72 MODEL AVIATION
THIS IS THE fifth monthly column in
which I try to give you the best answers
to questions you have written in or Emailed.
I’ll make this introduction in a
few more columns for those who are not
yet familiar with the routine. Each
question is given a sequential number for
identification purposes. Because
publication space is limited, these and
additional questions and answers will be
posted on the AMA Web site. Let’s
start!
Q38: “After discharging my batteries
(either by flying or when simply
discharge testing them), should I
recharge them before storing or just
leave them in a discharged state?”
A38: Believe it or not, you can store Ni-
Cd or NiMH cells either way. I recharge
them when I return from a flying session
and usually recharge them every month
or so until I fly again. If I perform a
discharge capacity check (also called
cycling), I also recharge the battery when
the test is concluded.
Since Ni-Cd and especially NiMH
cells lose much of their charge in just a
month’s time, these cells are never
exactly topped off at “full.” Keeping the
cells close to full charge while storing
them has worked for me for many years.
On the other hand, my flying partner
Tom Hunt has always stored his batteries
discharged and only recharges them just
before a flying session (or let’s say the
night before).
Bob Aberle
F r e q u e n t l y A s k e d Q u e s t i o n s
E-mail: [email protected]
AstroFlight 110 Deluxe is for fast-charging 1-24 Ni-Cd or NiMH
cells with adjustable current levels from 50 mA to 8 amps.
The popular and versatile ACE DDVC is intended for overnight or
C/10 battery charging. The author owns three of them!
The AstroFlight Model 109 Lithium battery charger. The tip of the pen is pointing to the
current adjustment control (knob).
However, he does make sure that the
pack has more than 1.0 volt per cell (at
rest, with no load) before leaving it
dormant for any length of time. If the pack
has too low a potential, it could damage the
cells if the voltage drops too low during
self-discharge. He has had no problems
using this technique for many years.
So it seems that either way is okay and
is apparently not that important. The only
thing that is important is that the batteries
are at or close to full charge potential just
before flying. But regardless of the way
you store your batteries, it will take a few
“cycles” to wake up the pack to full
capacity after it has been dormant for some
period of time.
With respect to the new Li-Poly
batteries, the jury is not in yet! Most
“experts” say that you should store them
charged. Since the Li-Poly batteries lose
very little charge—only 1% or 2%—during
09sig3QXD 6/24/04 8:36 am Page 72
a six-month period, it’s easy to store them
at full or close to full charge for long
periods of time. You could conceivably
store a charged Li-Poly battery pack and
fly with it six months later, with a perfectly
normal motor run time.
By the way, you should not tricklecharge
Li-Poly batteries!
An interesting thing has come up
recently concerning Li-Poly battery
charging. It has been suggested to me that
when you first connect your Li-Poly
batteries to the charger, you should
initially set the charge current for a low
value, such as 100 mA. Hopefully your
charger has variable charge current and an
LCD screen that lets you monitor current
and voltage.
Observe the battery’s voltage with that
initial charge level. Allow it to get to
approximately 3.5 volts per cell. That
should happen quickly, but it will depend
on how discharged the battery was at the
start.
Once it has reached 3.5 volts per cell,
adjust the current upward to the normal
recommended current of “1C” (or one
times the rated capacity of the battery).
Allow the charging to take place until it
cuts off at close to full capacity and at 4.2
volts per cell.
As I mentioned, this is a suggestion; the
need for this charging technique has not
been proven. Would any Li-Poly battery
experts out there like to comment on this
charging technique?
Q39: “I have an ‘onboard’ glow-driver
battery for my twin-cylinder engine that
requires two cells in series. Can I, without
damage, charge this battery on the receiver
side of a regular transmitter/receiver
charger? What about the receiver side of a
Sirius charger?”
A39: When you write in, please mention
the size (or type) and the capacity of the
batteries you are mentioning. That
information will help me provide the best
possible answer to your questions.
I’d guess that you are using 1 or 2 amphour
(Ah) Ni-Cd or NiMH cells. Most
dual-output RC-system chargers provide
only 50 mA current for an eight-cell
transmitter battery pack or a four-cell
receiver pack. That low of a charge current
would never really charge the battery
properly. If you did have a 1 Ah (same as
1000 mAh) cell, it would need 100 mA for
an overnight rate.
For fast charging, you would use a 3C
charge rate for Ni-Cd cells, which would
be 3 amps for roughly 20 minutes, or a 2C
rate for NiMH cells, which would be 2
amps for 30 minutes.
If you want to use an overnight (C/10)
rate, I recommend the ACE Dual Digital
Variable Charger, or DDVC
(www.acehobby.com/acehobby/products/el
ectronics/chargers/superDDVC/index.html)
, which has two variable outputs that can
handle one to at least 10 cells at currents
from 0 to well more than 300 mA.
For fast charging, the Sirius charger (I
believe) is intended for four or eight cells.
There is also one that starts at three cells,
but none, to my knowledge, will handle a
two-cell battery as you have. For fast
charging, I recommend the AstroFlight 110
Deluxe (www.astroflight.com). It can
handle one to 24 Ni-Cd or NiMH cells at
current levels from 50 mA continuously
variable up to 8 amps.
Q40: “What happens if you attempt to use
an electric motor speed controller that’s
either too big or too small (in amps)? How
do you know which one to use? It seems
each local hobby dealer has a different
explanation.”
A40: I find it hard to believe that local
hobby dealers have different explanations.
When operating any electric motor, you
must know the current drain (in amps).
That figure can vary depending on the type
of motor, the voltage (number of battery
cells), the propeller size, and the type of
drive (direct or gear/belt reduction).
It is important that you know the total
current drain from your battery for your
particular setup (application). That is why I
have repeatedly suggested that you
purchase an AstroFlight digital meter that
can quickly indicate motor current,
voltage, and power (wattage).
With the motor current known,
selecting the proper ESC should be easy.
Let’s say you measure your Speed 400
direct-drive motor current, and it is
determined to be 10 amps. Using a 10-
amp-rated ESC is okay. Most ESCs are
rated for maximum continuous current.
Any ESC rated higher than 10 amps is fine
for your application.
However, keep in mind that the higher
the ESC’s current rating, the greater the
weight (and cost!) of that device. So you
wouldn’t want to consider a 40-amp-rated
ESC for use in a Speed 400-powered
model where the motor is only drawing 10
amps.
On the opposite side, any controller in
this same example that is rated for less
than 10 amps might be expected to burn
out. The lower the rating (less than 10
amps), the faster that burnout is going to
occur.
With many individuals switching to Li-
Poly battery power, it is also important that
you be aware of your ESC’s voltage cutoff
point. In the “Introduction to Lithium-
Polymer Batteries” article I wrote
(published in the May 2004 MA), I
indicated how I switched from NiMH
batteries to a two-cell Li-Poly battery for
my little Scratch-One electric-powered RC
trainer. I used a Jeti JES-110 ESC in that
aircraft, but I didn’t make a point of
indicating the cutoff voltage in the article;
it is 5.5 volts.
Normally, Li-Poly cells should not be
taken lower than 3.0 volts per cell (or 6.0
volts for two cells in series). At 5.5 volts,
that works out to 2.75 volts per cell. That
is slightly lower than I would have liked,
but it’s still in the acceptable range.
New ESCs that are coming onto the
market, such as FMA Direct’s Super series
and certain types from Castle Creations, set
the voltage cutoff automatically or allow
you to set that point yourself (a custom
setting). This is the type of ESC you
should consider for the future. In the
meantime, make sure you inquire about
any ESC’s voltage cutoff point to verify
that it is acceptable for your particular
battery application. MA
September 2004 73
These two typical electric motor speed controllers (ESCs) are intended for controlling
brush-type motors. They are part of the new FMA Direct Super series.
09sig3QXD 6/24/04 8:36 am Page 73
Edition: Model Aviation - 2004/09
Page Numbers: 72,73
Edition: Model Aviation - 2004/09
Page Numbers: 72,73
72 MODEL AVIATION
THIS IS THE fifth monthly column in
which I try to give you the best answers
to questions you have written in or Emailed.
I’ll make this introduction in a
few more columns for those who are not
yet familiar with the routine. Each
question is given a sequential number for
identification purposes. Because
publication space is limited, these and
additional questions and answers will be
posted on the AMA Web site. Let’s
start!
Q38: “After discharging my batteries
(either by flying or when simply
discharge testing them), should I
recharge them before storing or just
leave them in a discharged state?”
A38: Believe it or not, you can store Ni-
Cd or NiMH cells either way. I recharge
them when I return from a flying session
and usually recharge them every month
or so until I fly again. If I perform a
discharge capacity check (also called
cycling), I also recharge the battery when
the test is concluded.
Since Ni-Cd and especially NiMH
cells lose much of their charge in just a
month’s time, these cells are never
exactly topped off at “full.” Keeping the
cells close to full charge while storing
them has worked for me for many years.
On the other hand, my flying partner
Tom Hunt has always stored his batteries
discharged and only recharges them just
before a flying session (or let’s say the
night before).
Bob Aberle
F r e q u e n t l y A s k e d Q u e s t i o n s
E-mail: [email protected]
AstroFlight 110 Deluxe is for fast-charging 1-24 Ni-Cd or NiMH
cells with adjustable current levels from 50 mA to 8 amps.
The popular and versatile ACE DDVC is intended for overnight or
C/10 battery charging. The author owns three of them!
The AstroFlight Model 109 Lithium battery charger. The tip of the pen is pointing to the
current adjustment control (knob).
However, he does make sure that the
pack has more than 1.0 volt per cell (at
rest, with no load) before leaving it
dormant for any length of time. If the pack
has too low a potential, it could damage the
cells if the voltage drops too low during
self-discharge. He has had no problems
using this technique for many years.
So it seems that either way is okay and
is apparently not that important. The only
thing that is important is that the batteries
are at or close to full charge potential just
before flying. But regardless of the way
you store your batteries, it will take a few
“cycles” to wake up the pack to full
capacity after it has been dormant for some
period of time.
With respect to the new Li-Poly
batteries, the jury is not in yet! Most
“experts” say that you should store them
charged. Since the Li-Poly batteries lose
very little charge—only 1% or 2%—during
09sig3QXD 6/24/04 8:36 am Page 72
a six-month period, it’s easy to store them
at full or close to full charge for long
periods of time. You could conceivably
store a charged Li-Poly battery pack and
fly with it six months later, with a perfectly
normal motor run time.
By the way, you should not tricklecharge
Li-Poly batteries!
An interesting thing has come up
recently concerning Li-Poly battery
charging. It has been suggested to me that
when you first connect your Li-Poly
batteries to the charger, you should
initially set the charge current for a low
value, such as 100 mA. Hopefully your
charger has variable charge current and an
LCD screen that lets you monitor current
and voltage.
Observe the battery’s voltage with that
initial charge level. Allow it to get to
approximately 3.5 volts per cell. That
should happen quickly, but it will depend
on how discharged the battery was at the
start.
Once it has reached 3.5 volts per cell,
adjust the current upward to the normal
recommended current of “1C” (or one
times the rated capacity of the battery).
Allow the charging to take place until it
cuts off at close to full capacity and at 4.2
volts per cell.
As I mentioned, this is a suggestion; the
need for this charging technique has not
been proven. Would any Li-Poly battery
experts out there like to comment on this
charging technique?
Q39: “I have an ‘onboard’ glow-driver
battery for my twin-cylinder engine that
requires two cells in series. Can I, without
damage, charge this battery on the receiver
side of a regular transmitter/receiver
charger? What about the receiver side of a
Sirius charger?”
A39: When you write in, please mention
the size (or type) and the capacity of the
batteries you are mentioning. That
information will help me provide the best
possible answer to your questions.
I’d guess that you are using 1 or 2 amphour
(Ah) Ni-Cd or NiMH cells. Most
dual-output RC-system chargers provide
only 50 mA current for an eight-cell
transmitter battery pack or a four-cell
receiver pack. That low of a charge current
would never really charge the battery
properly. If you did have a 1 Ah (same as
1000 mAh) cell, it would need 100 mA for
an overnight rate.
For fast charging, you would use a 3C
charge rate for Ni-Cd cells, which would
be 3 amps for roughly 20 minutes, or a 2C
rate for NiMH cells, which would be 2
amps for 30 minutes.
If you want to use an overnight (C/10)
rate, I recommend the ACE Dual Digital
Variable Charger, or DDVC
(www.acehobby.com/acehobby/products/el
ectronics/chargers/superDDVC/index.html)
, which has two variable outputs that can
handle one to at least 10 cells at currents
from 0 to well more than 300 mA.
For fast charging, the Sirius charger (I
believe) is intended for four or eight cells.
There is also one that starts at three cells,
but none, to my knowledge, will handle a
two-cell battery as you have. For fast
charging, I recommend the AstroFlight 110
Deluxe (www.astroflight.com). It can
handle one to 24 Ni-Cd or NiMH cells at
current levels from 50 mA continuously
variable up to 8 amps.
Q40: “What happens if you attempt to use
an electric motor speed controller that’s
either too big or too small (in amps)? How
do you know which one to use? It seems
each local hobby dealer has a different
explanation.”
A40: I find it hard to believe that local
hobby dealers have different explanations.
When operating any electric motor, you
must know the current drain (in amps).
That figure can vary depending on the type
of motor, the voltage (number of battery
cells), the propeller size, and the type of
drive (direct or gear/belt reduction).
It is important that you know the total
current drain from your battery for your
particular setup (application). That is why I
have repeatedly suggested that you
purchase an AstroFlight digital meter that
can quickly indicate motor current,
voltage, and power (wattage).
With the motor current known,
selecting the proper ESC should be easy.
Let’s say you measure your Speed 400
direct-drive motor current, and it is
determined to be 10 amps. Using a 10-
amp-rated ESC is okay. Most ESCs are
rated for maximum continuous current.
Any ESC rated higher than 10 amps is fine
for your application.
However, keep in mind that the higher
the ESC’s current rating, the greater the
weight (and cost!) of that device. So you
wouldn’t want to consider a 40-amp-rated
ESC for use in a Speed 400-powered
model where the motor is only drawing 10
amps.
On the opposite side, any controller in
this same example that is rated for less
than 10 amps might be expected to burn
out. The lower the rating (less than 10
amps), the faster that burnout is going to
occur.
With many individuals switching to Li-
Poly battery power, it is also important that
you be aware of your ESC’s voltage cutoff
point. In the “Introduction to Lithium-
Polymer Batteries” article I wrote
(published in the May 2004 MA), I
indicated how I switched from NiMH
batteries to a two-cell Li-Poly battery for
my little Scratch-One electric-powered RC
trainer. I used a Jeti JES-110 ESC in that
aircraft, but I didn’t make a point of
indicating the cutoff voltage in the article;
it is 5.5 volts.
Normally, Li-Poly cells should not be
taken lower than 3.0 volts per cell (or 6.0
volts for two cells in series). At 5.5 volts,
that works out to 2.75 volts per cell. That
is slightly lower than I would have liked,
but it’s still in the acceptable range.
New ESCs that are coming onto the
market, such as FMA Direct’s Super series
and certain types from Castle Creations, set
the voltage cutoff automatically or allow
you to set that point yourself (a custom
setting). This is the type of ESC you
should consider for the future. In the
meantime, make sure you inquire about
any ESC’s voltage cutoff point to verify
that it is acceptable for your particular
battery application. MA
September 2004 73
These two typical electric motor speed controllers (ESCs) are intended for controlling
brush-type motors. They are part of the new FMA Direct Super series.
09sig3QXD 6/24/04 8:36 am Page 73