The “skinny” on the new A123 batteries
May 2007 97
The Battery Clinic Red Scholefield | [email protected]
Computer display for a 4S A123 pack shows individual cell
voltages.
Computer display for Ni-Cd cells indicates classic charge
regime.
Also included in this column:
• Bantam e-Station BC8
• Whattmeter upgrade
• A reader letter/question
• Red’s conversion fleet
Left: The Bantam e-Station BC8
balancing charger with adapters.
A123 LITHIUM CELLS: Lacking any meaningful way to purchase
these breakthrough cells directly at a reasonable price, modelers are
eagerly grabbing up DeWALT 36-volt drill packs (model DC9360)
that are being offered on eBay for roughly $100 including shipping.
Salvaging the 10 cells they contain enables the modelers to build a 4S
pack for approximately $40.
This must be driving the DeWALT marketing department crazy
because far more “replacement” packs are disappearing off the shelves,
yet no complaints of short service life are coming in.
In tearing down three of these packs I found that if you fold the four
end cells over using the existing tabs, they form a nice pack of two
sticks side by side. I put a 1/8-inch spacer of hard balsa between the
ends of the cells as they are folded over. This helps keep the packs
straight. Then I tack the balance connector leads to the edge of the
folded tabs that were flush with the edge of the cells.
If you want to use the two cells that are left over, you need to buy
another DeWALT pack and build up the four-cell pack using the two
center cells. I found the Model Electronics Corporation power tube kit
handy for this, eliminating any need to solder connections between the
cells.
Flight-testing these packs so far has given excellent results.
Replacing Li-Polys on a 4:3 basis, they represent an economical power
system. Even more encouraging is that there have been no reported
incidents of bursting or fires.
Charging these A123 packs presented a problem since the only
charger was the one offered by A123Racing, and the company did not
address pack configurations we find useful in electric-powered flight.
Fortunately at least three charger vendors have stepped forward to
provide the charge algorithm needed for the A123 packs.
Tejera Microsystems Engineering’s Xtrema is the first to address
these cells, providing the programming capability to set the end-ofcharge
voltage to the required level. FMA Direct has modified its
popular Cellpro balancing charger for the 3.6-volt/cell cutoff required
and will update your Cellpro for a modest amount. Bantam has joined
the A123 parade with its e-Station BC8, which also has a balancing
feature.
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98 MODEL AVIATION
An Eliminator fun-fly model gets a new life with an electric conversion.
This Bantam II makes a lively conversion from glow to electric power.
A Checkerboard Air 40-size sport model
reworked for an AXI 2826/12 motor.
Sid Kauffman of SLK Electronics
(originator of the LiPoDapter, which is now
available for A123 packs) wrote the following
about A123 (M1) vs. eMoli cells.
“I see the eMoli as Li-Poly in a steel can.
They don’t have the discharge capability of
good Li-Poly and with a significant weight
penalty. I have also done enough stupid things
to the M1 (as well as Li-Poly) to know that
the M1 are way more tolerant of abuse.
“The eMoli weighs 3.5 ounces vs. 2.5
ounces for the M1. Agreed there’s more
energy there, but the discharge is limited.
“Can the eMoli be charged in less than an
hour? The M1 can be charged in 15 minutes
or less.
“Extracting eMoli cells from Milwaukee
power packs is a real pain; sticky junk all
over. The DeWALT packs come apart
cleanly.”
I have passed 75 charge/discharge cycles
on my 4S A123 packs, and there is no sign of
performance degradation.
Bantam e-Station BC8: Responding to the
need for balancing packs along with
addressing the A123 Lithium cells, Bantam is
offering its BC8. At a price of $269.95 it
covers the popular Li-Poly packs and A123
packs up to eight cells, Ni-Cd/NiMH to 27
cells, and Lead Acid up to 36 volts. The
charge-power limit is 150 watts, and the
cycling (one to five cycles) and discharge
capability is up to 25 watts.
The BC8 unit is housed in a substantial
aluminum case with rubber standoff feet. As
are most chargers, it is operated from any 10-
to 15-volt DC source.
Charge leads connect by way of banana
jacks, and there is a nine-pin socket for the
balancing function. Adapters are available to
interface with nearly all the popular Li-Poly
pack offerings. Align, E-flite, Kokam,
Graupner, MPX, Thunder Power, Poly-Quest,
Electric Power, and EVO are the ones I
verified.
Watch the polarity on some. I had to make
my own adapters for the Cellpro balancing
plug. If your particular pack is not covered,
Bantam provides an open-ended wiring
harness to enable you to make your own
adapter.
A total of 10 different batteries’
programs can be stored and retrieved. A
simple four-button programming and
operating system is employed with a
variable-brilliance backlit display. The BC8
can also monitor and balance individual
cells of the Lithium battery pack during the
discharge and charge processes.
A 20-page instruction manual
supported by a good flowchart leads you
through the BC8’s setup and operation.
You can find complete details in the
downloadable manual in PDF format on
the RC Accessory Web site at www.rc
accessory.com.
For the advanced user the BC8 offers a
PC-based program, provided on a CD, that
can analyze the characteristics of the
battery through your computer’s USB port
(using Windows 2000 and XP). The
software will graph voltage, current,
capacity, and temperature curves. It also
shows the individual voltages of each cell in
the Lithium battery pack.
The BC-8 is available from RC
Accessory, Inc., 3304 Foxridge Cir., Tampa
FL 33618; Tel.: (813) 765-0124.
AstroFlight Whattmeter Gets Upgrade: I
have not seen one, but I have been told that
AstroFlight has updated its popular
Whattmeter. Now the amp-hour readout
alternates with the watt-hour readout every
five seconds.
The Whattmeter reads amp-hours up to 95
and watt-hours up to 480. If you are at all
serious about electric flight, a Whattmeter
should be in your shop or high on your needs
list. If you save just one pack by not
overloading it, you have more than paid for
your Whattmeter.
Reader Letters: Michael Naylor wrote the
following.
“I bought a DX7 Spektrum radio system
from Horizon Hobby. I like the system but
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May 2007 99
noticed that the supplied ‘wall wart’ charger
was identified as a Ni-Cd charger with an
output of 50 mA for both transmitter and
receiver. The supplied transmitter battery is a
1500 mAh NiMH and the flight battery is a
1100 mAh Ni-Cd.
“Thinking that, perhaps, Spektrum had
shipped an early batch of DX7s with the DX6
charger, I contacted their customer service.
They claim that the supplied charger is
perfectly adequate—but I have always
believed that you should slow charge at C/10.
“Will a 50 mAh Ni-Cd charger actually
fully charge a 1500 mAh NiMH battery?”
The charge efficiency on a new, unformed
pack dictates that it should receive at least
150% of the rated capacity as an input. The
minimum recommended charge for a 1500
mAh pack to recharge it from a fully
discharged state in a reasonable time frame is
150 mA; 50 mA will not hack it.
Allowing for inefficiencies in charging,
you would need to input at least 120% of the
rated capacity. This means that to fully charge
a discharged 1500 mAh pack, you would
require an input of 1800 mAh. At 50 mA this
would take a minimum of 36 hours. The same
numbers apply to the receiver pack.
More Greasers Come Clean: In the last
column I mentioned two glow-powered
models I had converted to electric. I have been
so impressed with the AXI 2826/12 motor
running on three-cell Li-Poly packs or 4S2P
A123 packs that I brought down three more
old clunkers from my attic. All had served
well as sport and fun-fly models.
I have found that converting these models
to electric is not that hard. It just requires
hogging out some bulkheads (this is much
easier with a right-angle drive on your Dremel
to drive a rotobit), usually behind the tank, and
adapting the existing firewall or adding a new
one to radially mount the AXI motor.
Unlike what you would normally use for a
glow engine, you can get away with a much
lighter firewall. I found 5/32 aircraft plywood
to be ideal; 1/8 would be okay except the
barrel on the blind nuts I was using would
protrude through the plywood.
In the model shown I also had to fill in the
space where the head of the side-mounted
O.S. .40 had been. After I applied a few
patches over other assorted holes where
needle valves, fuelers, and switches were
removed, the modification was done.
I found that 1/2-inch-diameter hardwood
dowels made good engine spacers to move
the engine out to gain some weight in the
right place. When I removed the glow engine
I found, in each case, that the AXI had to be
moved 1/2-3/4 inch to bring the CG to the right
place.
I was happy to find that I had only added
3 ounces, to bring the total takeoff weight to 6
pounds, 9 ounces. Would that prove to be
more than the AXI could handle? Not at all;
flight is much like it was with the O.S. .40—
and I don’t worry about dead-sticks anymore.
Two other models got the same treatment
and had the same results. Just when I thought
I was going to have to find these old airplanes
worthy homes, they are back on active duty.
I have been focused on making the
electric conversion easy to move from model
to model since you are looking at a $200
investment for a motor and a 40-amp speed
controller. It is not all that bad if you can find
a buyer for used engines and all those
propellers you have accumulated.
Encouraged by these minor successes, I
might get started on a new model for a
change. I think the novelty of my “electric
resurrections” at the field might be wearing a
bit thin.
I’m still at 12219 NW 9th Ln., Newberry FL
32669, and please enclose an SASE. I answer
E-mail faster. MA
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