Battery
Information by Ron Dexter
There are well-made and reliable batteries from many
suppliers that will last many years if well treated. Anton Bauer has written
much about battery maintenance and NRG has a very good pamphlet on batteries.
(800-753-0357) Here is some information for unusual needs.
A battery's
amp hours (AH) rating is theoretically the amps a battery will provide for an
hour, but usually at a 1/10 of that rating for 10 hours. Film and pro video
cameras will discharge a 10 AH battery in less than an hour, even if it only
requires one amp current. The discharge curve of a lead acid battery voltage is
pretty much a straight line down. Ni Cd batteries maintain their voltage longer
and drop near the end of use which is good for their maintenance. Although lead
acid batteries have more energy per weight, much of that energy is not usable
because a 12-volt battery voltage drops below camera cutoff voltage, usually
11.5 volts. Video cameras shut off automatically at about 11.5 volts. 14-volt
batteries will allow much deeper discharge, but it is harder on the battery and
will shorten life.
Lead acid batteries and chargers are fairly cheap and
are readily available some parts of the world. The larger the battery, the
longer the cameras will operate. One 10 amp/hour (AH) battery will last longer
than two, 5 AH batteries as the larger battery will hold its voltage
better.
12 volt systems. Off the self, sealed batteries come in roughly
2.5, 5, 7, and 10 AH sizes. "Smart" chargers (ones that charge fast and then
trickle charge to avoiding damage) are available at electronic suppliers.
16-hour chargers are cheap, but take longer to recharge, but won't hurt a
battery if left on after the battery is fully charged.
12 volt wet
batteries and chargers for cars and motorcycles are also available in even more
places. A car battery will run a camera or 12-volt video monitor all day. Use
large cables (#12 or #14 gauge) to avoid resistance loss for cables over 6 feet.
Boxes for car batteries are available in marine and camping vehicle stores. DO
NOT AIR SHIP HIGH AMPERAGE BATTERIES. IT IS DANGEROUS TO THE PLANE. If you plan
to get batteries on location, take all the cables, boxes and connectors that you
might need. You might even rent a battery.
14-volt lead acid combinations
of one 6 and two 4 volt batteries will power a video camera much longer before
the camera shuts of at 11.5 volts. I know of no smart chargers for this voltage
available at electronics stores. There are 8 and 6-volt smart chargers available
from Bescor and they may have a 14-volt smart charger.
6-volt batteries
and chargers are available for 6-volt cameras.
8-volt batteries can be
made with two 4-volt batteries. So far as I know the only smart chargers are
from Bescor. These will run VX700, VX 1000 or other 7.5 volt camera a long time.
A battery and charger is about the cost of one internal battery. (The Sony TRV
900 runs a long time on one full size internal factory battery.)
When
buying lead acid batteries, check the manufacture or shelf life date. Don't buy
old lead acid batteries. Most Ni Cds are OK with age. I don't know about nickel
hydride.
Chargers. You can charge any lessor voltage battery from a car
battery with a light globe or power resistor. Let's say you want to charge an
8-volt battery at 1000 mils or 1 amp. If you need to drop 4 volts you need a
resistance of R=E / I = 4Volts / 1 Amp = 4 Ohms. To find the wattage of the
resistor you need P = I x E = 1 x 4 = 4 watts, which is a pretty large resistor.
You can also use a light globe to drop the voltage and also be sure that the
battery is charging. A 12 volt 25 watt globe should draw 25 / 12 = 2 amps. The
resistance of the globe at 12 volts would be R = E / I = 12 / 2 = 6 ohms. 4
volts dropped over 6 ohms would be I = E / R = 4 / 6 = .66 amps which is a good
charge for 10 Amp Hour battery. BUT light globes have a lower resistance at
lower than operating voltages and you might get a 1 amp charge rate, which is
just fine.
Wall transformer chargers are available for most voltages.
Resistors can reduce current. Transformers and diodes can make higher current
chargers. Check charge voltages and currents.
Ni Cds trickle charge at a
1/10 of their AH rating for 14 hours. That's 140% of their amount of discharge.
Most cells will not be hurt by this charge, but wet Ni Cds will vent water vapor
that has to be replaced with distilled water right after a full
charge.
Connectors. Matching the plugs on consumer camcorders is
difficult. Some power cables can be cut and reconnected with plugs. Some Sony
cables use 3 wires and all three are needed to use the factory power supply. A
stereo 1/4" plug or 4 wire Jones plug are cheap and easy to wire. Put the male
plug on the camera side.
For 2 wire systems I like the Jones plugs. If
you have 6 or 8-volt systems and also 12-volt systems you might use 4 pin Jones
for the 12-volt systems to avoid wrong voltage problems. Radio Shack stocks the
2 pin Jones.
Meters. To build, test and maintain batteries you must have
a VOM with amperage scales and know how to use it. They are useful even with
commercial batteries and for trouble shooting cables, batteries, fuses, lights,
and outlets.
Battery terminal voltages vary for many reasons: 1. The
charge remaining. 2. If on or off charge. 3. Rate of charge. 4. Time after
charge. 5. Time since discharge and amount of discharge. 6. If in use. A battery
can have an almost open circuit and can read full voltage with a meter, but not
run camera. A useful device is making an adapter between the battery and camera
that will check both the battery voltage and current with the camera running. I
feel this it the best test. The factors above still apply. You can also connect
a 12 volt 25 watt car lamp to a camera plug (XLR-3 male) and test cables and
batteries without a camera.
You can make your own Ni Cd "D" size 4 AH
batteries or replace cells in a bad back. You can replace one or two shorted or
open cells in a pack, but if more are bad, replace them all. A shorted cell will
read no voltage and the charger will keep charging and the batteries will get
hot and often self-destruct. An open cell will show a high voltage under charge
or discharge. Make sure to get solder tab cells and not 1.5 AH "D" cells that
are the same price as "C" cells. Include fuses in your pack.
When a pack
will run a camera for only a short time, but recharges too fast, it has partly
open cells. A larger voltage appears across the cell and tells the charger the
total voltage is up to full and the charger stops charging.
You can
parallel wire lead acid batteries for more AH rating, but not Ni Cds; they will
discharge each other.
When one cell of a lead acid pack goes bad, usually
most of the rest are about to go and should be replaced. A couple of years is
all you can expect under normal use.
DON'T LEAVE LEAD ACID BATTERIES
DISCHARGED. If you won't be using them for some time you can plug a trickle
charger into one timer set for one hour into another set for one hour and get a
1 hour charge every 24 days. Set the first one-hour and the second for 30
minutes and get one hour charge every 48 days. Most camera Ni Cds should not be
trickle charged. Some Ni Cds are made to trickle charge, such as toothbrushes
and raisers.
Other Ni Cd batteries. The batteries and chargers for remote
control cars are cheap and work fine for 6 and 7.2-volt cameras and DAT
recorders. They will run a camera for quite some time. These packs have
thermocouple cut-offs that open when the battery gets hot from charging or heavy
discharge.
Portable power tool batteries come in 7.2, 9, 12, 14, and 18
volts. They are cheaper than camera batteries. Many also have thermocouples. The
flashlights for these batteries can be converted to pocket or belt packs with a
cable. Watch polarity!
Ni Cd batteries loose about 1% of their charge per
day. Nickel Hydride even faster. Lead acid batteries hold their charge very
well
Most Ni Cd 9-volt transistor batteries are 7.2 volts and won't work
for radio microphone systems. There are a few 8,4 volt ones that will
work.
Dry batteries are not very useful for cameras because they loose
their voltage quickly. A camera will stop long before the battery is even partly
discharged. .9 volts is the lowest design voltage for a 1.5 dry battery with a
1.6 initial voltage. Even "D" size batteries won't last long. Maybe for the very
low current Sony TRV 900.
Used and surplus wet Ni Cd batteries can give
very large currents and can last many years with care. Unused ones can be many
years old and if they will take a charge will probably work fine. C and H Sales
in Pasadena California have some 28 volt 8 AH packs for $100 that will run a
30-volt Photosonics, XR-35 or Fries Mitchell motor. Be careful of polarity
because some of the same plugs have different polarity. These batteries can be
tapped for lower voltages.
A convenient pack for hand held Arri IIIs is
are 10 "C" Ni Cd cells in a 5 and 5 cell pack with cable attached that will fit
in the pocket or belt clip. A charged pack will shoot 2 or 3 mags. The same
thing could be done with 12-volt portable tool packs, which would have chargers
available. Try the flashlights for battery holders.
Photosonics 16 mm IVN
and 35 mm 4ML are sensitive to voltage over 28 volts. A Ni Cd battery just off
charge can have enough voltage to damage the electronics of the
camera.
110-volt packs can be made of 10, 12-volt car batteries or a set
of Ni Cds. The Ni Cds will hold voltage and color temperature better, but are
less efficient that lead acid per pound. Chargers can be as simple as a
rectifier and voltage dropping light in series from 110 volt AC. USE A ISOLATION
TRANSFORMER TO PREVENT DEADLY SHOCKS. Rectified 110 AC is about 140 volts and
can be reduced with lights. A 9 light FAY will allow different charge rates for
large car battery systems. The lights are running at a very low voltage and
won't effect their longevity.
A handy unit is the 6 globe 12-volt light
made by American Market. Each globe is switched and both halves will pan
separately for more control. This can light backgrounds where cabling regular
lights is not possible.
Battery care. Don't deep cycle lead acid
batteries. Using Ni Cds until video cameras quit is proper deep cycling and
other cycling should not be needed.
Recharge lead acid batteries as soon
as possible.
DO NOT RUN BATTERIES LOW WITH LIGHTS. It is bad for all
kinds of batteries. When a light gets a bit dim, turn it off.
Most Ni Cds
can be left discharged. I don't know about Nickel Hydride.
© Copyright
1999-2004 Ron Dexter. All Rights Reserved.