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FMA Balance Pro HD Charge/Discharge System (formerly Skyvolt)
By Jim Young
Dec 08, 2005, 02:00 AM
Introduction
With the rapid release of LiPo batteries for high current R/C aircraft applications there have been numerous band-aid fixes to handle the charging and balancing issues of these cells. LiPo battery chemistry is different from NiCad and NiMH chemistry, and initial chargers tried to treat a LiPo pack like NiCads. With NiCads, you could over charge a pack to some extent to keep all of the cells in balanced. Over charging LiPo cells is not an option (as many have found this out first hand), so you can't keep a pack in balance by charging the whole pack. Balancing must be done by another method. With large LiPo packs, initial chargers could only look at the overall pack voltage and guess that the individual cell voltage has not exceeded the maximum recommended per cell voltage. With repeated charge and discharge cycles, multi cell packs could become unbalanced, and over charging of one or more cells in a pack was a real danger. Further, over discharging of LiPo cells can damage them and reduce their life. To address this issue, LiPo pack suppliers added "taps" into the pack so that individual cell voltages could be monitored. To go with these taps, several cell balancing devices popped up on the market to balance a pack after charging. But since the balancing was performed after charging, you could still over charge a cell before the balancer was plugged in. Some balancers could be connected while charging, but they severely limited how fast a pack could be charged. The slow charge rate supported by these types of chargers made them only useful for periodic pack maintenance. Likewise, when discharging a pack in a model ESCs could only monitor the overall pack voltage to protect from over discharging cells. ESC suppliers quickly put out LiPo friendly ESCs, but none of these addressed the possibility of an individual cell being over discharged. Now, FMA Direct has put together a complete LiPo battery charge/discharge system that addresses all of these issues. The Balance Pro HD(formerly SkyVolt) system handles charging, balancing, and discharge of Balance Pro HD LiPo packs. Let's take a look at how it does all this.
Balance Pro HD Packs
Each Balance Pro HD pack comes equipped with a special connector. This is one of the best connector concepts I've seen for an electric flight system. The connector combines the high current connections to handle flight currents along with taps for each of the cells into one connector. All connector pins are gold plated and I measured the connection resistance of the high current pins at 3 milliohms. For comparison, a brand new Dean's Ultra measured at 4 milliohms, and an old Sermos PowerPole measured at at 3 milliohms. (A 4 wire, 6 1/2 digit multi meter was used for these measurements)
There are a variety of packs available with the Balance Pro HD system. All packs are based on the latest generation of Kokam cells and currently available packs use either the 2000mAhr 15C or 3200mAhr 20C cells. The 2000mAhr cells are available in 1P and 2P configurations from 2S to 6S. The 3200mAhr cells are available in 1P, 2P, and 3P configurations from 3S to 6S. For this review I used a 3S1P and 5S1P pack of the 3200mAhr cells. The performance of these cells is well known, and the current delivery capability of these packs is limited more by the Dean's Ultra connectors used in the system than by the cells themselves. The 3S 3200 pack weighed in at 10.4oz, and the 5S 3200 pack weighed in at 16.7oz. The 5S pack is 13.3oz lighter than a 16xRC2000 pack that it is replacing while providing over 50% more capacity. The 3S pack is 6.2oz lighter than the 10xCP1700 pack it is replacing, while providing almost double the capacity.
As with any LiPo cell, excessive heat can shorten the life of the cell. FMA recommends that pack temperature should not exceed 150F. Exceeding 180F will severely shorten the pack's life. To help the user keep an eye on the pack temperature, each Balance Pro HD pack comes with a pair of temperature indicators. These little stickers are similar to the Hot Spots available from R/C Model Works(review). One sensor is sensitive at 140F, and the other is sensitive at 160F. If the temperature of the pack exceeds these temperatures, the center of the corresponding indicator will turn black permanently. Incase you exceed this temperature while experimenting with your power system spare indicators are included with each pack.
Balance Pro HD 6S Charger
It is always recommended to closely monitor LiPo cells during charging and to charge them in an appropriate container, regardless of the charging method.
The heart of the Balance Pro HD system is the 6S charger. This little unit can charge any of the Balance Pro HD packs up to 6S at up to 3C of the pack's capacity. What this means is that at the field you can recharge any Balance Pro HD pack in approximately 20 minutes! The proprietary charging algorithm used in the 6S charger is a closely held secret. But what makes it superior to other LiPo chargers is that each individual cell is monitored. What this means is at no point during the charging process does the voltage of any cell exceed 4.2V unlike "after the charge" balancers. This has the potential to increase cell life and helps maximize system performance.
There is not much to the charger. It has heat sinks, a cooling fan, and a 3' cord with large clamps for connecting to a source battery or DC power supply. The only control is a dial to set the charging current. Two LEDs on the front panel display the status of the charger and the state of charge of the pack, with the third indicating power. On the side is a mating connector for the one found on each Balance Pro HD pack. There is no display on the 6S charger, but a 3 pin connector is available to connect the charger to a PC to monitor the charging process. There is also an optional External LED/Speaker Module (SV6S-SPKR), not tested in this review. This option gives you an audible and visible warning of pack condition. It's a plus for heli pilots and also good to notify you when you have forgotten to unplug the DPM after flying.
To charge any pack, simply set the desired charge current and plug in a pack. The charger does the rest. There is no algorithm guessing the number of cells. Since the charger has access to each cell voltage and the overall pack voltage it can even tell you if there is something wrong with the pack wiring. The charger takes a few seconds to check out the pack, and then starts the charging process. The charge current is ramped up slowly, so the pack is not shocked. The yellow LED comes on first, and as the battery reaches 80% charge the green LED starts to blink. At 90% charge, the yellow LED turns off and the green LED blinks faster until at 100% charge it is on permanently. An end of charge beeper would be a nice addition. If anything is wrong with the charger or the battery pack, an error code is blinked with both LEDs. A table in the charger manual explains each of the codes and what to do about it. Looking at the list of possible errors, it appears the FMA Direct has built extensive diagnostics into this charger.
There is no display on the 6S charger, but FMA has an optional PC interface cable for those of you who must know what's going on with their packs. The charger monitor software is available for download from the FMA website (link here), and it ran with no problems on my Windows 2000 laptop. You will need a RS-232 port or a USB to RS-232 adaptor to use the cable (FMA P/N FSIM1). A USB interface cable is in the works.
The 6S monitor software is easy to use and displays the charge current, each individual cell's voltage, the total pack voltage, and calculates the Ahr's put into each cell. There is even a graphing feature that plots each cell's voltage throughout the charging process. All of the data gathered during charging can be saved to a text file to help track a packs performance over time. The one thing I did notice while using the software is that the markings on the current adjustment knob on the charger are pretty rough. It would be a good idea to "calibrate" your charger by noting a few commonly used charge rates for various pack sizes. I don't see this as a big deal since as long as you are charging at less than 3C, you won't damage the pack. The nice thing is that you can change the charge current without a pack hooked up, and the software will display the changes.
Discharge Protection Module (DPM)
The last part of the Balance Pro HD system is the Discharge Protection Module. This little 1.5oz (with wires and connector) device must be used between each battery pack and ESC. There are two types of DPMs; one for use with BECs and an optically isolated version when using a separate receiver battery. Each DPM comes equipped with Deans Ultra connectors for connecting to the ESC.
The DPM monitors each cell's voltage during flight and when any one cell gets too low, it works with the ESC to cutoff the voltage to the motor. The throttle channel is routed through the DPM, and the DPM modifies the throttle signal to shut down the motor. The ESC plugs into the DPM via a three pin header, and an 8" pig tail with a JR/HiTech type connector plugs into the receiver throttle channel. With this arrangement, multiple DPMs can be daisy chained together for power systems that are combining multiple packs in series or parallel. This is also why there are BEC and Opto versions of the DPM. The BEC version allows the ESC's BEC output through to the receiver, while the Opto version does not.
The overall concept of the DPM is sound, but if you want to transfer it among several models, you'll need to have easy access to the receiver throttle channel. This is just something you should keep in mind when planning an installation or modifying an existing one. The DPM must be taught the off point of the throttle channel so it knows how to modify the throttle signal. You only need to do this once, but it can be re-programmed for use with another radio system. The instructions are a bit misleading here, in that they give the impression that the throttle will not work while programming the DPM. This is not the case, the throttle stick on the transmitter needs to be in the off position, but if you bump it on the motor will start even if switch #2 is ON. Finally, the DPM draws a small amount of power from the battery pack, so it should be disconnected from the battery when not in use.
For my three cell installation, I plan to use the DPM in several models so it just plugs into the model. For my five cell installation, I chose to solder the DPM directly into the existing model wiring. I already had an arming switch installed and the 5S pack will pretty much live in this model. I am also using a 12" extension that is available with the Balance Pro HD connectors in this model. Since the DPM monitors each individual cell, in theory two packs of different capacities could be linked in series with no risk of over discharging the weaker pack. LiPo technology has been changing so fast, it is often difficult to get another pack of a paticular cell a few months after the initial release of the cell.
Charge Protection Module (CPM)
With the Balance Pro HD system, I believe that FMA Direct has made most LiPo chargers you may already own obsolete. However, by making available the Charge Protection Module they at least let you to get some use out your current chargers. The CPM is for charging Balance Pro HD packs with a non-Balance Pro HD charger. The CPM does not provide any balancing features, but does prevent overcharging of the individual cells in a Balance Pro HD pack. When charging with the CPM, the charge is cut off when any cell reaches 4.2V. The charge rate must be limited to 1C or 10A, which ever is less when using the CPM.
I've been using the CPM to get a pack near full charge with my existing charger, and then connect it to the 6S charger to finish charging and balance the pack. The CPM indicates the status of the charging with a LED and beeper. A power up tune plays to let you know everything is working properly. When one cell reaches 4.2V, a repeating tone sounds. If your charger can handle more than a 6S pack, two CPMs can be connected in series to allow charging of two packs.
Putting it to the test
So how does all this work? In short, seamlessly. I put the Balance Pro HD system through several tests and here is what I found... The DPM worked with all ESC's I currently own. Which is everything from an old Jomar SM4, Jeti, Aveox, and MaxCim to Castle Creations Pheonix 45 and CoolRunnings A-12. Once the DPM detects the cutoff voltage, the throttle is pulsed (standard cutoff setting). Going to low throttle allows you to re-arm it for that last bit of power to make the field. The cutoff voltage of programmable ESC's should be set to their minimum voltage to allow the DPM to work optimally. After a complete discharge, I measured the individual cell voltage of the 3S pack as follows:
Notice that there is already a 167mV imbalance in the pack after a discharge. Next I charged the pack at 3C (9.6A) and the pack reached 80% charge in 15 minutes with 2.2Ahr put back in. At 22 minutes, the pack was up to 90% charge with 2.6Ahr put back in. At this point the charger current had dropped off to less than 2A. From here, the charge current continued to steadily decline. In another 10 minutes, the pack was topped off at 100% with 2.71Ahr to 2.75Ahr put back in. You can see that there is not much use in waiting the last 10 minutes, since only 0.1Ahr was added. Through out the charging process, the 6S charger was lukewarm to the touch and the cooling fan was running up until 90% of charge was reached. At this point the fan was no longer needed, and the charger actually cooled down further during this phase. The battery pack was room temperature while charging and showed no signs of heating up. During the charging process, the cell voltages never read above 4.204V. Right off the charger, I measured the individual cell voltage as follows:
So, you can see that the small imbalance was corrected and all cells were within 10mV of each other, all in 32 minutes! Next, I wanted to see how the 6S would handle a severely out of balance pack. I half discharged the pack, and then discharged one of the three cells another 750mAhr. Cell voltages before charging were measured at:
Don't try this with an ordinary charger! The Balance Pro HD worked on this pack for quite a while, and after 2 hours when the cycle completed, the cell #2 was within 20mV of the rest of the cells. What I conclude from this is that a severely out of balance pack will take more time to balance, but at no time did the voltage of the any cell get above 4.208V. If you had charged this pack with any other charger, you would risk significantly overcharging the other two cells. While the Balance Pro HD 6S was not very fast to balance the pack, any of the "after the charge" balancers would not have faster (assuming the pack survived the charging cycle). In fact, most would've been slower -- some work at about 250mA, thus taking 4 times longer than the 1A shunt on the Balance Pro HD. Further, if the pack is not optimally balanced the DPM will prevent over discharge of the weak cell. So, you can see how the whole Balance Pro HD system protects the cells and your models. Finally, I tried using my Astro 109 charger with the CPM. The cell voltages were measured before charging at:
With a 3.2A (1C) charge current, the CPM cut off the charge after 62 minutes and put in 2.5Ahr. I then measured the cell voltages at:
From there, I put them on the 6S at 1C, and in 11 minutes they were balanced and topped off at 100%. All cell voltages were within 20mV of each other.
Note: A Fluke 87 Multimeter was used for all voltage measurements.
Conclusion
FMA Direct has been very conservative in bringing out high cell count LiPo packs. There are well known charging and balancing issues with LiPo cells and rather than hope for the best, they took their time to develop a truly state of the art LiPo handling system. The wait has been well worth it. FMA Direct has thought of everything with the Balance Pro HD system. The 6S charger is state of the art and is the first LiPo charger to offer a charge rate higher than 1C. Now, you no longer need to charge two or three battery packs the night before to get in a few flights at the field. The optional PC connection and monitoring software provides monitoring and pack tracking features and more than makes up for the lack of a display. Kokam LiPo cells are well known for their quality and current delivery capability. Now, when taken care of by the Balance Pro HD system they should provide even better performance and durability. The modularity of the system allows you to expand it to suit your needs and even use chargers you already own. FMA is continuing to develop additional products in the Balance Pro HD line. Future products will allow other manufacturer's packs to be used with Balance Pro HD chargers and DPMs. Already, the BalancePro HD-to-Cellpro adapters are available for any Cellpro packs. So, there is even some use in your existing battery packs.
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Dec 08, 2005, 06:02 PM
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#2 |
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Registered User
Join Date: Jan 2005
Location: Twinsburg OH
Posts: 690
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Great Idea
Great Idea but the conncetors appear to be a little large
Did anyone ask what size they should be first. Was this designed from the field up or from corporate down. Looks like Kokam is getting very big and may be loosing contact with what RC flyers want? Keep trying good first step Well written article Very nice pictures |
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Dec 08, 2005, 09:31 PM
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#3 |
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Designer/Builder
Join Date: Jun 2000
Location: Brighton, MI USA
Posts: 1,154
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Thought's on the connectors
In regards to the connectors, I have found that they are a standard D-shell connector and can bought at Digi-key or Mouser. I work in the automotive industry, and the cost to tool an new connector like this would be extremely expensive, when compared to the number of connectors they will sell. Even when I build 1,000,000 modules a year, we use an off the shelf connector.
As far as the size, these packs are designed for higher power models and I'll have no problem fitting them in my planned applications. Even my Balsacraft FW-190 (48" WS) had no problem fitting them in. I like the idea of only one connector with everthing in it, and they are much easier to separate and handle than Dean's. -Jim |
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Dec 09, 2005, 06:41 AM
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#4 |
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Registered User
Join Date: Aug 2001
Location: Commerce Township, MI
Posts: 2,088
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Thanks for all the useful information. I was really wondering about this product. I don't see the connectors and modules being an issue for most sport and sport scale applications. The Flitter/Flutter fliers will surely have a supplier come along with something for them, but for now they can just use one of the many balancers that are showing up everywhere.
On the way to the EFO meeting last night, Keith and I talked a lot about connectors. Don't want to start a "religious" war about connectors, but we know what we use and why and they aren't Deans Ultras. Seems like this FMAdirect connector system does have a lot of advantages. It is the most advanced system on the market, and is pointing the way for others to follow. What we need now are the battery suppliers to provide all the same type of "tap" connections! |
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Dec 09, 2005, 07:06 AM
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#5 |
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Designer/Builder
Join Date: Jun 2000
Location: Brighton, MI USA
Posts: 1,154
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And the ESC suppliers as well. Hint, hint!
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Dec 09, 2005, 04:27 PM
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#6 |
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Registered User
Join Date: Feb 2003
Location: Edmonton Intl, Canada
Posts: 2,561
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Does this system offer any type of over discharge protection? I lost $300 worth of lipo packs when I plugged in a speed control and it shorted out and started on fire. Apparently the short created a very high current draw which damaged the internal connections inside the cells. The packs now cannot be dischared at more than 1C without the voltage dropping causing the speed control to shut down the motor. In its simplest form a fuse with a value of something in the neigbourhood of 1.5X the max amp rating of the pack would probably work for this. Unfortunately though, with most people taking advantacge of the BEC capabilities of speed controls, you would lose control of your model when it blew. I would like to see an active electronic device which would provide short circuit and over current protection. A device that will not let the speed control draw any more than the max amp setting set on the device. This is something I would definitely buy!
Brendin |
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Dec 09, 2005, 06:41 PM
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#7 |
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Registered User
Join Date: Mar 2001
Location: Ijamsville, MD, U.S.A.
Posts: 455
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Design Approach at FMA
All FMA electronic products are designed and produced in FMA facilities or associate firms in the US with minor exceptions. There are no US producers of competitively priced Li Po cells. However, Kokam has been most cooperative in developing cells that have been suggested from FMA. We leave that development to the true Li Po experts and make no claims of having designed or perfected Li Po cells. It is a costly process and Kokam spent over 10$ million US Dollars to perfect the HDR capability that they claim.
The need for high discharge rate actually comes from the power tool industry that purchases about one half billion Ni Cd and Ni MH cells per year. During marketing efforts to power tool manufacturers, the primary requirements are for safety and sanctity of intellectual property. From that, FMA derived the need for "locked -in" safety that had not been present in large Li Po packs that operate "open end" with only external protective devices that are not standardized. It may interest the reader to know that the Portable Power Institute reported that over 1.6 billion Li cells were produced in the past year. About 0.1% of those went to RC users. Regarding the size of the BalancePro HD connector: a means is described in the manual to reduce the size of the HD connector by removal of the metal housing. When that is done, the connector is just slightly larger than our standard Deans Ultra connector. It is the users choice. Design at FMA is done with professional input from all levels in the firm from the warehouse to engineering to marketing to management. All are competent modelers. Every product undergoes significant beta test. Our thanks to Mr Jim Young for as thorough a review of the system as we have ever seen for any RC product. Fred Marks, pres. FMA, Inc. |
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Dec 10, 2005, 01:20 AM
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#8 |
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Always right
Join Date: Feb 2003
Location: Chicago
Posts: 5,925
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I have to disagree on few points - I am not aware we have after charge balancers, standard procedure for all of them is to balance while charging, looks they most of them balance more precisely than this charger and new Hyperion balancer is actually much more capable than this in terms of balancing power and precision.
Another thing - these packs will be long gone from overcurent before deans ultra will brake a sweat. So yes, its yet another of many alternatives, I should mention negative sides - heavy, expensive, and please note actual vs rated packs capacity in the article. |
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Dec 10, 2005, 09:32 AM
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#9 |
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Designer/Builder
Join Date: Jun 2000
Location: Brighton, MI USA
Posts: 1,154
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I stand corrected, most of the balancers out there now support balancing while charging, but again are limited to 1C or considerably less charge rate. So, the 1A shunt capacity of the 6S is best in class as far as I can tell.
It's hard to keep up with all of the advances out there. I did a search and found the Hyperion chargers and balancers. From what I found they are limited to 5S and a maximum charge rate of 6A. Where as the 6S will handle 6S and a charge rate of over 10A. As far as cost, the 6S lists for $130, The LBA6 5SM I found for $40, and the EOS 5i for $84. So, the overall Balance Pro system cost is $5 more. For the Hyperion, then you need to add connectors and adaptors for your packs. FMA is also coming out with Balance Pro adaptors to connect to your cell of choice so you are not limited here. If you stay with Balance Pro packs, then you do need the DPM, but these can be moved around from one model to another, so I guess there is a cost issue but a benefit as well. From my research, I found that the Dean's connectors were rated at 60A, and I know that Keith Shaw has pulled well over 60A out of a 1P 3200mAhr Kokam pack. So that is where my statement came from. Also you can see my measurements that the Dean's connecotrs do have higher resistance than other available connectors (FMA included). If I am mistaken on the rating, please let me know. When you look at the targeted application for this system, the additional weight of the DPM is insignificant. Also, in my testing I looked more at the balancing and charge rate of the system than the cell performance, and I would direct you to other sources before you make any assumptions on the performance of the cells. -Jim |
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Jan 02, 2006, 12:17 PM
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#10 |
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Designer/Builder
Join Date: Jun 2000
Location: Brighton, MI USA
Posts: 1,154
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Update on system performance
I got out flying New Years Day, and took my FW-190 with the 3S 3200mAhr pack. Temperature was in the low 30's with light winds.
I got two flights in with the pack, and performance was great. The plane is now 6 oz. lighter and hand launched much easier, and got on step quicker. Max current draw is the same as the old 10xCP1700 pack at 35A static. In the air the verticle is as close to unlimited as I want. The throttle setting required for cruising around was noticably lower than with the NiCad pack. Both flights I flew until the DPM started pulsing the throttle. On the first flight I was in the middle of a loop when it kicked in! So, I would say that power was more than sufficient all the way to the end. On both flights I throttled back, and used a few bursts of power to control the landing approach with no problems. Both flights were about 10 minutes in length (more than double the 4.5 minute flight on the NiCad pack) and the pack came out barely warm. While this was a cool day, the NiCad pack would come out very hot, almost to the point of not being able to hold it. After letting the pack rest for a few minutes, I put it on charge, cranked up the current, and was back in the air in 30 minutes.  -Jim P.S. A side note, when I was loading up my car in the garage I had also put a small 3S pack on my AF109 charger, and the cold temperature fooled it into thinking it was a 4S pack and it puffed it. No flames, but I'm glad I was charging in the wife's corningware. |
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Apr 06, 2007, 02:40 PM
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#11 |
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Registered User
Join Date: Jan 2003
Location: Abbotsford B.C.
Posts: 2,988
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OK:
I'm kinda late to this thread/ review. I'm looking for a new charger as I am doing my first giant scale electric. The plan is to go 10S A123 cells maybe; 12S; as I hear that the voltage droop on the A123 Li-Ion cells, is a little more than Li-Poly cells. So far I haven't been able to find a charger that will charge a 10S2P pack in under 1 hour. So my question here is will this charger; charge a 6S2P; A123 batt pack at a charge rate that will result in the batt pack being charged; in roughly 1/2 hour? Thanks: Rick |
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Apr 07, 2007, 08:41 AM
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#12 |
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Designer/Builder
Join Date: Jun 2000
Location: Brighton, MI USA
Posts: 1,154
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Hi Rick,
I think FMA has an option for their CellPro charger to make is A123 compatible, they may have a similar option for the Balance Pro system. Call FMA and ask. -Jim |
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Apr 16, 2007, 09:38 PM
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#13 |
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Registered User
Join Date: Feb 2005
Location: Hatboro Pa.
Posts: 617
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Charger question
I like the idea of the connectors. My question here is: Does FMA make a connector for the 6s Charger that will work with lets say generation 1 Kokam packs with no cell taps for balance and a deans connector only? You see I have a few of the old old packs I still fly. But I want to get rid of my AF109 and get this charger so I can charge big packs faster. Also does it come with ANY adapters at all? Or do I have to buy everything seperate?
Fred chime in if you like...... Thanks guys. Yellowspider Last edited by Yellowspider; Apr 16, 2007 at 09:39 PM. Reason: spelling |
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Apr 17, 2007, 07:04 AM
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#14 |
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Designer/Builder
Join Date: Jun 2000
Location: Brighton, MI USA
Posts: 1,154
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Yellow,
You need to have taps on the pack to charge with either the Balance Pro or CellPro chargers. The whole reason they can charge safely at a faster rate, is becasue they monitor each cell during charging. The chargers don't come with any adaptors, but they have a wide variety available. -Jim |
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Apr 25, 2007, 07:49 PM
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#15 |
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Registered User
Join Date: Jul 2006
Location: Ventura, CA
Posts: 1,847
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The BalancePro is on sale for a few more days. (sorry for not linking this sooner).
http://www.rcgroups.com/forums/showthread.php?t=671185 |
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