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Batteries and the R/C Hobby Virtually all of the portable equipment we use in this hobby is powered by rechargeable
batteries. Power is needed to operate radio transmitters, airborne receivers, starter motors and glow plug ignitors to
name a few. In the 1960's, the primary batteries in use were Nickel Cadmium (NiCd) types. These are still in use today,
but in lower numbers; replaced with newer technologies such as Nickel Metal Hydride (NiMH) and Lithium Ion (LiIon). With the
development of electric aircraft and cars, the LiIon battery has become very popular. Lastly, lead-acid (Pb) batteries continue
to be a very popular choice of hobbyists to operate popular electric starting motors and field battery chargers. The low energy
density and relatively high weight of Pb batteries make them undesirable for airborne applications.
NiCd Batteries The
NiCd battery has been in use for some time in RC systems and throughout the hobby. It paved the way for smaller radio
control transmitters and helped in the development of a variety of hobby related devices . The primary chemistry is Nickel,
Cadmium and Potassium Hydroxide. A single NiCd cell has a nominal voltage of 1.2 volts. Cells are assembled into "pack"
of cells connected in series, parallel or a combination to achieve the desired voltage and capacity. Batteries can be discharged and recharged many times before it can no longer supply reliable energy. They can be
cycled up to several hundred times before requiring replacement. Today, the NiCd is used less than in years past due to the
introduction of the NiMH battery. NiCd batteries are still in use however, their use is in lower numbers in the hobby world. A 4 cell, 4.8 volt NiCd battery pack. Note the NiCd indication NiCd batteries are recharged with a small device that delivers a constant current to the pack until
the charger shuts off. Chargers can be powered from AC power in the home. There are portable chargers that are powered from
a 12 volt battery and are suitable for use at the flying field. The shut off time can be dependent on time alone or voltage.
Today, chargers are made to detect what is called "peak voltage". Once the pack reaches a preset level the
charger reduces the current to a lower level allowing the pack to remain connected without damage. The chargers we use in
the RC hobby (and elsewhere) are peak detection types. One of the negative characteristics of these batteries is known as
"memory effect". This happens when the battery is partially discharged then recharged. Many of these will not
fully recharge, thus providing less than 100% of their rated capacity. To correct this phenomenon, the batteries need to be
"cycled" (fully discharged then recharged) to return their capacity to normal. Cycling is also recommended to trend
capacity loss over time. Once the capacity reaches 70% of rated the battery should be replaced. You can read more about this
on page 31 of my tutorial. You can also learn more about NiCd batteries on the Wikipedia website. NiMH Batteries This
battery type was introduced in 1989 and offered improvements to NiCd batteries. Cells are also 1.2 volts nominal. When comparing
technologies, there are always pros and cons. You can read a lot more about batteries on the Wikipedia website. There is a lot of good information on those pages. The NiMH battery offered two major improvements over NiCd; higher
energy density (more energy in a smaller package) and no memory characteristics. They are also lighter; great for
model airplanes. You can buy either NiCd or MiMH battery packs for RC use, but most people buy the NiMH. One of the early
disadvantages of NiMH was the short charge retention time; shorter than NiCd. NiMH batteries today have largely overcome this
problem and many can hold 75-85% of their charge for nearly a year. The NiMH battery
is charged with equipment similar to that used to charge NiCd types. There are also chargers available that be programmed
to charged both types. An 8 cell, 9.6 volt NiMH battery pack. This is a common package
for a transmitter. The only way to distinguish between this and a NiCd is the label. Most ones I've seen have always
been marked. Sometimes, though, the chemistry may not be disclosed. I would avoid these unless you are sure of the type and
quality of the battery pack.
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Lithium Ion Batteries The newest technology to come on to the RC (and other) markets is the Lithium Ion (LiIon) type.
This battery possesses the highest energy density of the four discussed here. It is a unique chemistry, considerably more
expensive and requires specialized chargers and care. All rechargeable LiIon batteries are not created equal. This technology
is unique in a number of ways; one being the variety of chemistries that exists within the LiIon world. There are Lithium
Cobalt, Lithium, Phosphate, Lithium Manganese and Lithium Iron. There are others, but these are the ones used in the RC hobby
that I know of. Lithium Cobalt was the first to hit the scene and is the same chemistry used in cell phones, notebook computers
and other similar applications for consumer devices. A 3 cell, 11.1 volt lithium Ion battery pack. Cell
construction can be cylindrical or prismatic. The pack illustrated above is using prismatic cells. A single LiIon cell has a nominal voltage of 3.7 volts. Common battery packs start with 2 cells and
can go as high as 10 cells. One characteristic that separates the LiIon battery from all others is the ability for them to
deliver extraordinary amounts of current over a short period of time. Discharge currents of 100 amperes are common. This
has enabled the electric segment of the hobby market to explode into a seemingly endless variety of airplanes, helicopters,
cars, boats and accessories. LiIon batteries are also used in radio transmitters and airborne receivers.You can read much
more about this battery technology on the Wikipedia website. Other Types of Lithium Batteries Since I wrote this, I've learned of still more Lithium battery types. They include Lithium Phosphate, Lithium Manganese
and Lithium Iron. Each type has their own unique operating characteristic, voltage, advantages and disadvantages. You get
one thing with one type, but give up something else in return; a compromise.
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Lead-Acid Batteries The lead-acid (Pb) battery has been in existence for many years. Invented in 1859, by Gaston Plante', it
has been used in a wide variety of applications inlcuding automotive, industrial and consumer electronics. A lead-acid cell
is 2 volts nominal. We use Pb batteries primarily in the RC hobby to start our engines and recharge our NiCd, NiMH and LiIon
batteries at the flying field. The typical battery is a 6 cell, 12 volt unit that does not require water additions like some
lead-acid types. Due to their low energy density and high weight, they are simply not suited for airborne applications. Charging
is accomplished through the use of chargers that employ a constant voltage and current detection circuit. This is one of several
charging techniques. A 6 cell, 12 volt lead-acid battery
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Electrical Ratings of Batteries This discussion will focus on the ratings of NiCd, NiMH and LiIon batteries used
in our RC hobby. Lead-acid will be addressed later. The common expression of a battery's ability to deliver a specified amount
of energy over a given period of time is the amperehour. Rated capacity means nothing unless it is tied to a specific end
of discharge voltage. For NiMH and NiCd types the final voltage is generally 1.1 volts per cell. For LiIon it is 3.0 volts
typically. Temperature factors into capacity, but for hobbyists, it really isn't a consideration. Generally, though, lower
temperature translates into lower capacity (run time). Our RC batteries are typcally
rated in milliampere hours; that is, fractions of an amphour. A typical receiver battery pack is 4 cells, 4.8 volts and
its capacity is about 2000 miliiamp hours, or 2 amp hours. That rating means the pack will deliver 2 amps for one hour. At
the end of one hour, the battery will be at 4.4 volts (1.1 vols per cell). Alternatively, the same battery, when delivering
500 miliiamps (.5 amps) will operate a device for 4 hours down to 4.4 volts. 500 milliamps for 4 hours equals 2000 milliamphours.
If the same battery is discharged at a rate of 4 amps, it will operate down to 4.4 volts for 30 minutes. The relationship
between operating time under load and the load current is a linear one.
Product
Review-West Mountain Radio CBA II Battery Analyzer Back in 2007, I bought
one of these units and it sat on the shelf until this past June; 2 years + since I bought it. I just never got around to playing
with it until this spring. I didn't get a chance to do any write ups on it until I was on vacation and now it's the end of
that all too short time away from work. If you want the Reader's Digest version of my "report", here goes. It's
a great little unit that does just what the manufactrer says it does. Easy to use, simple to hook up. You need only know the
rating of your battery pack to program the software. The CBA II is no longer produced by WMR and has been replaced with the new and improved CBA III. If you want a CBA II, you can call them and ask about one.
I find they are still on the web for sale. One vendor being Power Werx. Between them and WMR, they've pretty much got you covered in the battery test and DC power hookup world. A Bit More In-Depth Please... The CBA II is
a battery discharge-only test set. There is no recharge functionality, so you'll need the services of your chargers to take
care of that function after you've tested a pack with this unit. There are two parts to the system; hardware and software.
The hardware consists of a cube-like unit consisting of a fan, heat sink and microprocessor control unit located in the base
of the hardware. Input/output ports, staus indicator LED's and a temperature probe socket are also included. The software
is essentially the method by which the end user make the CBA II do his/her bidding. It's included in the box and upgrades
are available from the WMR site. My upgrade to version 2 was free since I already had the original software. From the user
screen, test parameters are entered and the test controlled from start to finish. Actually, once started, it's an automatic
operation unles you, the user elect to stop the test manually.
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Rick Tressler - Columbus, Ohio
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