Sport VRLI

Model Airplane News, Dec 2004 by Aberle, Bob

FMA Direct

Li-poly power for glow-powered planes!

AT MODEL AIRPLANE NEWS, we not only tell you what's new, but we also try it out first so we can bring you mini-reviews of the stuff we like best. Manufacturers frequently send us their latest support equipment, and if we think a product is good-something special that will make your modeling experiences a little easier or just plain more fun-we'll let you know here. From retracts and hinges to glow starters and videotapes, look for it in "Product Watch."

With all the talk about Li-poly batteries and their advantages for electricpowered flight, you may have wondered whether they can be used for onboard RC systems as well. Because Li-polys have a characteristic voltage of 3.7 per cell, a single cell would not provide enough voltage to reliably operate most RC airborne systems (receiver and servos). Two Li-poly cells in series produce 7.4 volts nominal, which is too much for the average RC system. Enter FMA Direct's new add-on: the Sport VRLI (voltage regulator and LED indicator). At just 1.25x0.75x0.5 inches and weighing only 0.18 ounce with the connector, this unit allows you to use Li-polys to power your airborne RC system. It costs $21.95.

The VRLI reduces the higher voltage of two Li-poly cells (upward of 7.4 volts) to a regulated 5 volts, which is most suitable for operating the average RC airborne system. To set it up, plug the cable that exits the VRLI into your RC receiver, and plug the 2-cell Li-poly battery into the switch harness. The output of that switch harness plugs into a connector that's attached to the VRLI PC board. The regulated voltage can tolerate 2 amps of current on a continuous basis. It is claimed to be enough current to power up to five average-output servos and an RC receiver, but please don't consider using it for high-torque (high-output) servos or even digital servos. The VRLI's three LEDs (yellow, green and red) also indicate charge status-a plus for overall operation.

Half-amp and smaller glow-powered planes, hand-launched gliders and small sailplanes can all benefit from Li-poly power. Let me give you some examples to prove this point. A 4-cell, 150mAh Ni-Cd pack weighs 1.4 ounces, but a 2-cell, 145mAh Li-poly pack and VRLI weigh 0.48 ounce. That means you can get the same capacity (145 versus 150mAh) for about an ounce less! If you use a 4-cell, 50mAh Ni-Cd pack that weighs 0.6 ounce, you could get three times the capacity (145 versus 50mAh) at a still slightly lower weight of 0.48 ounce! Even that tiny decrease on a ½A model or a hand-launch glider could be significant.

There are several other advantages to using a Li-poly. The thin profile allows the battery to fit into very narrow (streamlined!) fuselage structures. The battery also has such an excellent shelf life that it would be ready for months on end to be used for a quick flying session (during 6 months, it will lose only a few percent of its charge).

If you have an application for a lightweight RC airborne battery with a greater than average capacity, the use of Li-poly batteries might be worth exploring. Keep them in mind the next time you consider your battery needs for a small, glow-powered model aircraft or for an equally small RC sailplane! -Bob Aberle

FMA Direct Inc. (800) 343-2934; (301) 668-7614; fmadirect.com.