FMA Cellpro & BalancePro Lipo System

The following is a review of the Cellpro and BalancePro lipo system. My thanks to www.Aurorra.com for supplying the equipment in this review.

The equipment in this review is as follows:
BalancePro Skyvolt 6S charger (this charger is now just called "BalancePro" I believe but also goes by the name Skyvolt)
Cellpro 4S charger
4S BEC DPM (discharge protection module)
6S opto DPM
BalancePro to Cellpro adapter cable
Cellpro balance adapter (for Polyquest and Thunder Power type balance connectors)
BalancePro pigtail, Cellpro pigtail
Charger computer connection cable
BalancePro skyvolt charger software

Below are pictures of the items reviewed in this article:

 

FMA SkyVolt 6S Charger

Let's start by looking at the skyvolt charger. This is a charger capable of charging up to 6S lithium polymer packs. This charger is a dedicated lithium polymer charger and does not charge nickel cadmium, nickel metal hydride or lead acid batteries. The charger is a fast charger capable of charging at a maximum of 10 amps. The charge rate is set via a dial on the front of the charger. This is in fact the only control on the charger and therefore operation of this charger is extremely simple. You set the charge amperage on the dial, plug in your pack and the charger takes care of the rest of the work for you.

What makes the skyvolt charger different from other chargers on the market is that it charges the pack on a cell by cell basis, balancing the pack whilst it charges. In fact the balancing algorithm will balance the pack within the first four minutes of the charge, during the rest of the charge the balancing algorithm just keeps all of the cells in balance and within 10 mV voltage difference.

The charger has two LEDs on it's front panel. The orange LED shows that the charger is in fast charge mode, the green LED shows when the charger is going into "top off" mode. This is when the charger is getting towards the end of charge and is reducing the charge amperage slowly until the pack is 100% full. When you plug in a pack the orange LED lights and the pack starts to fast charge, the green LED starts flashing once the charger hits "top off" stage. Both the orange and green LED go solid when the pack is fully charged.

On the side of the charger are two interface ports. One of them is the BalancePro male connector into which you plug the pack to be charged. The second port is for plugging in the optional computer interface cable. This cable allows you to connect the skyvolt charger to your computer. With the aid of the skyvolt software you now get a display on your computer showing individual voltages of each pack, how much mAh each cell has been charged, the overall charge state of the pack (expressed as a percentage), the amperage set on the charger's dial and the actual amperage being charged into the pack. Additionally by clicking on a button the software will show a graph of the charge in progress. This graph shows the voltage over time for each individual cell in the pack. The software records each and every charge and they can be accessed and referenced through the software. Each pack can have its own data file containing all of the previous charges.

Due to the per-cell charging it is possible to safely charge packs at higher charge rates as there is no danger of overcharging a cell. FMA allow up to a 3C charge rate. It is only recommended to do this with FMA approved packs. The monitoring and careful control of each individual cell makes this charger one of the fastest, safest and most accurate ways of both charging and balancing a pack.

The charger has a rugged case and comes with large crocodile clips for connection to a 12 V DC battery. It has its own removable fuse and an internal fan for cooling purposes. The internal balancing shunt can divert a very large charge current meaning that balancing occurs even at 10A charge rates and again the whole pack is drawn into balance in the first four minutes of charge.

Another nice feature on this charger is that it will recover a cell that has been deep discharged. As an example if a cell in a pack was accidentally run down to well below 2 V the charger will not reject this cell like many other charges would. Instead the balancing circuit works on the cell individually and brings it up to normal voltage. The charger is particularly adept at doing this and allows the safe recovery of the bad cell without worry of overcharging the other cells in the pack.

 

 

FMA CellPro 4S Charger

The Cellpro charger is the smaller brother of the BalancePro charger described above. This charger is capable of charging up to 4S packs. It can charge at a maximum rate of 3 amps. Just like the skyvolt charger it charges on a per cell basis and balances the pack as it goes. It has exactly the same charge algorithms as the BalancePro charger and therefore functionality is extremely similar between the two.

Whilst these chargers share the same charge algorithms there are a number of differences between them. Firstly the Cellpro will only charge up to 4S packs, it has a lower maximum charge rate of 3 amps and it is designed to connect to packs with the Cellpro balance plug rather than a BalancePro balance plug. Most noticeably it also has an LCD display. It does not have any configuration buttons or dials except for a single button on the side of the charger which changes the LCD display mode. Similar to the BalancePro charger it can be connected to a PC using the PC interface cable.

The LCD display provides a status showing the current charge level expressed as a percentage and also all of the individual cell voltages for a pack connected to the charger. The display also shows the current charge rate for the pack connected to the charger.

Most significantly there is no need to set the charge rate. The charger is an intelligent charger and will work out for itself an appropriate charge rate for whatever pack is connected. It aims to initiate the charge at 1C. However, for those who like to have some control it is possible to set the charge rate manually using the little button on the side of the charger. This button will allow you to set the charge rate from .25 amps upwards in increments of .25 amps. This can be set up to the charge maximum of 3 amps.

If connected to a PC via the PC interface cable the charger connects with the charging software and allows the user to display charge graphs and so on. Exactly the same as the skyvolt charger and software.

 

 

4S BEC DPM

The DPM (discharge protection module) is a small electronic device designed to sit between the battery pack and the speed controller. The battery pack plugs into the DPM and the DPM plugs into the ESC. Additionally the speed controller throttle cable plugs into the DPM and a servo wire from the DPM plugs into the receiver.

This rewiring allows the DPM to monitor the pack cell voltages individually in flight. If the DPM detects that one cell is nearing its discharged state the DPM will automatically start to pulse the motor. This is the initial indication that a cell in the pack is nearing 3 V. If the pilot chooses to ignore this warning then the DPM will shut down all power once any cell in the pack reaches 3 V. Effectively the DPM has full control over how far any cell in the pack is discharged. This removes any responsibility from the pilot and stops accidental over discharge of the pack.

Effectively the DPM is a safety device to stop the pilot from damaging his pack. The DPM in this review is the BEC variety which is designed to work with speed controllers that have an inbuilt BEC. FMA also produce a DPM suitable for use with opto-isolated ESC that do not have an on-board BEC.

The only calibration required on the DPM is to follow the instructions for setting low stick (so the DPM knows what throttle setting to adopt when shutting down power). There is also a switch which controls on how sensitive the DPM is to the cell voltages. One setting will terminate power earlier than the other. The pilot can select what level of protection they would like for their pack.

The DPM is fitted with an on-board Cellpro connector to accept any pack fitted with a Cellpro balance connector. It also has another smaller connector which is there to attach the optional audio/visual device. This is effectively a lipo alarm and warns you by beeping and flashing the LED when any cell in the pack is approaching its cut-off voltage.

 

 

6S Opto DPM

This is effectively the bigger version of the 4S DPM. This larger version can handle up to 6S packs and is designed to work with opto-isolated ESC. It is configured in exactly the same way as the smaller version but is designed to work with the BalancePro connector rather than the Cellpro connector. The optional lipo alarm can also be fitted to this DPM. The DPM can be used in a daisy chain with another DPM for running packs together. In this way the system can handle up to 12S. Again the DPMs will protect all of the cells in each pack respectively. This makes the system scalable for the majority of pack combinations.

 

 

BalancePro to Cellpro Adapter cable

This is just an adapter cable that allows packs with the Cellpro connector to be compatible with the Skyvolt 6S charger.

 

 

Cellpro to PolyQuest and Thunderpower adapter board

The adapter board plugs directly into the Cellpro charger. On the adapter board are several male adapters into which either Polyquest or Thunder Power lipo's can be plugged via their balance connector. The adapter board has plugs for 2, 3 and 4 cell packs. Also on the adapter board is an LED which will light if you accidentally plug the pack into the wrong connector. The connector board has a maximum charge rate of 5 amps. This effectively gives you two options if you own Polyquest or Thunder Power packs. You can either fit Cellpro connectors to those packs and plug them directly into the Cellpro charger or you can plug them into the adapter board via the existing balance connector. The Cellpro charger will then charge the pack directly through its balance connector just as if it was a native Cellpro pack.

 

 

BalancePro pigtail & Cellpro pigtail

These are just the balance connectors that can be bought to fit to any other manufacturers pack. Allowing that pack to be used with either the Cellpro or BalancePro charger.

 

 

Charger computer connection cable

The computer connection cable allows either the Cellpro or BalancePro charger to be connected via a serial port to a computer. I purchased separately a serial to USB converter cable so that I could plug directly into a USB port. The computer connection cable allows the charger to send data directly to the computer so that the FMA charger software can display information regarding the current battery on charge.

 

 

FMA Charger Software

The FMA charger software is more of a necessity for the Skyvolt charger than it is for the Cellpro charger. The Cellpro charger has its own LCD display which shows most of the information that the charger software displays. The only missing information on the charger LCD panel is the graph of the charge which obviously cannot fit on a small LCD panel. The Skyvolt charger does not have any LCD panel or feedback mechanism other than a couple of LEDs which show whether the charger is fast charging or in the "top off" mode. The software allows you to create a file for each of your packs. This file must be opened for each charge of that specific pack. The charger software then records every single charge into that file. The software allows for navigation backwards and forwards through the various charges in the data file. The software also has the graphing function which shows the progress of each cell in the pack as it is charged. The graph allows easy identification of out of balance cells and shows how the charger corrects that balance issue very quickly (within the first four minutes of charge).

 

 

System and Component Reviews

All of the above is just an overview of the various functionality provided by the FMA Cellpro and BalancePro systems. Having explained how all of these things work, how well do they perform their job?

Initially let's talk about the two chargers. The Cellpro charger is in my opinion what all chargers should be aiming for in terms of functionality. This small field charger does an excellent job of balancing packs and charging packs to their full capacity. The LCD display shows in fine detail the status of each cell of the pack on charge, overall progress for the whole pack and monitors the entire charge process such that no individual cell can be overcharged. Not only this but the charger brings even badly balanced packs back into balance within four minutes of the charge starting. The Skyvolt charger is in the same league except that it does not have the excellent LCD provided on the Cellpro charger. Therefore the Skyvolt charger requires computer connection if you want to be able to see exactly what is going on. Both chargers are at the cutting edge of charger design and I believe we will see more chargers mimicking this design in the future. Having used both chargers extensively they have become my favoured charging equipment. Most specifically because of the fantastic job they do in balancing packs at high charge rates. Bear in mind that both the Cellpro and the Skyvolt are capable of charging a pack at 3C charge rate and therefore a full charge can be accomplished in approximately 20 minutes. Obviously neither charger can go above its defined charge rate which depending on pack size might prohibit 3C charging (particularly for the large packs, 4000mah or more). Both of these chargers come extremely highly recommended by T-Rex Tuning.

Having created two superb chargers FMA then go on to introduce this new device known as a discharge protection module (DPM). The DPM is designed to stop over discharge of any cell in a pack. In practice both the small 4S DPM and the larger 6S DPM do exactly what they say. Having deliberately tried to damage my packs by running them for too long the DPM in all instances has cut in and stopped me from flying before any cell gets close to its 2.5 V limit. In most cases it is quite obvious when the pack starts to sag and the initial reaction from the DPM is to go into slowdown to make it clear to the pilot that the pack is almost spent. Once any cell in the pack reaches critical voltage the DPM cuts in completely and will not let you fly any longer (having cut the throttle first).

So, with the addition of the DPM we have completely safe charging (as each cell is monitored during the charge) and we now have completely safe discharging as the DPM will not let any cell get so low that it is damaged.

Thirdly we have various accessories which allow the use of other manufacturers packs with these chargers. Again these work very well indeed and I have not encountered any problems using either the Cellpro adapter or the Cellpro adapter board. Also in support of other manufacturers packs FMA will provide Cellpro or BalancePro connector cables for wiring to those packs.

Lastly, FMA provide the computer connection cable and charger software. The connector cable has always worked well with my PC and I have had no issues. The charger software is more of a necessity for the Skyvolt charger and allows visibility of the finer aspects of cell by cell charging.

The only problem I did encounter was some minor interference on the throttle channel when using the large 6S DPM on a T-Rex. There wasn't room for the DPM and all the electronics ended up being too close together and caused a pulsing affect on the motor. Since then I have always kept the DPM separate from any sensitive electronics.

Conclusion

Finally we have a safe charging and discharging system that protects the end-user from damaging those all-important (and expensive) lithium polymer packs. The chargers are technically superior to other non balancing chargers on the market. The DPM is a good idea and much-needed to stop those who are less well educated on lithium batteries from making an expensive mistake. When considering these chargers one has to bear in mind that this system was designed specifically for charging lithium polymer batteries. This is different to the majority of other chargers on the market which are essentially updated NiCd chargers with some lithium polymer functionality added. This approach of designing a lithium polymer charger from the ground upwards has allowed FMA to introduce some proper innovation to the charging market.

Overall I am seriously impressed with this charging system and have no issues recommending it. I use the skyvolt charger almost exclusively now for all of my packs and would not want to be without it. Additionally both my T-Rex 450 and T-Rex 600 are fitted with the DPM. I still time my flights and land before the pack starts to lose power but it is very comforting to know that the DPM won't let me do any damage even if I wanted to.

Lastly both of these chargers introduce fast charging of up to 3C. However, these chargers can claim to do this charging properly in that they are monitoring each individual cell in the pack very carefully. The biggest worry whenever performing a fast charge with a non balancing charger is that the pack is not in balance and pack damage will ensue.

If you are in the market for a new dedicated lithium polymer charger, look no further.