Overall photo of the new FMA Direct/Revolectrix CellPro 10S charger

Let me first provide some background information before getting into the new FMA Direct CellPro 10S charger. FMA Direct, under its founder, AMA Hall of Fame member, Fred Marks, has been involved in much of the electronic aspects of our hobby for a lot of years. They have produced RC systems, auto pilot systems, ARF and RTF aircraft, test equipment and in recent times, lithium battery chargers and battery packs. Fred’s sons, Tim and James, now run the day to day business with the technical development area being headed by FMA President, Tim Marks.

I think it safe to say that FMA was just about the first company in the USA to get into the lithium polymer (Li-Poly) battery business. That was something like five or six years ago. As we now all know, Li-Poly batteries provide about 95% of the power requirements for electric powered model aircraft. There are literally dozens of companies now involved in distributing both Li-Poly battery packs and their companion chargers.

Much has happened over these six years. For example, there was obviously a learning curve involved with the application of Li-Poly batteries. Early on, some fires were reported and the safety aspect of using these new cells initially became a big concern. (See Part Three of the Sport Aviator article “Those Things We Call Batteries” for complete Li-Poly details.)

The techniques employed for charging and discharging Nickel Cadmium (Ni-Cd) and Nickel Metal Hydride (Ni-MH) batteries had to be learned all over again when it came to the new Li-Poly batteries. But, with a few years of experience under our belts, safe Li-Poly battery operation has become once again the routine for experienced electric power flyers.

One of the first lessons we learned is that Li-Poly battery cells should not be charged over 4.20 volts and they shouldn’t be discharged below approx. 2.70 volts per cell under load (3.00 volts being better!). Going higher in charge voltage or lower in discharge voltage will ruin the battery cell quickly. Normal charge current rate is recommended at a “1C” level or 1 times the capacity of the battery; rated in amp/hours. A 2 amp/hour rated battery would be charged at 2 amps and if that battery were close to being fully depleted, it would take approx. an hour to reach full charge. Everyone learned early-on these several constraints associated with the use of Li-Poly batteries.

But the real breakthrough with Li-Poly batteries came as a result of development work done by FMA Direct. They were the first to recognize that, upon completion of charge, Li-Poly cells within a pack must all have the same voltage or close to it. When each cell is at the same voltage the pack is said to be “balanced”. Following this concept you will be able to safely charge and discharge your Li-Poly battery packs and obtain excellent service life from them.

To make this concept work, FMA Direct wired all of the battery packs they sold so that each cell was brought out separately into a multi-pin connector. This connector has now been called a “node” connector and can have any number of pins based on the total number of cells in the pack. With node wiring, each cell can be charged separately until they reach the same voltage. The concept is actually more technical than that, but I think you will get the basic idea.

Besides having this added connector you need a special charger with multiple outputs. As part of this “balanced” Li-Poly battery pack process, FMA Direct developed the necessary companion charger, the Balance Pro 6S.

The Skyvolt Charger, later known as the BalancePro 6S, which is now being phased out in favor of the new CellPro-10S Charger

When balance packs and charging was first introduced, FMA Direct introduced their SKYVOLT charger and Li-Poly battery packs. The name was changed later to BALANCE PRO 6S. It was their first time effort. The node connector was large and heavy. The battery packs were sized primarily for larger models. There was no LCD screen on the charger to tell you what was going on. To obtain any info on the charging parameters you had to connect up to a PC and use special, FMA supplied freeware. This proved a great nuisance at the flying field. But the charger did work well! I’ll have some further comments on the “6S” later on.

CellPro 4A Charger, the forerunner of the new CellPro 10S, can handle up to 4 cells and at up to 4 amps charge current

Recognizing some of the BALANCE PRO 6S shortcomings, FMA developed the now very popular CellPro 4A charger. This is a “balanced” charging device that can handle up to 4 cells in series and at up to 4 amps charge current. It also has a multi-function LCD display that tells you important parameters, such as the capacity remaining in the pack, the individual cell voltages, the charge current when charging and when charging is complete. This charger can be used with battery packs intended from micro indoor/parking lot size on up to approx. 3 pound model aircraft. You might be able to extend this limit to even larger models, but then the charging time would have to be increased.

Typical Li-Poly battery packs at the top of this photo, with an A123 Li-Ion battery at the bottom – The CellPro 4A and 10S can charge both types of batteries

With the success of this CellPro 4A, FMA added a feature that allows for charging the A123 Lithium Ion (Li-Ion) batteries from this same unit. It also has a “STORE” mode for Li-Poly battery packs that charges the pack only to half capacity, which provides the most optimum storage life. Best part of the CellPro 4A is that presently (April 2008) it sells for only $74.95.

Li-Poly balanced battery charging is now employed almost exclusively throughout our hobby. It is safe to say that except for the smallest of packs, all new Li-Poly batteries now have individual cell wiring to permit balance charging (charging each cell in a pack to the same voltage level). To allow you to select and purchase a Li-Poly balanced battery pack of your choice, FMA is offering an extensive array of adapter cables that will allow almost any node connector on the market to plug into their CellPro chargers.

New CellPro 10S Charger on the left and the CellPro 4A on the right. The CellPro 4A Charger will continue to be offered to modelers who are only interested in charging up to 4 cells with a 4 amp maximum current

The new FMA CellPro 10S charger does every thing that the CellPro 4A charger does and much more. If you don’t own any balanced Li-Poly charger at this time, you would want to consider stepping right up to the “10S”. If you were going to concentrate on parking lot size models, as well as moderate size models up to approximately 3 pounds total weight, the CellPro 4A might fill your needs and it costs less than half of the CellPro 10S.

But if you contemplate much larger electric powered aircraft ,upwards of 10 to 15 pounds, or you need to charge two packs simultaneously (such as the Hobbico NexSTAR EP or the Hobbico ElectriStar trainers), then you will definitely want to consider the “10S”.

The CellPro-10S is charging two separate Li-poly battery packs simultaneously

There is also another important consideration. With FMA balanced charging technology, you can now safely charge at current rates higher than “1C”. You can, in fact, go as high as 3C, which will provide full charging in 20 minutes or less depending on the state of charge in the pack.

If you own the CellPro 4A the maximum current is 4 amps. That means that the highest capacity pack that you can charge at the 3C rate is going to be around 1300 mAh (3 x 1300 = 3900 mA or 3.9 amps!). When you move up to the CellPro 10S, you can charge packs at the 3C current rate with up to approx. 3300 mAh (3 x 3300 = 9900 or 9.9 amps.). The higher output current allows for faster charging times in larger capacity packs.

Of course, the 10S can also charge at a slightly lower rate of 2C, which provides a full charge in 30 minutes. It can do that with packs rated up to 5000 mAh. So, the higher current output of the 10S can charge at higher rates and in faster times.

Another nice feature of the CellPro 10S is that two Li-Poly packs can be simultaneously charged. Think of two packs being charged at the field, while you are flying with a third pack. Let’s just summarize the CellPro 10S capabilities at this point:

It can charge Li-Poly, Li-Ion and A123 battery packs up to a total of 10 cells and at a total maximum current of 10 amps.

Backlit LCD screen showing individual cell voltages in a three cell li="Poly" battery pack

The new backlit LCD screen on the 10S works much the same as on the CellPro 4A. It tells you the capacity remaining in the battery pack, the voltage of each cell in the pack, the charge current and when charging is completed. A new feature is a reading of the IR (internal resistance) of each cell in the pack measured in milli-ohms. Once we get used to reading and recording this parameter, we will be able to determine the quality of the cells in the pack and will be able to note early on when cells are beginning to lose capacity and drop off line. Much will be said about this feature in the future.

This screen display shows the percentage charge presently in the battery pack. In this case it is almost fully charged.

The CellPro 4A allows you to connect to a PC to record and store (file) battery pack data and plot graphs using an FMA freeware called “Viewer Software”. The new 10S goes much further, utilizing new 2-way interface between the PC and charger, the “Charge Control Software” or CCS allows you to establish, and download to the charger, up to six pre-set charging routines for your favorite battery packs.

It also allows you to adjust the contrast of the LCD screen, set LCD scrolling options and adjust the speaker volume. There is also a special check box for setting charge optimization to choose between faster charging and accurate balancing. But perhaps the most exciting new capability provided by the new software is the ability to automatically receive the latest software and firmware updates for your charger via the Internet.

It works much the same, and is based on, the basic “engine” used by Microsoft ™ Corporation for Windows Updates and has been adopted by many other industries. This substantial innovation to the industry is something that will be incorporated into many other FMA Direct products and stands to bring the R/C industry into the “modern age”.

Never return a charger to the factory again for firmware updates. Keep up with the latest updates at the click of a mouse button. It’s easy and it keeps your charger tuned up and equipped with all the latest features “for free”.

A special 2-way USB PC interface cable is available as optional equipment, or can be purchased as part of a combo deal. FMA provides the proprietary “Charge Control Software” as a free download and promises to continually update this software as experience is gained with the 10S in the future.

The two cables that make up the FU1M2 cable assembly are used to connect the CellPro 10S to your PC allowingyou to download software revisions or to record and plot charging data

This is how the FU1M2 interface cable attaches between the CellPro 10S and a USB port on your PC