Sony CCD-FX620 vs. Sunpak 3000mAh battery.

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 
news:OizOj.3325$em5.799@fe117.usenetserver.com...
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.

Hi Jerry,

I called the manufacturer of the battery, Tocad America Inc., and talked to an engineer. By the way, this a nickel cadmium battery. We agreed that the battery was exhibiting some very strange properties. We also agreed that even if the charger was defective, it could not increase the battery voltage past its normal fully charged state. So I'm sending off my battery directly to the engineer I spoke with this morning and hopefully he can figure this out.

Thanks for your reply.

--
David Farber
David Farber\'s Service Center
L.A., CA

I'm not so sure. I'd drop the charger in the box with the battery. Never "assume".

I read the small print on the charger. It says, "DC out, 7.5V 1.5A(VTR) 10V

1.1A(BATT)" So maybe it isn't a surprise that the charger is able to charge the battery to 8 volts or higher.

I haven't sent the battery in just yet. I'm still not convinced the camcorder is working properly. There are times I will power it up with a

6.5V supply voltage and moments later, the overload light comes on my power supply. 6.5 volts is what the schematic indicates as the battery input voltage. This is a full volt lower than the 7.5 volts that the charger/supply outputs (the charger can also power the camcorder when the power switch is moved to DC out). I've set the current limiting of the power supply to 1.6 amps, the value of the fuse, even though there are other branch circuits that don't go through this same fuse. The rated power stated in the camcorder service manual is 6 watts. At the moment, I have my bench supply set at 7.75 volts and the current protection at 1.6 amps which would provide over 12 watts of power. The current reading is steady and shows, 550ma, and it is not shutting down. I've also noticed that the power supply will sometimes shut down when the camcorder is in the "off" mode if I crank up the voltage somewhere in the high 7 volt range. There is never any slow increase of current. It just jumps from 550ma to a shut down situation.

Thanks for your reply.

--
David Farber
David Farber\'s Service Center
L.A., CA