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Amperage, wattage, C/rate, -delta V, memory, full discharge... the confusing
jargon goes on and on. Choosing a suitable power product in today's
world of advertising hype, rumors, and well-meaning advice can be a
frustrating adventure. To make the proper choice it is important that
you have a basic understanding of the most important component of any
DC power product: the battery. To help you in that understanding the
next few pages are devoted to basic, factual information about battery
technology. We hope it will prove informative regardless of which product
or brand you purchase. Taking time to read these pages will give you
the facts necessary to choose intelligently the most effective solution
for your power needs.
Nickel Metal-Hydride, Zinc-Air, Lithium-Ion, and many other innovative
battery types are the focus of massive R&D efforts, and significant
breakthroughs are made daily. Both Nickel Metal-Hydride and Lithium-Ion
cells are greatly extending the runtimes and reducing the weight of
numerous consumer and professional products. At present, they have been
primarily applied to products with low discharge requirements, such
as cellular phones, laptop computers and camcorders. that is because
these cell types have typically had high internal resistance characteristics
which would cause them to break down under heavy loads such as video
lighting.
In our opinion, these limitations have kept them from being ready for
the rigors of the professional video power environment. In the last
few years, however, dramatic improvements have been made in the capacity
and performance characteristics of newer cell chemistries. Shortly,
they may be equal to or surpass traditional cell chemistries in the
applications our products are used for. At the point that these new
battery types are proven to offer both superior performance and reliability,
you can expect many new products from NRG designed to bring you the
benefit of these advances.
While the future holds great promise, there is no need to wait since
outstanding and proven battery performance is available now. The two
main battery types presently used for powering video cameras and lighting
are Lead-Acid and Ni-Cad. Before deciding on a brand or style of power
product, it is wise to decide which of these battery types will best
meet your power needs. Let's take a quick look at each type.
- Lead-Acid Batteries
Despite new-fangled nicknames such as "gel-cell" and "starved
electrolyte", the basic lead-acid battery is one of the oldest
of cell types, with a history dating back to the mid-1800's. Lead-acid
batteries exhibit good physical durability and can withstand poor charge
habits and high rate discharges. Unfortunately, lead-acid batteries
are almost twice the weight of a comparable Ni-Cad battery and can suffer
damage if not recharged regularly. Their popularity in the consumer
video market is primarily because of their appealingly low up-front
cost.
Despite their low initial cost, the long-term disadvantages of lead-acid
batteries should be understood and carefully considered since they may
prove limiting in many professional situations. Lead-acid batteries
have a low energy-to-weight ration - which means that for any given
capacity a lead-acid battery will be much larger and heavier than more
efficient battery types. They have a short life, especially under the
power-hungry requirements of video lighting which can make the cost-per-charge
higher than for other cell types. But the most significant drawback
is the substantial load depression and poor voltage regulation exhibited
by lead-acid batteries during discharge. Load depression is a lowering
of the battery voltage under load due to internal resistance and heating.
This is further compounded by the sloping nature of a lead-acid's voltage
under load. Since the voltage of the battery drops and continually slopes
downward during discharge, maintaining the intensity and color temperature
of lighting is impossible and other equipment may shut down prematurely.
Storage presents additional difficulties as lead-acid packs cannot be
stored discharged for extended time periods without irreversible damage
due to internal sulfidation. Regardless of the charge state prior to
storage, periodic charging during storage is necessary to preserve cell
function.
- Ni-Cad Batteries
Ni-Cad batteries also have a long history, with the first designs dating
back to experiments by Edison in the early 1900's. Because of their
performance potential, these cells have undergone far more significant
design improvements than other cell types. Ni-Cads have an extremely
high power-to-weight ratio, weighing 20% to 50% less than other types
of equivalent power.
Ni-Cad batteries can be stored for extended periods of time without
damage and they deliver outstanding performance even in extremes of
hot or cold. The most notable characteristic of Ni-Cads in a video environment
is their superior discharge performance, even under heavy loads (such
as lighting). They allow the delivery of stable voltage, with minimal
voltage drop, even during high discharge. These characteristics allow
the color temperature and intensity of lighting to remain quite consistent
during discharge and premature equipment shutoff is avoided.
Ni-Cad cells have one barrier that limits their exclusive use: cost.
Because of the sophisticated engineering required to manufacture quality
cells, the expense of raw materials and the manufacturing complexity
of peripherals such as chargers, Ni-Cad-based products have been typically
two to six times as costly as those based on other cell types. Application
of Ni-Cad cells has, therefore, typically been limited to power products
intended for professional and broadcast use. NRG was an early pioneer
and remains one of the few companies that has been able to bring products
using high-grade Ni-Cad cells to market at a price realistic for a broad
range of videographers.
Later, you will learn more about how battery capacity affects runtimes.
As critical as capacity is to the usable runtime of a pack, there is
another factor of equal importance: the "Discharge Profile"
of the battery. This term refers to the way a battery's voltage drops
during discharge. Even if the capacity of a battery were unlimited,
when its voltage reaches a level at which your equipment shuts off or
performs poorly, its power would be unusable. Clearly then, capacity
is not the only specification to be considered. A discharge profile
is useful to illustrate this point because it graphically shows the
battery's voltage over the time of discharge. By comparing the discharge
profile of a typical Ni-Cad and lead-acid pack we can begin to better
understand the differences we have been discussing.
When a battery is placed under the load of the equipment you are operating
and begins to discharge, the voltage of the pack drops continuously
as the pack empties. As we have discussed previously, the voltage of
lead-acid batteries tends to constantly shift downward in a sloping
fashion. Ni-Cad cells, on the other hand, tend to discharge with a stable
and relatively flat voltage profile until full discharge has been reached.
Only then does the voltage drop rapidly.
While these differences might seem of little importance, they can have
a major impact on your equipment and the look of your finished production.
For example, the color temperature and intensity of the lighting will
be lower and continually shifting when used with a lead-acid-type battery.
Because of this, high-wattage lamps may have to be used to obtain the
light intensity required. In addition, footage shot with a freshly charged
pack could exhibit noticeable differences in intensity and coloration
from shots that were made near the end of discharge.
Thanks to stable voltage and low voltage drop under load, lights powered
from Ni-Cad cells provide a purer and more intense light. This often
allows lower lamp wattages to be utilized for increased operating time.
Cameras and accessories benefit as well, since a Ni-Cad-based pack takes
longer to reach the voltage point at which devices power down. Low-resistance
Ni-Cad cells like those used by NRG deliver smooth discharge voltage
levels and such a small voltage drop under load that, many times, multiple
devices can be powered from a single pack.
It is important to consider not only the cost and performance of a power
source, but also how long it will be around to use. It's not pleasant
to think that the product you are now purchasing will some day wear
out. Nevertheless, battery life is an important selection factor.
If you plan to use the battery infrequently, its life may not be of
much concern and the initial cost savings of a lead-acid system may
make it an attractive choice. When battery life is averaged out to a
cost-per-charge, however, a Ni-Cad-based system will not only provide
greater comfort and performance, but may actually cost less as well.
For the frequent user a Ni-Cad-based system generally represents the
best value.
When looking at claims for how many cycles a battery will provide, it's
important to know at what point the product's manufacturer considers
the battery to be unusable. Reputable manufacturers, including NRG,
often consider 50% of a pack's original capacity to be the end of its
useful life. Take this into account when planning your runtimes. Buying
a product that gives longer runtimes than you initially require ensures
adequate runtimes as the pack ages and its capacity decreases.
Nothing in the video power realm has been more misunderstood or given
more cause for discussion than the term "memory". This one
word has become the catch-all for every bad experience associated with
battery products of any type, from any manufacturer.
"Memory" is the coined term mistakenly given to a phenomenon
correctly called "voltage depression". Here again the adjoining
discharge profile may prove useful to graphically illustrate the problem.
As you can see, this type of voltage depression is an abnormal dip in
the discharge voltage curve. It begins unnoticed near the end of discharge
and then over many charge cycles progresses toward the beginning of
the cell's discharge. If the equipment being powered has a preset shutoff
point, i.e., a camcorder, it may mistake the voltage dip for an empty
pack and shut down prematurely. This can cause the user to suspect that
the battery has failed prematurely. It is important not to confuse the
voltage depression discussed here, with the load depression of a battery's
voltage under discharge as discussed in the previous section.
So what causes voltage depression? There are many rumors in circulation
but our opinion, based on extensive research, observation and input
from leading manufacturers, is that voltage depression is caused primarily
by subjecting a Ni-Cad battery to overcharge for an extended period
of time. Overcharge can occur when a charger fails to sense charge completion
efficiently, a user does not follow the manufacturer's directions, or
a battery intended for a slow charge rate is charged too rapidly.
The fact that voltage depression can be easily eliminated is probably
responsible for the "memory" misnomer. The slight dip in the
discharge voltage profile caused by voltage depression can be eliminated
and a proper voltage profile restored - by fully discharging the pack
(to slightly below one volt per cell), and recharging it.
Unfortunately, unless the cause of overcharging is resolved, the condition
will likely recur. In addition, the life expectancy of a battery pack
is substantially reduced when deeply discharged. Thus the pack user
is caught in an endless cycle. Fully discharging the pack before each
charge wastes stored power and shortens battery life, but failure to
do so may lead to voltage depression.
Some manufacturers of lead-acid power products and Ni-Cad discharge
units have gone to great lengths to build up the "Memory"
stigma. In most cases voltage depression is not the cause of a user's
problem. Age, use patterns, and unrealistic claims are more likely culprits.
Indeed it has been our experience that many people who fear their batteries
are suffering from "Memory", are not even using Ni-Cad-based
packs.
Lead-acid batteries do not experience voltage depression but they often
suffer far more serious and irreversible effects from overcharge and
the formation of lead-sulfate crystals during self-discharge. This,
along with the short life of lead-acid cells, has led most professional
power product manufacturers to utilize primarily Ni-Cad batteries.
NRG's combination of overcharge-tolerant rapid-charge cells and charging
systems virtually eliminate voltage depression - and thus the memory
stigma for our users. Our Ni-Cad packs may be charged at any time and
used even if the charge cycle is not completed.
Nothing could be more important when selecting a battery pack than ensuring
it will operate your equipment for the needed length of time, yet few
things are as frustrating as trying to make sense of manufacturers capacity
ratings. Have you ever wondered why a so-called "two-hour"
battery only lasted 20 minutes, or why a 13-amp lead-acid battery would
only run an 8-amp load for 40 minutes? It seems logical to expect a
battery rated at 13 amps to power a 13-amp load for one hour or a 1-amp
load for 13 hours. In most cases however, this conclusion would be incorrect
due to the real-world physics of a battery during discharge.
During discharge, a battery's chemical makeup and internal resistance
play a vital role in determining what the actual capacity of the battery
will be under a particular load. The more quickly power is drawn from
a battery, the lower its voltage will drop and the less efficient it
will become at delivering power.
Many users consider the amp-rating of a battery to be the most accurate
indicator of its capacity. But the amp rating is not a useful figure
without knowing under what rate of discharge the claimed capacity was
measured and how the battery will de-rate from that figure at the rate
you plan to use it! For example, if a battery was rated 20 amps at a
twenty-hour rate (almost all lead-acid cells are rated this way), it
would theoretically produce one amp for each of 20 hours. If, however,
you suddenly demand power typical of the video environment - for example,
a 100-watt video light which pulls 8.3 amps - the battery will become
far less efficient at delivering its power. It may now only produce
a small amount of its originally rated power, as little as 10 or 12
amps. Thus a light that "should" run for 2-1/2 hours might
instead run for much less than two.
Many manufacturers publish amp-ratings based on slow rates of discharge
over long periods of time. Others unfairly compare their products' performance
at an optimum rate to a competitor's performance under a heavy load.
This can lead to inaccurate comparisons and the purchase of a product
incapable of meeting your power requirements.
In order to properly compare power products you should determine what
the power consumption of the equipment you wish to power is. The amperage
or wattage draw is often listed on the equipment or in the owner's manual.
Converting wattage to amperage is easy. Just divide the wattage by the
equipment voltage. If you know the amperage just multiply it by the
voltage to find the wattage for example: 2 amps x 12 volts = 24 watts.
Once you have found and added together the amperage or wattage of all
your equipment decide how long you wish it to operate. Once you have
done this finding the necessary battery capacity is simple. Let's assume
for purposes of illustration that your equipment will use about 55 watts
(4.6 amps) per hour. To run this equipment for one hour, a pack rated
at least 55 watt-hours or 4.6 amps at a one-hour rate would be needed.
As you can see, it is important not only to find a battery with 4.6
amps of capacity, but one capable of delivering 4.6 amps of capacity
over a one-hour period. Always ask a manufacturer for not only the capacity
of the battery, but its capacity at your anticipated rate of discharge.
The voltage level at which your equipment shuts off can also play a
significant role in runtimes. If a battery pack's voltage drops below
the minimum level the connected equipment requires to operate, all the
capacity in the universe won't keep your equipment running. This issue
is discussed further in the "Voltage Choice" section that
follows.
Because lead-acid batteries are typically rated at a slower discharge
rate than Ni-Cads it has always been difficult trying to compare the
amp-ratings of various power product manufacturers. Attempts to do so
have resulted in confusing claims and counter claims. Most manufacturers,
including NRG, have now adopted a clearer and more meaningful method
of rating pack capacity: the watt-hour rating standard. When correctly
calculated, the watt-hour rating expresses the pack's total delivered
capacity in watts when it is discharged over a one hour period. Since
the power consumption of most equipment is expressed in watts, this
figure makes it easy to estimate equipment runtimes. For example, if
a camera draws 30 watts and it is powered from a 60 watt-hour pack,
it's a safe bet it will run for over two hours. Since a battery's efficiency
will increase when it is discharged over a period longer than an hour,
the one-hour rate generally represents the worst case available capacity.
This method of rating and expressing pack capacity had eliminated the
variables in other performance specifications. Unfortunately, some manufacturers
still publish enormously inflated watt-hour ratings that are incorrectly
based on a 20-hour discharge rate rather than on the correct one-hour
rate. Following this section you will find a comparison chart with a
sampling of brands representative of products from entry to broadcast
level. You will also find a summary of all our power products' performance
under the full range of ratings mentioned here.
Professional-grade equipment such as an industrial- or broadcast-level
three-chip camera generally has a high shutoff voltage (usually 10.9
to 12 volts). This high shutoff voltage prevents the equipment from
fully accessing a 12-volt battery's capacity, since the equipment will
shut off before the pack is fully drained. Using a 13.2-volt pack generally
allows equipment to fully access all the capacity of the pack and prevents
early shutdown. In many cases it also allows lighting to be used simultaneously
from the same power source.
Some users fear using these higher-voltage packs on their equipment.
It is important to realize that while 12 volts may be specified as the
input voltage, every power supply has a wide operational latitude, in
many cases as high as 16 or 17 volts. Also, when placed under a load,
a 13.2-volt pack drops almost immediately to around 12.5 volts, a perfect
operational voltage for professional equipment. While you should always
check with the original manufacturer of your equipment, the performance
of almost any deck or dockable will be safely improved by utilizing
a 13.2-volt pack.
In order to have power available to take out of a battery, it must have
been effectively stored to begin with. This task falls to the charging
device. While many equipment owners take their chargers for granted,
there is nothing other than the battery type itself, that has such an
impact on the capacity, performance and life of a power product. An
improperly designed charger can prevent even the best cell from attaining
maximum capacity or even damage it permanently by overcharging it.
If you have a collection of packs and chargers, never try to utilize
a charger designed for one product with another, especially not a lead-acid
charger with a Ni-Cad battery or vice versa. Lead-acid and Ni-Cad chargers
are fundamentally different. A Ni-Cad battery charges optimally with
constant current, whereas a lead-acid battery charges with constant
potential. In addition, many newer packs share information from sensors
with the charger to assure maximum safety and pack life. Since a charger
is generally matched to the pack it is intended to charge, it is best
to use only the manufacturer's recommended charge unit.
One of the most frustrating aspects of charging is simply waiting for
a charger to restore the pack's power. Many standard chargers can take
24 hours or longer. Thankfully, quick-charge-capable Ni-Cad cells such
as those utilized by NRG can be charged in record times with a quick
charger. It's easy to imagine how this can open up a whole new world
of convenience. By alternating two packs on a quick charger you can
have virtually non-stop power even from small packs. Unfortunately,
the electrochemical and internal resistance characteristics of lead-acid
batteries prevent them from being effectively rapid-charged.
Charger size and weight are important considerations if the charger
is to be frequently transported. Many advanced chargers utilize a Pulse
Width Modulated power supply in place of a conventional transformer.
This results in a much smaller and lighter charge unit.
If you will be traveling with the charge unit, consider a unit which
can adapt to worldwide voltages without an external converter. Some
units can be switched between one or two worldwide voltages such as
110 or 220. More sophisticated units automatically adjust for any incoming
voltage worldwide.
It may be necessary to charge a pack in remote locations where no conventional
AC power is available. If you might find yourself in such a situation,
make sure charging options such as car chargers and solar panels are
available for the power product you choose.
The variety, quality and safety of a manufacturer's chargers, along
with the potential to replenish a pack's power quickly is yet another
important factor in choosing what type and brand of pack to purchase.
Now that you know the basic pros and cons of the two main battery types,
you can decide which is right for your needs. As a general rule of thumb,
if you are working with consumer-grade equipment, your plans don't call
for the use of much lighting, and cost is a primary factor, consider
using a lead-acid-based product. It won't be as light and comfortable
or have the life span of a Ni-Cad-based product, but it will provide
extended runtimes at an unbeatable cost.
If you are involved with video on an ongoing basis either as an advanced
semi-professional or a full-time working videographer, the extra cost
of a Ni-Cad pack is generally well-justified in light of its reliability
and performance. The extra up-front product cost will be quickly forgotten
after experiencing the comfort and convenience of a high-performance
power pack.
As you continue reading, we trust you'll have a better understanding
of both the lead-acid and Ni-Cad battery types and be better prepared
to make an informed choice as to what type of product may be the best
suited to your individual needs.
Once you have decided on a cell type and capacity, you should consider
what style of physical pack housing is available and will best suit
your needs. The physical packaging of a battery can make a big difference
in everything from its comfort to its long-term durability.
Many low-cost packs are housed in a single cloth pouch which can be
slung over the shoulder or attached to a belt. This is a convenient
configuration for packs up to about 3.5 lbs., but in greater weights
can cause you to list like a sinking ship.
Packs sometimes called "bricks" are made by several manufacturers.
A brick-style battery is housed in a hard plastic or metal shell which
attaches directly to the rear of most broadcast cameras. This pack style
substantially increases the "on-shoulder" weight of the camera
but is convenient and effective for short, ENG-type shoots with a low-wattage
fill-light.
A belt-style pack is a comfortable and efficient way to carry batteries
designed for long shoots and higher-wattage lighting. The belt style
eliminates the weight of the pack from the camera and disperses the
weight of the pack evenly around the waist, an area where many of us
are already used to carrying some baggage... :) A power belt can also
be wrapped around the legs of your tripod to give it better stability.
Some belt styles offer removable packs. This allows you to exchange
a discharged pack for a fresh one without removing the belt or losing
power. In addition, different capacities of packs can be used to accommodate
a variety of shooting situations.
A vest style provides the ultimate combination of comfort and weight
distribution. The weight of the batteries is shared by both your shoulders
and waist. It looks great and has lots of pockets for spare goodies.
In a "can" or "lunchbox" style a large battery is
placed in a container with a carrying handle. Often the charge unit
is in the same housing. Usually reserved only for large, heavy batteries,
this style does not lend itself to rapid mobility. Once on location,
however, you will be amazed by the brute power these packs can deliver.
Regardless of what pack style you choose, give weight and size significant
consideration in the selection process. These factors may seem unimportant
now, but they will take on amazing significance when a 20-lb. "Leadmaster
2000" belt pulls down your pants for a day.
The last decision in selecting a power product is how it will adapt
and connect to your equipment. Manufacturers such as NRG make a wide
variety of cables and adapters to interface almost any equipment to
a power source. In fact, one of the major but often overlooked advantages
of an external pack is that it does not become obsolete when your equipment
changes and it can power many different devices. This can be a significant
cost savings over individual proprietary packs.
An interface cable has a plug or jack to connect into the equipment
being powered. An adapter is similar except that it generally has a
special fitting or plastic case that allows a manufacturer's proprietary
connector or battery mount to adapt to your off-board power source.
If the equipment requires a voltage lower than that of the power source,
the adapter may also house a small power supply to reduce and regulate
the voltage. To assure maximum battery life and reliability it is important
that this power supply be a switching type and not a linear supply.
On the other end of the cable which plugs into the battery pack, you
will need to choose between the two main styles of DC power connectors:
cigarette-lighter plug or the 4-pin XLR. The cigarette-lighter plus
is used widely on consumer equipment due to its low cost and compatibility
with automotive cigarette-lighter receptacles. This connector allows
equipment to be conveniently powered in a car but it has a bad habit
of popping loose at inopportune times. Because it is made of plastic
it is also easily broken. The 4-pin-style connector is the choice of
video professionals and is used almost exclusively on professional equipment.
This is because its locking mechanism provides a secure connection,
its pins make better contact for power transfer, and the metal connector
itself is nearly indestructible. For users who may on occasion wish
to connect 4-pin equipment in a vehicle, compatibility can still be
maintained through an inexpensive 4-pin-to-cigarette jumper cable. NRG
is one of the first manufacturers to offer choices and combinations
of these popular connector styles.
Choosing a power product is an increasingly difficult decision. Equipment
is changing rapidly and there are many power solutions to select from.
Here at NRG we have always believed that our best customer was an informed
customer. That's because an informed customer is capable of choosing
the best equipment to meet their needs and is able to access and appreciate
the product they have chosen to purchase. We truly hope the preceding
section has been of assistance to help you better understand our products
as well as those offered by other manufacturers. Whatever your choice
in power sources, please accept our best wishes for success.
 
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