The A123 FAQ for Giant Scale and IMAC

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Thinking about Migrating to A123's? Here's the Definitive A123 Overview and FAQ for Giant Scale

For the past 5½ years I’ve been watching the deployment of A123 into commercial transportation operations and tooling applications and the natural migration of this technology into the hands of modelers all across the hobby.. Electric Flight, RC Cars, and my particular area of interest and expertise.. Commercial/Military RPV’s, Giant Scale Warbirds and 3D IMAC type applications. If your looking for application info and assistance with the pressing questions of what motor pack, controller options and props would work best for your buggy or your electric powered airplanes.. move along. Nothing for you here. For you folks that are looking at this technology to replace the NiCad and NiMH Rx, Ignition, Servo and ECU packs in your big birds.. you are in the right place. I’ll try and hit the high points first, then move into general application and use notes as we progress with this. As with the NiCad and NiMH FAQ I’ve put up on this site, it’ll be a work in progress.

NOTE:Be sure and vist our A123 Setup Guide for application information on connectors, chargers and aircraft set up.

First.. what is A123? Well, simply put; this is the iteration of Lithium Technology that won’t burn your shop, plane or house down if you do everything right. Or wrong. In the ‘industry’, these cells are referred to as LiFe PO4 cells.. also called ‘nanophosphate’ or Lithium-Iron… confused yet? Yah; me too. For the sake of sanity and ease of labeling I’ll be calling them what the MFG/Importer calls them.. A123 LiFe, type M1.

Ok, now that we’ve identified what we’re talking about, let’s look at what they can do for us Giants and Big 3D fliers... Again, for ease of digestibility, I’ll compare them in broad terms to the technologies we’re flying now and try and keep the relationships on a level we can all relate to without finger paintings.

Q: How do these compare to the Sub-C NiCad’s I’ve been using for the last 3 decades?

Ok, this one will need some breakdown.. first; size and weight. Dimensionally, the cell is FULL C in diameter, and about half again as tall as a Full C cell.. and that’s bigger than Sub-C Nicads like the 2400 Sanyo. On the other hand, they’re verylight.. and only two cells are required to build up an Rx or Ignition pack. Next, weight savings on the plane usually amounts to half the weight of a sub-c NiCad and about the same rated capacity. Pay attention to that rated capacity bit.. I’ll get into that a bit later.

Q: Are they as dependable as NiCads?

A dependability comparison against NiCad’s has been the Achilles Heel of Lithium technologies… until now. Folks, these cells astonish me.. and this is the first cell I’ve ever seen that will actually outlast in calendar life AND duty cycles the venerable Sub-C NiCads.

Right along with dependability also rides the pressing question of our use of these cells in Giants and 3D birds.. the performance under load. Here, they again out perform NiCad’s. Yes, they are stable. Yes, they are capable of handling far more current that we will ever be able to load them with in a Servo/Rx environment on ANY size 3D bird. Here, the typical off the shelf R/C wiring, connectors and switches tend to lag significantly behind the newest demand loading capabilities of today’s massive high torque, heavy duty digital servos used at the 33-45% level… Obviously, focus still needs to be applied to the power handling capabilities of modern 3D radio gear in the REALLY big birds.. Finding 22g cabling and tiny industry standard servo connectors on a 200in oz digital servos is laughable. But, that’s what they sell… improved switches and power sharing boards from outfits like SmartFly and Duralite are leading the way and at this writing the new 9100 Series JR power share receivers show promise.. but the point is, power handling and impedance with the LiFe M1 cells is just not an issue.

Q: What about NiMH.. I use the big Sub-C NiMH packs, they have lots more capacity than the A123 packs..

Ok, here’s where we get to compare some definitions of ‘rated capacity’ vs ‘usable capacity’. Again, without getting into numbing graphs and finger painting, the short explanation is that we get to use a LOT more of the A123’s rated capacity when compared to NiMH or NiCad. Why? Hugely low internal impedance as the pack discharges.. a marked difference in these vs NiMH or NiCad.. as the pack discharges the impedance does not increase. This means we can use a significantly larger portion of the rated capacity without worrying about those low voltage spikes kicking our Rx’s into failsafe or reset.

Next.. Lets look at the emerging Achilles Heel of NiMH for a moment.. longevity and self-discharge. This has been a rats nest of problems.. folks used to NiCads are routinely disappointed by the short cycle and calendar lifespan of NiMH vs NiCad, let alone the self discharge issues. Getting more than a season or two out of them is problematic, if the bird is flown infrequently there’s often issues with dead cells from overdischarge. And for folks running them, the A123M1 is a godsend. There is NO significant self-discharge issue. Charge retention across 9 months in the tests we ran here was 94%. Simply amazing. We’ve not been able to determine yet what the serviceable calendar lifespan is.. duty cycle lifetimes in the electric flight world at insanely high current loads indicate capacity loss is detectable.. but cell serviceability and impedance remains unaffected. In a Giant Scale or 3D 40% application.. I just don’t know what the lifespan limit is yet; but I do know they’ll outlast any NiCAD, NiMH or LiPoly/LiIon pack.

Q: How do they compare to Li-Ion and Li-Poly Rx Packs??.. I’ve been using those with pretty good results so far in my big 3D birds.

Aren’t you the lucky one! And, as far as LiPoly goes, I’m convinced that luck has a lot to do with satisfaction and success. At least more of it than I’ve got. The biggest gripe I have against LiPoly is the flame up issue.. closely followed by the dependability issue. The wafer thin plates and cell straps, fragility, vulnerability to vibration alone are enough to keep me away.. add in the need for a regulator and you’ve lost my interest entirely. With LiIon.. high impedance and short longevity and the need for that pesky voltage regulator also keeps them off my table and out of my planes. With Li-Ion, the only way to keep the impedance at a workable level was parallel systems. The weight build up, complexity and short lifesapn (plus the regulators again) leave a lot to be desired. Now we've got something better!

Which finally brings us to why I like this cell so much in Giant Scale and IMAC 3D.. it’s robust ability to handle loads, it’s refusal to flame up even when abused, it’s light weight, it’s over-all longevity, it’s seamless transition into aircraft already equipped with conventional LiIon/liPoly or Nicad/NiMH systems. For the LiIon LiPoly guys.. you get to ‘lose’ the regulators, cut the costs in half and at least double or triple the longevity… and get a more dependable system. For the NiCad/NiMH guys, you’ll need a quality charger that can handle A123 (LiFe) balance charging and a quick mod to your existing chargeport switches.. that’s it. The cost of the charger (about 70 bucks) is offset in the second year.. by not having to replace the packs.

Q: What's the difference between A123 LiFe packs and LiFe PO4 packs like Hobbico's LiFeSource™ packs?

Two big differences. First, A123's patented 'Nano' plating technology.. at a molecular level the negative plate material stands like a shag carpet rather than laying 'end-to-end'. This produces an incredible amount of surface area gain for A123's negative plate and it's why A123 can tolerate immense current loading without voltage sag. Another benefit to the nano plating technology is a huge increase in cell life. All stored energy systems consume negative plate over time.. with 100+ times the negative plate surface area generated by any competitors plating process the lifespan of the A123 cell is extended immensely. Next, A123's are aluminum cased cylindrical cells with welded alloy end plates and towers like a Nicad cell. This enables a rugged welded strap pack assembly system (like Nicads) that is exceptionally robust and very resistant to vibration and hard knocks. The LiFeSource™ packs are built with wafer stacked 'bag' prismatic cells.. like LiPoly. And, like LiPoly, they are fragile, the cell link tabs are very thin alloy strips and the entire assembly is as a result susceptible to rough handling and vibration. Further, the prismatic cells and their tabbing system are unable to handle anywhere near the current loading the A123 system can tolerate with ease.

Q: Ok, so, where’s the Achilles Heel with LiFe?

Mostly in mindset and field habits of folks used to NiCads and NiMH.. there's new things to learn & some folks don't like things moved in their cage. On the 'technical' side, there are several 'issues' that routinely crop up, in no particular order they are:

1. Non Balancing 'smart chargers' and the myth that A123's 'don't need balancing'. A close to fully charged pack, deeply discharged pack or out of balance pack may be easily mis-identified by a 'smart' charger WITH THE WRONG CELL COUNT. The results are usually always a ruined pack. If a quality balancing charger is used and correctly connected, the charger will see the individual cell voltages in the pack, correctly identify it's cell count and usually report on the individual cell voltages all the way through the charge routine. If 'smart' means stabbing a button and waiting for a green light... well; that might not be an appropriate charger for a critical application battery pack.

2. Connector Gripes.Plugging the three wire charge cord into the switch chargeport or universal cell tap backwards (upside down) will usually result in the charger 'seeing' just one cell.. the results are an out of balance pack. The cure is to use the chargers 'balance charge' or 'accurate charge' routine ALWAYS... and then YOU check the display to be sure the charger has correctly identified the cell count

3. Compatability with Smart Chargers that ain't all that smart. I actually had a R/C dedicated charger mfg tell me I had to stop putting R/C standard plugs for balance charging on my 2 cell Rx packs. His customers were plugging the R/C standard (JR/Univ) plugs into their supplied balancer board which apparently cooks the balancer circuit. I asked him why their charger doesn't provide the ability to interface with every R/C standard switch chargeport commonly in use.. or provide an adapter? Or, in case the guy plugs it in wrong... not cook itself?

I do see his point... JST-XH is the 'standard' goofly little white molex plug used or supported by 90% of balancing chargers and packs available in the hobby. Unfortunately, in this thin slice of the hobby (the one I build for) checking and charging individual cells in a 2 cell A123Rx pack while in the plane is a requisite for safe operation of 30-50 pound aircraft. That's not open for debate OR compromise.. it's just a fact. And, last I checked; molex connectors are not compatible with R/C system standard chargeport switches. And that's why I'll continue to supply my packs to my giant scale customers with the R/C standard Univ connector (FJ/JR/Hitec/AirtZ) balancing plug.. which covers just about 100% of my customers chargeport switches.

Q: I have an A123 pack that's 2 years old from another supplier and when I was charging it yesterday (Turnigy accucell 6) the charger alarm went off and it said “broken connection”. The battery was really hot. Obviously a short somewhere. I stripped the shrink wrap off of it to see if one of the connections had come loose. Nothing apparent on the outside, so my conclusion was that it fried on the inside. I get a .14 volt reading from my meter. Any idea what may have gone wrong with the pack? Since I only use A123s and only use the Turnigy Accucell 6 on all my planes, I need to know if I’m doing something wrong.

Yup.. sounds like a short failure on one of your cells in that pack. Uncommon but not unusual.. biggest root cause we found so far relates to 1^st, (most common) an incorrect charger sub-routine, such as accidentally triggering a liIon, LiPoly, Nicad/NiMH charge setting at some point in the packs history and/or routinely using a non-balanced charge setting. Repeated non-balanced charging will set up a severe imbalance, results are one cell hugely over voltage on charge and that cell eventually shorting.

2^ndmost common root cause of cell shorts and breakdowns is pack installation… the prime enemy of all stored energy systems is heat and vibration. Seems like a lot of folks ‘graduate’ to Giant Scale from smaller electrics and they never learned the Engine Powered Flight equipment setup basics.. pad the pack and radio gear, isolate them from vibration sources as much as possible and keep them away from heat sources. Despite this very basic install principal learned over decades of fuel powered R/C & RPV darwinisim I still see ‘naked’ packs and Rx's wire-tied, velcroed or strapped to firewalls, formers and cross members. Not good. The constant low frequency vibration imparted by the engine to the airframe breaks down the internal structure of the cell and creates chafe-wear shorts between plates and insulators and in extreme cases, shears welded straps.. Better to fully wrap the pack in a layer of dense foam with tape, then ‘soft’ velcro that package to a padded cross member some distance from the engine (NOT a firewall), and kept well away from heat sources.

The Reply: Great help!! Thanks! I understand about padding the batteries. I grew up in the age of 40-60 size glow engines and learned early on that receivers and battery packs don’t last long in a harsh vibration environment. I think it is entirely possible that the charger routine could be the issue. I once left the switch on and ran the battery completely down. My charger wouldn’t recognize the battery because the voltage was too low. Your competitor told me to put it on a NiCd routine for 6-7 minutes to get the voltage up and then switch it over to the LiFe routine. I did and the battery came back up. I used it happily thinking that I had saved the pack. I’m also not the best at using the balancing plug. I have a tendency to charge it and fly it. Won’t do that again unless I’m at the field and putting in an extraordinary number of flights.

A: “Your competitor told me to put it on a NiCd routine for 6-7 minutes to get the voltage up and then switch it over to the LiFe routine.”- That didn’t do any damage.. it’s allowing the cells to climb above terminal voltage further along in that charge process that would damage it. A ‘run flat’ would set the problem up tho; this situation can cause one of the cells to be slightly degraded (impedance and capacity is affected) and from that point on, keeping the pack balanced is very problematic if you don’t routinely balance charge. The Key Issue in your case is revealed in your reply.. not checking individual cell balance every time you charge and before you fly.. THAT is how you stay outta trouble and it’s why we put a JR/Univ balance plug on the A123 packs.. so with a simple adapter you CAN easily check the pack and it’s cells via a simple R/C standard chargeport while the pack is in the plane.

Q: Can I use a Load Tester to check my A123 packs relative state of charge?

Here's an area where A123's are radically different than Nicad or NiMH packs... Load Testing A123's in the traditional way is ineffective for determining state of charge... the beasties just don’t 'react' like we expect.. a 1 amp load for 10 seconds will convince somebody not familiar with them that there’s something wrong with the load tester or the pack.. the needle starts to sag after a few seconds with some meters, (resistor impedance values jump up rapidly under the continuous load) and decreasing voltage displayed on the meter usually indicates approaching doom for the resistors, switch & connectors rather than reflecting any useful info on the state of charge for the pack. Continued loading can melt out connectors, meter resistors, switches, etc. ESV 'loading' just doesn't work with A123's in the tried and true sense as the cells are quite happy delivering enough amperage to melt out your gear, even when nearly discharged. Because of the incredibly flat discharge curve and the ability of the cell to deliver massive amounts of current, using a standing voltage level under load to decide when to recharge can lead to a disaster via damage to switches & connectors... Further, when A123's DO go flat, they do so remarkably fast. So, we go to the next question..

Q: How do I know when to recharge?

This one still gets me smiling.. old codgers like me already know the answer.. the same way we did it before some bright boy came up with the hobby ESV. We fully charge the pack, cycle it to determine capacity. We recharge, fly three or 4 flights, keeping track of the time and the voltage on the pack under the 1 amp load after each flight. At the end of the sessions, we'd discharge the pack to determine capacity remaining and do a bit of math.. we divide the time by the total capacity used and determine how much air time we can safely expect to get out of the pack.. and then cut that in half. Thankfully, most quality A123 capable chargers have a MAH charge counter.. it records the amount of energy it puts in the pack so we don't have to resort to the 'antique' methods of yesteryear.. just charge before you fly and charge again after you fly... the amount of energy used in the flight will be right there on the charger's screen.

Some specifics.. the M1 cell rates average 22-2300ma. Voltage drop cliff starts at about 2,000ma. I don’t like to get lower than about 50% remaining before recharging. (I’m a very conservative old codger) My bird used 800ma from the pack in four 10 minute flights (big warbird). I figure I got 5 flights to 50%.. so I field charge on the end of the 4^thflight. Yes, I still use the load tester.. and yes, old habits die hard, and checking the voltage between flights is still how I recommend you stay outta surprise territory… but a Load Tester alone is not enough to keep you out of trouble. There are however ways of improving your odds... and this one's important: These are NOT NiMH or Nicad packs. The act of balance charging them at 1C just does not stress the cells a bit. So, if in doubt, CHARGE! Use a quality balancing charger, and get in the habit of checking individual cell voltages. Since virtually all of the quality A123 capable chargers have a MAH counter that records the amount of charge transferred to the pack, before very long, you'll get a good feel for what's 'going on' with your new technology packs in your bird and your confidence in yourself, your power system and your charger will benefit greatly.

Recommendation: FMA's Multi4 and CellPro chargers can help keep track of relative charge state (the charger has a very conservative 'fuel gauge' feature as well as MAH transfer recording and displays individual cell voltages) and VoltMagic can keep track of Peak Low Voltage on board the aircraft.. Below is the discharge graph from VoltMagic on comparative technologies.. this inexpensive device is a godsend for A123 users. Click here to read more about VoltMagic.

VoltMagic PLV Trigger Points, Various Pack Types

click picture for more detail

Q: How does Nicad or NiMH useable pack capacity compare to A123's? Same flight time for the same capacity?

The example plane here is a 1/4 scale warbird equipped originally with a single Sanyo 2400ma 5 cell NiCad pack. Load testing between flights, I’d get 4 flights before the ESV at 1 amp would display under 6v, indicating ‘recharge’ time. Cycling the pack at that point revealed the same amount of ma consumed on average… but that was it for flying the pack. In essence, the NiCad gives up a bit more than half it’s rated capacity before I got to a required recharge point.. the LiFe would go much further.. if it had to. The Nicad wouldn’t. Net effect is seamless to me though.. either way, I was recharging after 4 flights… but carrying significantly more ‘reserve’ useable capacity with the LiFe pack. It must also be mentioned that both Nicad and NiMH INCREASE impedance as they discharge.. the LiFe pack did not.. another significant bonus.

Q: Can I use my ‘XYZ’ brand NiCad /NiMH charger or Wall Wart on LiFe?

No. Let me be specific… HELL NO! Here’s what’s going on.. LiFe’s nominal voltage per cell is 3.3v. While the charge routine is similar to LiIon or LiPoly, the max allowable voltage under charge is lower than any other Lithium technology cell, usually about 3.6v; so using a standard LiIon or LiPoly charger will do damage. For you NiCad - NiMH guys, the entire charge sub-routine is different . As of now, there are a number of LiFe capable superchargers coming into the marketplace.. these will deal with ‘em as well as the various other types of Lithium and NiCad/NiMH packs but assume my first answer of HELL NO applies until you review your chargers manual. If you not sure, contact the charger mfg or distributor. Don’t let ‘em blow smoke up your backside either. Get it in writing if it’s not called out in the manual.

Q: What in heck is the 'Cell Balancer' function all about?

Simply put, this monitors voltage of the individual cells and keeps them closely matched or ‘balanced’ in voltage during the charge routine.. Some A123 enthusiasts (and charger MFG's) will try and convince you that A123 packs don’t 'require' balancing. This claim is bunk for those of us that value what we fly... Unbalanced charging may be adequate for a tool pack or a ground application, however the reality of field trials with a wide variety of non-balancing LiFe capable chargers has demonstrated that balance charging is the best way to avoid damage to the pack and reduce risk for the aircraft. Balancing= Good for the pack, good for the plane. See the A123 Setup Guide for how to easily accommodate balance charging at the field.

Q: My A123 pack has 2 connectors.. which do I charge thru?

In the most common A123 pack wiring configuration there are two leads. The 3 lead wire and connector is the 'cell tap' or 'node' connection.. The heavy gauge 2 wire lead wire is the standard pack 'feed' that connects to the switch harness. Don't attempt to hook the 'cell tap' lead to anything BUT the node or celltap port of a balancing charger via an appropriate adapter for your charger's balancing port. While the pin spacing on the JR/Univ celltap connector we install on our packs will fit in some 'balancer boards' it likely does NOT have the correct pin polarity for your charger's balancer. You'll need an appropriate adapter to 'translate' the JR/Univ celltap to your charger's pin convention. This 'balance'connection is used by balancing chargers that require a seperate three wire connection to the charger in addition to the two wire pack feed to accomplish a balance charge. If you are not balance charging, or are charging at high rates, charging should be done on the standard pack feeds as with NiCad and NiMH packs.

Q: I've seen some NoBS A123 packs that have just one ONE heavy three wire connector and no separate two wire power feed. How come?

That's the 'Combo 3 Wire 20g Feed' option. This cabling & connector setup allows quick and easy access to the pack via a standard chargeport switch without need for a second separate chargeport dedicated to just balancing and cell voltage checks.To make use of this, a simple mod has to be performed on most switches... the 'third' lead or 'signal' wire that runs from the switch to the Rx has to be removed to enable the feature. We've got pics and a description with complete instructions on how to take advantage of this on our A123 Setup Guide.

Q: Why do you have a JR/Univ celltap on your packs instead of either a JST-XH or FMA molex plug?

A: We've learned that the key to safe and trouble free operation of ANY Rx pack (including A123 two cell Rx packs) is dependent on the pilot being able to readily access the pack to check it while inthe plane before flight. This is even more critical with A123 packs, cell voltages and balance condition are crucial to the 'fly-no fly' decision. If the aircraft has to be 'broken down' to gain access to this basic flight safety check.. then the pack will not get checked before flight. Sadly, not one of those goofy little molex plugs (FMA, JST-XH, etc) will mate with an R/C Standard HD chargeport switch. Since the chargeports on these switches are how we all have for the past 2 and a half decades gained access the pack in the plane to check it, that's the connector we put on the pack. ... so you CAN easily check our A123 packs and charge individual cells or balance charge the pack easily. You'll need an adapter to mate your chargers balance port with the JR/Univ standard switch chargeport. You can either make one of your own or purchase one pre-made to fit your charger's balance board, they are available on the A123 packs page.

Q: I have an FMA Charger .. it charges ONLY through a 'node connector'.. do you have an adapter for your 'standard univ' cell tap?

Yep.. See the question above & check the notes below on how to make an extension from the univ celltap or charge switch port to any brand chargers balance port.

Q: I need to make an adapter cable for my 'Brand X' balancing charger for your 'Univ' cell tap. What are the color codes on your univ tap plug?

The 22g univ tap connector on our two cell packs is very easy to build an adapter for. Using an aileron extension to make an extension/adapter cord is a snap for any charger.. Just snip off the 'male' servo end from the aileron extension and solder a 'pack side' plug that mates with your chargers balance port.. red is pack positive, black (or brown) is pack negative and the white (or yellow) lead is 'node 1' on your balance plug. Another way to explain what that white or yellow lead is relative to the red and black.. it's the 'negative' for the red lead, or the 'positive' for the black lead, allowing the charger to 'see' the individual cell voltage during the charge.

Q: Do I need to ‘balance’ the pack every charge?

The only way to avoid costly and aggravating fried battery packs is by using a balance charger EVERY TIME.. Here's the prime issue: A close to fully charged pack, deeply discharged pack or out of balance pack may be easily mis-identified by a 'smart' charger WITH THE WRONG CELL COUNT. The results are usually always a ruined pack. If a quality balancing charger is used and correctly connected, the charger will see the individual cell voltages in the pack, correctly identify it's cell count and usually report on the individual cell voltages all the way through the charge routine. Virtually every pack failure I've seen to date relates back to a 'smart' charger incorrectly identifying the cell count or state of charge of the pack.. with a wiped out pack (at the minimum) being the end result. I Use the FMA Multi-4 and like it's ability to balance charge with just a single 3 wire connection between the pack and the charger.. it reports on individual cell voltages, provides a conservative 'percent of charge' report on the pack at the start of the charge and reports on individual cell voltages at the end of the charge. This is utterly crucial with A123... to stay out of trouble, knowing and observing individual cell voltages at the start and end of the charge is the only SURE way to determine relative charge state and condition for the pack.

Q: What changes do I need to make to charge these in the plane? I’m using HD JR switches.. do I need new ones?

Nope.. no new switches required although you will likely need to 'mod' the output lead from your switch to the Rx from three wires to two. (see question below this one) Two approaches to use here depending on the type of charger you are using. Most balancing chargers use two connections to the pack; a three wire 'balance tap' lead as well as the power feed. Some balance chargers, like FMA's Multi-4, will balance charge with just one connection to the charger. EyebalI the Setup Guide to determine how to take advantage of the simpler 'single 3 wire combo' set up if you have an FMA charger. If your charger requires the dual connection setup, you'll order the pack with a separate balance tap and separate power feed. Since virtually every ‘balancer’ equipped charger out there uses a different oddball plug to connect the balance tap to the charger I standardized the packs tap to the industry standard universal servo connector for the balance tap lead. To connect to the universal balance tap on the pack all you need is an aileron extension with the plug that fits your charger balance port spliced onto the other end. Now, if you balance charge during setup before the first flight of the day, no extra stuff need be added to the plane.. hook the chargers accessory balance lead to the pack tap. The ‘bonus’ part with the ‘standardized’ tap on the pack pops up when you decide to balance charge in the plane with your two-connection charger.. all you need is a ‘ernst’ type chargeport in some convenient spot on the plane and a standard aileron extension from that to the battery balance tap connector... and then you can use the same cable you used to connect directly to the packs tap to plug into the 'ernst' chargeport to connect to the charger. I like simple. A LOT.

Q: My A123 packs are just a few months old and now they won't balance.. Cell #1 is lower than Cell #2 and my balancing charger won't re-balance the packs. Is there something wrong with my Packs?

A: This one has been cropping up quite a bit lately; most often, when I find just cell #1 way under voltage, a check of the switch reveals the cause.. the plug going to the Rx has three wires. Folks, if you plug a three wire lead from an A123 pack into a switch with three wire inputs and three wire outputs, the switch will pass the connection of that 'third' lead out of the switch and into the three wire cable going into the Rx, Smart Fly Power Expander, Ignition Module or any other aftermarket device the switch output is plugged in to.. That third lead IS HOT!.. and this unwanted connection of the cell tap PAST the switch will drain cell #1, knocking the pack drastically out of balance. In some cases it can also mess with the Rx, causing unstable operation. If the cell is run flat, you may damage that cell. If the voltage spread between the cells gets large enough, the charger will likely NOT be able to re-balance the pack. To correct the voltage spread, you'll need to charge cell #1 independently of cell #2 to get them close in voltage, then you can re-balance the pack with the balance charger in the usual way. To keep this from happening again, make sure you remove the third wire from the plug on the Rx (or output) side of your switch! See the notes in the question above and refer to the Setup Guide for 'Switch Mods' (towards the bottom of that page!) on how to easily mod the switch's output lead from 3 wires at the Rx plug to two to avoid this issue.

Q: I've got the same situation as above... but my switches are 'modded' and I have an FMA Multi-4 and I'm charging thru the switch chargeport. Why is cell #1 three to four tenths of a volt lower than cell #2?

A: You've likely been reversing the charge cord plug.. plugging it in 'upside down'. When that happens, the charger will only 'see' cell #2 and come to the conclusion that it is being asked to charge a single cell (1S) pack. You don't get a reverse polarity charge... you just get nocharge to cell #1. How to avoid this? Your CellPro or Multi-4 has several 'mode' screens when the charger starts.. the various screens display a ton of info.. including pack cell count and individual cell voltages. CHECK IT! Every time. I use the 'accurate' charge routine and as soon as the charger accepts the charge command after verifying with me that it is an A123 pack, I scroll the screens using the 'mode' button to confirm cell count and cell voltages. If you see '1S' displayed and only one cell's voltage is reported, you are plugged in upside down. Just unplug, invert the plug, plug back in and restart the charge. When you are plugged in correctly, you will see '2S' and two sets of voltage data when you get to the cell data screen, one for each individual cell in your two cell Rx pack. Regardless of what type of charger you use, with A123 packs being charged through charge ports with Univ three wire connectors, it would be a very good idea to mark your charge port for correct charge plug orientation. Remember, This is utterly crucial with A123... to stay out of trouble, knowing and observing INDIVIDUAL cell voltages at the start and end of the charge is the only SURE way to determine relative charge state and condition for the pack.

Q: My packs occasionally get far enough out of balance that my balancing charger doesn’t bring up the low cell in a reasonable amount of time. Why? Seems to take forever!

Here’s a good chance to discuss briefly cell balance or ‘equalization’. One of the striking differences between a 5 cell Nicad or Nimh Rx pack and a 2 cell A123 Rx pack is the relative effect ‘balance’ between the cells has on the security of the flight system . When the relative state of charge in the cells of a 5 cell Nicad or NiMH pack get out of balance, or in other words, the pack is not ‘equalized’, the impact of the one or two slightly ‘out of balance’ cells to the system is minimal when the pack is in the upper half of it’s discharge curve. While the overall capacity of the system is reduced to the capacity of the lowest cell, since we normally don’t get very deep into the lower half of the pack’s discharge curve during normal use ‘cell balance’ rarely crops up as an issue. Next, because Nicads and NiMH systems use ‘constant current’ charge algorithms, the process of slow charging or ‘topping off' after a peak charge does the ‘re-equalization’ for you as part the normal charge process and small differences in cell capacity and impedance between the cells are massaged right out of the picture as a result.

Since Lithium types (A123 is a lithium based system) require terminal voltage control as the charge algorithm and ‘going overvoltage’ kills Lithium cells outright, the charger terminates the rapid charge as soon as the first cell in the pack hits the voltage ‘roof’. The end eventual result with unbalanced charge routines on A123 packs is that normal variances between cells in capacity and impedance are not ‘massaged’ out of the picture. The net result is that over a relatively short number of unbalanced charge-use-recharge routines the imbalance condition can get very pronounced. If the imbalance is large enough when a ‘balanced’ charge routine is finally used on a seriously out of balance pack most chargers will kick into a very low charge rate at the point the charger senses the high voltage cell is near full charge, either cutting charge off to the near fully charged cell and/or sending a paltry 100ma ‘balance’ charge to the ‘low voltage’ cell in the pack. And if your packs low voltage cell is only half way to full charge when the other cell gets to ‘full voltage’, then that’s why you may be staring at that charger for quite awhile (sometimes many hours) waiting for it to get the pack back in ‘balance’. * Now, here’s the crucial issue with flying an un-equalized or unbalanced two cell lithium pack…If the ‘lower voltage cell’ has only 800ma of capacity remaining and the higher voltage cell has 2000ma... you have a 800ma capacity pack. Now, here’s the bit of info that will make you squirm in your chair… only three TENTHS of a volt separates a fully charged A123 cell from a dead one. This is why it’s crucial to have BOTH cells at or near full capacity when you start using the pack, why it’s crucial to monitor and check individual cell voltages and why you should routinely employ your chargers balance charge feature (if it has one) or equalize the pack routinely rather than occasionally… it not only keeps the pack’s cell voltages ‘in range’ of the packs ‘balancer’ feature, it gives you the benefit of the full range of capacity of the pack. An un-equalized or ‘out of balance’ 2 cell lithium pack is not conducive to that ‘warm and fuzzy feeling’ we’re all looking for from our Rx power system, folks.

Q: Ok, I get why it’s important to keep the cells close to each other in voltage but I’m a bit fuzzy on the difference between ‘balancing’ and ‘equalizing’.

A: Nothing other than how it’s accomplished.. ‘balancing’ is what the charger tries to do when you put it in a balanced mode charge routine (FMA calls this ‘Accurate’ charge mode). On the other hand ‘equalizing’ is when we do it ‘manually’ as outlined below by fiddling around with the individual cell tap connections or with a Balance Buddy, charging one cell at a time. Both wind up with the same net result.. both cells in the pack at full charge.

Q: At what point do you consider the 'balance' is bad? 10th of a Volt? More? Less? My packs have cells that are never identical. Are they bad?

Several hundredths of a volt either way is not an issue.. a few tenths of a volt is a problem. My rule of thumb has been if the cells are at more than a 10th of a volt separation, I re-equalize or start a balance charge. The variation creeps in over time due to the A123's unique molecular 'shag carpet' lattice of the plate material. Every cell will have small differences in plate area right off the production line which gives rise to a slightly different rate of charge absorption and rate of discharge so small voltage differences between cells are routine. Letting them go unattended (not checking and balancing or equalizing routinely) can lead to trouble, but finding the cells in your pack not perfectly balanced at all times does NOT mean you have a problem.

Q: Is there some way I can just rapid charge each cell; one at a time, to get the pack back in range of the charger’s balancer?

A: Yep, it’s not overly difficult really; you’ll just need to charge the cells independently (separately). Fortunately, and unlike Nicad or NiMh packs, your A123 packs are likely already wired to allow access to each cell separately thru the three wire balance tap. The ‘usual’ way to gain access to the cells individually is to make up a couple of short aileron extensions with the contacts moved around in the housings allowing you to access the cells one at a time. Use caution and a voltmeter to confirm polarity of the individual cells. (on the back of our packs is a color code to tap info sticker) If you don’t want to fiddle around with contacts and sweat polarity issues you can use a Balance Buddy. In either case, once you have access to the individual cell via your jury rigged aileron extension or a Balance Buddy, just connect your A123 compatible charger and fully charge that cell. You can use a charge rate as high as the connectors you are using can handle, however I just use the charger’s default 1C rate (making sure the charger correctly identified it as a 1S single cell A123 battery) and when the charger completes topping off that cell, I’ll check/charge the other cell to get it to full voltage too. (Remember to re-check for the change in polarity on the other cell if using a modified aileron extension before starting a charge!!)

Q: So, what’s a “Balance Buddy”?

A: It’s a 2 cell A123 pack ‘Equalizer’ module that sits between your charger and the pack, plugged into the packs three wire lead.. Basically it’s just a simple little 20 dollar switching gizmo we cobbled up to take the grief out of fussing with modified aileron extensions to gain instant access to the individual cells via the Univ cell tap. You just plug it into the packs Univ cell tap connector and then plug your A123 compatible charger into the Balance Buddy. There’s a three position switch.. Cell 1, Both and Cell 2. Just pick which cell you’d like to charge, (1,2 or both) set the switch to that selection, and start the charger. The Balance Buddy makes it fast and easy to quickly ‘equalize’ an out of balance pack with any A123 compatible charger… with or without a balance feature!Used with an ESV, you can check and load each cell individually, and check the packs total voltage. Used with a reversed (two male, 1 female) ‘Y’ harness and a voltmeter, it turns a ‘dumb’ (no voltage display) type basic unbalanced A123 charger into a competent ‘check, charge, equalize’ capable ‘smarter’ charger. Best of all, it means simple, fast, no hassle re-balancing at the field without wasting any time waiting on a 100ma ‘balancer’ in a ‘smart’ charger to finish it’s job. Click here for more info on the Balance Buddy

Q: These are Lithium’s.. don’t lithium’s need a Voltage Regulator for use as a an Rx pack?

Once more for you folks out there with LiPoly or LiIon systems.. no regulator is required for modern Rx’s and Servos with these A123 LiFe 2 cell packs... because these packs at full charge and under load are operating at about 6.6v.. the same voltage level as a fully charged and loaded 5 cell 6v NiCad pack. If you have the latest generation 2.4 radio system and digital servo’s rated at 6v and your system exhibits twitching or instability on an A123 2 cell pack then something is wrong with your Rx or Servos.I’ve had folks with 5 cell Nicad packs complain about twitch and jitter with some recent Hitec servos.. these were replaced by Hitec, problem solved. Folks, if your running some dinosaur Rx or antique servos, all bets are off; proceed assuming you’ll be using 4 cell NiCad packs until you upgrade your radio gear. However, if your running antibody's 2.4 Rx system and modern digital servos rated for 6v operation you’ll find the A123’s operate the system perfectly. Rule of thumb, if your running 5 cell 6v Rx packs without regulators, your good to go with A123’s and no regulators. Note: If you’re a Heli pilot with a gyro that won’t operate with a 6v Rx pack, then your outta luck too.

Q: I’ve got a DA Engine.. can I use this as an Ignition pack?

Yup.. according to DA there are no issues with LiFe packs with their ignition modules. Again, no regulator required. If you’ve got something other than a DA engine with a different ignition module, you’ll need to check with that mfg or distributor; but again, as a rule of thumb, if you’ve had no difficulties running a 5 cell NiCad or NiMH pack on your ignition without a regulator then the A123’s should do just fine. Remember the loaded voltage of LiFe ignition pack is 6.6v.. the same as a fresh NiCad 5 cell pack.

Q: How about use for Turbine ECU’s?

Since a 2 cell LiFe’s nominal operating voltage under load is @ 6.6v attempting to use them as a drop in replacement can (and likely will) lead to flamer starts and lousy throttle controllability response. We've made available 3 and 4 cell liFe Turbine packs for those folks that need higher voltage for the ECU, as always, check with the ECU/Turbine MFG or Distributor for the required input voltage for their device. Please note that these 3 and 4 cell packs need Balance Charging support and for those packs the only balance charge connector I have available is the FMA CellPro plug. If you already have a Cellpro or Multi-4 charger, you will be good to go with a NoBS A123 ECU pack.

Q: I read somewhere that A123 LiFe cells can be charged at up to 10 amps.. does that make sense?

Yup.. that’s correct. According to A123’s specs.. 10 amps. Of course, here’s where a brain on the part of the end user comes into play. What are your connectors and switches rated for? If your like me and use HD system switches and industry standard battery and servo connections, then you’d better cut the charge rate down to what those connectors can handle.. 3-4 amps. Tops. If your using direct connections from the pack to the charger via 18g wire and Deans or Anderson connectors, then you can use the 10a charge rate if your charger will go that high. For most of us, the 3 amp rate through the HD switch ports makes sense, and the difference in time (15 min vs 3 minutes for a normal battery refueling at ½ discharge) is of no consequence.

Q: I've got a 25% Sized Yak with a DA 50, all digitals and I fly the pants off it.. what A123 LiFe setup would you recommend?

Keeping things light is always important.. and in the 25% birds, battery system weights have a bigger percentage of total weight impact than in the larger birds. In your situation a minimum setup would be a single 2300 A123 LiFe pack with dual leads and feeding dual switches. For the Ignition, a single 1100 A123 LiFe pack and with this setup, you'll likely get 3-4 flat out flights between charges at least.. maybe more. See the notes above about how to find out how many flights you can get with your bird the way you fly it.

Q: I’m Running two 2400 Nicad 5 cell packs with dual switches in my 40% Extra.. DA-150 up front. What will I need to upgrade to A123’s?

An A123 Charger, a charger cable to connect to your pack or switch, a balancer cable, a servo extension to make your balancer cable out of and a pair of A123 two cell 6.6v 2300 packs. You MIGHT want to pick up a pair of 'ernst' type charge ports for the side of the plane to use the balancer for on-board charging if you don't have the FMA Cellpro or Multi-4 charger.. Note that your CG may change.. this dual pack A123 system will weigh approximately HALF of what the two 5 cell pack NiCad system weighed. For the ignition.. one more as above.. it'll probably run the engine all day.

Q: Same Question, same size bird, but I have a single 4500 NiMH 5 cell pack with dual leads & switches and I don't want to lose flying time with the 2300 LiFe's.

Same answer as above.. use a Dual 2300 LiFe pack setup with your two switches. You won't lose a bit of flying time.. in fact, you'll probably gain a flight or two and will have improved the dependability a bit to boot without adding a bit of weight.

Q: Do I have to buy a new charger?

Yes.. Normally. Unless your charger is A123 compatible. There’s a work-around available called the ‘dapter’ to allow safe charging of A123 cells with a NiCad/NiMH charger.. do a quick internet search for this device to see if it fits your needs and will work with your current charger. The feature that I like to see most on a charger used for A123 support is the balance feature.. while there’s likely to be ongoing debate on the 'need' for balancing A123’s with every charge there is absolutely no doubt that 99% of the issues experienced to date with A123's would have been avoided outright had the user employed a quality balance charger and checked individual cell voltages on every charge routine.

Q: Do I need to disconnect the switches from the Rx if charging two packs at the same time like I did with my NiCads and NiMH parallel setups?

Ahh... the insidious 'common ground issue'. Yup; chances are; unless your charging through a power box designed to eliminate this issue, then you'll need to unplug one of the switches to eliminate the common ground.

Q: Do I need to Formation Charge A123 LiFe packs?

According to A123, nope. However, prudence dictates that establishing a capacity number and verifying the pack is stable before putting it in service is good practice with any battery technology. Bear in mind that in a charging/cycling situation and with these cells the concept of ‘slow’ charge' and ‘fast charge’ and 'formation charging' no longer have the meaning we associate with NiMH and NiCads. The normal check routine for A123 would be to charge WITH the balancer feature in use and the charge rate should be 2 to 3 amps. Use a discharge current of 1 amp, and a discharge cutoff voltage value of 2.5v per cell. Bear in mind that with these settings pack capacity reporting with your cycler will be somewhat less than the MFG's rating since we have adjusted the discharge cutoff up a bit to provide a safety margin for the cyclers discharge cutoff trigger. Since A123's do not benefit from forming or 'cycling' in the traditional sense, there's no need for repetitive cycles. I run the check cycle once on a new pack and again, once at the start of a new flying season or any time I note a change in pack performance.

Q: My Charger can charge A123 and has a cycler, but when I set a 2v per cell cutoff, at the end of the discharge one cell is way below 2 volts! What's up with that?

We've seen this in the Hitec X4, it's also common across several other multichemistry charger/cyclers. Whats happening is the cyclers discharge cutoff trigger is watching the total pack voltage and ignoring the individual cell voltage. This is a source programming error in my opinion, just as the charge routine is individual cell voltage controlled, it's no less important for lithium packs to terminate the discharge routine based on individual cell voltage. Here's the 'issue': A123's have a very,very sharp 'knee' in the discharge curve and actual capacity varies as much as 5-10% between cells. (an artifact of A123's 'nano' plating technology.. negative plate surface area varies a bit from cell to cell) This issue can set up an overdischarge condition on the lower capacity cell, so we've adjusted the discharge target up from 2v per cell to 2.5v to give a cycler that does not have individual terminal voltage control a bit of 'padding' as a safety margin.

Q: I have a standard A123 Charger that won’t ‘cycle’ or discharge. Can I use my programmable NiCad/NiMH charger/cycler (Triton, Triton II, Multiplex LN5014, Accucycle Elite, etc) to discharge them and get capacity numbers for evaluation and testing?

Yes.. IF you can set the voltage cutoff on discharge and discharge load, no problem. (most cyclers are programable for low voltage cutoff in the Nicad or NiMH menu's) Again.. this is for cycling for formation or evaluation.. not for charging. The discharge rate should be 1amp, the voltage cutoff should be 2.5v per cell. (was origially 2v, recently updated, see question above) See your charger/cyclers manual for how to effect these changes and use an A123 LiFe Compatible Charger to balance charge A123 LiFe packs.

Q: What Charger do you recommend?

Lordy.. well; there's an awful lot of chargers out there that'll handle LiFe now.. FMA's Cellpro and Multi-4 are my personal on the field favorites since they accommodate balance charging with just one three wire connection to the pack and with a simple adapter can balance charge, check individual cell voltages and produce a reliable reading on the percentage of charge in the pack right through the switch chargeport. (switch mod may be required, see the setup guide!) Hitec's X4 is an excellent multi-port charger at it's price-point that has a cycler in it and it's easily upgraded to single cable charging with our available adapter. Since it's quite a bit larger than the FMA Multi-4, I prefer it for 'bench work'. You'll find there's a fair number of charger reviews on the modeling discussion websites with plenty of opinions out there.. in my experience, if a pack can be easily checked and balance charged via the switch chargeport, the chance of a pack or charger issue ruining your day are reduced by a potentially dramatic degree. See our Setup Guide for charger and cabling discussions and various setup solutions.

Q: What Field Charge rate do you use?

I normally field charge at 3 amps.. but that’s the limit of my switches and connectors. When I field charge with the balancer on the first charge of the day, it’s at 2 amps. How you set up and charge is really limited by the connectors and wiring and the charger capabilities. If you feel the 'need' to charge at higher rates, one work-around to speed up charge time with chargers that can work at higher rates is to charge the pack directly.. not through the standard system connectors on most chargeport switches. Install an Anderson or Deans connector on the switch input side, order the pack with Anderson or Deans plugs to match and disconnect the pack from the switch and charge through the pack feed.

Q: My NiMH packs are often pretty low after just a couple of days of sitting. Will these (LiFe) hold their charge better?

Yup. Lots better. And better than NiCad’s, too. The rapid self discharge characteristic present in low impedance Nicads and NiMH cells is just not present with LiFe cells. BUT.. (there’s always a ‘but’.. you notice?) we are in a brave new world or radio gear and systems applications. In an awful lot of equipment out there I’m finding system loading present at the pack even with the system ‘off’. On some of the 2.4 systems and most ECU’s and some ignition modules there’s a constant current draw of 2-4 milliamps.. so, leaving packs plugged into the switches for weeks or months at a time can cause grief and surprises. I don’t like grief and surprises. I unplug my packs from the switches when I’m done flying. I strongly recommend you do the same. Get in the habit, just do it.

Q: How should I store A123 packs?

My preferred method is to balance charge and cycle, record the capacity info, then balance charge again and disconnect them from all devices. What these cells DON’T like is discharge to 0 volts under a load and they don’t like sub zero weather conditions. Since they have a very low self discharge characteristic there’s no risk of finding a zero voltage pack in the spring after a winter layup. If you keep your plane in an unheated environment and suffer with sub-zero conditions where the plane is, it would be prudent to take the packs out of the plane and bring them in where you are. Like most batteries, they like the same temperatures you like.

Q: What happens when the plane gets hot? My NiMH packs suffer on hot days, I notice lower voltage and capacity. Same when it’s real cold out.

Another thing I like about the LiFe’s is the thermal increase performance… these cells are more resilient than any other battery type to temp build-up inside the application it’s powering. A123’s specs indicate routine operating temps as high as 140 degrees with only a 12% drop in capacity. So, if your big bird has a lot of canopy glass cooking your NiMH packs down quickly, LiFe will be a pleasant improvement for you. On the other end of the scale, once the outside temps drop to 4 degrees below zero F we see about 20% loss of capacity. Just in case you like to fly in Alaska in the winter, take a flight or two less than in the summer.

Q: What happened to A123 Racing? According to their website A123 Racing is no more?

A123 Systems officially discontinued all A123 'Racing' products back in January 2011... they don't market directly to or in the R/C hobby anymore and they have discontinued retail oriented 'A123 Racing' branded pack assembly and products. Frankly, the finished pack product they made available to R/C customers was not assembled to anywhere near the same standards American assemblers demanded for their customers. Simply put, US shops like ours declined to purchase their 'finished' product and built a better pack with their raw cells, properly cabled and reinforced for our R/C flying, RPV and Robotics applications than they could. A123 Systems is still very much in business, and we are still buying cells from them. A123 Systems is quite 'healthy', has no plans to discontinue either of the cells we use in the R/C hobby as those same cells are also exceptionally successful within the portable tools market.

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Q: Can I get custom electric flight packs from you built out of A123’s?

Not without using a gun. I worked for a guy that was a pretty smart feller once.. he used to love to say ‘Just because you can do something, doesn’t mean you should’. Over the course of the last 20 years I’ve had a lot of folks tell me ‘I’m missing the boat’ with electrics and electric flight. Gent’s, I built that boat… back when we used to tear down Drill Motors for gearboxes and measure current draw by the amount of smoke coming out the back on the climb out. I have a wall full of trophies and fond memories of the days when ingenuity in electric powered modeling and pilot skill made a bigger difference than the amount of money thrown at the challenge.

My current joy in the hobby is The Big Birds.. it’s what I fly when I finally get out to enjoy a day as a modeler. This is my retirement, and what I do is a labor of love.. not a driving grind to rake in the bucks and fleece folks. So, there's no big shop, no leveraged inventory, no staff to supervise, no national ad campaigns, no smoke and mirrors and 'man behind the curtain' crap. It’s just me and my many decades of experience in this narrow field, and that’s the way I like it. Since I'm still working despite the crushed economy, I guess it's how my customers like it too. The amount of work that comes in here from the commercial/military RPV end and the folks flying Giant Scale and IMAC keep me more than busy enough to pay the bills; they are, by the nature of what they are doing and the level of investment in time, effort and craftsmanship they do it with; competent modelers and pilots... and they keep food on the table without driving me batty with ‘is the red wire important’ questions. So, no.. I’ll not be building packs for the electric flight folks in our fine hobby any time soon. Don’t ask, and I promise not to promptly skin you alive and feed the cat with your entrails. J

Steve Anthony

NoBS Batteries / Hangtimes Hobbies

October 2008, updated April 2012

email: hangtime@hangtimes.com

*A123 & Nanophosphate are trademarks of A123 Systems, Inc. All A123 cells and chargers assembled and distributed by Hangtimes Hobbies and NoBS Batteries are acquired from A123's sole licensed US Distributor. All rights to A123 technology and trademarks reserved by A123 Systems Inc

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