i am wondering if my car charger is no longer efficiently charging.it
has a 6v and 12v setting. a test with the multimeter on the 6v shows
7.3v. on the 12v setting it shows 12.0 volts.

now i read a car battery varies from 12.39 discharged to 12.6 fully
charged.

to add to my confusion, this charger has an analog ammeter which does
register a current flow of 3 amps into the battery when connected. can
a 12.0v charger charge a 12.6v battery? or is my 'open' reading by
multimeter an incorrect way to measure voltage pressure available?

thx

"beerismygas" wrote in message
ups.com...
i am wondering if my car charger is no longer efficiently charging.it
has a 6v and 12v setting. a test with the multimeter on the 6v shows
7.3v. on the 12v setting it shows 12.0 volts.

now i read a car battery varies from 12.39 discharged to 12.6 fully
charged.

to add to my confusion, this charger has an analog ammeter which does
register a current flow of 3 amps into the battery when connected. can
a 12.0v charger charge a 12.6v battery? or is my 'open' reading by
multimeter an incorrect way to measure voltage pressure available?

thx


Without a load on it, a 12V charger will normally read 16-18V, when you
connect it to a battery the voltage will drop down to whatever the battery
wants it to be at.

"James Sweet" wrote in message
news:K1Hii.4029$wu5.1154@trndny03...

"beerismygas" wrote in message
ups.com...
i am wondering if my car charger is no longer efficiently charging.it
has a 6v and 12v setting. a test with the multimeter on the 6v shows
7.3v. on the 12v setting it shows 12.0 volts.

now i read a car battery varies from 12.39 discharged to 12.6 fully
charged.

to add to my confusion, this charger has an analog ammeter which does
register a current flow of 3 amps into the battery when connected. can
a 12.0v charger charge a 12.6v battery? or is my 'open' reading by
multimeter an incorrect way to measure voltage pressure available?

thx


Without a load on it, a 12V charger will normally read 16-18V, when you
connect it to a battery the voltage will drop down to whatever the battery
wants it to be at.

How old is the charger ? In the good ol' days, there was no electronics in a
car battery charger - just a pretty inefficient rectifier glued on the end
of a power transformer. This produced a very 'pulsy' output, which if you
read with a digital multimeter, may very well give a reading of less than
you are expecting A fully charged battery is likely to read over 13V. Your
car charges it at 13.8V nominal. Most '12V-rated' equipment for use in cars,
is *actually* specced at 13.8V. The accepted output voltage range of a
stand-alone charger is about 14 to 15V.If the meter on the front shows *any*
forward current flow at all, then the output of the charger *must* be above
the terminal voltage of the battery that it's connected to, at least *some*
of the time - ie at the peaks of the output wave, if it is an old tranny
plus reccy design. It's basic physics really.

Arfa

In article . com,
beerismygas wrote:
i am wondering if my car charger is no longer efficiently charging.it
has a 6v and 12v setting. a test with the multimeter on the 6v shows
7.3v. on the 12v setting it shows 12.0 volts.

now i read a car battery varies from 12.39 discharged to 12.6 fully
charged.

That's incorrect. The accepted figure for a discharged battery is 10.8
volts. Could also be zero, of course. ;-)

to add to my confusion, this charger has an analog ammeter which does
register a current flow of 3 amps into the battery when connected. can
a 12.0v charger charge a 12.6v battery? or is my 'open' reading by
multimeter an incorrect way to measure voltage pressure available?

If the charger has some form of electronic regulation the open circuit
voltage could be anything - as it may not 'switch on' properly until it
sees a load. But if it did produce 12 volts it will partially charge a
flat battery, but not fully. However, you should measure the voltage it
produces while charging. Something near 14 is needed to charge a battery
that is near fully charged - the voltage will likely be lower if the
battery is near flat.

--
*I never drink anything stronger than gin before breakfast *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Meat Plow wrote:
Without a load on it, a 12V charger will normally read 16-18V, when
you connect it to a battery the voltage will drop down to whatever
the battery wants it to be at.

Nominally 14-15 VDC.

I doubt any domestic charger could give 15 volts across a good battery,
nor is it desirable.

--
*Middle age is when it takes longer to rest than to get tired.

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Meat Plow wrote:
On Wed, 04 Jul 2007 13:30:37 +0100, Dave Plowman (News) wrote:

In article ,
Meat Plow wrote:
Without a load on it, a 12V charger will normally read 16-18V, when
you connect it to a battery the voltage will drop down to whatever
the battery wants it to be at.

Nominally 14-15 VDC.

I doubt any domestic charger could give 15 volts across a good battery,
nor is it desirable.

Ok you doubt it so what? An ensuing argument about a ****ing battery
charger?

No - just a realistic answer. Say 15 volts in a reply to someone who has
to ask this sort of question and they'll be looking for just that.

--
*Speak softly and carry a cellular phone *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
Meat Plow wrote:
Nominally 14-15 VDC.

I doubt any domestic charger could give 15 volts across a good
battery, nor is it desirable.

Ok you doubt it so what? An ensuing argument about a ****ing battery
charger?

No - just a realistic answer. Say 15 volts in a reply to someone who
has to ask this sort of question and they'll be looking for just that.

It was a /range/ and the answer was realistic even though you /doubt/ it.

Well, you do the maths and tell us the charging current into a good
battery if the charger is putting out 15 volts...

--
*Succeed, in spite of management *

Dave Plowman London SW
To e-mail, change noise into sound.

However, you should measure the voltage it
produces while charging. Something near 14 is needed to charge a battery


i tried it while charging and read 14v this time. thx

beerismygas wrote:
i am wondering if my car charger is no longer efficiently charging.it
has a 6v and 12v setting. a test with the multimeter on the 6v shows
7.3v. on the 12v setting it shows 12.0 volts.

now i read a car battery varies from 12.39 discharged to 12.6 fully
charged.

to add to my confusion, this charger has an analog ammeter which does
register a current flow of 3 amps into the battery when connected. can
a 12.0v charger charge a 12.6v battery? or is my 'open' reading by
multimeter an incorrect way to measure voltage pressure available?

thx

The output waveform from the charger is a rectified sine wave. It will
not read correctly on a dc meter. If it is a half wave rectifier, it
will not read correctly on the ac scale either. If you want to see what
it is doing, look at it on a scope. You can charge a 12v battery with
a waveform that reads nearly zero on a voltmeter because of the peak
to average ratio of a waveform.

If the meter reads a real current going into a 12V battery, it is still
charging.

On Tue, 03 Jul 2007 22:40:10 -0700, beerismygas
wrote:

i am wondering if my car charger is no longer efficiently charging.it
has a 6v and 12v setting. a test with the multimeter on the 6v shows
7.3v. on the 12v setting it shows 12.0 volts.

now i read a car battery varies from 12.39 discharged to 12.6 fully
charged.

to add to my confusion, this charger has an analog ammeter which does
register a current flow of 3 amps into the battery when connected. can
a 12.0v charger charge a 12.6v battery? or is my 'open' reading by
multimeter an incorrect way to measure voltage pressure available?

thx
Chargers today have lots of features that may make measuring the
charger output voltage pointless. Even the simplest chargers use an
unfiltered, unregulated voltage source. When you convert from RMS
voltage to peak voltage you gain 1.4142 times the RMS voltage - the
battery only sees and charges on the peaks of the rectified sine wave.

To check mine I use a large capacitor and charge it to 9 volts then
place that across the charger terminals - then read the voltage. 14.9
volts most days.
--

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