Q-83: With all the advantages being pointed out concerning Li-Poly batteries for electric-powered flight, I wondered if these same batteries might be put to good use powering RC systems used to control fueled-engine aircraft? Is there some way I might use several Li-Poly batteries to power my RC receiver and servos? Would there be any advantage in doing that?
A-83: Yes! Most RC airborne systems (receiver and servos) are
powered by four-cell (4.8 volts nominal) Ni-Cd or NiMH batteries. In some cases,
five-cell packs (6.0 volts nominal) are used to provide faster servo transit
time.
Each Li-Poly battery cell has a nominal voltage of 3.7. A single Li-Poly cell
would not supply enough voltage to an RC airborne system, but two Li-Poly cells
in series (7.4 volts nominal) would be far too much voltage.
Several companies are marketing voltage-reducing or -regulating devices that
drop the two-cell Li-Poly pack's 7.4 volts to 5.0 volts, specifically to operate
an RC airborne pack. I received a sample of FMA Direct's VRLI voltage regulator.
It is physically small—1-1/4 inches long, 3/4-inch wide, and 5/8-inch thick—and
weighs only .12 ounce. You insert this device between the cable coming from your
receiver and a two-cell Li-Poly battery pack.
As a bonus, the FMA engineers added three colored LEDs to the VRLI circuit
board. When you turn on your RC receiver, if the green LED glows, you have a
charged battery and are ready to fly. If the yellow LED is on, your battery
could use recharging. If the red LED is on, don’t fly until you recharge.
You have to work your numbers to determine when using two Li-Poly batteries is
an advantage over using four Ni-Cd or NiMH cells. You must consider the
batteries' weights and their rated capacities. This is just an introduction to
the subject matter.