The Battery Clinic - 2007/11

Put your charger to work
November 2007 81
The Battery Clinic Red Scholefield | [email protected]
Also included in this column:
• Uses for old computers
• Battery specs: where to find
them
• Bob Lloyd goes electric
• What an electric propeller
can do to you
• Winter battery storage
• Electric gift suggestions
• Battery questions and
answers
• Battery education sources
Hard-drive magnets from old computers
make good tool holders.
Adapters for cordless products enable them to be used with your hobby charger.
The Triton charger is hooked up with an adapter on a Makita drill pack.
THE CHARGER YOU bought to take care
of your hobby needs can do many other
charging cycling tasks on cordless appliances,
cell-phone batteries, MP3 players, and almost
anything that uses batteries.
Has the charger gone south on your
cordless drill? Are you suspicious of the
capacity delivered by your cell-phone battery?
Your hobby charger can come to the rescue.
The only catch is how to make the
connections to the battery or device itself if
the battery is inaccessible. If the charger has
gone bad you can salvage the part that
interfaces with your battery and simply add
leads with banana plugs to go into your
hobby charger. Others require that you get a
little more creative and make an adapter.
Don’t trash that old computer. Give it a
new purpose in your shop as a data
11sig3.QXD 9/21/07 10:42 AM Page 81
82 MODEL AVIATION
Ouch! Electrics just don’t give up. The
text includes Brad Faul’s experience.
Bob Lloyd’s Goldberg Eagle 2 goes clean with electric power.
logger/programmer. Several battery
maintenance devices are being offered with
computer interfaces that enable you to set up
the test and/or monitor them.
Devices such as the West Mountain
Radio CBA II discharge analyzer, the Orbit
Microlader, the recently introduced FMA
Direct BalancePro and Cellpro, and the TME
Xtrema, with its latest update, take
advantage of a computer interface. The
handy RadioShack digital multimeter also
comes with a computer interface, enabling
you to record voltage or current and graph it.
Then you have programming devices for
Castle Creations’ Phoenix ESCs that greatly
simplify setting them up, with break on/off,
cutoff voltage, hard/soft timing, etc. Plus the
computer will give you a place to keep all
your modeling notes that you are forever
filing and forgetting where.
And if you do decide the computer has no
further use, pull the hard drive and take out
the two crescent-shaped magnets. They are
great for holding tools, hanging up plans
while you are building, etc.
Where to Find Battery Specs: My favorite
source is the Sanyo site. Another
manufacturer is Yuasa (field box and Lead
Acid starting batteries). Some battery
suppliers, such as FMA Direct, have taken
the bold step of providing battery
performance curves for Li-Poly packs on
their Web sites.
If you know the name of a manufacturer
(not the distributor, which can seldom give
you any meaningful information), you can
type it into the Google search engine. That
will usually lead you (albeit on a somewhat
tortuous path through all the marketing hype)
to some useful information if you are patient.
Another Old Faithful Gets Electrified: Bob
Lloyd, a member of the Staten Island NY RC
Modelers, sent in a picture of his Goldberg
Eagle 2 designed for a .40 glow engine. He is
powering it with two six-cell, 3300 NiMH
packs. An E-flite 46 brushless motor is
controlled with a Phoenix 60-amp ESC.
Bob claims that the Eagle 2 is a great
success. Why am I not surprised? It has great
breeding.
Something that constantly bothers me at the
field is seeing electric-power fliers hover
over models with the surgically efficient
APC E propellers only millimeters away
from a wrist, throat, or other vulnerable part
of the body while twiddling with airplanes
and having the battery plugged in. Maybe
what Brad Faul (aka Tommygun@RCU)
submitted will get their attention.
Included is a picture of what a small
outrunner can do if you are careless during
setup. Always remove the propeller before
setting up a computer radio and hooking up
connections.
The throttle channel was reversed, and an
inadvertent arming sent Brad to the
emergency room. He received nine
stitches—worse than from any glow engine
he can remember.
Some people don’t realize that unlike
with a glow engine, an electric-powered
propeller will keep slicing away like a
blender—unless the propeller breaks. Hell
hath no fury like a runaway electric with
only one propeller blade.
As some of you are reading this it is time to
put your models away for the winter.
(Shudder!) Your batteries will hibernate fine
in most cases. It does not matter in what state
of charge you store your Ni-Cd or NiMH
packs.
However, it is best to remove them from
your model in case a cell shorts out during
storage and leaks electrolytes. You have
probably heard of black-wire disease so I
won’t go into it here, other than to point out
that it can cost you a wiring harness or worse
if it makes its way into any of your
electronics.
According to the manufacturers, Lithium
packs should be stored 40%-60% charged for
best results. How do you get to that level?
Discharge the packs in your model,
checking the voltage occasionally. When
they get to roughly 3.7 volts (open circuit)
they are good to store. An easier way is to
use a discharger that will let you set the
voltage, such as the CBA II.
A couple chargers will let you set the
charge voltage (after complete discharge) to
a storage level. Those are the Cellpro and the
Xtrema. You can even use other chargers if
you monitor the voltage while charging and
shut down the process at the desired level.
Li-Polys should never be left in the
airplane after use. My shop refrigerator is a
good repository for packs that are not going
to be used for a while, even if we don’t enjoy
your nice, long building season.
People have asked about leaving their
models in an environment where it
frequently drops below freezing. Ni-Cd and
NiMH specs give -40º as the lowtemperature
storage level. Lithium can be
stored to 20ºC (-4ºF) per some
manufacturers’ specs. It would probably be
better to store them where there are fewer
broad temperature swings.
As the number of people going clean
(electric) increases, many are still operating
blind in regards to the abuse they are giving
their equipment and batteries. Yes, they can
detect the smell of overstressed components,
but by then it is too late.
Motors and batteries have limits. If they
are frequently pushed beyond those limits,
they become unhappy. A wattmeter of some
type would make a great Christmas gift.
The AstroFlight Super Whattmeter (part
101) has been a popular unit. Although I
have never used one, Medusa Research
also has some nice units: one standard and
one with several options for more bells and
whistles. Give your family a clue; leave
the magazine open on this page with this
item circled.
11sig3.QXD 9/21/07 11:15 AM Page 82
The Hard Ones: The following are
battery-charging questions.
“Hello, I have a question about battery
charging and I can’t seem to get a straight
answer. Can a 1600 mAh battery be
charged safely with a 2 amp charger?”
One thing I saw was that each cell can
be charged at .5 amp (this is a five-cell
hump pack), which would mean that the
pack can handle rates up to 2.5 amps.
Another thing I saw was that the battery
shouldn’t be charged at more than 10% of
its mAh rating, so the 1600 mAh battery
shouldn’t be charged at more than 1.6
amps.
“Please help, I have a 2 amp charger
and I want to know if I would be ok using
it. Thank you.”
That is not how it works. (Not that I
had the slightest clue what his 2-amp
charger was.) The pack charge rate is the
same as a single cell when they are
connected in series. Ten percent of a 1600
mAh pack would be a charge rate of 160
mA (0.16 amp)—not 1.6 amps.
What kind of a charger do you have?
If it is a peak charger, yes, you could
charge the 1600 mAh pack (Ni-Cd) at 2
amps. Maximum for a NiMH pack would
be 1.6 amps.
84 MODEL AVIATION
Back to Basics: There are many good
sources for basic battery information,
including The R/C Battery Clinic,
BatteryUniversity.com, and Hangtimes
Hobbies. For electric flight in general there is
no better resource than the Electric Flyers
Only Web site. For Lead Acid batteries
check out BatteryStuff.com.
Space here doesn’t permit my going into
the detail necessary to give you even a
minimal battery education. The basic
seminar on my Web site exceeds 5,000
words.
For those without computers, your local
library has them for your use. It might cost
you a few nickels to print out all the
information you are going to find that you
might want, but you won’t have to buy a
computer to get it.
Lithium battery pricing is coming down.
The cost of battery packs has a significant
impact on the cost of electrics, but it appears
that there is some light at the end of the
tunnel.
Following is a survey of the market as of
July 2007. I picked a typical pack to use as
an example.
Air Thunder—3S2200 mAh, 25C—$69.99
Amondotech—3S2100 mAh, 10C—$49.75
Apogee—3S2200 mAh, 20C—$51.99
Common Sense RC—3S2100 mAh, 15C—
$69.95
DN Power—3S2150 mAh, 15C—$74.96
Flight Power—3S2100 mAh, 18C—
$62.99
FMA Direct Cellpro—3S2100 mAh,
18C—$47.95
Hurricane Flight Systems—3S2000 mAh,
12C—$40.20
Max Amps—3S2100 mAh, 20C—$57.95
Poly-Quest—3S2150 mAh, 20C—$79.90
Thunder Power—3S2100 mAh, 12C-
18C—$69.95
That’s it for this month. I’m still at
12219 NW 9th Ln., Newberry FL 32669,
and my computer still accepts E-mail on a
regular basis.
Take care. MA
Sources:
AstroFlight
(310) 821-6242
www.astroflight.com
BatteryStuff.com
(800) 362-5397
www.batterystuff.com/tutorial_battery.html
BatteryUniversity.com
www.batteryuniversity.com
Electric Flyers Only
http://members.aol.com/kmyersefo
FMA Direct
(800) 343-2934
www.fmadirect.com
Hangtimes Hobbies
www.hangtimes.com/rcbattery_faq.html
Medusa Research
www.medusaproducts.com/Power-
Analyzers/PA-Main.htm
Sanyo battery specifications
http://sanyo.wslogic.com
The R/C Battery Clinic
www.rcbatteryclinic.com
Yuasa Lead Acid batteries
www.gs-yuasa.com/gyin/en/products/pdf/
NP_200609.pdf