FMA Direct Cellpro 10s Charger Review

The FMA Direct Cellpro 10s is a balancing lithium battery charger, capable of charging a single battery up to 10 cells, or two batteries simultaneously up to 5 cells, with power up to 10 amps. It can handle lithium polymer, lithium ion, and the M1 lithium cells from A123 Systems. Let's dig in and put it through its paces.
Specifications Chemistry
Lithium polymer, lithium ion, lithium manganese, and A123 M1 Pack capacity
100 mAh to 65 Ah
Input voltage
10 to 16V DC, reverse polarity protected


Input current
Up to 25A, can be limited between 1A to 25A


Charge rate
Up to 10A (300 watts)


Dimensions
6 5/8 x 3 3/8 x 1 5/8 inches


Street Price
$189 USD

FMA Direct was kind enough to provide a sample unit for review. The charger comes with 4mm bullet connectors on the power input leads, as well as alligator clips, which can be used to connect a car battery or other power source. Also included are two 5s-to-4s converters that let the 10s work with any generation of Cellpro batteries. Finally there is a plug blocker which can be installed across the main charging terminals, allowing charging through the balancing ports only (up to 4 amps). Five dollars extra buys two sets of 4mm charging leads without connectors, so you can solder Dean's ultra connectors, PowerPoles, or whatever you prefer for charging at above 4 amps.

It's hardly news that the state of balancing connectors in this hobby is a mess. It seems that every major manufacturer of batteries has its own balancing tap, and a few even share connectors but differ by polarity. Fortunately FMA has taken a comprehensive approach by offering optional adaptors for all the major connectors in use. I evaluated two adaptors: one board has both PolyQuest and ThunderPower connectors up to five cells, the other has Align/ElectriFly and Kokam up to four cells. Since beginning the review, FMA has introduced new adaptor boards which handle 2 to 6 cells each. There's a lot of flexibility to this system, and you'll have no trouble connecting up your collection of batteries.

The charger itself is smaller than I expected, given its power rating. The construction is very solid with metal heatsinks along the sides. The top has a large, backlit LCD display, and cooling holes for the fan, which only runs when needed. I found the manual clearly written and easy to understand, with a lot of detail about different connection possibilities and error codes.

Like FMA's Cellpro 4s , control is simple. There are two buttons on the right side which control all functions. The Mode button is used three ways: short presses cycle through the six presets from the main screen, or change values in the other screens. A long press enters the menu mode, where continuing to hold the button gives a choice of battery chemistry, charge rate, and exit to the main screen. Lastly, a quick double press on the Mode button changes the charge rate in whole amps, rather than tenths of an amp. The second button, labeled Start/Stop, does just that.

While this style of programming works, it is a little unintuitive, and I sometimes made mistakes. Given that the hardware only has two physical buttons, I would have preferred a more traditional arrangement, where Mode (button one) is only used to change between screens. Then the Start/Stop (button two) could be renamed to Set, and used to change values, changing them faster if held down. This is just a personal preference, and not a serious issue. I got used to the interface quickly and it's now second nature.
One thing I applaud is the user-upgradable firmware. Although the required USB interface is optional, new versions can be flashed at home, for free. The Windows-only software checks online for the latest versions, and describes the changes in each, another nice touch. The update takes a couple minutes and was reliable in my experience.

The PC application has a number of other functions, like displaying individual cell voltages live, and a graphing mode while charging which is very cool. You can also configure and name your presets, which is fast and easy using the keyboard. Lastly, there are a number of settings which are not available from the charger front panel. In particular, the ability to limit the amp draw on the power supply is very useful and could prevent damaging your power source. I wish this setting could be set on the charger itself, or that the $20 USB interface was included in the purchase price.
I tried a variety of LiPo packs with the charger, from 2S 300 mAh packs up to the biggest I had on hand, 3S 2100 mAh. Because these packs are relatively small, I installed the plug blocker across the main terminals and charged entirely through the balance connectors. I find this very convenient as there's less to connect and fewer wires in the way. You can either set the amps manually or select 1C, 2C, or 3C charging (if your batteries can handle these higher rates). Since the Cellpro 10s detects the number of cells automatically, using 1C mode is dead-simple - it just does the right thing with no fiddling.

If you need to charge at 4 to 10 amps, connect both the main leads and balancing taps for each cell. As a safety feature, the Cellpro 10s will not charge without the balancing connectors hooked up. Although that makes perfect sense for LiPo packs, it is a drawback for A123 users who either use solderless end-to-end packs or didn't bother to add a balancing tap to their brick packs. There are mixed opinions on whether M1 cells require balancing, and FMA has taken the cautious route here.

Initially I tried the Cellpro 10s using a computer power supply with banana plugs added to the 12V rails. However it was not able to maintain 12 volts during a charging cycle, and when the charger detected the insufficient voltage it halted the charge. I don't think the Cellpro is particularly picky about power supplies, but a switching unit between 12 and 15 volts is best.



To work around this problem, FMA sent me their top-of-the-line power supply . This serious looking piece of hardware delivers up to 28 amps at 13.8 volts on its main terminals, and can simultaneously supply 7 amps to a cigarette lighter jack and a pair of clips for bare wires on the rear panel. It has a quiet fan which runs all the time, and in all my testing it never even got warm. I'm very impressed with its quality of this unit. FMA offers this power supply separately or in a bundle with the 10s if you don't own a suitable source of DC power.



They also sell a 5 amp supply which would be adequate if you only use small park flyer packs. In my testing, I was able to charge two 3s 1500 mAh packs at the same time, drawing 4 amps from the power supply. Consider this a way to squeeze by on a budget though, as you won't be able to really let the 10s shine. Any larger than 1500 mAh and I recommend a more powerful 12V source.

As I mentioned, the 10s can handle all three popular lithium variants. It does this by changing the cutoff voltage appropriately: 4.2V per cell for LiPo, 4.1V per cell for LiIon, and 3.6V per cell for A123. If you charge two packs at once they must be of the same chemistry. The 10s does not charge NiCD or NiMH batteries, which doesn't bother me a bit, since I haven't used either in a couple years. In fact, I planned to try a safety check to make sure the 10s wouldn't start a charge when connected to a NiMH pack, and couldn't even find one in my workshop.

The 10s is essentially two chargers in one when used with packs up to five cells. I found it convenient to put a couple 3s 2100 mAh packs through my T-Rex and charge them together in under an hour. You need to start and stop both packs at the same time, but I didn't find this to be an issue. The only possible drawback involves charging two batteries of very different capacities, whether they are of different sizes, or the same size packs depleted to different levels. Once one battery is done, the charger will slow down to 1A to complete the other.

Pictured are the various information screens the 10s offers during a charge. When charging a total of more than four cells, the display alternates automatically within the individual cell voltages screen.

One question that's come up on the forums is whether to buy the 10s or two Cellpro 4s chargers. This is largely a matter of personal preference. If you can't see ever going beyond 4s packs, the two independent chargers are a bit cheaper. On the other hand, the 10s has more features and more room to grow. Helicopter pilots in particular often want to step up from their 450 sized models into something bigger, and that typically means at least 5s or 6s LiPos, or up to 10 cell A123 batteries.