On Sat, 24 Mar 2012 13:07:44 -0400, wrote:

On Sat, 24 Mar 2012 12:39:01 -0400, Gary wrote:

On Sat, 24 Mar 2012 12:25:02 -0400, wrote:

On Sat, 24 Mar 2012 12:12:39 -0400, Gary wrote:

Hi everyone!

Any reason why AC can't be used to charge a car battery? Reason I'm
asking is that I have an old Fedtro Powerhouse charger
which is outputting AC.

More likely, the charger puts out rectified but unfiltered DC.

Put a 100mf 30 volt capacitor on the output of the charger (watch
polarity) then measure the DC voltage.

If there is no DC voltage across the capacitor, then the rectifier(s)
in the charger are toast.

OK, except I can't see anything inside the charger that looks like a
rectifier: aside from the main transformer, there is just a small
coil of wire (the buzzer?) and a 6V/12V switch.

Depending on the age of the charger, it could have a selenium
rectifier (looks like a stack of square or round metal plates wih
washers between them) or it could use solid state diode(s). Depending
on the amp rating of the charger, a solid state diode(usually silicon)
coud be stud mounted or it could look like a "blob" on a wire.

When the selenium rectifier in an old adjustable EICO 6/12 volt
battery eliminator/charger (that I've had for years) finally died, I
replaced it with a silicon bridge rectifier on a heat sink. The
maximum output voltage is now higher, thanks to the differece in
voltage drop across a silicon diode (0.6 volt reardless of load)
versus the several volt drop (that increases with load) across the
original selenium rectifier.

You need DC (even if it's unfiltered) to charge a battery - AC won't
work.

OK, I will try as you suggest. You said something about watching the
polarity across the output of the charger - what exactly did you mean?