, into the damagingly low realms where sulphating of the plates is rapid. If your brand new battery is discharging from 12.7v to 11.7v in a week, you definitely have a leak and this could be down to one or more of the diodes in the voltage regulator failing. The alternator will tend to give out a high voltage long after it should have reduced, as it is pushing power into both the battery, and the leak, rather like pumping water into a tank with a hole in. When you switch off the supply, your briefly full battery continues to leak back through the diodes. When you leave your car after you have been for a drive, try disconnecting the wires from the alternator. If the battery remains fully charged, you have isolated the problem. If it continues to discharge, then it isn't the alternator!
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Old 24th November 2019, 20:34   #8
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Thanks for that.
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Old 24th November 2019, 20:53   #9
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Quote:
Originally Posted by Comfortably Numb View Post
12.7V is a more than adequate starting voltage, damage is likely to occur if it is regularly allowed to discharge to around 12.2V or less, and it is also likely to present starting problems at such a low voltage, and discharge the battery further, into the damagingly low realms where sulphating of the plates is rapid. If your brand new battery is discharging from 12.7v to 11.7v in a week, you definitely have a leak and this could be down to one or more of the diodes in the voltage regulator failing. The alternator will tend to give out a high voltage long after it should have reduced, as it is pushing power into both the battery, and the leak, rather like pumping water into a tank with a hole in. When you switch off the supply, your briefly full battery continues to leak back through the diodes. When you leave your car after you have been for a drive, try disconnecting the wires from the alternator. If the battery remains fully charged, you have isolated the problem. If it continues to discharge, then it isn't the alternator!
Just to clear this up.

It's not the speed of sulphating but it's how long the plates remain in a sulphated condition.

New sulphate is crystalline and will easily take part in a chemical reaction.
However when left for several months the crystalline sulphate compacts into a solid. In this condition it will longer take place in a chemical reaction when trying to charge the battery.----The battery is DEAD>--
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Old 24th November 2019, 20:56   #10
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For info. I bought an AGM battery this time round. Apparently it doesn't suffer as much when the voltage does drop down too much.
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