January 2011 87
Red Scholefield | redscho@The Battery Clinic bellsouth.net
Also included in this column:
• OK Hobby’s Buffalo Pack C
rating challenged
• Many options for making a
9-volt unit
• CamCap enables reader to
record his own flights
Manufacturer recommends against using LiFe pack
Left: In this discharge test a 6.6-volt LiFe discharge is compared
with a standard 4.8-volt Ni-Cd of the same 1100 mAh capacity.
Notice the steep drop at the end of the chart; never run your
packs too far down.
Steve Kaluf of Hobbico narrates several product videos on the company’s YouTube
channel. In this capture he shows a Hobbico LiFe pack running the Futaba S-Bus system.
Bright-yellow protective covering on OK Hobby
Buffalo-brand Li-Poly packs makes them easy to find.
Short tests proved that the product is worth a try.
HOBBICO LIFE Pack Revisited: In the
September column I wrote about the
Hobbico LiFe battery pack for
receiver/servo use; my concern was the
higher voltage. Readers have since
contacted me to let me know that they have
used this pack with no problems.
Nick Gaynor wrote:
“I’m following up on our previous
emails, and I have a comment on your
September 2010 Model Aviation Battery
Clinic column ‘Is a two-cell Lithium
battery too much for your receiver/servos?’
“What I would like from Futaba is an
explanation, hopefully technical, as to why
LiFePO4 batteries are not recommended.
“Ironically, perhaps even funny, is that
in Futaba’s S.bus video, they feature their
S-bus system being powered by guess
what … the Hobbico LiFe Source 6.6v
battery pack.
“I, for one, am going to start using the
LiFe packs to directly power my receiver
electronics, Futaba or Spektrum or any
other brand for that matter. And of course,
only 6 volt rated servos, but that’s just
common sense.
“The current argument of people using 6
volt NiCD packs (which when fully charged
do peak at about 7.2 volts, like the LiFe
packs) successfully for years is the main
factor of my decision. I am mindful, of
course, of the steep LiFe voltage discharge
curve below the 6 volt point. The easy
solution of course is not to let your pack
become too discharged, but doesn’t that
apply to any pack?”
I posed the question again directly to
Futaba service, and personnel remain
adamant that the LiFe unit should not be
used with their system in spite of Steve
Kaluf (former AMA technical director)
showing the pack in the Futaba video of its
new S-Bus system.
I asked them about that, and their reply
was that Steve must have picked up one to
use with the system without their
knowledge.
Since I have gone to 2.4 GHz, I had a
receiver and some servos to donate to
01sig3.QXD_00MSTRPG.QXD 11/22/10 8:10 AM Page 87
88 MODEL AVIATION
pack was delivered
in the normal
storage charge
state.
Let’s look at the
Buffalo Li-Poly
pack’s three
discharges done
with a West
Mountain Radio CBA II, and the charging
done with FMA Direct Cellpro 4S and 10S
systems. After three cycles, the following
data was produced.
• Charge at 3 amps input 3.226 Ah;
Discharge at 3.2 amps to 9 volts = 3.143
Ah
• Charge at 3 amps input 3.212 Ah;
Discharge at 10 amps to 9 volts = 3.067 Ah
• Charge at 3 amps input 3.019 Ah;
Discharge at 9.9 amps to 9 volts = 3.138
Ah
After the third cycle, one of the cells
read 2.90 volts while the others were 3.20
volts, which
indicates that that
particular cell might
have a lower
capacity. When the
3-amp charge input
was applied, the
same cell that read
2.9 volts at the start
of the charge took
in 3.182 Ah. So it
was good and
drained. Its internal
resistance, as
measured on an
FMA Cellpro 10S,
read 6.9 mohms.
The pack was
next bench-run in a
model with an AXI
2820-14 battery,
Turnigy 40-amp
ESC (set to a
conservative voltage cutoff), and 12 x 6
APC-E propeller. The high-throttle start
readings were 31 amps and 356 watts.
Total run time was 7 minutes, 5 seconds
when the voltage cutoff engaged. Output
before cutoff was 240 watts. It all equaled
3.183 Ah delivered as shown on the
AstroFlight Wattmeter. This is what you
would expect in an actual flying
environment.
Other modelers’ testing on Buffalo
packs indicates that those rated at 40C are
actually close to 20C. This is based on the
140º heat that developed and is the
temperature we know can have a serious
impact on Li-Poly cell life.
The 40C-rated Buffalo battery discharge curves, using the West
Mountain Radio CBA II, show that limits vary greatly when the
discharge current is increased.
If you’ve ever wondered what a 9-volt battery is made from,
here’s a look. Sources from top to bottom are Energizer,
Walgreens, and an obvious brand.
Wear a hat to the field, and you can film your own flight. Bob
Schumann came up with a method to obtain his own flight
footage in a simple, quick, cost-effective way.
“science.” I fully charged the LiFe pack and
then set it up to power a Futaba FPR127DP
receiver, two Futaba S148 servos,
and two Futaba S3003 servos.
It set my Futaba 9C transmitter to
“servo” function, where it slowly ran the
servos from one extreme to the other. This
went on for more than two hours, with an
occasional deliberate stalling of the servos
(where they drew approximately 900 mA).
I found no problem. In fact, the current
being drawn was only slightly more than
with a four-cell Sanyo KR-1100-AAU
pack. There was no evidence of heating. A
discharge of the two packs shows a
significant difference in voltage delivered.
Are we comfortable using Hobbico’s
LiFe packs without a regulator? Hobbico
thinks that we should be and I have found
no reason not to be, despite Futaba’s stand.
No other RC system suppliers seem to have
a problem either.
OK Hobby sent me one of its Buffalo Li-
Poly packs to “evaluate.” It is a 3S 3200
mAh, rated at 40C.
Discharging at this rate gives you less
than 90 seconds of flight time. Most pilots
look for a six-minute flight minimum with
their electric-powered models, which
equates to 10C discharge. That brings up
the question of why to rate something at
40C if it won’t see that kind of use?
“Testers” in the hobby market basically
agree that there is more “marketing” than
“engineering” in these ratings. We also
agree that the C rating is an indication of
the internal resistance in the pack; the
higher the C rating, the lower the internal
resistance (if they are honest). Lower
internal resistance means a higher voltage
delivery, particularly at higher rates.
The battery weighs 10.098 ounces
without connector; a Deans Ultra plug was
installed for testing. The open circuit
voltage, as received, showed cell 1 at 3.919
volts, cell 2 at 3.928 volts, and cell 3 at
3.920 volts. This basically showed that the
01sig3.QXD_00MSTRPG.QXD 11/22/10 8:12 AM Page 88
I am going to continue field-testing this
pack, in models with the same motor/ESC
combination. One is a powered glider
spinning a 13 x 6.5 Graupner folding
propeller, and the other is the bench-test
aircraft (Stick 25e). Flights will be
terminated before a noticeable drop in
power is reached.
My conclusion so far is that the battery
is strong and offered labeled capacity at
higher rates, 10C. I would say that it is
worth a try at $33.17. Now for the longterm
field-testing in a real RC environment.
I expect to put in four or five flights each
week on the test pack (with the help from
my fellow electric-flying club members).
Others have done more extensive tests on
Buffalo Li-Poly packs. One series on a 2S
2500 mAh unit indicates that the packs are
more realistically 20C capable.
Temperatures at rates above 20C exceeded
the 140° that was deemed destructive to the
packs.
The 80-amp test went to 160 degrees
Fahrenheit. The 100-amp test went to 160°
when it was terminated and appeared to be
headed for 180°-200°.
I wish there was a way to get some good
life data on these packs other than simply
flying them and occasionally monitoring the
capacity. By the time any meaningful data is
accumulated, the technology has advanced.
In addition, trying to draw conclusions
from one sample isn’t all that meaningful.
Too many variables need to be considered,
and that takes many test resources and
requires a fair quantity of samples to
provide an appreciable test matrix. One
would think that that manufacturers (not the
distributors) would make data available to
substantiate their claims.
As with numerous products on the hobby
market, we will have to judge by our
modeling friends’ collective experience
what is good and what is not so good.
If you want to see results of tests that
competent electric-power modelers have
performed on a variety of Li-Poly packs, go
to the Battery Graph Vault. The Web site
address is included in the “Sources.”
While rummaging around in my “junk”
drawer, looking for small metal pieces that I
could use for a magnetic hatch, I saw some
depleted 9-volt battery packs in a recycle
can. I found that the metallic cases would
marry to the magnets nicely. However, in
removing the cases I found different ways
that a 9-volt battery is made.
One way, shown, uses a cylindrical cell,
similar to an AAAA. These are
interconnected via pressure contacts held in
place by the crimped metal case.
Another sample was made from plasticclad
button cells, with tabs to a connector
place. It also holds the cells together with
the crimped metal can.
The last sample was a rechargeable 9-
volt with six button cells. All of those were
welded together.
What does this mean? Not much unless
you are looking for AAAA-size primary
cells for a special project. Energizer uses the
AAAA cells, and the other pack, which has
a Walgreens label, uses the more
conventional technique for building a 9-volt
pack. Cells from the 9-volt rechargeable
pack can be broken apart for an ultrasmall
90 mAh battery.
Do you want pictures of your flying? If so,
Bob Schumann came up with a simple idea
to obtain them. He wrote:
“I am attaching some photos of my
‘CAPCAM.’ It is a vehicle for a mini video
camera to take pictures of you flying your
RC plane.
“I got one of these $25 cameras and
Velcroed it to the bottom of my electric
powered Radical RC Intern 66 and took
several shots of our field. After a while they
all looked the same so I thought about
taking pictures of folks flying. Panning with
the plane worked out ok, but I wanted
pictures of me flying my plane and no one
at the field offered to do that.
“I took a freebie hat and cut a hole in the
brim that would accommodate the camera
body while pointing to the front of the cap.
This gave me a self following mount for the
mini cam and the results turned out great!
Not often does a 5 minute solution work as
well as this did.
“Spelling out how it works is easy; you
should never take your eyes off your plane
while flying it. This arrangement meets that
test as long as you wear the hat bill forward!
(Is this permissible in today’s society?)”
There are even smaller cameras than the
one shown, available for much less money,
and they do a good job. With some fiddling,
you can use this mounting/tracking system
with the smaller cameras too.
I wish you all a great building and flying
new year. While you are warm and cozy
making balsa chips in your workshop, we
are braving the elements, trying to fly yearround
where our building season starts
immediately after we crash our last
airplane.
Keep those cards and letters flowing. No
e-mail connection? Drop me a note at “The
Battery Clinic” at the address in the
“Sources” section. Since it’s our flying
season, it might take me a day or so to
answer you. MA
Sources:
Futaba S.Bus System:
http://2.4gigahertz.com/sbus/index.html
OK Hobby
www.okhobby.com
Battery Graph Vault:
http://bit.ly/ci5B5h
The Battery Clinic
12219 NW 9th Ln.
Newberry FL 32669
January 2011 89
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01sig3.QXD_00MSTRPG.QXD 11/22/10 8:12 AM Page 89
