"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