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FMA Cellpro Multi4 Charger Review
March 04, 2009
Last updated January 28, 2011
INTRODUCTION
FMA is well known for making battery chargers that are safe and simple to use and the Cellpro Multi4 is no exception. The Multi4 is based on the CellPro 4S but includes advancements from the CellPro 10S development plus many hours of additional development, making it even more versatile and advanced than its predecessors that we love so much. A simplified view would be to think of the CellPro Multi4 as a CellPro 4S but with a processor having 4 times the program memory space, powerful 2-way PC interface, backlit LCD, and multi-chemistry support.
The 2-way PC interface (requires an optional FUIM2 cable) is adapted and evolved from the Cellpro 10S, it utilizes a program called Charge Control Software (CCS) to enable reading and graphing of charging data on a PC, setting of advanced features on the charger, firmware updates, and remote control of the charger. The PC interface is not required, but of you like to tweak and fiddle you will want to get the FUIM2 interface cable. The Multi4 charger is built in Indonesia, but the quality of the components and soldering appears to be excellent and is far superior to the poor quality of many cheap imports. The manufacturing may be overseas, but the charger was designed by and is support by English speaking people located in Maryland. This also means the manual and software are written in clear English that is refreshingly easy to read and understand, and if you don't understand just call (301-668-4280) or e-mail FMA for help. FEATURES
SafetyThe integrated balancer in the Multi4 gives it an inherent safety not obtainable by unbalanced chargers, even if coupled with an external balancer. Since the Multi4 can only connect to a battery via a balance tap this ensures the charger always knows the voltage of every cell in the pack (except for the newly introduced unbalanced charges). Access to every battery cell allows the charger to not only balance the cells, it also allows it to know the exact cell count and prevent cells from being overcharged. An external balancer can only discharge cells and only a few can stop the current flow if needed, but they cannot provide a cell count to the charger or have it reduce the current flow as required to maintain cell balance or restore a overly discharged cell. Many LiPo battery fires are reportedly caused by a charger that was set to the wrong cell count or a charger that changed the cell count after the charging began, with the Multi4 when in balanced mode there cannot be a miscalculation of cell count.Another frequent problem with battery chargers is setting the charge rate, which can be problematic and error prone if frequently charging packs of different capacities. The Multi4 automates the charge current selection by using a unique "fuel table" technology which allows the charger to automatically estimate the appropriate 1C charge current for that battery pack. A cold weather mode stops the charge at a specified voltage when the ambient temperature is low (typically 4.1V at <50F for a LiPo) to prevent overcharging batteries in cold weather. And finally, the charger comes equipped with a set of internal self-diagnostics and over 60 error messages to alert the user to all manner of abnormality. Chemistry supportAll manner of lithium batteries are supported, including LiPo, LiFe (A123), and LiMn. Additionally, the Multi4 can charge NiCd, NiMH, and lead-acid (SLA and gel cell) batteries. Lithium packs of 2-4 cells can be charged in balance mode or 1-2 cells in unbalanced mode. Similarly, LiFe (A123) packs of 2-4 cells can be charged in balance mode or 1-5 cells in unbalanced mode. NiCd and NiMH packs of up to 10 cells and lead-acid of up to 8 cells can be charged in unbalanced mode. Basically any cell combination of most any chemistry with a termination voltage of 18.25 volts or less can be charged. PresetsThe Multi4 is preset driven, but that is not to say that you need a preset for every battery pack or that the presets require much work to set up and use. In fact, if you just leave the 25 presets at their default settings and use the charger normally you would end up using one preset for each chemistry of battery pack. If you use LiPo and A123 you could get by on just 2 presets for charging and a third for storage charging. However, if you want to optimize the presets to your preferences the PC interface and CCS will allow you a very large range of control with up to about 70 different possible settings per each preset, and take advantage of new presets as they are released by FMA. There is a library of up to 50 presets that are provided by FMA (only 27 are currently in use) and any of these 50 may be used as is or customized and placed into one of the 25 available preset slots. ConnectorsPower is supplied to the Multi4 via 16 AWG wire with banana plugs and removable battery clamps that are ideal for clipping onto a deep cycle lead-acid battery. The battery pack to be charged is connected via a Cellpro 5-pin plug and a push button near it is used to navigate the menus. Near the input power cables in a 3 pin connector for the PC interface, it is not keyed physically but there is a polarity indicator printed near the connector and plugging it in backwards will not harm the charger.Power and current capabilitiesThe power supply to the charger must be capable of supplying 5 amps at 10-16 volts, but the rated output power of 50 watts cannot be obtained unless the supply voltage is approximately 11 volts or more. When charging a 5S A123 pack I have seen an output of as much as 57 watts when powered from a deep cycle battery. Keep in mind that at pack voltages over about 12.5 volts the output current is reduced from 4 amps in order to stay withing the power capabilities of the power supply inside the Multi4. If your power supply is incapable of supplying at least 10.5 volts at 5 amps the charger will automatically reduce the charge current to maintain the supply voltage. The CCS can also be used to manually limit the input current, a setting that can be overridden temporarily by holding down the mode button while turning on the charger.Other featuresAs with the other FMA chargers, the Multi4 has the ability to restore lithium cells from 0.5 - 2.7 volts and LiFe cells from 2.0 volts or less. Another feature unique to FMA is that the balance tap wires can be as long as 3' or even 6' as the charger can compensate for the resistance in the wires.BOX CONTENTS
OPTIONAL ACCESSORIESIf you happen to have Cellpro balance taps on all of your batteries or are only going to be charging unbalanced packs then you're good to go. But if you're like me your batteries don't have Cellpro balance taps so you have two options: replace your battery balance taps at $1.99 each or get an adapter board for $9.95. In the picture below is a CellPro balance tap and an adapter board. 
Optional balance tap adapter board Entirely optional, but highly recommended is the FUIM2 PC interface cable for $19.95 as this enables a high level of customization, logging, and firmware updates. 
Optional FUIM2 USB PC interface cable The included unbalanced connector can have one or more plugs soldered onto it to fit your various types of batteries. If you are not the soldering type you may find the $14.95 Versatile Adapter suites your needs. 
My own unbalanced connectors on the left and FMA's optional accessory on the right 
FMA's adapter for charging up to three 1.25mm cells in parallel. FMA also sells a 12VDC, 5A power supply with banana plugs for $29.95. It plugs into a wall outlet and provides sufficient power for the Cellpro Multi4 or a 4S. 
Optional AC power supply for the Multi4 Multi4 Combo DealsThe Multi4 may be purchased individually or in combos with various accessories. These combo deals typically save about 10% compared to buying the products individually.MANUALThe manual is 20 pages long and is a rarity in that it is easy to read and understand since it was written in English and is not a poor translation. The manual covers all of the features, connectors, power requirements, and operation. At first glance the map of the menu is overwhelming and one wonders if they'll ever learn to use the charger, but if you follow the directions then revisit the map after a few uses of the charger it'll make sense and you might even learn of some new menu selections that you missed the first time around. Don't worry, you won't need the map or even the directions since you'll get the hang of it right away. The main focus of the manual is on using the charger so only the basics of using the CCS are covered in it, detailed CCS help is available within the program. The manual may be updated from time to time so check for the latest manual available from FMA to see if there have been updates. There is a date code on the last page in the format YYMMDD which you can use to quickly check to see if there has been any updates. My manual was dated 081224 but recently version 090126 was released to fix some minor typos and to add descriptions of the factory installed user presets. PICTURES
CHARGER MENUThe Multi4 menu can be thought of as having three main levels; choosing the preset (the "Preset Menu"), selecting preset options (the "Operations Menu"), and battery charging data (the "Charging Menu"). The menu for choosing a preset is straightforward and is where the charger begins when powered up, just pick the preset appropriate for the battery and move to the Operations Menu. In the Operations Menu you'll most often just select to start the charge, but you can also adjust the charge rate, clear the preset, or load one of the library presets into that location. When the "start charge" option is selected the charger will check the battery pack and ask you to confirm the chemistry and in some cases the cell count, after that it displays the battery charging data. Navigating the menu consists of four variations of pressing and holding the mode button (see the key in the menu map below). In general a press and release of the button causes the menu to advance forward or changes a value, such as the charge current. Holding down the button is used to move from one menu to another, to bring up the option to cancel a selection, or to confirm a selection. A slight variation of the button holding operation is that after the button is pressed and held to enter the operations menu, it is held and not released until the desired entry is scrolled to. Those actions alone are enough to use the charger, but for speed of access the direction of scrolling through a menu or list of selections can be reversed with a quick button press and release followed by pressing and holding the button until a special tone sounds to indicate the direction has been reversed. I find this last button manipulation to be the most trouble prone as I sometime mess up the timing and instead of reversing directions I accidentally initiate a charge which then has to be canceled. Remembering the variations of pressing a single button is not too problematic, but I think FMA should consider adding another button as they are pushing the limits of what can be done with a single button. 
The menu map shown in the manual BATTERY CHARGING EXAMPLESCharging SafetyThe safety rules for charging your batteries are probably no further away than the labels on your battery packs, some of these rules are as follows:
A word on presetsTalking about charger presets can conjure up mixed emotions, some people love them and others hate them. Let me start by saying that these presets can be as simple or as complex as you like. The Cellpro 4S can be thought of as a charger with two presets, one for A123 and another for LiPo, but of course with LiPo you had to scroll through all the various LiPo charge rates as you try to navigate from LiPo to A123 and back again. The Multi4 has fixed this by making presets designed at a high level to be targeted towards certain types of batteries and charge behaviors. For instance, you pick a preset based on chemistry, how much effort you want put into balancing, termination voltage, balanced or unbalanced, and small or big batteries. You will most likely end up using just a handful of presets, even if you have a diverse selection of batteries. The only customizing that can be done to a preset from the charger is to change the charge rate, all other preset changes require the CCS and FUIM2 interface cable.Quick Start (my version)The back of the Multi4 manual has a 10 step "quick start" guide that while accurate and easy to follow, I feel that it could mislead someone into thinking that the charger is difficult to use. Therefore I offer two quick start examples in order to demonstrate a typical usage. For these examples assume that the last time the charger was used was to charge a LiPo battery using the first preset which gives a 1C charge and an accurate balance.Examples
Now let's do a more complex example. Let's say that you normally use the 1C accurate charge that is in preset 1 but you want to adjust the charge rate to 2C. You could use preset 2 but you would like to also keep the accurate balance features of preset 1.
Now let's do a LiFe battery example and create a new preset for it. Let's use a 3S 1100 mAh A123 pack as the example, the default "accurate charge" rate for this battery in the Multi4 is 3.3 amps, but I would like to have a dedicated preset for it that is set to 4 amps and still has the balancer settings of the FMA supplied preset.
Data displayed on the LCD while charging
Canceling a chargeIf at any time you wish to cancel the charge press and hold the mode button and release it when "STOP CHARGE?" message is displayed. Press and release the mode button to change "N" to "Y" and then press and hold the mode button again till the the "CHARGER STOPPED" messaged is displayed and a beep is sounded. Error codesIf there is a problem during the charge an error message will be displayed. At this time there is table of error codes in the back of the user manual but no detailed description. FMA has announced that in the future descriptions of the error codes will be added to the manual. If you cannot discern the problem based on this table just contact FMA via telephone or e-mail and they can help you out. CHARGE CONTROL SOFTWAREThe Charge Control Software (CCS) is rich and complex enough to deserve its own review. It is not technically part of the Multi4 charger but is free to use if you have an FUIM2 cable. It is so useful that I am going to give it a brief coverage and highly recommend everyone that purchases a Multi4 purchases an FUIM2 cable if they do not already own one. Tabs
The "Presets" tab is the only tab that is not fairly self explanatory, but FMA has included two types of help, one pops up when you hover the mouse pointer over a setting and a more detailed help pops up when you click on the name of a setting. There are approximately 70 different settings that can be adjusted depending so it is not feasible to mention them all here. However, in general these settings control the following behaviors:
GraphingThe other major component of the CCS is the graphing window which plots various information, depending on the charge type. This is typically individual cell voltages, pack voltage, charge current, and fuel percentage. The graphing tool can be customize to use colors of your choosing (as I have done) and has a very handy built in capability to save the graphs as images. The X and Y coordinates of the cursor are displayed on the graph so you can easily read the voltage or current at any point on the graph.
Plots of cell voltages and charge current of a 3S 2500 mAh LiMn pack. Custom fuel tableAs battery technology changes the fuel table in the Multi4 presets may not generate a correct 1C charge current for your newer battery packs. If you have the FUIM2 and CCS you can charge a battery with a manually set 1C charge rate then import the data from that charge into the CCS and it will automatically generate an appropriate fuel table. I have a 2S 640 mAh pack and a 3S 350 mAh pack that were being charged at about 0.5C so I did a 1C manual charge of the 640 mAh pack and imported the data. Subsequent charges of both battery packs resulted in charge rates of about 0.95C which is very close to ideal. This procedure is detail in this guide by FMA.
Fuel table settings. Saving and sharing of presetsPreset customization can represent significant time spent tweaking and testing settings, FMA has thoughtfully provided a means to save a backup file containing the settings of the whole charger or just one preset. If your buddy has a preset you like or you want your charger set up just like his (or hers) all you have to do is have them e-mail you their settings file and you can import it to your charger.Firmware updatesAproximatly once every two weeks since Multi4 sales began FMA has been releasing firmware updates. Initially the fixes were for FMA factory use, but once input started pouring in from the users the fun updates started rolling out. They are so good about it that once I had noted a bug and was going to email FMA to inform them of it, but before I could do so the next firmware was released, fixing it and some other issues. One of the most notible CCS and firmware updates is in the works as I write this, the ability to stop and start the charger from your PC. This is a bonus feature that was not even mentioned in the intial product announcement and shows FMA's dedication to improving and adding to the CCS.
Firmware update tab and the new PC remote control feature. USER FEEDBACKFMA is one of those rare companies that listens to their customers and makes changes based on their feedback. Rest assured that when you download a new version of the firmware or CCS that it has already been tested by FMA and several other hobbyists like yourself. Recently a Multi4 owner suggested on RCGroups.com that he should be allowed to hide empty presets so that he does not have to see them when scrolling through the preset menu. Within a few days that change was in beta testing and a total of 12 days after the suggestion was made the change was released to the public. Find me one charger manufacturer in our hobby that has done that. ACCURACYI am a stickler for details and accuracy, when I see a product like the Multi4 I want to know just how accurate it is. The charger may say it just charged my cells to 4.201 volts at a rate of 2.00 amps, but I want to know what the voltage really is. The Multi4 manual states that it balances cells to within 5mV, has a voltage accuracy of 6mV, current accuracy of 1%, and a charge accuracy of 1%. My reference for checking voltage and current accuracy is a Fluke 87-V which has a DC voltage base accuracy of 0.05% and a DC current base accuracy of 0.2%. All measurements were performed using a charge scenario chosen to minimize that rate of change of the parameter being measured. For example, the voltage accuracy was tested while performing a 5 mA charge into a 4600 mAh A123 battery pack near a state of being half charged. I have also included a few measurements from my Watt's Up meter as a point of comparison. The numbers in the parentheses are the percent error as compared to the Fluke 87-V DMM. One of the problems with testing the accuracy of the Multi4 is that there are often three different places to find the indicated value of and one parameter and they can all be different. For example, the charger LCD will display a supply of 12.4 volts, the CCS will show 12.50 volts, and the .cp4 file that records the charging data shows 12.46 volts. For this reason I have chosen to record the accuracy of each of these displayed values.
Let's take a look at how the Multi4 measures up. In the first row we can see that the cell voltage is displayed consistently and accurately, but in the second row the .cp4 file records a pack voltage 10 mV higher. The values shown on the LCD and in the CCS are the sum of the individual voltages so I'm not sure where the .cp4 file gets its value from, possible a direct measure of pack voltage rather than simply summing the cell voltages. Notice that the Watt's Up meter and Multi4 agree on the charge very closely, but the Fluke 87-V value is different, I believe this may have to do with how the DMM calculated the average current. In this case I believe use of the DMM and stopwatch to measure charge is not very accurate, but the closeness of the Multi4 and Watt's Up meter results show that the Multi4 is quite accurate in measuring charge. Finally, in the last two rows the supply current and voltage are fairly accurate and it only suffers in cases where fewer significant figures are used. Based on these numbers the Multi4 is functioning well within its published accuracy. The Multi4 is advertised to balance cells to within 5mV. To test this claim I charged a few of my well used 3S LiPo and LiFe packs and measured the voltage shortly after the termination of the charge. A typical result is shown in the table below. As before, the number in the parentheses is the percent error. Notice that the charger balanced to within 3mV, within its advertised performance rating.
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