Most new RC pilots use the batteries that came with their radio set. These batteries are, for the most part, rechargeable Nickel-Cadmium batteries (Ni-Cd for short). The first rechargeable RC batteries, Ni-Cds remain the mainstay of the RC world.

Ni-Cds are usually reliable, vibration resistant, widely available and very cost effective. Model pilots have relied on them for nearly 40 years. True, they have a few performance negatives, but on the whole Ni-Cds are a very user friendly power system for our transmitters and on-board systems.

The first performance problem Ni-Cd batteries have involves their sudden voltage loss when the cells reach near-discharged levels. The nominal Ni-Cd voltage, regardless of the cells rated capacity such as 700 mille-Amp hours (700 mAh), is 1.2 volts. Therefore a 4-cell receiver battery pack using 700 mAh capacity cells would have a nominal voltage of 4.8 volts. A transmitter battery pack usually contains 8 cells for a nominal voltage of 9.6 volts.

What is all this “nominal voltage” stuff? Since Ni-Cd batteries are rechargeable, their actual voltage fluctuates over a range. Freshly charged, a single Ni-Cd cell has a “surface” voltage of around 1.4 volts. The term “surface voltage” means that this voltage is not really useable as it disappears as soon as an electrical load is applied to the battery or a few hours have elapsed since the last full charge.

After a few hours, a charged battery’s voltage drops to about 1.35 volts. This is a useable voltage which decreases quickly when current is drawn from the battery. Under load, a good Ni-Cd’s voltage drops from 1.35 to between 1.2 and 1.3. Therefore we say that its nominal voltage is 1.2 volts. A Ni-Cd battery remains at this 1.2-volt level for most of its time under load.

As current continues to be drawn during operation, the voltage very gradually drops to around 1.1 to 1.05 volts. After reaching about 1.05 volts however, the bottom drops out of a Ni-Cd and voltage drops to almost nothing in just a few minutes. What this means to an RC pilot is that there is little warning, and even less time to do something, once a Ni-Cd reaches the end of its capacity.

Everything works well then there is a sudden slowing of control response, in the case of a receiver pack, or a big range loss for a transmitter, when the battery reaches the end of its charge. In either case, the end result is a re-kitted, or re-ARF’d, aircraft to retrieve. The moral here is to make sure never to push a Ni-Cd battery anywhere near its limits.

The other Ni-Cd problem is the loss of capacity over time. Unlike the “dry cells”, like a Duracell® battery, a Ni-Cd battery is not made of just one chemical-containing package. Instead, it is made from many small plates, packed closely together with a chemical media in between and then enclosed by the metal container. Over time, small chemical deposits build up between the many plates. The deposits reduce the battery’s ability to absorb and store a charge. Therefore, the battery’s mAh capacity is reduced.

After two years of regular slow charging with the charger that is packed with the usually RC system, most Ni-Cd batteries have only about 80% of their rated capacity. The result is less safe flight time.

The Sirius Charge Pro Series, made by Peak electronics, is designed to overcome both these Ni-Cd problems. I first encountered the Sirius Charger about six years ago at a trade show, the Westchester Radio Aero Modelers (WRAM) show held every February. This nice gentleman spent 20 minutes telling me about this “Wonder Machine” and I didn’t believe a word he said as the claims were just short of magic.

But he was insistent and I finally agreed to try one. The Sirius Charge didn’t live up to the claims. Instead it exceeded them. Rushing home from the show, I put this charger on an 18-year old Kraft receiver battery. While the 500 mAh battery pack only had about 100 mAh capacity, I had kept it around so I could use the plastic case (battery packs had hard plastic cases in those days) sometime in the future.

I charged the battery overnight on a slow charger and then discharged it using an Ace R/C Abacus discharger (no longer available). The battery had just 75 mAh in it after 16 hours on the slow charger. I then charged it with the Sirius Charge charger.

The Sirius charger is a fully automatic charger. It senses the battery’s voltage and then sets itself for either four cell (4.8 volts) or five cell (6.0 volts) receiver packs. The transmitter side is always set for 9.8 volts. It also senses the amount of charge current that can be safely used, usually 550 mA and when the battery is fully charged.

Once full charge is reached, the Sirius charger switches to a Pulsed Maintenance Mode. This is not a trickle charge like most other fast chargers. It is a computer controlled full current charge that alternates charging with discharging. This system is designed to recondition the chemicals inside the battery, removing those small chemical deposits on the plates.

I left the old Kraft battery in the Maintenance Mode for 24 hours, it only took one hour to charge it, and then I again tested the old battery on the Abacus. It tested out at 125 mAh. It took five repeated cycles but that 18-year old battery actually reached 375 mAh. I would never fly with it but that is an amazing recovery.

 
Photo 1     Photo 2

If the Sirius Charge charger could do that with an old battery, what could it do with a newer one? I have an older JR MAX 6 Computer transmitter. This reliable radio system dates from the early 1990’s and has had a few battery changes in its eventful lifetime. It was just about time for a new one. Instead, I elected to try the Sirius Charge Charger on its 700 mAh battery.

Photo 3

First I charged the transmitter battery for 18 hours. Then I tested the battery’s capacity using the Sirius Super Test precision battery tester (more on that device later) and found it only contained 300.7 mAh (photo 2). I followed the same 24 hour Sirius Charge Charger protocol as with the Kraft battery. The next test (photo 3) revealed a 460.1 mAh capacity. That is quite an increase.