y apologies. I had every
intention this month of
publishing my new Radio
Control (RC) electric
sailplane model that I hope
beginners will build from scratch. (It’s not a
kit or an Almost Ready-to-Fly
[ARF]/Ready-to-Fly [RTF] model!) As I
learned, designing, building, flying,
photographing, and writing about it takes
more than four weeks. I promise to publish
my “Scratch-One” design next month.
This month (the eighth installment I’ve
written) will be devoted to the all-important
battery basics. In the previous seven
chapters I’ve referred to the RC-system
batteries and the electric-motor batteries on
many occasions. I will probably repeat some
of those points to emphasize their
importance.
The battery power to your RC system is
like putting gas in your car; if you run out of
gas, the car doesn’t run. If your RC system
runs out of electrical power, it doesn’t work
(fly)! During this presentation I will
concentrate mostly on the RC-system
batteries, but I will get into some aspects of
the electric-motor batteries as they are used
in electric-powered flight.
Types of Batteries: In the RC hobby today,
modelers typically use Nickel Cadmium
(Ni-Cd) or Nickel Metal Hydride (NiMH)
cells. Both are rechargeable batteries. Under
normal operation they can be recharged
hundreds of times and have been known to
last an average of three to five years and
more.
From a beginner’s perspective Ni-Cd and
NiMH cells provide roughly the same kind
of service, so you need not worry at the
start about what kind of cells were supplied
with your particular RC system.
The NiMH cell is the newer of the two. It
can offer more capacity than the Ni-Cd cell
of the same physical size. More capacity
means that it can operate your system longer
or fly your airplane longer. NiMH cells have
a slightly lower characteristic voltage under
load than Ni-Cd cells. From an RC-system
standpoint, that difference is of little concern
because the load is relatively low.
However, when using NiMH cells for
electric-powered flight, the difference can be
important. If you fly a model with a sevencell
Ni-Cd pack, then substitute a pack with
NiMH cells, you might have to go up one
more cell to a total of eight to achieve
comparable performance. With every
passing day, advancements in NiMH battery
technology are removing this deficiency.
Some inexpensive (economy-type) RC
systems are sold with no batteries included.
54 MODEL AVIATION
Battery
Basics
■ Bob Aberle
Ni-Cd NiMH Alkaline Li-Poly
Many typical battery cells used in RC systems and electric flight look almost the same physical size; it’s important to read labels. L-R:
two typical Ni-Cd cells, NiMH cell, AA alkaline nonrechargeable battery cell, new Li-Poly cell.
M
If that is the case, you will have to purchase
12 AA-size alkaline (nonrechargeable)
batteries (eight for the transmitter and four
for the receiver or airborne side). Although
these cells will last a long time (possibly 10
hours or more!), they must eventually be
replaced since they can’t be recharged.
Balsa Products sells a charger and eight
individual NiMH cells which must be
removed from the transmitter and placed in
the charger. After charging is complete, the
user inserts the cells back in the transmitter.
The charger is $22.95 and a set of eight
1300 milliampere-hour (mAh) NiMH cells
is $8.50. It’s an interesting solution to what
could become a costly long-term batteryreplacement
problem.
There is a new type of battery
technology called Lithium Polymer (Li-
Poly), which has emerged thanks to the
cellular-telephone industry. There isn’t
much application for this type of battery cell
for RC systems at this time, but you will be
hearing and reading more about the great
advantages of low weight and high capacity
for electric-powered flight. There will be
more about that in another installment.
Battery-Capacity Ratings: All batteries
have a capacity or rating. The capacity can
tell you how much power the battery can
supply in a period of time, or how long the
charge will last while powering your
system, appliance, etc.
Battery capacity for our purposes is
usually stated as mAh, and ampere-hours
(Amp-hr) are used for larger-capacity cells.
Most RC systems through the years have
been powered by Ni-Cd cells of
approximately 600 mAh capacity. Thanks to
the newer NiMH technology, highercapacity
cells are being offered with some
systems. I’ll use that 600 mAh capacity for
this discussion.
For most purposes, the Ni-Cd cell’s
nominal (average) voltage is 1.2 volts. If
you applied a load of 600 milliamps (mA) to
a fully charged Ni-Cd cell, it should take
exactly one hour for that cell to reach 1.0
volt. At that 1.0-volt level, the cell, by
definition, would be considered discharged.
If you continued to load the cell, the voltage
would rapidly head for 0.0.
We usually see RC transmitters with
eight-cell battery packs. Using the nominalvoltage
rule, eight of these cells in series
would produce a total of 9.6 volts. If we
used a commercially available battery tester,
we would apply a load until that pack
reached 8.0 volts (8 x 1.0 volts), at which
point the testing device would cut off and
the capacity in mAh could be read off of a
monitor, meter, or Liquid Crystal Display
October 2003 55
Typical RC system battery packs and charger. On left is RC
transmitter with rear compartment cover removed, exposing
eight-cell Ni-Cd battery pack (yellow). In center is dual-output
battery charger normally supplied with RC system. On right are
two typical four-cell Ni-Cd airborne battery packs (the ones that
go in model).
Balsa Products sells this eight-cell Ni-Cd or NiMH individual
battery-cell charger which comes with a set of 1300 mAh NiMH
cells, all for $22.95. You charge these cells by removing them
from RC transmitter.
Many of Bob’s battery packs for electric flight. There are too
many to keep on trickle charge at once, so he doesn’t!
After charging the individual cells, you load them back into the
transmitter’s battery compartment.
Photos courtesy the author Graphic Design by Lydia Whitehead
56 MODEL AVIATION
A typical RC transmitter and airborne battery pack are charged at
the same time using the supplied RC-system dual-output battery
charger. It’s left on overnight, or for at least 10 hours.
Bob holds the wall-plug dual-output charger. Green and red LEDs
are lit, indicating that charge is taking place. If the indicators are
not lit, it is not charging and you better figure out why!
ACE R/C Digipulse Multi-Charger can separately charge as many
as six battery packs at currents ranging from almost 0 upward of
200 mA. After a 16-hour charge, the charge current reverts to
pulsed trickle level which can remain indefinitely.
This is how Bob uses his Digipulse Multi-Charger to maintain six
RC-transmitter battery packs. The nice part of this charger is that
you can set the current for each battery pack.
LED screen on ACE R/C DDVC indicates that current was set to
110 mA. This charger has two separate outputs.
DDVC is excellent overnight adjustable charger, shown charging
1100 mAh RC transmitter pack at 110 mA: correct current for
C/10 overnight charge rate.
(LCD) screen. I’ll get into more specifics about battery testing later.
Charging: With respect to charging, you will hear the following
terms: overnight charging, field fast charging, and trickle charging.
The overnight charge rate is the one with which you should become
most familiar.
All battery charging, regardless of the type, is done as a function
of the battery’s rated capacity. You want to know what a battery’s
capacity is before you put it on a charger because too small a battery
charged at too high a charge rate will be “cooked.” On the other end
of the scale, too big a battery charged at too low a rate will never get
to full charge.
The overnight charging rate has been established for many years
as the capacity of the battery divided by 10 (usually written C/10).
This is the rate most RC-system dual chargers use.
When employing a C/10 overnight rate, you are instructed to
leave the batteries on charge for at least 10 hours. You could let
them go for 16 or even 24 hours, and you would never hurt the
batteries. This rule applies to Ni-Cd and NiMH cells.
As a beginner in the hobby, you shouldn’t experience any
problems if you use the unit that came with your new RC system to
overnight-charge (the night before you intend to fly) the transmitter
and airborne battery. As you progress in the hobby, you will learn
the rest of what is necessary to maintain your battery packs.
I need to repeat several items I have already mentioned in this
series because they are so important. First, when plugging your
charger into a household 115VAC outlet, make sure that the outlet
remains “live” during the overnight-charge period. If you plug your
charger into an outlet that is connected to your shop lighting, you’ll
turn off your charger when you turn out the lights, and nothing will
be charged.
Second, don’t be tempted to restore only enough charge to cover
what you took out at the flying field. When you return home, don’t
put the batteries on charge for only two hours if you flew for two
hours that day. Ni-Cd and NiMH battery chemistry is such that it
needs the C/10 charge current (rate) and a minimum of 10 hours of
charging. Anything less than 10 hours can cause problems.
Third, never charge a relatively high-capacity battery at a lower
rate, then leave it on for a much longer period of time to
compensate. In the past couple of years, new NiMH cells of the
same pen cell (or AA size) have come on the market with higher and
higher capacity ratings. The AA Ni-Cd cells were usually rated at
500-700 mAh capacity. Now these same-size cells have capacity
ratings upward of 1600 mAh.
Let’s say you replace your original RC-system batteries with
1600 mAh cells. Apply the logic that the charge rate must be C/10,
or 1600/10, which would require a 160 mA charge current, but your
RC-system charger produces only 50-60 mA charge current. Being
smart, you use that RC-system charger and compensate by leaving
the batteries on charge for 24 or 48 hours.
Don’t do this! That battery will never achieve full capacity unless
you get the current up to C/10. When using the higher-capacity cells,
you must purchase a charger with increased output.
One of the best for this type of charging is the ACE R/C Digital
Dual Variable Charger (DDVC). It has two outputs that can be
adjusted continuously from 0 up to approximately 300 mA current
and is capable of handling as many as 10-12 battery cells. In the
preceding example you would attach your 1600 mAh eight-cell
battery to the DDVC, dial up 160 mA current, and let it run
overnight for at least 10 hours.
Don’t worry about how many times you charge your batteries
overnight. At that rate, you could practically leave them on charge
all the time. I’ve never gone quite that far, but on many occasions
I’ve left batteries on the C/10 rate for 24 or 48 hours with no
degradation in performance.
I generally put my battery packs on C/10 charge (such as the RCsystem
charger) the night before I plan on flying. If it is raining the
next morning then several days go by before I have the opportunity
to fly, I charge the batteries overnight again. There may have been
only a few days between charging, but at this safe charge rate more
is always better!
Trickle charging is done at a rate considerably lower than C/10.
October 2003 57
Popular field-type fast battery chargers. Clockwise from top left:
AstroFlight 110 Deluxe, Watt-Age PF-12 Park Flyer AC/DC Peak
Charger, tiny Dymond Modelsports four- to eight-cell mini-peak
charger, FMA Direct Super Nova automatic peak-detect charger.
All employ peak-detect-type circuitry—as it should be!
Watt-Age charger is capable of operating at home on 115VAC
and at flying field off of 12-volt DC car battery. The 110 Deluxe
requires separate 115VAC to 12VDC power supply (at rear) to
operate from home shop.
FMA Direct Einstein XL dual-output battery discharge
tester/cycler (at top) and 115VAC power supply for it.
We generally refer to a trickle charge as
C/50, so that a typical 500 mAh battery
would be charged at only 10 mA (500/50 =
10). At that rate the battery can be left on
trickle for an indefinite period.
All of my RC transmitters are left on
constant trickle charge following overnight
charging. I have four transmitters that have
been on trickle charge for more than five
years and still have close to their full rated
capacity.
The advantage of trickle charging is
that the batteries are available the moment
you want to fly. However, you can only
maintain a charge level at trickle; you
can’t recharge a battery that has been
used at the trickle charge rate.
Photos show my shelf-mounted ACE
R/C Digipulse Multi-Charger. It has six
individual outputs, each of which can be
adjusted for charge currents of roughly 5- to
200 mA. A charge current can be set up and
will remain until you change it. After a
timed 16-hour period, each output reverts
back to a pulsed trickle charge that will keep
the batteries at peak performance, ready
when you are.
There is even a backup battery that
protects the charger’s memory in case of a
power failure. With the variable-chargecurrent
feature, you can set each output to
produce exactly the C/10 rate for each
battery capacity employed (up to
approximately 2000 mAh).
As I stated, all of my RC transmitters
stay on trickle charge. On the other hand,
almost all of my airborne RC equipment is
powered from the same cells that run my
electric motors. For those packs, of which I
must have more than 50 at any given time, I
don’t employ trickle charging because it
could be a logistical nightmare of chargers
and wiring.
Field fast charging is a high charge rate
that allows Ni-Cd cells to be completely
recharged in approximately 20 minutes
and NiMH cells to be completely
recharged in 30 minutes.
58 MODEL AVIATION
Close-up of Einstein XL. Note two separate outputs. You
physically switch meter function between output 1 and 2. On
each you can select charge current and number of battery cells.
When discharging, load is fixed 300 mA. After charging, outputs
revert to fixed 12 mA trickle-charge level.
FMA Direct helps connector situation with “junction box”
featuring variety of popular RC-system connectors. Very helpful!
Typical test of RC transmitter and receiver batteries using
Einstein XL. It tests battery, saves capacity measurement, and
does everything automatically, including recharging battery after
discharge test is completed.
Einstein XL just finished test and recorded 576 mAh capacity.
Note use of FMA Direct Versatile Adapter. Since pack was rated
at 600 mAh, it is okay!
The specific rates are 3C for Ni-Cd and 2C for NiMH. If your
Ni-Cd battery pack is rated at 300 mAh and you want to field fast
charge it, you would select a 900 mA current (300 x 3 = 900). At
that current, a totally depleted battery could be fully charged in
roughly 20 minutes.
All field chargers operate from 12-volt DC expressly so that they
can be conveniently connected to your car battery. The question is,
Why would you want to field charge if you had charged your
batteries overnight at home before you came to the flying field?
A person might resort to field fast charging to extend his/her
flying time at the field. I get approximately two solid hours of
operating time from a single RC transmitter; that is a lot of flying.
Because of that, I have never resorted to field fast charging any of
my RC transmitters.
There is a more compelling reason not to fast charge a
transmitter. Most RC transmitters have a protective fuse in the
Because many RC transmitters use blocking diodes in power
circuit, you may need to remove battery pack, as shown, to be
able to discharge-test it.
Testing battery packs often involves using adapter cables. Bob
has been accumulating his for many years. You can make your
own adapters or obtain them from RC or battery distributors.
Popular Hobbico Digital Voltmeter Mk III can test four-, five-, or
eight-cell Ni-Cd or NiMH batteries under load at flying field. When
allowable minimum voltage is reached, meter instructs you to
“recharge.” Couldn’t be any simpler!
Digital Voltmeter is usually plugged into charging jack on
fuselage side; that way you don’t have to remove wing to access
battery each time. Typically leave load on for roughly 10 seconds
before noting voltmeter reading.
In this case voltage dropped under load to 4.74 volts, and
Hobbico meter indicates that it is time to recharge.
October 2003 59
primary power lead, which is sometimes rated at only 0.5 amp (500
mA). If you hit that circuit with a fast charge current of 1.5 amps
(1500 mA) you will likely blow the fuse. In many cases that will
require the unit to be returned to the factory for maintenance.
The only time I ever have the need for “extra power” at the flying
field is when I compete in the AMA Nationals at Muncie, Indiana.
Because of the possibility of a flyoff (in the event of a tie score) at
the end of the day, I bring a second freshly charged battery pack and
simply swap packs. My general rule is not to fast charge a
transmitter battery pack at the field.
Four- and five-cell receiver (or airborne) battery packs tend to
run out of power faster than the transmitter, so you might want to
fast charge this type of battery pack. I prefer to substitute a freshly
charged second pack rather than resort to fast charging. Many RCsystem
batteries were not intended for ever being field fast charged.
If you are into electric-powered flight, as I am, you will have to
resort to field fast charging for the second and all subsequent flights
of the day. Most of my electric-powered models employ battery
packs with 10 cells or less. This enables me to use an electronic
(motor) speed controller that includes a Battery Eliminator Circuit
(BEC).
The BEC allows me to share the single large airborne battery
pack between the motor operation and the RC system. After each
60 MODEL AVIATION
The i4C C-VOLT is another neat testing device. This small digital
voltmeter mounts flush on side of model fuselage; it goes for the
ride. Moving controls (such as elevator and rudder at same time)
will generate suitable load current to make accurate voltage
readings.
The i4C Products Loaded Battery Tester operates much the
same as Hobbico unit but offers choice of three load currents:
500-, 1000-, 1500 mA. This is valuable when checking capacity
remaining in larger battery packs. This unit is self-powered,
requires no extra battery.
Some RC transmitters have built-in voltmeter along with lowvoltage
audible alarm or warning. This typical voltage reading
remains on screen at all times. Less expensive RC transmitters use three colored LEDs to note
battery-charge status. It is usually green for go, amber for
caution, red for time to recharge. Simple yet effective!
Be safe! If you leave several chargers on all the time in your
shop, have a smoke detector mounted close by. If anything ever
went wrong, at least you would be warned!
flight, that battery is field fast recharged
in 20-30 minutes. After that, it is ready to
run the motor and the RC system. Because
of this “sharing” advantage, I rarely use
the regular four- or five-cell RC-system
airborne battery packs.
I’ve painted the picture of charging.
Field fast charging, under most normal
conditions, is unnecessary for the average
fueled-powered-model enthusiast, but that
capability is a must for electric-power
modelers.
The only “fast” charger of choice is
called a “peak detect” charger. The peakdetect
circuit will permit fast charging up
to the moment of full charge, at which
point the battery will also be at peak
voltage potential. Within a few seconds
thereafter, the peak-detect circuit operates
and turns off the charger. This feature
provides for full charging (up to full
capacity) and for automatic cutoff after
full charge is reached. This is the only
way to go!
Some inexpensive chargers simply
employ a 15- to 20-minute timer. The
problem with this is that it cannot sense
the state of the battery’s charge, so it is
easy to undercharge or overcharge the
battery—a bad idea!
There are several “automatic” peakdetect
chargers on the market; two that
come to mind are the FMA Direct Super
Nova and the Dymond Modelsports Super
Turbo. In automatic mode, these chargers
sense the battery’s cell count and capacity
rating, and they automatically set the
proper charging parameters. The concept
involves averaging many of the
parameters and applying conservative
charging numbers, but it does work and is
worth your extra attention if you become
serious about electric-powered flight.
With regard to field fast charging, only
peak-detect charge Ni-Cd or NiMH
battery cells. Make sure your particular
cells are rated for fast or elevated-level
charging. Ask your battery dealer or
distributor if you’re in doubt.
Only fast charge your battery packs
after they have had a chance to cool
down; never charge a hot battery pack!
(Warm to the touch is okay.) Never use a
peak-detect charger to charge any
Lithium-type battery, be it metal, ion, or
polymer.
Testing: You know what capacity is and
how to charge a battery; now you must
learn how to monitor or test your batteries
to determine when they are running out of
power and when they must be replaced.
Just because a battery is only a year old,
you can’t assume that it has to be good
and not worry about it. Some batteries die
after only a few months of service!
There are two places where you will
want to test batteries: at home (in your
shop!) and at the flying field. Generally the
at-home testing is necessary on a regular
October 2003 61
basis to determine whether or not your
battery continues to provide power at or
close to its rated capacity. At the flying field
you want to know when it is time to stop
flying because you are running out of power.
At that point your options are to go home,
fast charge the battery, or swap with a
freshly charged battery.
For at home there are probably close to a
dozen popular battery discharge testers on
the market. I use the FMA Direct Einstein
XL, which costs slightly less than $100 with
the power supply. This device might soon be
out of production, but that decision was not
final as I wrote this article.
However, I wouldn’t want to disappoint
readers by describing a product that is no
longer available, so I’ll use the Einstein for
this discussion. At the end of this segment I
will supply the names and sources for
several other testing devices I know are still
on the market.
The Einstein is convenient because it has
two separate outputs, making it possible to
charge and/or discharge test, or even trickle
charge, two different battery packs. The
basic idea is to be able to charge/test a
transmitter and receiver battery, and at the
same time keep the two totally separate.
Many of these battery-testing devices have
two separate outputs.
The Einstein is especially nice because it
allows you to select discrete charging
currents of 25-, 50-, 80-, 120-, and 140 mA.
It also lets you select battery packs
consisting of anything from two cells up to a
total of 12. This applies to Ni-Cd and NiMH.
Another of the Einstein’s features is the
ability to overnight-charge battery packs up
to 140 mA and 12 cells, then after a fixed
16-hour period have the charge level revert
to a trickle. This can be accomplished
without ever evoking the discharge test
mode.
The basic use of any discharge battery
tester begins by fully charging the battery at
the overnight rate. If you’re using the
Einstein the next day, press the “Cycle Start”
button, and a fixed 300 mA load will be
placed on the battery. An LCD screen will
begin to register your battery’s capacity,
expressed in mAh.
When a minimum voltage of 1.0 volt per
cell is reached, the Einstein stops the
discharge load and begins to recharge the
battery at the rate you previously selected.
The last mAh reading on the LCD screen is
saved until you disconnect the battery from
the output cable. Charging will continue for
a timed 16-hour period, after which the
battery will revert to a fixed 12 mA
(nonadjustable) trickle-charge level.
The rest of this story depends on how you
interpret the mAh reading. I generally discard
a battery when the capacity drops 20% from
its normal rated value. If I have a 600 mAhrated
pack, I will continue to use it until it
gets down to 480 mAh (600 less 20%).
Keep a logbook containing capacity
measurements made on each identified
battery pack during a period of time. You’ll
usually observe that a pack will provide
close to its rated capacity for two or three
years, then all of a sudden the capacity will
begin to drop off.
Although I normally test-cycle my
batteries only every three months or so, the
minute I see the capacity start to drop I’ll
check it at least once a month. My
experience is that a pack showing this
characteristic will usually “go south” in a
hurry. When it does, I discard the entire
pack; I never “perform surgery” after
locating the bad cell. It isn’t worth it, and it
can waste a great deal of time.
When discarding any battery pack, don’t
just put it in your garbage. Follow the
manufacturer’s recommendations and return
it to a certified disposal organization (that
goes for any type of battery cell).
Besides FMA Direct, there are several
other sources of battery discharge testing
devices that I recommend. Tower Hobbies
and Great Planes Hobby Distributors sell the
Hobbico Accu-Cycle. You can learn more
about this unit at www.hobbico.com/
chargers/hcap0260.html, and you can
download its operating manual there too.
One of the nice things about the Accu-
Cycle is that it has two separate monitoring
meters—one for each output—so you don’t
have to keep remembering to switch the
62 MODEL AVIATION
meter from output to output. The price is
roughly $80, which is reasonable.
Horizon Hobby Inc. sells the Hangar 9
Sure Cycle Battery Cycler (tester). You can
find information about it at
http://horizon.hobbyshopnow.com/products/
description.asp?prod=HAN9525. The
Hangar 9 unit does the same job of battery
discharge testing. It has a single output
meter, as does the Einstein. At $60, it is a
bargain.
I wish everything in this hobby was
perfect and easy, but it is not. One major
problem with battery testing is that almost
all RC transmitters manufactured in the Far
East come with a diode placed in the
charging-jack circuit. It is done to prevent
the main power source from accidentally
shorting, but at the same time the diode
essentially blocks your access to the battery
pack. This means that when you hook up the
transmitter, via an adapter cable, to any
battery tester, you will not be able to
discharge it.
To correct this problem, some clever
modelers have gone inside the transmitter
and shorted out the diode. In the process of
doing this, they could cause problems to
other circuits and they are canceling the
factory warranty.
I prefer to simply remove the battery
pack. Most transmitter battery packs can be
accessed easily by removing a hatch cover,
and the battery is usually attached with a
connector. The trick is to unplug and
remove the battery, then obtain an adapter
cable that will allow you to connect the
battery pack directly to the tester. The RC
manufacturers usually sell these adapters, so
try them first.
Trusting that your batteries are up to
their rated capacity, it’s time to address the
next problem: How long can you fly at the
field before charging or battery swapping is
required? That answer is easy on the
transmitter side of the RC system.
Most transmitters will have an analog
voltmeter; better still, a digital voltmeter;
sometimes an audible warning alarm; or on
the less-expensive units, several colored
LEDs that go from green (fully charged) to
yellow or amber (as a caution) to red (when
you are supposed to stop flying).
These transmitters usually consume 100-
200 mA load current, which provides for a
meaningful test. Never attempt to test a
transmitter (or any) battery with only a
simple voltmeter. Without a load, most
batteries will always appear suitable for use,
but if you place a load on those same
batteries, they could quickly plunge below
minimum.
For the receiver batteries (usually four or
five cells), as used with fueled models or
electric-powered models of more than 10
battery cells (where you can’t use a BEC),
the best quick field check is done with a
“loaded” voltmeter.
Years ago we used an analog-type meter
with an expanded scale for more resolution
(and accuracy). We called these test units
“expanded scale voltmeters,” and the term
“ESV” has stuck. But today we have
modern digital-readout voltmeters, and
expanding the scale is no longer necessary.
All of these field-testing devices generally
impose a load of 250-500 mA current.
I like using the Hobbico Digital
Voltmeter Mk III (stock number
HCAP0356) from Tower Hobbies. The
special price was $21.99 at the time of this
writing. When you purchase this voltmeter,
the 9-volt supplied battery is wrapped in
plastic inside its compartment. You must
remove the battery, unwrap it, and plug the
connector into it, then the LCD screen will
light up.
The best way to use this field tester is to
have a charging jack located on the side of
the fuselage. That way you won’t have to
remove the wing to gain access to the
airborne battery pack.
After every flight, plug in the tester and
select it for the correct number of battery
cells, with the load on. Wait approximately
10 seconds, then look at the LCD screen.
The Hobbico unit has been thoughtfully set
up to tell you when it is time to recharge. It
will clue you in on a four-cell pack when the
voltage gets to roughly 4.8 volts under load.
That is somewhat conservative, but I
support this choice.
There are more sophisticated field-type
battery testers on the market. Rod Johnson
of i4C Products has a Loaded Battery Tester
October 2003 63
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(281) 479-9600 www.tru-turn.com
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PRECISION MODEL PRODUCTS
that will let you select load currents of 500-,
1000-, and 1500 mA. This would be
appropriate for larger-capacity batteries, as
are used in larger model aircraft. The i4C unit
is powered from the battery under test and
needs no extra battery, so it is always
available.
Rod has another interesting battery
monitor called the C-Volt. It is a small LCDreadout
digital voltmeter that you mount on
the side of your model’s fuselage. It goes on
when you power up your airborne RC
system. It doesn’t contain a load since that
would draw too much extra power.
You observe the C-Volt meter while you
operate a few aircraft controls
simultaneously, such as the rudder, elevator,
and ailerons. By doing this you will load
down the battery, providing a meaningful
check of the remaining power. At 4.7 or 4.8
volts for a four-cell battery, it is time to
recharge or replace it.
Testing batteries used for electric power is
a slightly different story. If you are using a
BEC and sharing power, the radio is using
only a fraction of the battery’s power (such as
a few hundred mA), and the motor itself
might be drawing a few amps or more power
(much more significant). You are recharging
this battery after each flight, so you know you
start every flight at a full charge.
That being the case, there is no reason to
really test the battery. When your model goes
to take off, if it appears sluggish or wants to
land after only a minute or two when it’s inflight,
look into the possibility of a bad cell in
the pack. In this instance, the way the model
flies reflects on the battery’s condition.
Replacing Batteries: I’ve written my
opinions about the minimum capacity at
which point it is time to replace your
batteries. Then the choice becomes whether
to buy the same battery pack direct from the
RC manufacturer or from a reputable
aftermarket battery-pack supplier.
Since most RC manufacturers supply only
500-700 mAh-capacity packs with their
systems, your first choice for replacing
batteries is to go to higher-capacity cells of
the same physical size. I hate to suggest that
you not go back to the manufacturer, but the
aftermarket suppliers have some great stuff
these days. I’ll list as many as I can at the end
of this article.
Keep in mind what I wrote about when
you go from a 500 mAh-capacity battery to
one that has 1600 mAh capacity; you won’t
be able to use that same charger that came
with your system. You must get something
such as the ACE DDVC or Digipulse Multi-
Charger.
When you get some experience under
your belt, and especially if you pursue
electric-powered flight, you may want to
make your own battery packs from individual
cells. The aftermarket battery suppliers sell
individual cells with solder tabs for your
convenience. When you get into the highercapacity
cells which draw much more
current, you will have to resort to copper
bars or copper braid to make the intercell
64 MODEL AVIATION
★ ★ ★ ★
Four Star 120
For .90 - 1.20 engines
“An amazing performance.” “Talent like this
doesn’t show up anywhere else.” “It’s hard to
follow this act.”
These are just a few of the comments heard
around flying fields when a SIG Four Star
airplane shows up.
Based on a very simple design goal, SIG
Four Star airplanes have impeccable flight
characteristics without looking like a box with
wings.
Featuring laser cut parts, SIG Four Stars go
together fast and true for even the most novice of
builders. Add in a molded canopy, complete
hardware package, large decal sheet, full size
plans, and a fully illustrated instruction booklet
as only SIG can do for a value-packed Build It
Yourself kit unlike any other on the market.
Performance-wise, the Four Stars shines. Tear
through the air with anything you can throw at
it, and the SIG Four Stars stay right with you.
Landings are trainer-slow with no unwanted stall
tendencies.
Sized to fit every flyer, SIG Four Stars are
available wing-sized from 59” to IMAA-big 81”
and for .40, .60, and biggie 1.20 engines. Each
kit delivers the same easy construction and
outstanding flying distinctiveness you expect.
Now showing at a hobby dealer near you.
Pick one up and give your two thumbs a reason
to go up.
SIG MANUFACTURING COMPANY, INC.
P.O. Box 520 • Montezuma, Iowa 50171-0520
www.sigmfg.com • 641-623-5154
Four Star 40
For .30 - .40 engines
Four Star 60
For .60 - .75 engines
connections. But that’s for a later article.
Charge Retention: If I’m unable to fly on a
given day and several days or a week goes by
before I get another chance, I recharge the
night before that next flight attempt. Ni-Cd
batteries do lose a certain amount of charge
each day after they are fully charged.
Specifications indicate that charge
retention depends on battery temperature. Ni-
Cd cells stored at 32 degrees Fahrenheit can
be expected to lose approximately 10% of
their charge in 30 days. Those same cells
stored at 68 degrees Fahrenheit will lose 30%
of their charge in 30 days. At 104 degrees
Fahrenheit, the loss will be almost 70% in a
30-day period! NiMH cells tend to lose
charge at an even faster rate.
From this information you can probably
understand why I instruct you to be safe and
recharge at the C/10 overnight rate if a week
goes by. The new Li-Poly cells exhibit
excellent charge retention, losing only 1% or
2% of their charge in a six-month period.
Battery Storage: There are two schools of
thought on this topic: to store the Ni-Cd or
NiMH cells fully charged and to store them
when fully discharged. Either way is okay,
but experts tell us not to store cells at partial
charge.
I find it easier to return from the flying
field and put the cells on overnight charge.
That way they go back on my battery shelf at
full charge. If I don’t use the battery in a
month or two, I recharge it again. I have many
battery packs, so some will be forgotten.
However, most survive and provide three to
five years (and more) of service.
Memory: Since Ni-Cd cells were first used in
the early 1960s, we have been told that they
can acquire a certain capacity memory. It was
said that if a modeler made six flights each
week, his/her batteries would get accustomed
to supplying that level of energy. If that
modeler made eight flights during a particular
week, he or she might find the batteries
incapable of supplying the extra power.
Why? The batteries supposedly developed
a “memory” for that amount of power. This
subject has been greatly debated through the
years. The newer NiMH cells don’t seem
affected, and the even newer Li-Poly cells are
not affected at all.
Regularly discharge testing (or cycling)
your battery packs would eliminate the
problem if it actually ever existed. RC-system
batteries tend to be used at roughly the same
rate, so periodic testing (cycling) can’t hurt in
that regard.
Batteries used for electric-powered flight
are usually taken down to the minimum
charge level on each flight; as such, they are
essentially cycled on every flight. It would be
difficult to conclude that batteries used in this
manner require additional cycling in your
shop. When your electric-powered model
refuses to take off or support flight, then you
know you have a battery problem and can
investigate further. But don’t bother to cycle
these batteries; it’s unnecessary.
Li-Poly cells will be the subject of a separate
article sometime in the future. Progress in this
area is being measured in weeks—not in
months. Considerable recent development
work is gradually producing cells that are
capable of supplying more capacity at higher
current (load) levels, with ever-decreasing
weight. At the same time, the cost of Li-Poly
cells is coming down.
Right now Li-Poly use is limited to
roughly 10-amp loads, which can handle up
through Speed 400 power (such as the Aero
Craft Pogo in last month’s article). However,
these load-level limitations are constantly
improving, so it is just a matter of time.
Although I don’t see the need right now, Li-
Poly batteries may eventually be used to
power our RC systems.
Don’t ever attempt to charge Li-Poly
batteries with peak-detect chargers; they have
a completely different chemistry and should
only be charged with their own chargers. You
might be tempted to write in that there are
chargers available—such as the Great Planes
Triton—that can peak-detect charge Ni-Cd
and NiMH cells and have a separate function
for charging Li-Poly cells. That is correct; the
Triton is new, and it works well. But don’t
leave it set on peak detect and try to charge
Li-Poly cells.
I’ve written many articles about batteries
throughout the years. No matter how basic
and thorough I am, these articles generate the
most inquiries. Readers have been relatively
quiet to date when it comes to questions. Now
$3495
+ $450 S/H
BMJR Model Products
Box 1210, Sharpes, FL 32959-1210 • 321-537-1159 www.BMJRModels.com
Rambler 30
• Old Time
Replica
• 30" wingspan
• .020 gas or electric
• Laser cut
is your chance! Please write in and let us
know how we can continue to help you. What
else would you like to see in this series?
Address suggestions to Bob Hunt at Box 68,
Stockertown PA 18083, or to
[email protected].
Next month look for the Pogo follow-up:
a new design which I hope you can build
from basic materials without a kit. This will
be your first scratch-built RC model. I think
you can do it! MA
Bob Aberle
Manufacturers/distributors:
ACE Hobby Distributors Inc. (chargers,
testers)
2055 Main St.
Irvine CA 92614
(949) 833-0088
Fax: (949) 833-0003
www.acehobby.com
Airtronics Inc. (RC systems, batteries, cables,
connectors, adapters)
1185 Stanford Ct.
Anaheim CA 92805
(714) 978-1895
[email protected]
www.airtronics.net
Balsa Products (RC systems, batteries and
alkaline-battery replacement [charger/cells])
122 Jansen Ave.
Iselin NJ 08830
(732) 634-6131
www.balsapr.com
Batteries America (batteries, cables,
connectors, adapters)
68 MODEL AVIATION
2211-D Parview Rd.
Middleton WI 53562
(800) 308-4805
[email protected]
www.batteriesamerica.com
Dymond Modelsports (batteries, chargers,
testers, cables, connectors, adapters)
3904 Convoy St. (new location)
San Diego CA 92111
(858) 495-0092
www.rc-dymond.com
FMA Direct (RC systems, batteries, cables,
connectors, adapters, testers)
5716A Industry Ln.
Frederick MD 21704
(800) 343-2934
Fax: (301) 668-7619
[email protected]
www.fmadirect.com
Futaba Corporation of America (RC systems,
batteries, cables, connectors, adapters)
and
Great Planes Model Distributors
Box 9021
Champaign IL 61826
(800) 637-7660 or (217) 398-6300
[email protected]
www.futaba-rc.com
Hitec RCD (includes Multiplex RC systems)
(RC systems, batteries, cables, connectors,
adapters)
12115 Paine St.
Poway CA 92064
(858) 748-6948
www.hitecrcd.com
Hobby Lobby International (batteries, cables,
connectors, adapters)
5614 Franklin Pike Cir.
Brentwood TN 37027
(615) 373-1444
E-mail sales: [email protected]
www.hobby-lobby.com
Horizon Hobby Inc. (batteries, chargers,
cables, connectors, adapters, testers)
and
JR Remote Control (RC systems, batteries,
cables, connectors, adapters)
4105 Fieldstone Rd.
Champaign IL 61822
(217) 403-3279
Fax: (217) 352-2010
www.horizonhobby.com
i4C Products Inc. (testers)
6924 E. 92nd
Tulsa OK 74133
(918) 492-9435
[email protected]
www.i4cproducts.com
Maxx Products International (batteries,
cables, connectors, adapters)
815 Oakwood Rd. Unit D
Lake Zurich IL 60047
(847) 438-2233
[email protected]
www.maxxprod.com
New Creations R/C (batteries, chargers,
testers, cables, connectors, adapters)
Box 497
Willis TX 77378
(936) 856-4630 (calls are preferred)
Peak Electronics Inc. (chargers, testers)
12520 Kirkham Ct. #8
Poway CA 92064
(858) 679-4952
[email protected]
www.siriuselectronics.com
Radical R/C (batteries, cables, connectors,
adapters, chargers, testers)
5339 Huberville Rd.
Dayton OH 45431
(937) 256-7727
[email protected]
www.radicalrc.com
SR Batteries Inc. and Techniques technical
journal (batteries)
Box 287
Bellport NY 11713
(631) 286-0079
Fax: (631) 286-0901
[email protected]
www.srbatteries.com
Tower Hobbies (includes items identified
with Great Planes and Hobbico) (RC
systems, batteries, cables, connectors,
adapters, testers)
Box 9078
Champaign IL 61826-9078
(800) 637-6050
www.towerhobbies.com
SPAD ARF’S are here:
We are offering a wide selection of SPAD ARF’S
for the amateur and experienced flyer.
From trainers to 3D planes without the
frustration of the normal off the shelf product.
www.aspad.com or call 630-768-2043