Associated Electrics RC10T - Battery Charging and Management

CHARGING BATTERIES
It
is
impo
rtant to undertand the
cha
racteristics
of
the battery
pack
in your tru
ck
because how you use it
will
greatly
affect both its performance and its
life. With proper
care your
pack
will
pe
rform well
for many hundreds of
cycles.
The ROAR legal
battery for use with your truck
is
composed of six
or
seven
"sub-C"
size
cells
with a rated
capacity of between 1.2-1.8 amperes for one hour,
or
2.4
amperes f
or
1/2 hour, etc. T
hi
s char
ge
capacity is the
same
regardless
of
the number of
cells
in the pack
because the
cells are connected in series and the same
current passes throu
gh
each one.
CHARGER. A
good
qua
lity
char
ger
will last longer
for you than an economy unit, so
please
do
not cut
yourself
short here
by
trying
to
save a
co
u
ple
of
dollar
s.
Any good
name
brand charger
wi
ll
do
the job correctly.
The more
sophisticated
cha
r
gers
have extra features that make
charging
less
time-consuming and can easily handle
the
abuse of heavy back-to-back type charging. The choice of
a
DC
only
or
an
AC/DC
charger should
be
based on
personal
needs
(w
here you
will
be
using your truck, etc.)
and
usage.
OVERCHARGE. There is no way to make a
Ni-Cd
cell
accept more charge than it is designed to hold.
This
means
that as the
ce
ll
approaches a
fully
cha
rged condi-
tion
, the portion
of
charging current not being stored
becomes heat and pressure.
If
charging
co
ntinues after
the
cell
is
fully
charged,
all of the current is converted to
heat
and pressure--about40 watts worth,
or
the equiva-
lent of the heat produced
by
an average
soldering i
ron.
High temperature and pressure is damaging to the
cells,
so
overcharging
mu
st
be
avoided.
Ni-Cd cells have a
built-in
process for re
co
mbin-
ing
the accumulated gas
(actually
oxygen) produ
ce
d
by
ove
rcharge, but the process
produ
ces heat and takes a
lot
of
time
.
If
you overcharge your battery and it seems to take
a
long
time to
coo
l
down, it's because this pressure
reducing reaction is taking
place. Once
the
gas
is recom-
bined the temperature
drop
s.
pag
e 45
HOW
TO
TELL
WHEN
YOUR
CELLS
ARE
CHARGED
One of the problems
with Ni-Cds is their inherent
voltage stability; the
voltage
of a
f
ully
charged
cell
is
not
much different from one that's just about dead. For that
reason
several
indicators,
along
with some common
sense, are needed
in
order
to
get
the most out of your
battery. The following
is a
list
of
indicators you
can
use to
detect
full
charge.
TEMPERATURE METHOD. This works only
if
you start with a
cool
battery pack. As the
pack
charges,
f
requently
check
its temperature by
feeling
the
cells
dire
ct
ly.
As soon as you notice an increase in tempera-
ture, stop charging.
If
the
ce
lls become too hot
to
hold
onto, your
cells are excessively
overcharged. Let them
cool.
TIMED
CHARGE METHOD. This works
on
ly
if
you have confi
dence
in the timing accuracy of your
charger. Many chargers
on
the market
only
approximate
a constant charging current; they
may
vary from six
amps
when you first start charging,
all the way down to two
amps if the Ni-Cd pack is
nearly charged and the
voltage
of the charging source
(automobile
battery) is
low. If
the
charging
cur
rent varies,
it
becomes
difficult
to estimate
the average cur
rent. However, if your charger is reasona-
bly dependable,
you can use the
following
method.
Charge
your
pack
using the
"
tempe
r
at
u
re
method" above and ke
ep
track of the time required
to
reach
full
cha
rge.
Once
you have
established
the time,
you can use it as a setting for the timer on your
charger
.
To be safe, use a setting about a minute
less
than what
you
established.
T
hi
s method
allows
you to charge with-
out
constantly
monitoring the battery temperatu
re.
If you charge a
ba
ttery that is
still
hot f
r
om
runni
ng
, re
du
ce
the time about 20%.
Then, after the
pack
has
cooled, finish charging with the temperature
me
t
hod
.
VOLTAGE METHOD.
Voltage
is a poor indi
ca
-
tion of a
cell's
state of charge.
In
fact, other factors
like
temperature, current drain, and "cell memory"
have as
much
of
an effect on
voltage
as the state of charge
does
.
However, if current
flow
and
temperature are
held
con-
stant, it is
possible
to see
th
e
cell voltage gradually climb
during the charging process. The
absol
ute value
of
this
voltage
isn't of much u
se-
how the voltage
changes is
an
ex
ce
llent
indi
ca
tor. To use this method, you
will
n
ee
d a
digital voltmeter or an expanded-scale
vo
ltmeter
ca-
pable
of
resolving 0.01 volts
on
the
10 volt range.
Connect the voltmeter
across the
Ni-Cd
pack
,
preferably
right at the
ce
ll terminals, or, if that's
not
possible,
across the
terminals
of
the
throttle control