Q-57: I recently read about using a 24-hour appliance timer to operate
a power strip, to which I can plug in a series of RC-system chargers. The idea
is to set the timer to come on for something like one hour in each 24-hour
period. This effectively provides a trickle charge on the batteries. Is that a
good idea?
I also have a question on battery cycling. I’m on a low budget so I’m not ready
to buy a fancy device to discharge my batteries. What kind of an inexpensive
load can I use to discharge-test my batteries? How low should I allow the
voltage to go during a test discharge?
A-57: I’ve heard of that 24-hour timer technique for many years. The
idea is to leave the chargers on just long enough, in a 24-hour period, to
maintain a full charge level. The trick is knowing exactly how much time to
leave the chargers on. Many would debate whether it should be one, two, or three
hours in a 24-hour period. I doubt if any two people could agree to the amount
of the “on” period.
RK Products sells a product called the Lil' Trickler (www.liltrickler.com),
which accepts as many as three RC-system chargers. The Lil' Trickler controls
the time on for these chargers during a 24-hour period that will essentially
maintain the charge level. It is much more sophisticated than using a 24-hour
timer.
I’ve never used one of those devices, but I have heard nothing but good reports
from modeling friends who have used it for years. It is also relatively
inexpensive.
As I have explained many times, I only trickle-charge my transmitter batteries.
I’ve successfully used the ACE RC Digipulse Multi-Charger for many years. It has
six adjustable outputs. It will charge for a timed 16-hour period and then
revert to a pulsed trickle-charge level. I’ve had at least three of my six RC
transmitters on this unit for more than five years, and the batteries are still
at their rated output.
I have so many electric-power battery packs that it would be impractical to put
them on trickle charge. When the airplane gets really sluggish in flight or
lands much sooner than expected, then I discard the pack. Just flying with
electric power does all the cycling you could ever want.
You can discharge your own batteries, but it requires considerable discipline
and time on your part. You can use an old electric motor, some power resistors
from your local RadioShack, or even some 12-volt automotive bulbs as a load.
You will have to monitor the voltage and the current while the load is
applied. You must also time how long it takes the load to take your battery down
to approximately 1.0 volt per cell for Ni-Cd or NiMH. Li-Poly batteries should
be taken down to 3.0 volts per cell.
If you get bored during your testing, walk away from the battery, and forget to
return, you could easily destroy the battery. With a Li-Poly battery, you might
even have a fire on your hands. For these reasons, I tell my modeling friends to
buy a dedicated battery discharge tester. I like the Peak Electronics SuperTest
PRO, which sells for less than $100. It can handle up to 14.0 volts (in 0.1-volt
increments) and loads up to 2.0 amps.
When people say they can’t afford this product, I ask them how many RC systems
they own. Most say three of four. I usually counter by telling them that the
first thing they should buy after their first RC system is a battery
discharge tester. The other thing they need, especially as an electric flier, is
an AstroFlight digital volt, ampere, watt meter.