We often seem to take our
batteries for granted, or at least those that sit in our 'planes, I suspect we all keep a wary eye out on the transmitter
voltage meters, don't we....? But how often do we think about those 4.8V batteries tucked away under the tank?
Firstly, do we always remember
to charge them fully before we go out to fly? Sometimes we forget that the newer high capacity cells will need proportionally
longer to charge on a standard receiver charger, as supplied with the outfit. If this was intended for the old "Standard"
500mA .hr cells, and took 14 hours to charge them, then you will need to leave a newer 1000mA.hr pack for 28hours ,
or a 1200mA.hr pack for 34 hours, to get the same result! If they only get the overnight charge, probably about
10 hours, they may not be up to full charge at the beginning of the day.
OK so you play it safe and
give them to someone to charge at the site. DON'T try to charge them too quickly!
Another problem, again associated
with the increasing capacity of the newer cells, is that they require a relatively much longer initial charge to get them
going from new. Typically, the 1000mA.hr size will need to be charged for about 36 hours for the first "from-new
charge" in order to properly condition and balance the cells, if this is done on a charger intended for the older 500mA.hr
cells. In addition, they may need a few cycles of charging/discharging before they reach full capacity. If this "pre-flight"
care is not done, the actual capacity for the first few flights may be much less than the stated capacity.
There are a number of things
you can do to avoid troubles with your RX batteries.
Firstly, always use
some form of battery checker before flying. The sort you plug the battery in before putting it in the model should put
a load of between 250 and 500mA on the battery - it's no good doing a voltage check under no-load conditions. The on-board
types give confidence before each flight, but read this type while stirring the sticks and beware if the lights drop towards
the red while doing this.
Secondly, never let your
batteries completely flatten, for example by leaving them in the model with the switch left on (don't laugh - it has been
done many times by many folk). It is quite likely that one or more of the cells will have been "reverse charged", which will
damage them. Sometimes they will recover after a few cycles of charge/discharge under controlled conditions, but it
is more likely that the damaged cells' capacities will be much reduced.
Finally, it pays to check
the condition of the batteries every so often. If you know the current drawn by your battery tester (you did go out
and buy one, didn't you?), then plug the fully charged battery in, and time how long it takes for the indicator to drop
into the red. A rough value for the capacity is found by multiplying the current in milliamps by the time in hours (or minutes,
then divide by 60!) A better way, of course, is to use some
form of analyser, setting
the discharge rate to about between 250 and 500mA - some chargers ( such as the RipMax "SuperNova") have a facility for discharging
batteries and recording the capacity directly. These gadgets may seem expensive, but could save your model. Any battery
that shows less than 80% of its rated capacity should be dumped and replaced immediately!
Q. What is an
acceptable test reading relative to the stated capacity rating of the battery?
As most new nicads will test out to a capacity slightly greater than that printed on the side of the case one must aim for
a value equal to or no more that 5% lower than this value. Don’t assume that a 1000mAh rated pack that checks out to
500mAh is actually as good as a 500mAh pack. It is already 50% gone and the rest of its capacity will die soon!
Receivers will cause greater
variations in battery loading due to servos operating at different times. As such, it is even more requirement to have a good
nicad with the Rx, than with the Tx.
Q. How often should nicads be cycled?
Cycling nicads is only necessary as part of a true capacity, peace of mind check. If nicads are used heavily for long
flying sessions there is less need to cycle. However, if a battery has been stored for several months, say during a winter
lay-up, it is a good idea to cycle/test them a couple of times before use. Normally cycle checks should only be necessary two
or three times a year on each battery. More often than that is considered of little benefit. Remember, it is always better
to highlight pending faults at home rather than on the field.