On Sun, 03 May 2015 00:45:45 -0700, sms
wrote:

On 5/1/2015 11:03 AM, micky wrote:
Someone gave me an old car battery charger.

6 volts 10A and
12 volts 2A and 10A, determined by a slide switch.

A friend brings over a dead 12v battery.

On the charger, on 10A, it charges at 9amps.
On 2A, it charges at 7 amps.

Based on the meter on the charger.

What does it mean to be a 2 amp charger if it charges at 7 amps?


After an hour the charging rate dropped to 6 amps on the 10A setting,
and then it was 5 amps on the 2A setting.


I have similar 2A/10A charger and on mine the meter does not have two
different scales for 2A and 10A.

Neither does mine. Two of you seem to have gotten the impression that
my ammeter had two scales, but I don't know where you got that
impression.

On mine, if it's set for 10A it charges more quickly but it also shuts
down the charging earlier. At the 10A rate the green LED indicating
fully charged turns on but if I then switch it to 2A it charges some more.

As to voltage, a fully charged lead acid battery, with no load, will be
2.3V per cell x 6 cells = 13.8V. Once it's under load, it's 2.1V/cell or
12.6V. If you have a shorted cell (or more than one shorted cell) it's
easy to check because under noload the voltage will be lowered by the
number of shorted cells x 2.3V.

An alternator/rectifier/voltage regulator, or battery charger, needs to
put out 14.4-14.8V to properly charge a car battery. While people call
car batteries "12 volts," they are not 12 volts except under load where
they are between 12V and 12.6V.

An article entitled is "Car Batteries Are Not 12 Volts" is available at
http://www.landiss.com/battery.htm.

Thanks for the info.