RE: (ET) Elec-Trak charger

["Elie, Larry (L.D.)" <lelie ford com>]

I stand corrected Rhett.  Apparently the cap is not just for 
power factor correction.  The bottom line is charge voltage, so 
that is probably why I got away without the cap so long.

Larry Elie


-----Original Message-----
From: Rhett T. George [mailto:rtg ee duke edu]
Sent: Wednesday, June 27, 2001 9:06 AM
To: elec-trak cosmos phy tufts edu
Subject: (ET) Elec-Trak charger


 - Greetings -

Chris Meier just asked a fine question related to charging our GE
Elec-Traks.  For those of us who have kept the GE charger, power
line voltage variations from 120 V are not much of a problem.  This
is due to the design of the transformer and the assoicated capacitor.
In a good light you can see the primary and the secondary on the
transformer and the space between which seems to be filled with 
something.  That something is transformer steel which reaches almost
across the gap.  This is the mark of a (fairly) constant voltage
transformer, usually called a ferro-resonant transformer.  The 
capacitor and its winding on the secondary side resonate around 
60 Hz, producing a high voltage which saturates the iron on the 
secondary side of things.  The filler blocks of iron allow that
part of the primary magnetic flux rejected by the secondary side
to flow an alternate path.  This is reactive and involves little
power dissipation.  By keeping the secondary voltage fairly constant
against input variations and output current demands, this charger
takes a longer time to overvoltage the batteries and cause gassing.


Changing the capacitor changes the charging voltage and consequently
the effort put forth by the charger to bring up the battery voltage.
As others have pointed out, 42 volts is a pretty good stopping point
when charging.  At what is thought to be the end of a charging cycle
(just before the timer turns off), the battery string voltage should 
be 42 V.

Hope this helps.

                                        Rhett George