RADIO CONTROL ELECTRICS - 2003/03

THIS COLUMN OFFERS comments on
the 2002 NEAT (Northeast Electric Aircraft
Technology) Fair, the new AstroFlight 110
Deluxe Digital Peak Charger, and powering
chargers. It also looks at Ni-Cd versus
NiMH charge/discharge rates, gives a
personal-preference answer to the question
When is a pack too hot?, discusses “motor
voltage” ratings, and offers a caution
regarding insect-repellent spray.
I attended the 2002 NEAT Fair in
Downsville, New York, September 13-15. I
was there with more than 290 registered
pilots from 37 states, two Canadian
provinces, and the United Kingdom—all
who seemed to be having a great time!
NEAT ’02 was no doubt the largest Egathering
in the US—ever. Several years
ago, just before its discontinuance, the KRC
Electric Fly had grown to approximately
240 pilots from 33 states and some other
countries. NEAT has picked up where KRC
left off (thank you!), and it continues the
historic growth pattern. NEAT is a function
of the Silent Electric Flyers of Long Island
(SEFLI) club and is ably managed and
directed by Tom Hunt with a great deal of
support from club membership.
In past years I had the happy opportunity
to cover the NEAT Fair for Model Aviation.
This is a mixed blessing; it can become allconsuming,
leaving minimal opportunity to
be active within the meet. This year my
friend Chris True picked up the meet
coverage, so I had more opportunity to
mosey about the flightline, fly, etc. It was a
chance for me to “see” the meet directly
instead of through a camera lens! My thanks
to Chris for that.
Several months ago I got the opportunity to
try out the new Astro 110 Deluxe Charger.
The now-classic 110D, a long-running Astro
product, has been a long-standing favorite of
mine for many years. I’ve had a total of
three 110s with two still in routine use. The
Deluxe is the most recent version in this
established charger family line, and it offers
some surprising and useful new features.
The Deluxe comes equipped with a
backlit readout. So? This little addition
makes a big difference in the fading sunlight
of late evening when there’s one more flight
to be had, because now one can actually
read the readout! I love it!
More pragmatically, the Deluxe offers
much more “bang.” The classic 110D had a
maximum current output of 5.0 amps, but
the Deluxe can deliver roughly 8.0 amps.
Like most chargers I’m familiar with, the
maximum output rate is available for a
limited number of cells (see graphic), but
within that range of application this higher
value makes a huge difference.
In the “early” days of Electric when the
largest Ni-Cd in routine use was the 1.2 and
1.4 Ah cell, a 5.0-amp charge rate got your
model in the air in approximately 15-17
minutes. Nowadays, charging the 2.4 Ah Ni-
Cd stretches that roughly double. Here’s
Bob Kopski, 25 West End Dr., Lansdale PA 19446
RADIO CONTROL ELECTRICS
The new AstroFlight 110 Deluxe Charger is the latest version in the long-running “110”
series. This unit has many new features. The price is listed at $129.95.
AstroFlight’s Bob Boucher (center) and helper John Liberg man the booth at NEAT
2002. This and the many other vendor booths were constantly busy; it was always a
challenge to get a clear photo!
114 MODEL AVIATION
03sig4.QXD 12.20.02 8:36 am Page 114
where the higher available charge current is
a worthy feature! Now you can now spend
less time charging and more time flying.
Unlike the predecessor 110Ds, the
Deluxe includes a battery-discharge feature.
Sometimes one winds up with a fully
charged pack and no flight opportunity. One
can resort to running the motor to run the
pack down, but I always felt this was a bit
“crude.” Others just leave the pack in this
charged state until the next session, but this
practice may risk imbalance among the cells
through uneven self discharge. Having a
quiet, safe way to discharge a pack has a lot
of merit, and the Deluxe can do that. But
there’s more!
Although I always liked the simplicity of
the 110D with its simple single “push to
start” button (no programming!) and current
setting knob, the Deluxe is even simpler. It
has no button to push! When connected to
the 12-volt supply, the readout advises that
it is waiting for the battery to be connected.
When the connection is made, charging
commences, then one sets the current
control knob for the desired charge current.
If a pack is connected first then the charger
is connected to the 12-volt supply, the
Deluxe goes into discharge mode.
Other features include a built-in cooling
fan and an end-of-charge beep alarm—two
things the 110D could have used throughout
the years. And unlike the 18-cell limit of the
historic versions, the Deluxe accommodates
one to 24 cells. With this expanded cellcount
range, an adjustable charge current of
50 mA to approximately 8.0 amps, and
applicability to Ni-Cd and NiMH battery
chemistries, the 110 Deluxe is well worth
your consideration for your next charger.
While on this subject, every now and then I
receive a reader inquiry about using an auto
battery charger as a power supply for motor
battery chargers such as the Deluxe and
others. The simple, almost universal answer
is no!
All contemporary chargers I’ve seen are
filled with electronics. This is vastly
different from the “early” days when a
charger makeup included a time switch, a
meter, and a variable resistor. Nowadays
charger electronics require a reasonably
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116 MODEL AVIATION
means that most people are unable to tightly
grasp and hold something at this
temperature. Using this as a guideline, if I
can’t hold a pack I consider it too hot!
Actually I consider less than this
temperature “too hot,” and I won’t charge
until such a pack cools some.
I’m sorry (and troubled as well) about
this unscientific approach to the question,
but it’s the best I’ve got to offer and it is
easy to apply. I don’t think you can go
wrong using it.
Modelers have long been known to
establish their own product “application
guidelines,” especially with batteries. This
has happened throughout time with Ni-Cds,
and it continues with the growing use of
NiMH chemistry. And “modelers” include
“aero” and “auto.”
In time, modelers learned by doing what
good (and not good) charge/discharge rates
are for Ni-Cd cells. Large numbers of
modelers with even larger numbers of packs
“learned the hard way”—often at
considerable personal expense. I think
modelers have historically even taught the
Ni-Cd manufacturers things they didn’t
know about high charge and discharge
applications!
More recently, NiMH cells have come
along with the same sort of unknowns as the
early Ni-Cds, and again modelers are
applying the same trial-by-fire approach to
learning what and what not to do with the
new chemistry. While the NiMH product is
rapidly evolving (as did Ni-Cd technology),
modelers seem to be homing in one some
associated rules of thumb. One practice I’m
noticing concerns charge rate.
I think most modelers tend to charge
NiMH at roughly one-third to one-half the
familiar high rate value as used with the
“same size” (same capacity) Ni-Cd. If one
used a charge current of 3.0 amps for a 1000
mAh Ni-Cd pack, 1.0-1.5 amps might be
used for a 1000 mAh NiMH pack. This
takes much longer to do—not a “nice”
feature. As in the past, I expect this practice
to adjust as the product and practical
experience with it matures.
It seems that nearly the same guideline
applies to discharging most NiMHs as
well—at least for now. One thing that
remains the same for the Ni-Cd and NiMH
chemistry is the slow charge rate. As best I
can tell, most modelers use the “1⁄10 C”
guideline for both. Thus for slow
(overnight) charging both types, use a
current 1⁄10 the capacity rate for
approximately 14 hours—to be sure. Use 50
mA for 500 mAh packs.
Beginners are routinely troubled by motor
voltage ratings. Consider the popular Speed
400 series of motors. You can buy several
clean and stable input power supply, and an
auto battery charger is anything but!
Auto battery chargers incorporate a
simple transformer and full wave rectifier,
and the output has high ripple content; i.e.,
it’s not smooth DC. In addition, this ripple
level can reach open circuit peak values of
22-25 volts. The instructions included with
the Deluxe specifically warn against using
such a supply, and I’ve seen the same
warning with similar products. If you want
to run your motor battery chargers indoors,
you need a portable 12-volt auto battery or a
proper line-operated 12-volt high power
supply—period!
One common question that routinely
troubles E-fliers concerns battery
temperature. End-of-flight pack temperatures
can get quite high, and it is common advice
not to recharge while the pack is “hot.” But
what is “hot”?
I do not know the quantitative answer to
that question. I’ve not met anyone who does.
I don’t even know where to go to get
guidance on this issue. Furthermore, I
suspect I’ll never know the answer! But I do
have a personal approach to this common
quandary. It’s easy to apply and, I think,
conservative.
Most people have a pain threshold of
roughly 140 degrees Fahrenheit
(approximately 60 degrees Celsius). This
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03sig4.QXD 12.20.02 8:37 am Page 116
120 MODEL AVIATION
versions of the “same” motor with different
operating voltages right on the motor labels.
Popular voltages include 6.0, 7.2, and 8.4
volts. But what does this mean?
Appreciate that using any motor with a
speed control—which “everybody” does—
immediately imposes a varying voltage on
the motor. (Varying voltage is how one
varies motor speed.) Just because a motor
label says “6 volts” does not mean you must
always apply 6.0 volts. The speed control
actually delivers voltages from full pack
level to zero (full on to full off). The number
of cells determines the maximum voltage. A
five-cell pack is commonly called “a six volt
pack” (five cells x 1.2 volts/cell = 6.0 volts
total). But what about using higher cell
counts (higher than “label”) voltage?
Applying somewhat higher voltages is
routine practice! Limiting motor current is
far more important than not exceeding
motor voltage. Using the Speed 400
example, it is generally accepted that
exceeding 10.0 amps dramatically shortens
brush/commutator life, but exceeding cell
count by one or two is of little consequence.
Since power input is the product
(multiplication) of motor voltage and
current, increasing the voltage (with more
cells) while holding a safe current level does
increase motor input power. All that’s
needed to do this safely is to reduce
propeller size—diameter, pitch, or both.
Alternatively, if you are using a gear drive,
lower the gear ratio to reduce propeller rpm.
Use motor input current—rather than
voltage—as your guideline.
Of course, there is such a thing as “too
much” voltage. One cannot safely increase
motor voltage without limit. Since motor
speed increases with applied voltage, there
will always be some voltage (shaft rpm) at
which a motor will be physically damaged.
One common manifestation of too high a
voltage are thrown windings. Armature wire
can actually be “spun off”—physically
thrown off—an armature running at too high
a speed. The same might happen with
commutator segments. Actual limits vary
with the motor, its quality, and so on, but
I’ve never seen a motor that would not
tolerate 30% or so more than “rated” or
“label” voltage. So go ahead and run your
6.0-volt Speed 400 on six or seven (some
do eight) cells—it won’t hurt it—as long as
you watch the current!
Insect repellent is often necessary on the
flightline, given the nature of flying fields!
However, I did experience one adverse
consequence with its use. Somehow I got
overspray on my transmitter face and did
not realize it until the next day; then I saw a
light-gray speckle all over the black and
chrome and Liquid Crystal Display (LCD)
faceplate.
This speckle does not wash off; it
actually seems to be small permanently
etched spots on the plastic surfaces, and this
effect was most adverse on the LCD screen.
The only thing I found that helped was
carefully using light-duty rubbing
compound with a Dremel buffing wheel. I
got most of the screen cleaned up (polished)
this way. The speckle remains over the rest
of the transmitter face.
So ends another column. Come oooon
happy springtime Electric flying!
Please include an SASE with any
correspondence for which you’d like a
reply. Everyone so doing does get one! MA
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