I don't know your camera unit to advise you on what to check.

I can tell you that the battery charger with no load has to put out a
higher voltage than the chargeable battery is rated at. There is usually
about a 20% overhead. The charger is current regulated to the proper
amount for the battery specs. It works with the principal where the
battery regulates the charge voltage. The charger regulates charge
current.

In an automobile, if the battery was disconnected, which I would not do
while the engine is running, the open end voltage would read about 16 to
18 Volts. If you leave the car stopped over night and come in the
morning. the battery would most likely read about 12.5 Volts. When you
start the car, the batter voltage should go up to about 13.5 to about
14.7 Volts. It nominal should be about 13.8 Volts.

As chargeable batteries age, they tend to not be able to hold their
charge as long. After some time the battery may start to go shorted or
opened a little. If the battery is opened, the voltage across it will be
very high in comparison to what it is supposed to be. If the battery is
shorted or has internal leakage, the voltage will read lower than
normal. In both types of defects the battery will not be very useful.
Normally, as chargeable batteries age, they lose their ability to hold
their charge. They discharge more quickly under load.

For example, if a battery is rated at 12.5 Volts, the charger may put
out 14.5 to 16.8 Volts for charging. When the battery is released from
the charger, it may read about 13.6 to 13.9 Volts with no load.

To measure the charge current from a simple DC output charger, the
process can be a bit involved, but it is simpler that from a charger
that uses DC pulse drive, and varies the duty cycle to control the
charge current.

With a DC charger, you can put an amp meter in series with a known good
battery that is discharged. You can take an Ampere reading and see what
the actual discharged battery charging current is. As the battery is
charging up, the current should decrease. Eventually, when the battery
is fully charged, you should be able to see the sustaining charging
current.

For a pulse drive charger, you would need a scope with a current probe.
The procedure is the same, but you will be reading the peak current. To
have the RMS current, this would be complicated since the pulse drive is
not an AC sinewave. A good digital scope should have the option of
having an RMS translation to the screen.

With many of the battery chargers for industrial and consumer camera
products, they also use current and voltage sensing for the battery
condition. These chargers are fairly sophisticated. If the battery gets
too hot during the charging cycle, the charger will lower the charging
current. If the temperature is too hot according to specs, the charger
will stop charging the battery and indicate an error. If the battery
demands too high a charge current, or it is not charging properly, the
charger will shut down.



--

Jerry G.


"David Farber" wrote in message
...
I've had this Sony CCD-FX620 since it was new in 1994. A while back I
replaced the smd caps on the audio/video board and it restored the poor
picture and audio back to normal. I powered it up a few days ago,
ejected
the tape that was in it, and inserted a brand new one. Then it went
dead. I
tried a different battery and still nothing. Upon disassembly, I noticed
that one of the two 1.6 amp fuses, F951, in the power supply was open. I
mulled over the situation, replaced the fuse, and powered it up again
but
this time with my bench power supply hooked up to the battery terminals.
My
bench supply can be set to shut down at a predetermined current
threshold. I
set it for about 1.8 amps and it powered up again no problem. I then
tested
my battery to see if it wasn't holding a charge. It's a Sunpak 3000mAh
RB-90. I used the charger that came with the camcorder which is an
AC-V25A
to charge this battery. I was quite surprised to see that my meter
displayed
a reading of 8.18 volts. It's supposed to be a 6 volt battery. The
schematic
indicates the battery input as the 6.5V unregulated supply. Despite
this
finding, I hooked up the battery again to the camcorder and the same
fuse
immediately blew. I've not come across this type of situation in the
past
where a battery would charge to a voltage so high, that it would take
out a
fuse in a portable device. I suppose there could be something wrong in
the
camcorder which cannot tolerate an 8 volt input. I've had this battery
for a
while and never had this problem before. I tried to disassemble the
charger
but there is something preventing me from opening it without an extreme
amount of force. I don't want to use a crow bar on it just yet.

I'm anxious to hear the s.e.r. wisdom as to what could be causing the
high
battery voltage or the camera's quick blowing of fuses.

Thanks for your reply.
--
David Farber
David Farber's Service Center
L.A., CA